Revised Fifth Edition . . December, 1975

First Edition . . ..... July, 1971

Publ ished in Japan

by PIONEER ELECTRONIC CORPORATION

4-1 , 1-chome, Meguro, Meguro-ku, Tokyo 153, Japan

Copyright © 7 972 by Pioneer Electronic Corporation

Contents TH E HI-F I IDEA Hi-fi and stereo Hi-fi and live sound ..... Hearing errors

Chapter 7

TH E HI -F I CHAIN OF EV ENTS Audio sources .................. . Ampl ifier/Receiver ............... • .. Speaker systems/Headphones . ............... .

Chapter 2

THE TURNTAB LE Motor and drive system .. Turntable platter ..... . Pick-up system ....... .

2 2

4 5 5 6

7 7

9 9

Phono cartridge . . . . . . . . . . • . . . • . . . . . . . . . . 10 Sty lus .............................. . 12 Demands upon phono cartridges ...... . 12 Tonearm ......... . 13 Auto-return tonearm . . . . . . . . . . . . . . . . . . . . 14 Automatic record changer ....... . ... _ . . . . . 15 Anti-skating device . . . . . . . . . . . . . . . . . . . . . . 15 How to read turntable specifications . . . . • . . . . . . . . 16

Chapter 3

THE TUNER . . . . . . . . . . . . . . . . . . • . . . . 18 AM and FM Fu nctio n of FM tuner .......... .

18 19

FM MPX (stereo) . . . . . . . . . . . . . . . . . . . . . . . . 2 1 Tuner co ntrols . . . . . . . . . . . . . . . . . . . . . . . . . 22 How to read tuner specifications . . . . . . . . . . . . . . . 24

Chapter4

TAPE EQUIPM ENT 21 Record ing a nd playback process 28 Tracks . . . . . . . . . . . . . . . . . . 28 Tape speeds . . . . . . . . . . . . . . . . . . . . . . . . 29 Tape quality . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Low-noise high-output tape . . . . . . . . . . . . . . . . . . 30 Chromium dioxide tape .......... _ ......... .

Tape deck, recorder, player? . . . . . .. _ ..... 31 Dolby noise reduction system . ..... . _ . . . . . . . . . 31 Open reel, cassette, cartridge? . . . . . . . . . . . . . . . . . 32 Drive mechanism . . . . . . . . . . . . _ . . . . 33 2 and 3 motor systems . . . . . . . . . • . . . . . . . . . . . 34 Recording and playback heads . . . . . . . . . . . . . . . . . 34 3-head decks . . . . . . . . . 35 Amplifiers, equa lization . . . . . . . . . . . . . . . . . 36 Automat ic stop, auto-reverse . . . • . . . 37 How to read tape deck spec ifications . . . . . . . . . . . . . 37

Chapter 5 THE AMPLIFIER ................... . 39

. . . ted amplifier receiver 39 Pre-amplifier, power a mplifier • Integra • 40 Pre-amplifier functions · · · · · · · · · · · · · · · · 41 Phono equalization · · · · · · · · · · · · · · · · · · · · · · · 42

•• • 0 •••

Inputs . · · · · · · · · · · · · · · · · · · · · · · 42 • • 0 0. 0 0

Tape monitoring · · · · · · · · · · · · · · · · · · 43 Volume, balance, tone contro ls · · · · · · · · · · · · · · · 45 . ........ Filters, loudness contour · · · · · · · · 46

• • 0 • ••••

Headphone jack · · · · · · · · · · · · • · · · · 46 Power amplifier function · · · · · · · · · · · · · · · · · · · 46

Criteria of quality · · · · · · · · · · · · · · · · · · · · · · . 47 0 • • 0 0 ••

Protector circuits · · · · · · · · · · · · · · · 48 Speaker terminals . · · · · · · · · · · · · · · · · · · · · 48 How to read a mplifier specifications · • · · · · · · · · · · ·

Chapter 6 51 LOUDSPEAKERS AND HEADPHONES 51

Structure and functions · · · · · · · · · · · · · · · · · 51 Double co ne and coaxial spea ker s · · · · · · · · · · · 52 Two-way, three-way, four-way systems . . . . . . . 53

Directionality · · · · · · · · · · · · · · · · · · · · : : : : : : 53 Speaker enclosures · · · · · · · · · · · · · · · · · 54 How to choose speakers .. · · · · · · · · · · · · · · · · · · ·

55 Crossover network, level contro ls · · · · · · · · · · · 56 How to read loudspeaker speci fi cations : : : : : : : : : : : 57 Headphones · · · · · · · · · · · · · · · · 58 E1ectrostatic headphones · · · · · · · · · · · · · · · · ·

Chapter 7 MULTI-AMPLIFIER SYSTEMS · · · · · · · · · ~: Reaso ns fo r multi-amplifier systems · · · · · · · · • ·

59 Electroni c crossover network · · · · · · · · · · · · · 60 Features and drawbacks · · · · · · · · · · · · · · · · · ·

61 Hints concerning multi-amplifier systems .... . •...

ChapterS FOUR-CHANNEL STEREO . . . . . . . . . . . . 63

63 four-channe l systems · · · · · · · · · · · · · · · · · · · · · · 63

••• 0 •••••••

Discrete system · · · · · · · · · · · · · · 64 Discrete four-channel tape · · · · · · · · · · · · · · · · · · ·

64 Discrete four-channel disc (CD-4 disc) · · · · · · • · · · · ·

66 Discrete four-channel FM broadcasts · · · · · · • · · · · · ·

66 Regu lar matrix system · · · · · · · · · · · · · · · : : : : : : 67 SQ matri x system · · · · · · · · · · · · · · · · · ·

Chapter 9 OF DOLLARS AND DECIBELS .. ..... . 68

Chapter 70 DO'S AND DON'T · · · · · · · · · · · · · · · · · · 69

A GLOSSARY OF AUDIO TERMS · · · · · 70

PURCHASE PLAN FOR RECORDS 89

& TAPES ... . . · · · · · · · · · · · · · · · · · · · ·

Tile Hi-Fi Idea Ever since the first grammophones began squeaking their scratchy messages into

the ears of a surprised world around the turn of the century, there has been an uninterrupted search for better, clearer, finer methods of recording and replaying sounds. Yet all the major breakthroughs were made in the last two decades - the first LP records, the invention of stereophonic recording and reproduction, the beginning of FM and FM stereo broadcasting, the development of noise-free amplifiers, the intro­duction of solid state engineering into audio equipment and, quite recently, the advent of four-channel stereo sound.

HI-FI AND STEREO Here we must make a distinction between two terms

that are often confused: high fi delity and stereo. High fidelity or hi-fi makes very much the same demands as an oath sworn in a court of law: " ..... the truth, the whole truth, and nothing but the truth." The goal of hi-fi is to record, preserve and rep roduce sou nd, chiefl y music, exactly the way it was pl ayed by the performers, without adding anyth ing, without leaving anything out.

Stereo, on the other hand, means that sound is recorded and reproduced via two channels in order to add a directional , spatial sensation. Stereo creates th e same effect to the ear that 3-D photography offers to th e eye. To continue the visual analogy: hi-fi demands sharp, clear, undistorted pictures; stereo creates an illusion of space, width, and locations.

Unfortunately, the two don't always go together. There are stereo sets on the market wh ich do not deserve the name "hi-fi" because thei r sou nd quality is inferior. Conversely, there are hi-fi systems with only one channel (" monophon ic"}.

The ideal hi -fi system has never and will never be built, simply because the demand to speak the whole truth and nothing but the t ru th cannot be realized. Between the perform ers in the recording studio and the li stener in his living room, there is a long and com­plicated chain of equip ment and transformations, tearing off something from the original sound here, adding something there. These unwanted fiddlings and diddlil)gs can be reduced to a min imum - an d th is is what h i-fi technology is all about - but they can never be totally

·eliminated.

2

HI-FI AND LIVE SOUND On the other hand, hi-fi has things to offer that no

live performance can match. Freedom. You, the listener, choose what you want to hear, when you want to hear it and with whom, how many times. From this poin t of view, hi-fi isn't a substitute for live concert per­formances, it's an addition or, if you want, an alternative.

This brings us to another common misconception, one that you find repeated in too many advert isements: that a good hi -fi system will bring the concert hall into your home. It's simpl y not true, and it wou ld be bad if it were. First, much of the world's great music, both old and modern, wasn't composed to be played in that 19th century inventi on, the concert hall . Chamber music, first of all the str ing quartet, calls for th e intimacy of small rooms. Bach wrote his organ works as an integral part of church li turgy. Brass bands are for outdoors, and much modern music is composed especial­ly for the recording studio and electronic reproduction. But even those works which were intended for concert hall performance, such as the classical and romantic symph onies, can't and shouldn 't be played over a living-room hi-fi system with concert hall volum e - the cannon in Tchai kovsky's 1812 overture wou ld shatter the window panes. No, hi-fi isn't supposed to put the concert hall in you r living-room; it's supposed to put the music in your living-room, and that it does remarkabl y well.

HEARING ERRORS While we're on the subject of misconceptions: there's

another one that says "whe n choosing hi-fi equipment, trust your ears rather than the manufacturer's specifica­tions." Several reservations mu st be voiced against this advice. The most important is that a person who buys a hi-fi system for the first time in hi s life is in most cases ill-equipped to judge the quality of musical sound reproduction. Subjected from morning to night to the ceaseless trickle of non-hi-fi sou nds - the t raffic din,

the bass-heavy bellowing of jukeboxes, the babble and squall of cheap transistor radios and TV sets -- the hi-fi novice hasn't had opportunity to train and hone his sense of hearing. Experience shows th at, left to his own resources, he wi ll usually choose an "impressive sound­ing" sys tem, mostly with exaggerated bass response and poor bri ll iance. As his hearing becomes sharper, as he gets used to the possibilities of his system and compares it with his friends' hi-fi installations, he will gradually ou tgrow his original purchase and wi ll begin to grade up. But since every replacement costs money, he will finally end up wi th a good system that has cost him much more than if he had bought it in the first place. We feel that ou r - and every conscien tious hi-fi salesman's -advice to the hi-fi novice should be to trust a reputable manu facturer and store more than his own as ye t underdeveloped hearing. Even though, his fi rst encounter with hi-fi sou nd may not be pl easant at all, simply because he is unaccustomed to hearing musical sounds as they really are.

With these remarks we have fi nally touched upon the main theme of this booklet: How to choose a hi- fi system, and how, as a salesman, to help a customer make a wise choice. At Pioneer, we want you to thin k in terms of Pioneer hi-fi equipment, of course, and the purpose of this brochure is to provide you with the tec~nical knowledge essential for ma king the right cho1ce. In the fo ll owing paragraphs, you will find concise explanations of the function of each component i~ a ~tereo hi-fi installation, as well as hints concerning llsten mg rooms, com ponent match ing, and a glossary of technical terms. We have tried to limit the technical explanations to the bare essentials (and even these have come out quite voluminous) while avoiding over­simpl ifica ti ons and pure advertising. You may wish to read on from this page to the end, or to skim, reading onl y those sections that deal with things you are hazy ~bout. E_ither way, we have tried to keep it interesting, mformat1ve and unbiased.

3

4

Fig. 1- 1 Recording and Playback in a Monophonic System

Chapter I The Hi-Fi Chabt of Ewents

What happens to the sound between the recording studio and the listener's living-room? A brief explanation of the "musical flow char t " may be helpful in answering this question, in as much as it creates an awareness of the many transformations - and accompanying dif­ficulties - that the sound has to go through.

Playback process Record player

AUDIO SOURCES At the recording studio, the sound waves em itted by

the voices or instruments are caught by, in a stereo recording, two or more microphones and converted into electrical signals. These signals are recorded on the so-cal led mas ter tape in th e form of magneticall y charged particles. Recording engineers control the conditions and later edit the tapes to obtain the desi red sound effect and to get rid of background noise, etc. What results is called a "master tape" (or simply "master") and from it are made records, tapes (in open-reel, cassette or cartridge formats), or broadcasts via radio waves, and these "delivery systems" are what are available to you for reproduction in your hom e.

To be more specific, let's take th em one at a time. First, records. The signals on the master tape are con­verted in to mechanical vibrations wh ich are engraved on a rotating disc, usually made of lacquer, in a process known as '''cutting. " From this engraved disc (also called a "master") the record manufacturer makes a metal mold which in turn is used to press "biscuits" of viny l which end up as the records you buy and play. Mak ing pre-recorded tapes (open-reel, cassette or car­tridge) from the master tape is simpl er: the signals from the master are passed from a playback head to the recording head of a tape duplicator and stored on the "dubbed" or duplicated tape in the form of magneti zed particl es of iron ox ide (see "Record ing and Playback Process" in Chapter 4). For broadcast on AM or FM waves, the master tape (or a copy of it) is pl ayed on equ ipment in the studio and transmitted ; you receive it and reproduce it with the proper equipment.

This brings us to the play back or reproduction end of the chain, and the equipment you need to reconvert the information contained in the three delivery systems described above into sound. In a stereo system, these three di fferen t kinds of playback systems are comm only called "sound sources," although they are, of course, not the original sources of sound. They are: 1) turntable, cartridge and stylus (NOTE: the nam e "record player"

5

6

is perh aps more apt, but in today's usage it usually denotes low-priced equipment withou t claim to hi-fi performance.); 2) tape deck (NOTE: the name "tape player" also can be used, but like " record player" it usually denotes someth ing less than high quali ty hi-fi perform ance.); and 3) AM, FM or FM Stereo Tuner.

None of th ese sound sources by itself can produce a signal strong enough to drive a hi-fi speaker system, as is explained below. Therefore, they must be connected to an ampli fier (or a receiver, which simply is an integrated preamplifier and power amplifier combined in the same cabinet with a tuner capabl e of receiving FM and also usually AM broadcasts).

AMPLIFIER/RECEIVER The signal sup pi ied by tuner, tape deck or turn table

is too feeb le to be converted into audible sound . There· fore, an ampl ifier is required to augment the signals and supply them to the speaker systems. The ampl ifier also provides a convenient opportunity to control the volume, tone quality and other characteristics of the sound which is why it usuall y has a whole array of knobs and switches. Very commonly, amplifier and tuner are combined into one unit which as mentioned above is then cal led a "receiver," a word that mu st not be confused with a regular radio or TV receiver.

SPEAKER SYSTEMS/HEADPHONES The speaker systems (or, for private listen ing, the

headphones) are the fi nal link in the chain of sound reproduc ti on. What fin ally comes ou t of the speaker systems is the acid test of the whole audio system, and they must be chosen with equal ly great care as all o ther components.

Now, a word from our sponsors: Pioneer makes (and sell s!) all parts of a hi-fi system, from tuners, turntables and tape decks to amplifiers, receive rs, headph ones and speaker systems, in a startling variety of models to match all needs and budgets. In the following chapters, the individual components, their functions and charac­teristics will be exam ined in some detail, together with explanati ons of how to read and evaluate thei r specifi ca­tions.

Fig. 1- 3 Hi·Fi Stereo System

Speaker systems

7

8

1 Arm Elevation Device 2 Stroboscope 3 Cartridge 4 Head Shell 5 Function Lever 6 Speed Selectors 7 Speed Control Knobs 8 Anti-Skating Control 9 Counter Weight 10 Lateral Balancer 11 45rpm Adaptor 12 Arm Rest 13 Tone Arm

Model PL-71

Chapter2

The Turntable The turntable, and its components including tonearm,

cartridge, stylus, etc., is the sound source which makes it possible to reconvert audio information stored in disc recordings. Those that are designed well and perform properly do this with maximum fidelity. On a stereo phonograph record, the sound information is contained in the microscopic grooves or rather, to be exact, in the undulations of the two walls of the groove. One (the inner) wall bears the information for the left stereo channel, the other (outer) wall that for the right channel. The two are at an angle of 90 degrees.

DRIVE SYSTEM The tas k of the turntable drive system seems simp le

at first glance: to do nothing but rotate the disc at a specified, constant speed. But at closer inspection we see the difficu lties hidden behind those innocent looking words " nothing but," " specified" and "constant. " Any mechanical system with moving parts generates vibra·

tions, inconsistencies and wobble, and in a turn table these wou ld cause noise, unevenness of pitch ("wow") and rum ble. Let us examine what is being done by turn table designers to cou nterac t these t roubles.

First, the phono motor in a hi-fi tu rntable has to meet six conditions: (a) it must revolve at a specified, constant rotational speed; (b) its speed must remain constant even if the supply voltage fl uctu ates; (c) it must operate almost withou t vibrations; (d) it must have power ful torque (rotati onal force) to overcome changes in its load and to bri ng the turntable qu ickly up to the speci fied speed, (e) it must not produce any magnetic tl ux leakage as this would induce noise ("hum") in the pickup system; and (f) it must be able to operate con­tinuously for many hours.

Essential ly there are three types of drive systems: 1) rim drive; 2) belt drive; 3) direct drive. In the rim drive system, one or more idler wheels transfer the power fro m the motor pu lley to the tu rntable platter by way of frict ion of their rubber rims. Advantages arc relatively low cos t, easy speed changes an d the possibility to use motors of comparatively low torque. On the o ther hand, as the rubber rims wear ou t, a certain amount of slippage is bound to occur.

The common belt drive system employs a rubbe r or plas tic belt to convey the motor power to the turn­table. Speed changes are made by guid ing the belt around either of two motor pull ey secti ons with dif­fe rent diameters. The belt prevents motor vibrations from reaching the turntabl e, thus reduc ing noise and rumble. In precision engineered hi-fi turntables, the belt is often made of polyu rethane because of its resistance to heat, hum id ity and oil and its low elas ticity.

Recently, a third drive system - direct drive - has appeared on the market, receiving much atten tion and winning many customers despite the relatively higher cos t attached to turntables which use it. Basicall y, the term "direct dr ive" explains the system: a brush less DC motor is used to drive the platter direc tl y, with no connecting rim idl ers or belts. This is achieved by

Fig. 2-2 Belt Drive System

9

DIRECT DRIVE SYSTEM

10

centering the drive shaft of the pl atter in the center of the motor itself; the motor rotates at very slow speeds (33-1 /3 or 45 rp m) thus eliminating the need for speed­reduction mechanisms. The motor is controlled by an electronic servo mechanism to maintain speed accuracy.

TURNTABLE MOTORS For rim drive and bel t drive systems, onl y two types

of AC motors can be used: the induction motor and the synchronous motor. Of these, the induction motor is being used mainly for low priced turntables because its speed is liable to flu ctu ate with load variations. This leaves the synch ronous motor. Its speed is locked to the AC line frequency and therefore very constant even if the power voltage fluctu ates. A special - and ra ther expensive - variety is the hysteresis synchronou s motor whose features include freedom from vibrations an d noise-free operation. Most top class turn tables are equ ipped with hysteresis motors alth ough other designs (servo-controlled DC and AC motors, etc.) have been tried with good results.

As all of these motors run at higher· rpm's than th e 33-1/3 and 45 rpm required for turning the record, they must be coupled to the turn table by means of speed­redu ction mechan isms such as the rim drive or belt drive systems explained above.

TURNTABLE PLATTER The turntable platter must be large enough to ac­

com modate 12-inch LP's, but there's another reason for making it as large and heavy as the motor torque will perm it. A large, heavy pl atter, once in motion, serves as a fl ywheel an d keeps the speed cons tant by its own iner tia. Turntable platters are made of pressed steel plate or di e-cast aluminum alloys. The latter is preferable for high quality systems because of its better electrical properties (anti-magnetism) and greater machining preci­sion. To work as an efficient flywheel, the turntable platter must be balanced just like an automobile wheel.

PICK-UP SYSTEM

Most efforts in the design of hi-fi record playing equipment have been concentrated on the pick-up system, i.e. tonearms and phon o cartridges.

Head shell Tonearm Balance weight

"'- Cartridge Stylus Arm rest

Fig. 2- 4 Pick-Up System

The difficulties are caused by the great number of _ often conflict ing - factors that have to be taken into consideration. The theory of phono pick-up systems alone cou ld fi ll a boo k.

PHONO CARTRIDGE

The cartridge, mou nted in a shell at the tip of the tonearm, has the task of tracking the record grooves and transform ing mechanical vibrations into an electric signal. As the stylus ("needle") res ts in the rotating record groove, it is deflected laterally and vertically in accordance with th e undulations in the groove walls. Thi s function already expl ain s one of the greatest problem s: the stylus must fo llow ("track") the com­plicated meanderings of the groove instantly and without loosing contact with the wa lls or jumping out of the groove. To be able to do this, the mass of the sty lus and all moving parts must be kept as li t tl e as possible ·because the greater the moving mass, the higher its inertia, i.e. resistance to qu ick changes in movement.

Other conditions for good tracking are: a sufficient downward force called "tracking force" must be applied to the stylus to keep it in the groove - which, if too great, wi ll cause sty lus and records to wear out more qu ickly than necessary, however; and the stylus assembly must have enough freedom of movement, technically called "compliance" or sometimes "trackabili ty ."

The mechanical vibrations picked up by the stylus are converted into an electrical signal by any of a

~·~~~~

IIJIIJ a b c d

a: Left signal only b: Right signal only c: Left and right signal of

any phase d: Left and right signal of

same phase

Fig. 2- 3 The Groove of Stereo Disc and Stylus Movement

Dampers Elements

Stylus Cantilever

Flg.2- S Sc~ematlc VIew of a Ceramic Cartridge

Fig. 2-6 Schematic VIew of a Moving Magnet Cartridge

11

Fig. 2- 7 Schematic VIew of a Moving Coli Cartridge

Coils

number of systems. Let us briefly explain their func­tions and weigh their merits and demerits.

Ceramic cartridges utilize the so-called "piezo-electric effect. " Movements of the cantilever (which is fi xed to the stylus) appl y varying forces - twists and pressures -on a special crystall ic material wh ich generates an electrical voltage in accordance with the stylus move­ment. The rigid armatures required to exert this twisting force natu rally increase the moving mass, and the cerami c elements are sometimes affected by heat an d moisture. Although comm only used in low priced record players, they do not fu lfi ll the discriminating demands of real hi-fi.

Moving magne t (MM) cartridges have a tiny perma­nen t magnet attached to the cantil ever which, by movi ng freely between an assembly of coil s, induces a voltage in th ese coils. Mov ing magnet cartridges are the most commonly used hi-fi cartridges, offer ing the benefits of small moving mass and relatively high output voltage, i.e. efficiency.

The reverse principle is applied in moving coil (MC) cartridges. Here, the magnet is fixed and the coils- one for each channel - move in the magnetic fi eld, thereby receiving an induction voltage. The moving mass of MC cartridges is even smaller than that of MM types, but their output voltage is so low th at the amplifier mu st have special inputs of very high sensitivity.

In addition to low moving mass, MM and MC cartridges offer very good frequency response and channel separation, factors which explain their great popularity in hi-fi appli cations.

Induced Magnet (IM) cartridges have fi xed magnet and coil assemblies. Two tiny iron plates move in the

~ magnetic field, causing variations in the magnetic flu x Snlcon element and, thereby, in the coils' induction voltage.

Stylus All the cartridge systems described above generate an Fig. 2- 9 electrical signal directly from the mechanical vi brations. Schematic View of There are, however, two types of cartridges which a Semiconductor requ ire an outside voltage supply. This is the chief Cartridge ...._ __________ _. reason why they are not being used widely, although

12

they promise excellent resul ts. One is the sem iconductor .-------~----.

cartridge in which mechanical forces created by stylus vibration work upon a silicon semiconductor, changing its electrical resistance in correspondence with stylus movement. The oth er type is called "photo-electric." Light from a tiny bu lb in the cartridge falls upon a photo transistor which converts it into an electric voltage. By moving a slotted mask in the path of the light beam, the light intensity can be varied in ac­cordance with stylus vibrations.

STYLUS

The stylus in a hi-fi cartridge is made either of sapph ire or diamond. Diamond is pre ferable because of its longer service life which averages 400 to 800 hours of operation. Its durabil ity depends largely on the tracking force, i.e. the weigh t with which the stylus is pushed aga inst the walls of the record groove. The tip of th e stylus is machined to ex treme precision. It can be radial, with a tir radius of about 0.5 mil (1 mil = 1/1000 inch) for a stereo cartridge, or ell iptical, wi th its greater wid th across the record groove. Elliptical stylus usually deliver better response to high audio frequencies, i.e. they track high notes better.

Fig. 2- 10 Photo-Electric Cartridge

I mil (0.026mm) Paraboli c Sty lu s and Shibata Sty lu s For mono LPs

Mono/stereo Stereo

0. 7 mil (0.017mm) 0.5 mil (0.012mm)

Stylus tip radius

Newly-designed sty lus tip s hav ing " line con tact " with the disc grooves. Especia lly distinguishe d by frequen-

Stylus tip cy response and separati on cha rac-1 te rist ics, thus perfec t for C D-4

Fig. 2- 11 Various Stylus Tips d iscrete fou r-channe l d isc rep rodu c-""--~------------------J tion .

DEMANDS UPON PHONO CA RTRIDGES Let us sum up once more the demands made upon

a hi-fi cartridge. It must track the record groove with precision, fo llowing even abrupt movements such as sudden trumpet blasts with ease. This abil ity is usually expressed mathematically as "compliance." The cartridge should track th e record even at low force, because too

13

much pressure between stylus and groove causes disc and stylus to wear out quickly. Because of the ex tremely tiny area of contact between stylu s and groove walls, seemingly fantastic pressures occur - at a tracking fo rce of a few grams the pressure is several thousand atmospheres, in other words thousands of t imes higher than the air pressure in an automobile ti re.

The cartridge must separate the two stereo channels clearly and at all audible frequencies. And it must de liver an output voltage large enough for the stereo amplifier to work with.

TONEARM A cartridge can only deliver its full performance if

it is mounted on a tonearm of equall y high quality. The tonearm's main function is to hold the cartridge in its path while it travels across the record, and to apply the necessary tracking force while compensating for other, unwanted forces.

Most high quali ty tonearms are made of light metal alloy because of its light weight, stabil ity, and easy machining. By thei r shape, arms can be grouped into three types: straight (or 1-shaped) types, j-types, and $-types. In every case, the shell -car tridge assembly is at an angle (o:) to the arm axis, the line connecting sty lus tip to arm pivo t. This angle is called offset angle, and

.._ __ ......... _ __. ............ __ -....~ its purpose is to minimize the arm's track ing error.

(Tracking error is the angle that the cartridge ax is deviates from the record tangential at any given point on the record. The smaller the tracking error, the better.) On some economy type equipment, the shell cannot be removed from the tonearm ("in tegrated arm"). Most modern tonearms, however, have standardized plug- in connections for the cartridge-shell assembly, so that all cartridges following these standards can be freely interchanged.

Since different cartridges require different tracking forces, the tonearm should have a movabl e balance weight on its rear end, preferably with a graduated scale

.......,;;;...;.;~..;.;;;.;s.. _____ __. of tracking forces. The tracking force can then be

14

adjusted by fi rst balancing the arm horizontal ly, then ....-------------. applying the desired force by moving the balance ~a~~~\ weight (or a sub-weight) fur ther toward the arm pivot ~ ("static balance" ). On some arms tracking force is . Spring/ Jd, applied by the force of a spring {"dynamic balance"). Fig. 2- 14

On most high quality turn tables, the tonearms are Dynamic Balance equipped with several auxi liary controls to improve their performance and ease of operation. ~Only tracking force applied

It requi res a certain dexterity to set the stylus down on a record and to lift it off again, and coun tless records and cartridges have been damaged by careless handling. Fig. 2- lS Most hi-fi tonearms are therefore provided wi th a lifter or .._s_ta_t_lc_B_al_a_n_ce _____ ..J

cueing device, mostly a hydraulically damped piston which gently fl oats the tonearm down on the ini tial record grooves and li fts it up again at the end.

ANTI-SKATING DEVICE One other device must be men tioned here - the anti­

skating device provided on many high quality tonearms, also called sidethrust compensator or ins ide force canceler. To unders tand its function, we must realize th at a tricky combination of forces ac t upon stylus and tonearm as they track the record. Among these, the most disturbing is a force which tries to pull the tonearm inward, toward the center of the disc, th ereby pushing the sty lus aga inst the in ner wall of the record groove or, Anti-Skating Control in extreme cases, causing the stylus to jump out of th e .._ ____ (M_ o_d_ei_P_L_·_S_1_A_) ....... groove. To assure perfect trackin g of both groove walls (both stereo channels!), th is force mu st be compensated. Usuall y, a li ttle weight affi xed to a string applies a corresponding cou nterforce on the tonearm. As the skating force varies with the sty lus tracking force, the anti-skating device should also be re-adjusted each time the tracking force is changed.

AUTO-RETURN TONEARM

One step further advanced towards automation is the "auto-return" tonearm - at the end of the record it li fts off and returns to its rest position au tomaticall y.'

15

Speed selector

Model PL- 55X

16

Cartridge

Model PL-55X

The logical extension of this is the fully automatic turntable. A single function lever controls the entire operation. In positi on start, the tonearm moves over the initial record grooves, the platter begins to revolve, the tonearm floats down, the record is played, and at the end the tonearm li fts off and returns to its rest. There are usually two other controls: a speed selector, and a record size selector which adju sts the tonearm drop point for the three common record diameters (12, 10, and 17 inches).

AUTOMATIC RECORD CHANGERS Pioneer feels that at the present stage of turntable

technology it is not possible to manufacture an auto­matic record changer that will reliably and continuously live up to hi-fi requirements.

How to Read Turntable S&JerUiratlons When comparing and evaluating tu rntables on the

strength of their catalog specifi cations (you should listen to them, too, before buying), the fol lowing technical items deserve the greatest attention: a) Wow & Flutter Wow is a slowly cycling speed inconsistency causing an

up-and-down effect in the playback sound. Flutter is a high-speed quiver, especially noticeable in long-held notes. Both M C caused by defi ciencies in the drive 'system of the turntable and arc ex pressed as a percentage in the specifications. The smaller the figure, the better. Max imu m al lowable wow/fl utter percentage for high fidelity performance from a turntable is arou nd 0.1 5% (WRMS). b) Signal-to-Noise Ratio (S/N) This is a measure of the amount of low-pi tched " rum ble" a turntable produces in r·elation to the desired signal. The larger th e S/N figure, the better. Hi-fi perform ance requires the fi gu re to be 45dB or above. c) Turn tabl e Platter Weight is importan t here. The moment of inertia is related to smooth rotati on, and weigh t, in turn, is related to inertia. In belt-drive turntables the recom­mended weight is between 3 lb. 5 oz. and 5 lb. 8 oz. For direct-drive models the weight should be abou t 2 lb. 3 oz.

Hu'" to llt•ad l'm·ta·idnt• Sa•t•t·il il'alimtK a) Frequency Response The lowest and the highest audio frequ encies to which a cartridge will respond are used to indicate the cartridge's frequency response range. The wider the range th e bet ter. Also, there should be no peaks or cl ips within the range. Hi-fi cartridges should have a range of at least 20 l lz to 16,0001 1z ±3d B. For discre te 4-channcl reproduction, th e cartridge is requ ired to have an upper frequency response limit of at leas t 45,000Hz. b) Channel Separa tion The abil ity of a cartridge to separa te the two channels of a stereo record. The figure is expressed in decibels, and should be above 20dB at l ,OOOHz. c) Outpu t Voltage The voltage generated by the cartridge at a certain stylus-to-groove velocity and at a 1 ,OOOHz signal input. Th is voltage may differ according to the cartridge system, but should be greater than the sensitivity (in microvolts, expressed " mV") of the amplifier's phono

17

18

inputs. Generally speaking, about 2.5mV is recom­mended.

d) Load Impedance The amplifier's input impedance as seen from the cartridge. For MM and IM cartridges the standard value is about 47,000 to 50,000 ohms (47 to 50k0hms), which is what most amplifier phono inputs are designed to receive. MC cartridges have low impedance (2 to 20 ohms), and the amplifier must have special MC or "ceram ic" phono inpu ts. If no such inputs arc prov ided, the user will need a step-up transformer or booster ampli fier between the MC cartr id ge and the amp lifier. c) Compl iance A measure of the stylus' ab ili ty to follow sudd en and violent changes in the undu lations of the record groove. Com pliance is expressed as th e amount of deflection (in centimeters) that a force of 1 dyne upon the stylus will cause. The larger the figure, the better. The recommended figure depends on the tracking force, but should be at least 8 x 106 em/dyne. f) Tracki ng Force The required downward force that wi ll make a cartridge stay in the record groove and track it. Di rectly related to compliance : the larger the compliance, the smaller the requ ired tracking force. As a light track ing force will save wear and tear on the record and the stylus, the smaller the figure, the better. It shou ld never exceed 4 grams.

Chapter:)

The Tuner Next to the turntable, the tuner is the most common

sound source in hi-fi installations. In many cases, tuner and stereo amplifier are combined into one unit, a so-called "receiver"; in these instances, the tuner section of the receiver should fulfill the demands outlined below.

AM AND FM We are concerned with the two basic methods of

radio broadcasting here, AM and FM. In both, a signal (the music, etc.) is carried from the transmitter through the air to your tuner in the form of electronic impulses via a carrier wave.

AM stands for Amplitude Modu lation, that is, the Model TX-9500

carrie r wave is modu lated by a fl uctuating signal so that ,..-----------, h h Carrier ampl;tudt modulated bV audio signal.

its instantaneous amplitude varies in sympathy wit t e signal. The frequency of the carrier remai ns uniform.

FM stands for Frequency Modu lation. Here the carrier's instantaneous frequency is varied by an amount proportional to the instantaneous amplitude of the modu lating wave (the signal). In th is case the amplitude remains un iform. (See Fig. 3- 1. )

Most hi-fi-tuners are AM/FM models wh ich means FM_~~U~I::m

Amplitude . . ...L

that they rece ive AM broadcasts as well as FM and FM Catrlor frequoncv modulotod bv oudlo signal.

stereo programs. A few exclusive FM models ex ist, but ...._F..-ig,_. _3_- _l_ A_M_ a_n_d_F_M __ ~ since there is hard ly any difference in cost, the AM/FM tuner with its greater flexibility has advan tages.

AM reception in the 535 - 1605 kHz radio band has been around since the earliest days of the "wireless". Although there are built-in limitations which delegate AM to the realm of lo-fi , it won't hu rt to have it available for news, sports programs, etc.

When choosing a hi- fi tuner, its FM -and FM stereo - performance is of incomparably greater importance.

19

20

A good FM tuner will deliver the same degree of hi -fi sound purity as a turntable or tape deck - in many cases its sound will be superior simply because FM stations use top-grade professional reprod uction equip­mcnt outside the range of the hi-fi amateur. Add to th is the fact that the FM radio waves don't cost the listener a cent and that FM music programs can be tape­recorded with out difficu lty, and you will understand why for many budget-m inded hi-fi fans the FM tuner has become the chief source of sound.

Tuning meter Stereo indicator

I

J:~QtJLF:.ttD_ -----------_j Fig. 3-2 Block Diagram of FM Stereo Tuner Mono/stereo switch

FUNCTION OF AM FM TUNER The demands made upon a hi-fi tuner will become

clear if we exam ine its fun ction s step by step. Th e FM antenna supplies th e radio signal (FM occupies th e 88 -108 MHz band) to the tuner's input, i.e. the RF (Radio Frequency) ampl ifier stage. There, th e signal is ampli fied and, more importantly, separated from those of other FM stations and from random noise signals. This outlines the fi rst two tasks of an FM hi-fi tuner: sensitivity, i.e. the ability to pick up weak signals; and selectivity, which is its ab ility to "slice out" only th e desired station while suppressing adjacen t signals and noise. Another item found in tuner specifications and determined at the tuner's RF stage is cross-modu lation resistance which describes a tuner's abi lity to prevent the desired signal from being influenced ("modulated") by strong un-

wanted stations. In modern tuner designs, cross­modu lation resistance has been improved considerably by the use of field effect transistors (FET's) because of their higher linearity. Since cross-modulation depends largely on the strength of these unwanted signals, it can be further reduced by correct, precise orientation of th e antenna towards th e wanted station.

As the RF stage employs an oscill ator circu it, it must be designed in such a way that the oscillator frequency does not " leak" from the tuner, causing

fll SELECTIVITY

interference in nearby TV sets, radios, etc. !8 a=E~R!E,,~s=SE=ES The RF stage delivers an intermediate frequency ~ t-t-++-t-tm-t 1oo,f-++fii~H-+-IH-j

signal of 10.7 MHz, which is then amplified and again f? H-+t--t--i~H-t-++lltH-t-H-1

selected in the IF (Intermediate Frequency) stage. The ~ H--t-t+-i-llt-k-';;;;t--t-+HIH--t-+-H--1 bf 'BOdB'ti-H--t-t-t--1

problem is to amplify only the desired, sharply defined ~ t!l1~~E~~~7a0 3irJfBf1~ section of the band that contains the wanted sound ~ 60

~ '60d informati on. This is done by a series of fi lters of very .. r-.......,t--t-~+,-t_-Htt-H '~tt-..... ++_-t.--1.,..--I .. H.

precise electrical dimensions, preferably ceramic filters. ~ ~:-;.:.~.;;;to ---iJLfMi: .. l .. ,,l,!,.,. These are a major fac tor in determining an FM tuner's ""'""""::.., t; !~ l:±fl1T

'CISI.IItOI>GI'lALllVIL

selectivity. ~ IJ'I

The limiting circui t, also part of the IF stage, fu lfill s ' 20<18

- 600 - 400 200 0 200 400 600

FREQUENCY DIFFERENCE IN KHz one of the most important functions - it suppresses the atmospheric noise. This is one of the special features of Fig. 3-3 FM broadcasting and ex plains the high sou nd quality Selectivity attainable. The limiter begins to work only when a signal Characteristic of sufficient strength is present, and its function is ._C_u_r_v_e....;(!...,;T_X_·-.9_5_00_),_ ___ _

Lif'ter Noise is cut. Noise I A ~~

• I ~ n ~ I

v l j ~

S1gnal still noisy at A 1 l'f ' ! B

1

~ Noise is cut. mp 1 1cat1on RF stage output. in IF stage. Limiting effect

Fig. 3- 4 Limiting Effect

2 1

L + R

Fig. 3- 5 Carrier of FM MPX

therefore closely related to the tuner's sensitivity and antenna signal strength.

The muting circuit, usually switchable with a control on the tuner 's front panel, has a simil ar purpose - it cancels the noise encountered on unu sed FM channels, that irritating hiss that you hear between stations. The muting control can be either a simple on/off switch or, on expensive models, a continuously adjustable control. As the muting switch cancels out weak stations along with the noise, it must be turned off or turned down when such a weak signal is to be received .

After passing through the IF stage, th e signal is demodulated, i.e. the audio signal is extracted from it. This signal is stil l too weak, however, to drive the loudspeakers; it must first be augmented in the am plifier.

FM MULTIPLEX (MPX) FOR STEREO The greatest attraction of today 's FM tuners lies in

the possibility of stereophonic reception. (Of course, this is possible only in areas where FM stereo stations are operating. ) When broadcasting a stereophon ic (MPX} program, the station transmits a sub·carrier wave along­side the main carrier and removed from it by 38kHz, and a pilot frequency of half the sub-carrier i.e. 19kHz. A pilot detector circuit in the tuner detects the presence

Stereo ___ _. of this pilot signal and activates the so-called FM MPX demodulator circu it.

Let us call the sound information for the left channel L, that for th e right channel R. In a stereophonic FM broadcast, the main carrier contains the sum of both

-----------.... signals, i.e. L +R. An FM tuner with out a mu ltiplex Main carrier demodulator will receive only this signal and deliver

Pilot L - R signal

0 15kHz 19kHz 38kHz

Fig. 3- 6 Spectrum of FM Stereo

22

monophonic sou nd. The sub-carrier transports a dif­ferent signal, L- R. In the FM MPX demodulator, these two L +R and L- R signals are added and sub­tracted to re-gain the signal for each channel: (L +R) + (L- R) = 2L . . . . . . . . left channel sound (L +R) - (L- R) = 2R . . . . . . . right channel sound

For reasons too complicated to explain here an FM

stereo broadcast has only about half the reach of a monophonic program transmitted with the same power. This makes it easy to understand why a good FM outdoor antenna is needed in most cases to assure good stereo reception.

TUNER CONTROLS The quality and usefulness of an FM tuner are

determined not on ly by the precision of the circuits, but its operating convenience is equal ly important. Let us take a bri ef look at the controls, dials and switches found on upper grade AM/FM hi-fi tu ners.

The operation mode is determined by a function selector which usuall y has three positions: AM, FM MONO, and FM AUTO. In FM MONO position, all FM programs are received monophonicall y, i.e. the MPX demodulator is deactivated. In FM AUTO mode, the tuner automaticall y switches to FM stereo reception when tuned to an FM MPX broadcast.

~~~====~====~~~·; 1 II: 2

'I; ~ w=~~~~~~~~~~~l ~

9 10 11

l r--------------r------------~ 12 13 14 15 16 17 18 19 20

Signal Meter Tuning Meter FM Stereo Indicator Power Switch Headphone j ack Headphone Ou tput Level Con trol AM & FM Output Level Controls Function Switch Pu lse Noise Swi tch MPX Noise Fil ter FM Mu ting Level Switch Tuning Knob AM Ferrite Antenna AM An tenna Terminal Ground Terminal FM Antenna Terminals (300.n) FM Antenna Terminal (15.n) FM Multipath Terminals Fixed Outpu t Terminals Variable Output Terminals

23

SIGNAL TUNING

~~ Max. l <D

Min.J

<D Distortion <2> S/N <3) Separat ion

<2>

Optimum signal zone Fig. 3- 7 Signal Strength and Tuning Meters

Fig. 3- 9 Pulse Noise Suppressor Circuit his new circuit device is used to

Tuning is dcne by turni ng a large knob and watching one or two meters as well as the station dial. The signal strength meter deflects to the right when the station is turned in - tre greater its deflection, the stronger the received signal. (It is also helpfu l in finding the best position and direction for th e FM antenna.) The tuning or center zero meter moves into center position to indicate accu rate station tuning.

A close look at the tuning dials of different tu ners wi ll reveal a slight but important difference. On most tuners, the spacing between the frequency markings will become gradually closer toward the right en d of the dial. Others have dial s with equal distances between all FM frequency markings. These "l inear" dials are of cou rse easier to read an d permi t qu icker, more accurate tuning.

Non-linear scale

90

I 92 94 96 98 100 102 104 106 108

I I I I I I I I I MHz

88

I Linear scale

88 90 92 94 96 98 100 102 '?4 '?6 '?8 I I I I I I I I I t t tMHz Fig. 3-8 Linear FM Dial Scale

effectively cancel the pulse type noise (electrical equipment noise interference) such as automobile ignition systems, fluorescent ligh ts and othe r appliances without sacri· fic ing tonal quality and stereo '----------------------.....l separation. It is avail able on such advanced Pioneer products as the model TX-9100.

Aud iO 110n11 Willi diiiUibe

by PVI .. n011e

A udiO &jftlll WI~- w oU\ P\IIN notH elu,uni!H by P NS

24

The muting sw itch or continuous muting control has already been explained. In addition, top range tuners often are equipped with a switch or control called "M PX NOISE FILTER" or " HI BLEND. " Its function is to eliminate or at least reduce hissing noise which is often present in FM stereo programs of insufficient signal strength. As this circu it operates by blending a certain amount of the high sound frequencies of both channels, its use enta ils a certain loss in stereo channel separation.

Speaking of channel separation: some tuners are equipped with a semi-fixed screw or control for adj ust­ing the MPX channel separation. This is factory adjusted;

re-adjustments should be entrusted to qualified service engineers only.

Other controls found on tuners include output level controls, sometimes separate for AM and FM, wh ich regul ate the tuner 's output voltage in order to match its sound volume with that of other source equ ipment (turntable, tape deck). A headphone jack may also be provided, and some tuners have an extra pair of TAPE REC outputs, permitting direct tuner-to-tape recording without going through the amplifier. Last but not least, there may be an AFC switch (although its presence or

·absence says noth ing about the quali ty of the tuner) whose function is to lock the station to the tuning circuits, in other words to prevent station drift and fluctuations.

PLL (PHASE-LOCK-LOOP) CIRCU IT PLL is a relatively new development, and one that is

ex tremely useful in FM MPX (and other electron ic applications). Pioneer uses PLL in many of its newest FM M PX demodulators to replace conventional coils and capacitors of the resonance circuits. This greatly enhances du rability and re liability. A PLL circuit. consists of a phase comparator, an ampl ifier, a low-pass filter, and a voltage-controlled oscillator. It is commonly constructed as an IC (in tegrated circu it) . By deriving an output from the junction of the low-pass fil ter and the voltage-controlled oscillator it serves as a demodu lator for MPX, and derives an accurately synch ron ized 38kHz switching signal from the input 19kHz pilo t signal received from the FM transmitter. Overall , PLL improves stereo separation and reduces distortion over a wider frequency range than conventional coil-and-capacitor circu its, cuts down the number of parts required for the circu it, and further im proves performance by provid ing superior stability.

How lo llend Tuner Sa•edfirations Compared to a turntable, which is chiefly a mecha­

nical device, a tuner's specifications present much greater difficulties to the layman. Indeed, a rather close

25

26

familiarity with electronic circuits is requ ired to find one's way through al l the ratios, rejections, responses, and factors. Neverth eless, the following brief explana­tions should be sufficient guidance. a) Scnsitivi ty The minimum antenna signal which the tuner can convert into a satisfactory sound signal. Expressed in 11V (m icrovolts = 1/1 ,000,000 of a volt) and defined by the Institu te of High Fidelity Manufacturers (IH F) as the signal strength at which the tu ner will suppress noise by 30d B. Sensitivity ratings of 3J1V are qu ite respectable, values below 2J1V arc ou tstanding. b) Signal-to-Noise Ratio (S/N) Th e ratio, expressed in dec ibels, between a 400Hz fu lly-modul ated signal and the noise component. The rating 60dB, for example, means that the signal is 1,000 times stronger than the noise. Here, the higher the valu e, the better; for hi-fi FM it shou ld be at least SOd B. Some Pioneer tuners offer a superb signal-to-noise ratio as high as 7 Sd B. c) Capture Ratio Assume that two stations are broadcasting on the same frequency. "Capture ratio" descri bes a tuner's ab il ity to suppress the weaker of the two wh ile receiving on ly the stronger. Also related to the tuner's suppression of random noise. Exp ressed in decibels, smal ler values arc better. A rating of 4.5d B is usually sufficient. d) Sclcctivi ty This is similar to capture rat io, but instead of dealing wi th signals of di ffercnt strengths on the same freq uency, it deals with signals wh ich arc broadcast on frequencies very close to the one you arc trying to select. The tuner's ability to slice away the adjacent signals and select out the one you want is expressed also in decibels, the higher the better. A selectivity of SOdB is usually su fficicn l. c) Image Rejection " Image " means a tuner's undesirable reception of the same signal at two or more points on the dial, of which only one is the true station signal. Tuners which can't

reject the fal se image give you sound with "ghosts" (as in tv). This is caused by interac ti on of the oscillator frequency and the RF frequency. Image rejection is the tuner's abil ity to suppress this frequency. Bigger values arc better; they pay off as less probl ems in areas with many FM stations broadcasting. f) Spurious Response or Rejection An FM tuner's bad habit of creati ng unwanted, meaning­less " lie" signals which it then (a) emits through the antenna, causi ng interference in the neighbor's TV set or radio, and (b) picks up itse lf, affecting its own reception because this sci f-gcncratcd lie signal can in te rfere with the true wanted station signal. Expressed in decibels, higher values arc preferable. g) AM Suppress ion AM in this context has nothing to do with AM broad­casting; AM here means the (amp litude modulated) noise signals emanating from fl uorescent lamps, motors, automobile ignitions, etc. which, unless suppressed, cause that notorious irritating crackle during FM recep­tion. AM suppression is expressed in decibels, higher values are better, 40dB is about minimum. h) FM Stereo Separation The FM MPX demodulator's abi lity to separate the left and right channel signals of FM stereo broadcasts. For stereo effect, channel separation in the medium audio frequency range (400 - 1 ,OOO Hz) is most important. A good tuner should have 40dB separati on in this range or 30d B between 40Hz and 8k Hz or 25d B over the total 20Hz - 15k Hz range. i) Output Level This is usually in the 0.7V range, and is adjustable on high quali ty tu ners. You arc in terested in the output level of a tuner because it must match the input requi re­ments of you r ampli fier or receiver. In most Pioneer stereo tuners, two kinds of ou tput terminals (fixed and variable) arc provided. Thus, you can, for example, usc the fixed term inals to connect the tuner to a tape deck for off-the-air recording, while using the variab le terminals to connect with oth er equipment.

27

Model RT-1020L

28

Chapter 4 Tape Equipment

Turntable and tuner are "passive" sound sources ­they can only reproduce commerciaffy recorded or broadcast sound. Tape equipment, with the exception of so-caffed tape players, lets the listener participate "actively" in the selection and even creation of music programs. This great advantage, together with the operational ease and relatively low price of modern tape equipmen t, may explain the tremendous tape recorder boom that has been sweeping the world.

THE TAPE According to the tape form at, tape equipm ent can be

grouped into open-reel, cassette and cartridge . The recording tape itself is basically the same for all three types, and so are the essential functions of the machines.

Magnetic record ing tape consists of a thin polyester or ace tate film (usually about 15 to 35 microns thick, or as expressed in mils, 0.60 to 1.40 mils thick). This fi lm, called backing (consisting of the base and emul­sion), is covered with a layer of fi ne, crystal lic iron ox ide particles imbedded in an adhesive. These iron ox ide particles can be magnetized in a magnetic field and will

I Pause Switc 2 Power Switch 3 Reel Size Switch 4 Tape Speed Selector 5 MIC Recording Level Control 6 Line Record ing Level Control 7 Recording Indicators 8 Level Meters 9 MIC Input jacks I 0 REC Bias Switch II REC EQ Switch 12 Phones Jack 13 Output Level Control 14 Meters Switch I 5 Monitor Switches (L, R) 16 Play Switch 17 REC Switches (L, R) 18 Function Buttons 19 Tension Arm 20 Ta e Counter

retain this magnetism.

RECORDING AND PLAYBACK PROCESS The recording process is, briefly, as follows. Electric

signals supplied by a sound source are amplified and then applied to the coil of a small electro-magnet called a "recording head." This causes a magnetic field, alternating in accordance with the sound's rh ythm and intensity, in and arou nd a tiny gap between the two poles of the magnet. As the recording tape travels past the recording head, its iron oxide particles are magnet­ized by the altern ating magnetic field. The tape thus stores th e sound information in the form of magnetism.

To retrieve this informati on, the reverse process is used. The tape, transported past the so-called pl ayback head - another small electro-magnet with a similar structure as the recordi ng head - induces a small, alternating current in the magnet's coi l. As this current contains the same sound in formation as the original signal - provided that the tape travels at the same speed at recording and playback - it can be amplified and used to drive a speaker system.

TRACKS The fi rst tape recorders, bu ilt during and after World

War II , used up the ful l tape width for a single passage. Later, as tape recorder components, recording tape and techniques became more refin ed, the tape width was split into two and then four "tracks." This provides greater tape economy and, moreover, the possib ility to store two (or more) channels on the tape. Most modern open reel stereo tape recorders for amateur use are 4-track models, whereas in cartridge recorders and players the same tape width (1/4 inch) is divided into eight tracks.

'§j r>.~:·l >-·r;~T Tape Shield

4-track stereo Tracks 1 & 4 Tracks 3 & 2

Fig. 4- 2 Track Locations in Tape Heads

Magnetized particles

Emulsion

Fig. 4- 1 Schematic View of Recorded Tape

Current

Magnetic flux Fig. 4- 3 Structure of Tape Head

29

Antl·mll(lne,Jc fratnll

a~''"""'•' Shield case Fig. 4- 4 Permalloy Shields A~alnst High Frequencies

30

TAPE SPEEDS recording time. The tabl e (P.30) shows recording times r-----------. Another tendency in tape recorder design has brought (per track and per return trip) for common types of

about slower and slower tape speeds. Although profes- ree l tapes at 7-1/2 ips recording speed. Remember th at sional studio machines transport the tape at least the 3-3/4 ips speed provides twice the recording time, 7-1/2 o r usually 15 or more inches per second (ips), and1 -7/8 ipsfou rti mesas much.

most home·use tape decks offer a choice between 7-1/2 and 3-3/4 ips, and sometimes 1-7/8 ips. Cartridge player1 TAPE QU~LITY always run at 3-3/4 ips whi le cassette tape is transported The quali ty of the recording tape is equall y as at 1-3/4 ips. This explains the comparatively long important as that of the equipm ent itself. Poor qual ity <D Shleld case Q) Colls recording time of cassette tapes. tape wears out your tape deck fas ter than necessary. <%> Shield plate ® Core holder

Tape speed is of vital importance for the soun(j Some of the demands on quality tape are obvious: it Fig. 4-S <S> Ferrlte core

qu ali ty, especially in the high sou nd range, because must [)Ot break or stre tch easily, its edges must no t curl, ~~~r~!r~~~uJe of a tape recorder's upper frequency response limit il and its base must retain its strength and fl exibi lity for .__ _________ _, directly and mathematically related to the tape speed many years. Also, th e emulsion must not separate from and the gap width of its recording and playback heads. the base or wear off because this fouls the heads and The higher the tape speed, and the narrower the head tape path and causes "drop-aut." i.e. holes in sound. gap, the better the high-range frequ ency response. Most As the tape co~stantly rubs against the recordi ng and hi- fi fans with open-reel tape decks therefore prefer th e playba~k heads, 1ts surface should be as smooth and even highes t ava ilable speed for recordings they consideJ as poss1ble to assure long head service life. In addition, important. Recent advances in the technol ogy of record- there are numerous requiremen ts regarding the tape's ing heads have made it possible to manufac ture ul tra- electrical characteristics - its dynam ic range, frequency narrow head gaps so that excellent frequency response response and freedom from noise.

up to t~e limi ts of th e audible sound range can now LOW-NOISE HIGH-OUTPUT TAPE be obtamed even at the slow t d (F er ape spee s errite head, etc.).

In recen t years, a new variety of recording tape has Chromlum Dioxi<fe Tape

Tape speed is of course directly connected . been put on the market. These so-called "low noise tThls newly developed tape use

With h. h t II "I chromium dioxide particles In

1g ou put tapes, ava1 able on open reels and as ~lead of the conventional Iron THICK- LENGTH RECORDING t . . .

TYPE BASE NESS TIME(

7_112

ips com~ac cassettes, possess h1gher magne t1c particle oxide ones, and is distinguished

(mils) (m) (ft.) ONE BOTH dens1ty and therefore a wider dynamic range - they can from other tapes by its very high

Standard 100 2.08 WAY WAYS record and reproduce a greater span of sound intensities output and low distortion, as wei

Aceta te mils 370 1,200 32m in 64 min from a whisper to a roar. To make full use of these as Its excellent frequency response and wide dynamic range. To ge .. Polyester .. .. .. .. .. RECORD ING the most from this tape, you

Low noise high Acetate I (,TYPE BASE THICKNESS LENGTH TIMEl7·172 ips) tape deck should have a bias o

output 100 .. .. .. .. .. ONE BOTH

J .• (mils} (m) (ft.) WAY WAYS equalizer circuit for chromium

.. Polyester .. .. .. .. G-30 Polyester 0.72 45 ISO 15min 30m in tape as we ll as for LH tape .. Chrome tape technology Is prom·

Long play I 50 Acetate 1.40 550 1,800 48 96 C·60 .. 0.72 90 300 30 60 ising for cassette stereo since It~

.. Polyester .. .. II .. performance permits the user to .. Double play .. 1 740 2,400 64 128 ~-90 II 0.72 135 450 45 90 reach sound levels quite simila

Triple play II 0.80 1,100 3,600 96 192 C.120 II 0.72 180 600 60 120 to many expensive open reel tape

!deck~.

31

DOLBY SYSTEM Dolby system is a unique noise reduction system, wh ich elec­tronically eliminates the irritating noise (tape hiss, circuit noise, etc.) without sacrificing the original tonal quality.

Noise Level

Noise , Level .., . .f\,..,......,,.,

RECORDING PROCESS

ovu hrlt~'tM:---

Noise Level

@

PLAYBACK PROCESS

DOLBY SYSTEM (graphs) <D Noise level is not disturbing.

(Signai=Fortissimo) <2> Noise level is disturbing.

(Signal: Pianissimo) ® Fortissimo signals are

recorded naturally. @ Pianissimo signals are up­

leveled and recorded. @ Pianissimo signals are down­

leveled and played-back. @ Since noise level is down­

leveled by same degree, it is not disturbing.

DOLBY is a trademark of DOLBY LABORATORIES INC.

32

advantages, however, the tape recorder mu st have <

special provision, an adjustable or switchable "biaPPEN REEL, CASSETTE, CARTRIDGE? current." The choice between open reel, cassette and cartridge

(An audio frequ ency signal is never recorded orhas become very much a question of personal prefer­magnetic tape as it is: the tape develops its optimurrences. Until only a few years ago, no status-consc ious characteristics only after it has been "p rimed" with ;"eli te" hi-fi fan would go near a cassette recorde r, rather high frequency bias cu rrent. This bias currentbranding them as kid stuff for amateu rs. The latest usually applied through the recording head together wittgeneration of cassette decks have made many a "reel the audio signal, is different for ord inary tape and fo1snob" eat his words because they deliver, despite thei r low noise, high output tape.) slow tape speed and narrow track width, quite respecta-

Before we talk about the factors that determine thtble sound in addition to their great snap-in, pop-out qu ality of tape equipment, let's take a brief look at th1convenience. This was made possibl e by the development many, sometimes confusing, types bei ng marketed. w1of new precision drive systems, ultra narrow gap heads have already made a distinction between reel, cartridg1and; las t but not least, better recording tape. Cassette and cassette equipment. Each group is further dividecdecks can be recommended ch iefly to hi-fi fans who into "tape deck," "tape recorders" and "tape players." prefer to get their music the easy, uncomplicated way

and who don' t mind that cassette tape cannot easily be TAPE DECK, RECORDER, PLAYER? edi ted, i.e.cu tan d spliced .

A tape deck, the most com mon and sensible variet) Cartridge equ ipment for hi-fi install at ions owes much for use in hi-fi installati ons, consists of the tape transporlof its popu larity to its almost fully automated ease of and the required recording and playback pre-amplifien operation and to the wide-spread use of automobile but no power amplifiers or loudspeakers. A tape dec~stereo players which use the same tape cartridges. Most can record through microphones or from a tuner o1cartridges are recorded with eight tracks. Since one track amplifier, and pl ayback is also possible via an ex ternalcorresponds to one stereo channel, fou r stereo programs amplifier and speaker system. (or two 4-channel programs) are contained on one

A tape recorder is, in addition, equ ipped with it1cartridge. The tape is wound in an end less loop, travel ing own power amplifier and loudspeaker(s). It can be usedarou nd and around. At one point, a metal switching foil as a self-contained unit for record ing and playback. lnis attached which, when trave ling past the head, activates this class we find most portable tape equipment as wel[a switching relay . Thi s in turn makes the head move one as some self-contained home units. step down (the width of two tracks) so that it will scan

A tape player, finally, is a tape deck minu s thethe next program. In addi t ion to its great convenience, recording facilities, i.e. for playback of pre-recordedcartridge tape has the advantage of traveling at 3-3/4 ips, tapes on ly. Most cartridge tape equipment fall s intotwice the speed of cassettes, and can be expected to this class because stereo tape cartridges are chiefly solrdeliver better high range frequency response (which is with commercially pre-recorded music. There are, how-not always true, though). Also, a great deal of music, ever, a number of cartridge decks equipped for recordin1mostly jazz and popular, is available on commercial as well as playback and - the latest addition - 8-tradPre-recorded cartridges. 4-channel cartridges and players which serve as con· Despite the inroads made by cassette and cartridge

Model CT- F71 71 (F ront-access Cassette Deck)

Model CT - F6161 (Front-access Cassette Deck)

venient sound sou rces in a 4-channel stereo system. equipment, the open reel tape deck is still the most fig. 4- 6 common, most versatile, most advisable (and most Schematic View of expensive) recording and playback instrument for the _c_as~s_e_tt_e_T_a_.p_e _____ __,

33

Car.trldge Rae!

'~----~------~ ,, ' \

\ I I I

I

Fig. 4-7 Endless Loop Type Tape Cartridge

Model RT-1050 ( 15ips, Half-track Deck )

.. .-:.-~~-.:.. :: : __ , ... -

~~~!i~j{J{J,ii

Model MA-62 (Microphone Mixing Amplifier)

34

serious hi-fi enthusiast, and it is th e open-reel stere deck that wi ll be examined in the fo llow ing paragraph! although the principles appl y to cassette and car tridg equipment as well .

DRIVE MECHANISM The mechanical part of a tape dec k has to move th

tape past the heads at constant, specified speeds. This i done by a rotating capstan against which the tape i pressed by a pinch roller. In the design of thi mechan ism special attention must be paid to avoid tap slippage. Th e mechanism mu st perform two other fun( tion s: rapid forward winding and rewinding of the tapt All three tasks can of course be carried out by a singl motor and a system of belts, pulleys and idlers - Fit 4- 8 shows such a drive system.

Fig. 4- 8 One-Motor Drive Mechanism

TWO AND THREE MOTOR SYSTEMS Where highest precision and rapid winding speed

are required and cost is the minor consideration, separat motors can be used to drive the capstan and both reel or three separate motors for the capstan and each reel Such top class tape transports are often contro lled vi electronic relays and pu sh -buttons and embody tensio1 regulators and other devices to protect the tape fron excessive forces. In two and three motor transports, th capstan and reel motors are of radically different desigr

so that each can go about its task with maximum efficiency.

Pinch roller

Three-Motor Drive Mechanism

RECORDING AND PLAYBACK HEADS A tape deck needs at least two heads - an erase head

which cleans the tape of previous recordings and noise, and a combined recording/playback head. The im­portance of the head gap has already been mentioned. Other points of interest include the heads ' surface polish - the tape must travel over it with as little friction as possible - and its dimensional accuracy and adju stmen t. {The track locations on the tape are of course deter­mined by an international standard so that a tape recorded on one machine can be pl ayed back on any other provided they use the same 2-trac k or 4-track system.)

THREE-HEAD DECKS Hi-fi enthusiasts who wish to make their own record­

ings are well advised to bear the extra expense of buying a 3-head tape dec k, i.e. one with separate record ing and playback heads (p lus erase head). Not only can each head be designed especially for its own purpose, but 3-head systems offer the only really accurate recording control possibi lity: tape monitoring. It works li ke this: as the tape travels pas t th e recording head, it is " im­pregnated" with the audio signal. This same, original audio signal which comes from the sound source can

. . . . .. .. . ··""','.

f ..... \ 1 Flywhaal ••••• • Capstan

Pinch roller

4/8 pole capstan drive motor

Fig. 4- 9 Two-Motor Drive Mechanism

35

Input Mic o-..--o... _ line

Outputo.----+;...;.::..:.::..;~-------1

4- 11 Two-Head Mechanism

-Recording head

Level meter

Fig. 4-12 Three-Head Mechanism

EH : Erasing heed

PH : Playback head

RH: Recording heed

Fig. 4-13 Tape Monitoring

36

si multaneously be monitored through speaker systems (via the amplifier) or headphones. Then, as the tape travels on past the playback head, the just-recorded sound can again be picked up and monitored. Three-head tape decks are equi pped with a switch to switch back and forth between source monitoring and tape monitoring. Thus, the operator can compare the source sound instantly with the recorded sound and make necessary re-adjustments. Because of the distance from recording to playback head which the tape has to travel, there is of course a short time lag between source and tape monitor sound.

AMPLIFIERS, EQUALIZATION Although tape decks don't need power amplifi ers,

they do need electron ic circuits th at transform the signal to be recorded into a shape acceptable by the tape ("recording amplifier, recording equalizer" circu its) and others th at augment and again transform th e signals picked up by the playback head so that the amplifier

can work with them ("pl ayback equal izer, playback pre-ampl ifier" circuits).

(Technically speaking, an audio signal of flat fre­quency response, when recorded and played back via tape, would drop off in its very low an d very high portions. To compensate for this, the low and high parts of the frequency response curve must be ra ised. This is done accord ing to an intern ationally agreed-upon method, the so-called NAB equal ization curve. The high portion is boosted in the recording equalizer, the low portion in the playback equalizer so that the tape deck's outpu ts again supply a signal with fl at response.)

RECORDING LEVELS As recording tape has only a lim ited capacity for

storing magnetism, the recording level - th e st rength of the signal applied to the tape head - must be controlled. This is done with a control knob and usually two VU or level meters (one per channel). Excessive recording level causes di stortions, whi le an insu fficient level results in noisy, hissing tapes.

The need to apply a high-frequency bias to the tape while recording has been menti oned; this frequency, somewhere in the 30- 1OOkHz range, is gene ra ted by the "bias oscill ator."

AUTOMATIC STOP, AUTO-REVERSE

To make the tape deck as convenient to operate as possible, a number of auxiliary devices have been de­signed. Very com mon is an automatic stop mechanism that halts the reels when the tape runs out. Among the several possible meth ods, the most common one employs a lever which, normally held upward by the tape, drops forward and activates a stop switch when the tape runs out.

To get rid of the necessity to remove, turn over and re-thread the tape after each run, various au tom a tic reverse systems have been devised. One, the sensing-foil method, is the most popu lar. The user affi xes short pieces of metallic foil near either end of the tape. Tape

Frequency (Hz)

Fig. 4-14 NAB Equalization Curve

RPH : Recording;playback EH : Erasing heed

Fig. 4-15 Auto-Reverse Function

heed

37

38

gu ide and tension arm (two parts of the tape path! serve as contact points for a relay. When the meta sensing foil reaches these parts it closes an electri1

circuit, activating the reverse relay which, in turn, mak~ the tape travel back in the other direction. The length oi tape between the two sensing fo ils thus t ravels bacl and forth infinitely. At each reversing point, tape head! and tracks are switched accordingly. As illustrated in tht drawing, an au to reverse tape deck needs two erase head an d two double-action recording/playback heads.

How to Read Tape IJecl• Specifications a) Wow & Flutter Inconsistencies in the tape speed whi ch can cause pitd variations and quivering sou nd. Expressed as percen tagc1 with differen t values for each tape speed. Look for th lowest values. 0.25% is about the permissible maximum b) Signal-to-Noise Ra ti o Denotes the tape deck's freedom from sci f.create. noise. Expressed in decibels, higher values are bettct 45dB is about minimum. Pioneer decks arc 55dB o better. c) Frequency Response The lowest and highest aud io frequ encies that the tap deck wi ll record and reproduce. Should be as fl at a possible and cover at least 50 · 13,0001-fz at 7·1 /2 ipso 50· 1 O,OOOHz at 3-3/4 ips.

Parameter Excel· Good Fair Un lent

Signal to Noise Ratio 54- 56 50- 53 45- 50 dl

7-1/2 30- 50- 50- H 16,000 13,000 10,000 Frequency 3·3/4 50- 50- 50- H response 12,000 10,000 8,000

1·7/8 SO- 50- 50- H 8,000 7,000 5,000

d) Crosstalk The amount of signal that leaks (i) from one stereo channel in to the o ther and (ii) from one tape track int

another. Expressed in decibels. The higher the value, the better. Channel-to-channel crosstalk should be at least 30dB, track- to-track crosstalk of a 4- track mach ine should be above 55dB. e) Channel Separation Another word for channel-to-channel crosstalk (above). f) Maximum Reel Diameter 'The largest reel size that the tape deck will accept. Most open reel decks accept up to 7" diameter reels; All Pioneer decks accept the profess ional-sized 10-1 /2" reels.

39

40

........ , .... 0 • : oo e oo .... •o o:

Receiver

Fig. 5-1 Classification of Amplifiers

Chapter5

The Amplifier As the audio signals supplied by the turntable, tuner

or tape deck are much too weal? t o be converted into audible sound directly, they must firs t be raised to a higher level. This is done by the amplifier which thereby becomes the heart of every hi-fi installation. Before we examine the fundamentals, functions and features of hi-fi amplifiers, we must first clarify a few distinctions in terminology.

PRE-AMPLIFIER, POWER AMPLIFIER, INTEGRATED AMPLIFIER, RECEIVER

An amplifier system in a hi-fi instal lation consists of two parts: the pre-amplifier which includes all the controls for regul ating tone, volume and channel balance; and the power amplifier which, as its name implies, suppl ies a sufficiently powerful signal to drive th e loudspeakers. Manufacturers provide the audio enthu siast with a multiple choice: he can purchase separate pre-amplifier and power ampli fier un its, he can select a combination of both which is commonly called " integrated amplifier," "control amplifier" or just simply "amplifier," or he can opt for a receiver, i.e. a combina· tion of tuner, pre- and power amplifier.

Since units bui lt to very high performance standards can be found in each group, the question is not so much one of sound quali ty but rather a question of fl exibility versus economy and convenience.

It stands to reason that a combination of two or three func tions in one unit should be more economical than separate sets - just think of the cost of chassis and enclosures and power suppl y uni ts (i.e. th e transformer­rectifier assembly in each unit which supplies the needed operating current to the circu its). Wh at 's more, an integrated ampli fier or receiver saves space and eliminates the need for - sometimes troublesome -

cable connections. On the other hand, the pu rchaser of a separate tuner

plus pre-amplifier plus power ampli fier system may gain a little bit in performance and may obtain a more individually " selected" kind of sound, but he definitel y gains in flex ibility; he can replace individual units as technology progresses and new model s appear on the market; he can easily add an electronic crossover net­work and one or two more power amplifiers to upgrade his system into a multi-amplifier installation (see page 59); he can move on to a four-channel system (page63 ) without sacrificing any of his present equipm ent; and he gets, last but not least, the pride of owning his own custom-assembled personalized system.

The serious audio enthusiast, when deciding on the purchase of a receiver or integrated amplifier, shou ld, however, insist on one feature (found on most Pioneer models): the possibili ty to use the pre-amplifier and power ampl ifier stages separately. This is done by mov­

ing a rear-panel switch (in the case of Pioneer amplifiers) or by removing jumper cables or plugs, and permi ts the system to be enlarged into a multi-amplifier configura­tion at a later date.

The following expl anations deal with pre-ampli fier and power amplifier functions, in that order, but th ey apply to integrated amplifiers and receive rs, too; onl y the remarks about connections and matching of com­ponents may be disregarded.

PREAMPLIFIER FUNCTIONS

To the hi-fi novice, the need for and functions of the pre-amp li fier are usually more di fficult to understand than those of the power amplifier wh ich after all clearl y produces power. The pre-amplifi~r can b~ thought of as sort of super switchboard - it selects the sound source to be pl ayed, it determines th e mode of sound (4-channel, stereo or monophonic), it influences the sound color with its tone controls, it regul ates the volume and channel balance, and it brings the signals up to a voltage level which the power ampli fier can then

Stereo Receiver (Model SX-1 01 0)

Stereo tuner (Model TX-91 00)

Stereo Integrated A mplifier (Model SA-9100)

Stereo Preamplifier

41

11< Frequency (Hz)

Fig. S- 2 RJAA Equalization Curve

work with. The different sound sources are connected to the

preamplifier inputs: the turntable to the phono inputs, the tuner to the tuner inpu ts, the tape deck to the tape (or sometimes "monitor") inputs, .and an aux iliary source such as a cassette tape deck to th e aux inputs. Some ampli fiers also have microphone inputs.

PHONO EQUALI ZATION Let us observe the phono signal on its way through

the pre-amplifi er. First, it enters a circuit called an equalizer amp. To understand its function, we must be aware of a peculiarity of phonograph records. When the mas ter disc is cu t, th e high sound ranges are over­emphasized ("boosted") while the bass range is some· what suppressed. This must be done in ord er to obtain a record groove with sufficient modu lations in the high range for the needle to "feel" and, on the other hand, without excessively wild bass undu lations (because these would requ ire a wider groove). Technically, cu tting of a disc is not " fl at" but foll ows a frequency response curve as shown in Fig. 5- 2, called the RIAA curve (es tablished by the Record Industry Association of America). There· fore, the aud io signal delivered by the pickup cartridge would result in equally disfigured sound if it were passed on as it is. The RIAA curve must be "equalized" first to obtain natural sound - and this is the function of the equalizer amp.

~ ~~-----a:

'· '· ,_ ,_ , __ Recording--Equalization in amplifier-Resultant flat response

Fig. S- 3 Equalizing

INPUTS Because the phono inputs have to be equali zed, they

are called "non-linear" inpu ts as opposed to " linear inputs" such as those for tape, tu ner, microphone or auxiliary signals. Some high grade amp li fiers provide two or even th ree pairs of phono inputs, permitting two or more turntables or cartridges to be connected simu l­taneously for easy comparison. Also, the input sensitivity and impedance of the phono inpu ts is sometimes switch­able to accommodate cartridges of differen t char­acteristics. In this context, another value often foun d in pre-amplifier specifications is of importance: maxi­mum input vol tage of the phono inputs. Th is describes the highest signal level that the amplifier can accept through the phono inpu ts withou t ove rl oad ing, i.e. distorting. It should be at least 10 times higher than th e output level of the pickup cartridge.

Tape deck and tuner connections usually do not pose much difficulty because the electrical charac teris tics are pretty much standardized. With microphones, how­ever, it is important to choose the righ t type. Pioneer microphones of course are matched to Pioneer ampli­fiers, but mikes of other brands must correspond in their impedance to the amp 's mic input impedance, within a tolerance of about ±20 percen t.

TAPE MONITORING

Switching between the different connected sound sources is usually done with a program selector, mostly a rotary knob with five or more posi tions. Tape sound, however, is switched on and off with a so-called tape monitor switch with two posi tions: "source" and "play" (or "tape"). For tape playback, this switch is set in position " play," for all other program sources it must be in position "source." When making a recording on a tape deck with independent record ing and playback heads (a 3-head deck), this switch provides two ways of monitoring the recording quali ty. In position "sou rce" the original before-tape sound is heard from the loud­

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ speake~; in position ''play, " howeveG the already

42

Model DM- 30

Electret condenser type microphone

43

iTWIN TONE CONTROL SYSTEM ifhis system is unique with Pioneer. It features spec ial SUB controls in addition to the more conventional BASS and TREBLE controls. The SUB controls permit you to boos or cut the frequency in both the ow and high ranges without

affecting the midrange sound. Practical applications of this sys· tem are as ind icated in the follow mg diagram:

Frequency Response

50Hz 100Hz lOKHZ 20KHz Frequency Response

44

recorded after-tape sound is reproduced . By switching back and forth between th ese positions, th e source sound can be eas ily compared with the taped sound and readjustments made if required.

VOLUME, BALANCE, TONE CONTROLS The volume and balance controls of the stereo pre­

amplifier are more or less self-explanatory. Note, how­ever th at th e balance control, when turned to the right, doe; not increase the right channel volume but actually reduces the left channel volume. Al so, volume and balance controls do not affect the signal supplied to the tape deck for recording.

17 I

1 Speakers Switch 2 Protect ion Pilot Lamp 3 Bass Controls 4 Treble Contro ls 5 Level Set Control 6 Volume Control 7 Function Selectors 8 Power Switch, Pilot Lamp 9 Headphone jack 10 Muting Switch 11 Low Filter Switch 12 Tone Defeat Switch 13 High Filter Switch 14 Loudness Switch 15 Balance Control 16 Tape Monitor Switch 17 Tape Dupl icate Switch 18 Mode Switch

1 t is usually not difficult to tell the hi-fi greenhorn from the old pro - just watch him operate the tone controls of his amplifier. The beginner will show great delight in his abili ty to turn up the bass and suppressing the treble or vice versa, he will play around endlessly

with these knobs and will usually wind up with a setting of heavy, boomy bass accentuation. The more advanced hi·fi listener, however, will use the tone co ntrols sparing­ly and near the neutral level, except for tes t purposes. The true purpose of the bass and treble con trois on a hi-fi amplifier lies indeed not in th e dictatorial power pl ay of the novice, but in the ability to compensate for certain weaknesses in the program material , the listening room and, to some degree, th e speaker systems. With good, new LP records or tapes pl ayed on good equipment in a normal family living room, however, extreme tone control settings are almost never required.

How do tone controls - and th eir cousins, the high and low filters and the loudness switch provided on most ampli fiers - work?

In its simplest, bargain basement form - as found on portabl e radios etc. - a tone control is simply a combination of a capacitor with a res istance, and it cuts off the high parts of the sound spectrum. More suitable to hi·fi applications is the passive CR (capacitors· resistors) type which boosts or reduces frequencies above and below a " turnover" point in a way as illustrated in Fig. 5- 4. For even more precise, ac tive control, negative feedback techniques (NFB) have to be introduced whict- require rath er elaborate circuits with transistors, etc. The obtainable frequen cy response characteristics are illustrated in Fig. 5- 5.

On some amplifiers, the tone controls work on the left and right stereo channel simultaneously, which is quite sufficient for most home applications; on oth ers, there are separate knobs (usually concentric double knobs) for controlling the left and right channel separately which is useful in difficult listening room conditions.

FILTERS, LOUDNESS CONTOUR

Low and high fi lters (also referred to as rumble or bass filters and noise or scratch filters, respectively) have functions as shown in Fig. 5- 6. The bass filter is designed to cut off (or, more precisely, to attenuate by

45

46

so many decibels) the sound spectrum below a certain point, usually somewhere between 100 and 50Hz. This has the effect of cancel ing out very low hum and rum ble generated by turntables. The high filter, on th e other hand, attenu ates frequencies above 8,000 or 1 O,OOOHz, as the case may be, to eliminate scratching and hissing noise from records, tapes, FM, etc. It is bad practice, however, to use these filters indiscriminately because together with the noise they also cancel part of the desi rable musical spectrum . Use them only when necessary.

The loudness switch on an amplifier must not be confused with the volume control. A more accurate description of its function is found in the name " physiologi call y correct loudness contour compensa­tion." This name already hints at a deficiency of the human sense of hearing. Indeed, measurements demon­strate clearly that the human hearing apparatus is, even at its healthy best, a far from perfect hi-fi device. One of its short-comings is that it is rather insensi tive to extremely low and very high tones when the overall volume is so ft. The loudness switch, a special kind of tone control, overcomes this hum an error by boosting these extreme sound ranges at low volume settings. It should therefore be turned off at high listening volumes.

BACK VIEW QF INTEGRATeD AMPLIFIER ISA-9100)

HEADPHONE JACK In addition to the functions described above, the

pre-amplifier does of course amplify the signal level to

an extent. That is why headphones, which require very little power, can be connected to a headphone jack usual ly provided on pre-amplifiers.

POWER AMPLIFIER FUNCTION From the pre-amplifier, the signal enters the power

(or main) amplifier. There, its power is raised several hundred times to a value which can drive {and, if used fully, even destroy) the speaker systems.

Much concentrated effort has gone into the develop­ment of better and better hi-fi power amplifiers. Even the vacuum tube types of years ago- on ly very few are now on the amateur hi-fi market - produced some excellent results. To th is day, hi-fi enthusiasts brought up in that age swear by the vacuum tube amp I ifier and in terms of sound quality it does possess a ce,rtain mellow charm. Its bad habits - vacuum tube amplifiers guzzle electrici ty, create tropical heat waves in their

STEREO POWER AMPLIFIER

vicinity and break down or bu rn out at all too frequent .------------.­in tervals - made it easy for solid state designs to take over in a flurry. Today, the transis tor power amp has emerged as the almost undisputed victor.

CRITERIA OF QUALITY

Solid state power am plifiers of the latest generation are true marvels in audio engineering, with tremendous power reserves, a remarkable absence of distortions and very high reli ability. Design engineers have overcome the many inherent problems one by one by making use of improved components such as silicon · transistors, by developing new circuits such as quasi-complementary and pure complementary output stages, by getting rid of coupling transformers and capacitors.

Conventionally, capacitors were used to couple the individual stages of a power ampl ifier, and to couple the output stage to the loudspeakers. Direct cou pling techniques are posing a new challenge to circuit designers. They promise better results not only because they avoid phase shifts between the stages but also, and more importantl y, because they use so-called balanced

OCL CIRCUIT

power supplies - i.e. power supply circuits providing L--=---.....:....:..=...:.:.~;.:.;.......:::.l!..J

47

matched pos1t1ve and negative power correspondin g to the (+) and (- ) sections of the sound signal. Such direct coupled and OCL ("output-capacitor-less") circuits are already being used in most top grade Pioneer ampli fiers.

The purchaser of a stereo power amplifier often chooses a unit mainly on the strength of its outpu t power rating. But as practically all modern amplifiers provide more than a sufficient power reserve, he wou ld be well advised to consider other factors in his choice, such as distortion figures, power bandwidth, etc. which will be explained in the paragraph dealing with amplifier specifications. These give a truer picture of the sound to be expected than the power rating.

PROTECTOR CIRCUITS The expensive output stage of a transistor amplifier

can be easil y damaged by a short circu it in the speaker leads. To prevent this, designers have invented a variety of protector circui ts and combinations thereof which shut down the output stage at the first sign of trouble. These can be sim ple heat fuses or, more elaborately, circu its which detect a drop in output load impedance (in other words, a short circuit). A few top quali ty ampli fiers have protector circuits which detect the presence of DC current at the output stage. As DC current cou ld also lead to loudspeaker damage, these advanced protectors safeguard not on ly the amp I ifier itse lf but also the connected speaker systems.

SPEAKER TERMINALS Although one pair of speaker systems is usually

quite sufficient for a home stereo installations, som.e ----.,-----,.------, amplifiers includ ing most Pioneer models have provi­

sions for connecting two or even three pairs of spea ker systems which can then be driven separately or in pairs. One obvious use is to place a second pair of speaker systems in another room. This feature also permits direct comparisons of different speaker systems by connecting two or three pairs to the amplifier and

!J!l!~~~!:..:l±.:...d switching back and forth.

How lo llead i\mplifier H)Jerifiralions a) Continuous Power Output - The FTC Rule Pi oneer has and wi ll con tinue to comp ly with the new ru ling (effective November, 1974) es tablished by the Federal Trade Comm ission (FTC) of the United States as regards the listings and claims fo r the power output specifications for am plifie rs (including amplifiers in­corporated in receivers). Thus, all Pioneer specification sheets, adver tisemen ts, sales promotion materials and other printed matter which list power ou tput specifica­tions do so in the Un ited States by statin g the deta ils of the actual continuous power output for all channels, al l channels driven, in terms of minimum RMS (Root Mean Square) watts. The listings also give the exact conditions un der which the rating is taken, with the load im pedance {in ohms), and the amount of total harmonic distor tion {in percen tagc) given clearly. This information appears in the fo llow ing form (w ith slight variations as rcqu ired): "continuous power output of 60 watts* per channel {for example), min . RMS at8 ohms, all channels driven, 20 to 20,000 Hertz with no more than 0.1 % total harmonic distortion ."

The asterisk in the listi ng is a reference to the footnote, also carried in all Pi oneer printed matter listing specifica­tions, which reads "*Measured pursuant to Federal Trade Commission's Trade Regulation rule on Power Ou tput Claims of Amplifiers."

b) Music Power (Dynamic Power) Often encountered in advertisements. Of dubious va lue because measured under conditions other than norma l usc. Usually given as the sum of both stereo channels, unfor tunately often without distortion figures. judge an amplifier's power ch ie fl y by its continuous power rating (above)! The music power ra ting does, however, provide some in formation abou t the power avai lable temporari ly from the amplifier when reproducing volume peaks in the music. Good ampl ifiers have music power ratings not very much removed from their con tinuous power figures .

STEREO DISPLAY Model SD-11 00

For measuring and sco p ing var ious k inds of characterist ics of your equ ipment.

49

c) Frequency Response

The lowest and highes t audio frequencies th at th e amplifier will reproduce from input signals supplied to its AUX input and at 1 watt output power. To be meaningful , the frequ ency response rating must be accompanied by a ± dB figure which indicates by how mu ch the response varies from the standard level (OdB at 1kHz) over the given frequency range. Smaller decibels values are better - the same amp may have a frequ ency response of 20 - 18,000Hz ± 1 dB or 18 - 25,000Hz ±3d B. Example of an outstanding amplifier rating: Frequency . . . . . . . 15 - 40,000Hz ± 1 dB response (through AUX inputs) d) Power Bandwidth

..-----------., An important value th at puts output power and Power output (W) frequency response in a relation. Power bandwidth

\J~2

1rJNrJN signifies the audio frequency range (in Hz) over which

the amplifier will deliver at least half of its rated outpu t power withou t exceeding its rated harmonic distortion. For example, if th e continu ous output power of an

~~""""'.::o--:---..--_,........L.._ amp is listed as 20W per channel at 1% harmonic distor-30,000 tion, then a power bandwidth rating of 20 - 30,000Hz

.FI'fqUII\CY (Hz) means that the amp will deliver 10 watts at 20Hz and

'"~~:r-J!dwldth at 30,000Hz without distorting more than 1%. - - ----------" e) Signal-to- Noise Ratio

The ratio between (wanted) signal and (unwanted) noise delivered by the ampl ifi er at maxim um volume setting and with its treble and bass tone controls set at flat positi on. The higher the value, the less hum and noise there is. Signal-to-noise ratios should be listed individual­ly for each input; for instance: PHONO (MAG) 65dB, AUX 70dB. A 65dB ra ting means that onl y 1/2000 of the signal will be noise, 7 5d B means 1/6000. f) Damping Factor Mathemati cally, the quotient of the load impedance (i.e. speaker voice coil impedance) and the ampli fi er 's internal res istance. For example, if speaker impedance is 8 ohms and th e amplifier's internal resistance is 0. 1 ohm, the damping factor is

8 oh m 0.1 ohm

= 80.

Damping factor is a measu re of an amplifier's abi lity to damp, i.e. control unwanted residual speaker movements caused by forces other th an the audio signal. Higher values arc better, but anything over 20 is not really very meaningfu l. g) Input Level, Inpu t Impedance Inpu t level : the minimum level of the input signal supplied to the power amplifier from which it will deliver its full outpu t power. Shoul d be around 0.1 V-1 V must be close to the pre-ampl ifier's ou tpu t level. (Or~ l y important if separate pre- and power amps are used. ) Input impedance : The power amplifier's load impedance as seen from the pre-amplifier output. Should be at least 50 k-ohms when using a modern transis torized pre-am pli fier.

51

SPEAKER SYSTEMS

52

chapter&

StJeaker S}'slents and Headphones Speal?er systems in a hi-fi system are somehow like

the last pages of a novel. The plot gradually thickens, the parts of the puzzle fall into place, and from them emerges the solution and the revelation of the writer's intents. But, as in som e stories, speal?er systems are not always a happy end, sometimes leaving questions un­answered, wishes unfulfilled.

Speaker systems are as simple in theory as they are complex in fact. Let's look at their structure and func­tions first. And by the way, the use of the term "speaker system" is more technically correct than the terms "lou dspeaker" or "speaker," because as you wil l see a speaker system is made up of several ind ivid ual parts -speaker units, crossover networks, etc. - which toge ther function as a system. One "speaker system" is needed for each channel in a stereo insta ll ation; thus a 2-channel stereo set-up has a "pair" of " speaker sys tems" while a 4-channel set-up has two "pair" or a total of four speaker systems.

STRUCTURE AND FUNCTIONS The signal from the power amplifier passes through

a coil (cal led the "voice coil "} wh ich is suspended between the poles and around the center pole of a large, powerful permanent magnet. The interaction between this permanent magnetic field and the alternating magnetic fi eld generated around the coil by the signal makes the coil vibrate in rhythm with the signal. A cone-shaped membrane attached to the coil passes these vibrations on to the surrou nding air, creating sound waves. A cross section of such a speaker unit is shown in Fig. 6-1.

The speaker cone, being a mechanically vibrating mass, has a resonance point, that is a certain sound

frequency at which it " likes" to vibrate more than at others and in the vicinity of whi ch it wou ld therefore over-emphasize the sound. One major task of designers, therefore, is to el iminate this resonance or at least to bring it under con trol or lower it beyond the lowest audible sound frequency. This is done by means of speciall y se lected cone paper and cone designs.

DOUBLE CONE AND COAXIAL SPEAKERS

On the other hand, a speaker can reprod uce only a limited sou nd range - large-diameter speakers are best at delivering the low sound spectrum, small ones are most sui table for the high range. Th ough most portable and economy class audio equipment has only one full­range loudspeaker, various ways have been conceived to divide the sound spectrum into two or three ranges and feed each portion to a cone of the proper dimensions. One method is illustrated in the photo, the double cone speaker which does not really have two cones but a cone made of two diffe rent kinds of paper for the low and high ranges. The next logical step is the coaxial speaker shown in Fig. 6- 2, which has a larger, outer pape r cone for the low ran ge and a smaller horn speaker for th e medium and high spectrum. (Designs with th ree coaxial­ly arranged low, medium and high range speakers are called tri-axial.} In the coaxial speaker, there is some­times a crossover network wh ich divides the signal into the suitable portions, and level controls {attenuators} for each range.

TWO-WAY, THREE-WAY, FOUR-WAY SYSTEMS

By logical extension of this principle, we arrive at speaker systems with two, th ree or even four separate speakers mounted in one enclosure. According to the number of sections into which the aud io spectrum is divided, such systems are called 2-way, 3-way or 4-way. The number of speaker un its in such a box is not always the same as the number of ways, because the high range "tweeters" and mid-range speakers are sometimes

Fig. 6- 1 Cut View of Cone Type Speaker

Double cone speaker

53

Coaxial speaker

Plate \ Driver unit Voice coli

Fig. 6- 3 Horn Type Speaker

54

doubled , so that we get 3-way 4-speaker or 3-way 5-spea ker systems.

In such sys tems, each speaker unit can be designed to reproduce, as ideally as possible, its apportioned sound range. The low-range "woofer" is usually of large diameter (7-1 /2, 10 or 12 inch} and considerable weight because of its big, heavy magnet. The mid-range spea ker, about four inches or so in diameter, reproduces the sound range from approximately 500 to 2,000 or 3,000Hz. The top two or three octaves - up to about 20,000Hz in excellent hi-fi speakers - are the domain of the tweeter, either a small paper cone speaker or, increasingly, a dome-type with a dome-shaped membrane or a horn type with a metal horn instead of a cone. (Horns are more efficient in cou pling the sound vibra­tions to the air, li ke the bell of a trumpet.) A re latively new design is the multi-cellul ar horn used for mid-range and tweeter applications which is partitioned into a dozen or more ce ll s. The purpose of this is to diffuse the sound more evenly throughout the room.

Dl RECTIONALITY

This may require some explanati on. Speakers have the sometimes desirable, sometimes unwanted character­istic of radiating thei r sou nd in a certain, clearly defined angle which becomes narrower and narrower as the sound frequ ency becomes higher, so that twee ters show a ra ther strong directionali ty. As this would affect the sou nd diffusion in the listen ing room and limit the usable listening positions, speaker designers have come up with various methods of overcoming this deficiency. One of th ese is the multi -cellu lar horn design, o thers include the above-mentioned dome tweeter or a small reflector called "diffuser" mou nted before the tweeter.

What complicates matters for the au dio amateur is that the speaker enclosure wi th five speakers does not always sound better than the one with four - a number of other factors enter into the picture, including th e quality of each speaker unit and the way they are

matched, the size, shape and weight of th e speaker enclosure, an d the listen ing room.

SPEAKER ENCLOSURES Enclosures can be roughly divided into two types:

closed boxes and bass reflex types . A closed box is hermeti cally sealed at the back so that sound emanating ~~~t-:;; from the rear of the speakers is absorbed in the box ..._ __________ _. (which is usually lined or stuffed with sound absorbent glass wool or plastic foam}. Only the sound from the face of the speakers is radiated into the room. Closed boxes usually excel in sound clarity and subtleness, but they require rather volum inous dimensions to obtain satisfactory bass response. A modern variety of the closed box is the air suspension type, often used as compact bookshel f speaker systems, in which the woofer ,.-----------=--..., is mou nted in a soft baffl e suspension so that it can perform longer piston movements for better bass response.

The bass reflex type, on the other hand, boosts the bass sou nd by channeling part of the rear sound back to the front th rough a duct or port (see Fig. 6- 7.). In

Fig. 6- S other words, it behaves as if two woofers were instal led. Dome Type Speaker The key to successful designs of this type lies in the a.;;..;..;.;.;..;....;..:.:.....;..:... ____ __.

phase inversion which the box must perform, because otherwise the sou nd from the speaker and from the duct wou ld be out of phase and might cancel each other ou t. ~----:===-~~~~1 Bass reflex boxes are being used widely because of their smal ler volume in comparison to closed boxes, bu t their drawback is that the bass range sometimes sou nds a little boomy.

HOW TO CHOOSE SPEA KERS

The choice of speaker systems thus becomes rather tricky because specifications can say very little about the character of the actual sound. The ideal speaker system, of course, wou ld reproduce th e entire sound range without arbi trari ly add ing or subtractin g anyth ing, bu t such a system has never and can never be designed -all speakers have some individual habi ts and id io-

Sound absorbent material

Fig. 6-6 Infinite Baffle Enclosure

55

Sound absorbent material

syncracies whi ch are called "coloration " or "trans­parency" or other such abstract words. When purchasing spea ker systems, the specifications should be used to determine the general size, type and power range, but the final choice must be made ei ther after comparative listening tests. Restated, the effect of a speaker system on human hearing is what has been called a "psycho­acoustical phenomenon." Th at is, the actual, physical effect of a vibrating speaker on the air is translated to the listener's brain through a combination of the actions

Fig. 6-7 Bass Reflex Enclosure of his ear drum, etc., and his psychological reaction to L--------- - - -..1 th e physical perceptions he receives. This means that

Re : SPECIAL ENCLOSURE (Back loaded horn enclosure)

56

the "sound" of a given speaker system may be different­ly interpreted by different people. And what it means to the prospective buyer is that he should determine for himself what he is hearing. Ideally, a speaker system should be judged by the listener only when it is operat­ing from his own amplifier in his own listening room. When th is is inconvenient, the buyer should make every effor t to tes t the speaker system with equipment and in an environment which most closely match those he wi ll be using. Also, keep in mind that a reall y good speaker system should be able to satisfactorily reproduce any kind of music; there is no such thing as a "rock­music speaker system" or a "classical-music speaker system."

CROSSOVER NETWORK, LEVEL CONTROLS Auxiliary parts in a speaker system include the cross­

over network and, sometimes, one or more level controls. The crossover network is an electronic circuit which splits up the sound spectrum into the required number of ways - low and mid/high range in a 2-way system, low, mid and high in a 3-way. It consists of a combination of coils and capacitors, often equipped with ferrite coil cores which permit better damping and more compact design . The border frequencies between one range and another are called "crossover point." Unfor­tunately, they are fi xed an d unflexible in such a cross­over networ k, and they do not always deliver equal

response in each sound range. How these diff icu lties can be mastered wil l be explained in th e chapter about mu lti-ampli fier stereo systems.

The level control is a simple attenuator which permits the medium or high sound ranges to be suppressed or boosted to an extent - a helpfu l way of matching the speaker response to the charac ter istics of the listening room.

Crossover network Level control ,.:\ .... . I ,

+ I : : :

Power 1

amplifier

Fig. 6- 8 Wiring In a Crossover Network and Level Control

I]::J Tweeter

How In llead loudSJJenl•ers ti(Jecillcalitms a} Input Im pedance The load impedance of the speaker system as seen from the amplifier ou tput. 4, 8 and 16 ohms arc the inter­nationally standardized values for speakers to be driven by transistor amplifiers. Not cr it ical. b) Maximum Power Hand ling Ability Also called "maximum input power." The power (in watts} that the speaker system can handle continuously without fear of damage. Some times, a higher limit value is also given which describes the maximu m input power of short transien ts and peaks. Power handling abi lity docs not need to equal or exceed the amp! i fier's ou tpu t power unless the amplifier is to be operated at top volume - wh ich almost never happens in home applica­t ions. c) F rcqucncy Response The width of the sound spectrum (in Hz} that the speaker wi ll reproduce. Tak ing l ,OOOHz as the reference

57

Model SE-700 (High -Poly mer Headphones)

Model SE-L401 (Light-weight

Headphones)

(Sealed Headphones)

Model SE-0404 (4-channel headphones)

58

level, the lower and upper lim its arc the points at wh ich the loudspeaker wi ll still deliver 1/3 of the sou nd pressure level (= - 1 Od B). Look for wider frequency response ra ti ngs. 60 · 15,000Hz is quite sufficient.

HEADPHONES A good pair of stereo headphones is a very worth·

while, small investment for the serious listener. Head­phones serve two main purposes: they permit late-night listeni ng in com plete privacy and at fu ll volume levels; and they are indispensable for monitoring tape record­ings. Practically all modern stereo amplifiers, tape decks and even some tuners are equipped with standardized headphone jack. In some instances, the headphone volume can be adjusted with a special control, inde· pendently from the master volume setting. Al so, most ampli fiers are so designed that the loudspeakers are au tomatically cut off when the headphones are plugged in, or, have switches for tu rning off connected speaker systems while leaving th e headph one circuit "live. "

It must be noted that listen ing through headphones creates a fundamentally different sensation from listen­ing via speaker systems. As the sound enters directly into the ear, it acqui res mu ch stronger "presence." A monophonic program heard through headphones wi ll appear as if the sound sou rce were located right in the center of the sku ll. Stereophonic programs seem to be spread out in " interior space" - an ex perience that can be startl ing at first.

Good headphones should be light and comfortable to wear wi thout causing perspiration around the ears. They should also have a wide frequency response - the bass range is very critical - and should sound trans­parent, not stuffy. Pioneer offers a wide selection of stereo headphones including some models with built-in volume and tone con trols.

Chapter7

Multi-Amplifier Systems In the chapter dealing with speaker systems we

came across the terms 2-way, 3-way or 4-way, meaning that the audible sound range is divided into two, three or four portions. This division is usually made by a dividing network in the speaker systems, i.e. between the power amplifier and the speal?er units, but it is of course possible - and advantageous, as we will see -to do this at an earlier stage. The reasons are easy to understand.

REASONS FOR MULTI-AMPLIFIER SYSTEMS

Assume that two pure sou nd signals of 1OOHz and 1 ,OOOHz pass through a power amplifier. At the amp outpu t, we will obtain not on ly the original two signals, but also a number of other freq uencies: 1,1 OOHz, 900Hz, etc. These undesirable admixtures - sums and dif­ferences of the original frequencies - are caused by a bad habi t of all amplifiers called "in termodu lation dis­tor tion." Th is can of course be reduced by good amplifier design, but it can never be totally el iminated and can be rather irritating to the listener.

The atten tive reader wi ll also remember that a few minor problems remained unsolved in regard to the passive dividing networks in speaker systems - dividing is not always even and accurate, DC resis tance can degrade damping, and such passive systems are fixed, not flexib le. Wouldn't it be nice to get rid of these unwieldy networks al together?

Also, wou ldn't it be lovely to be able to control the intensity of each sound range - bass, med iu m and high - individually and to obtain tailor-made sound for every record, tape or listening room?

59

tv1odel SF- 850 (Electronic Crossover Network)

60

ELECTRONIC CROSSOVER NETWORK These are the main ideas behind mu lti-amplifier

systems. The signal obtained from the pre-amplifier outpu t is div ided into two, three or even four ranges in a so-called "electronic crossover network" {sometimes called "channel divider" or " dividing preampli fier"). From there, each partial range enters its own special power amplifier, is raised to the required power level, and then enters directly in to one or more speaker units of the proper type.

As each amplifier handl es only a small portion of the frequency spectrum, th at irksome intermodulation distortion can be easil y tamed. No passive dividing network is needed in the speaker system. And, best of all, crossover frequencies can be switched at will and each sound range can be controlled with accu racy.

FEATURES AND DRAWBACKS If this sounds too good to be true, let us reveal the

one great drawback: money. Two, three, or even four power am plifiers are needed, and the electronic crossover network isn't exactly cheap, ei ther. Therefore, mu lti­ampl ifier systems seem to be doomed to remain the privilege of well -heeled enthusiasts or those with extremely understanding wives. To the selected few, however, a multi -ampli fier install ation can really bring a degree of delicacy and realism in sound that deserves the name "highest fidelity."

{Fortunately, most Pioneer integrated amplifiers and receivers permit thei r pre and power stages to be used separa tely so th at a multi -ampli fier system can be built by adding only one or two more power amps and the electronic crossover network. The speaker systems must of course be equipped with separate input terminals for low, medium and high range.)

Tuner

==--o: · : oo·oo- oo:

Integrated amplifier

--- - -- 0 •000• 0 0 -------1 0 0 ••••• 0

Fig. 7- 1 Conventional System

Fig. 7- 2 2-Way Multi-Amplifier System

Fig. 7- 3 3-Way Multi-Amplifier System

Speakers

61

62

HINTS CONCERNING MULTI-AMPLIFIER SYSTEMS

Wiring and adjustments in such a system become rather comp licated so that a few hints may be usefu l.

Choice of add itional power ampl ifiers: it is of course ideal to use the same types for each range, but if different ampl ifiers are combined, the one with the highest power rating should be used for the bass spectrum. This is because, statistically, most energy in music is found in the low freque ncy range.

Power handling ab ility of speaker systems: if no separate power ratings are given by the speaker manu­facturer for the tweeter(s), mid-range speaker and woofer, note that the rating for each segment in a 3-way system becomes approxi mately 1/9 (not 1 /3) of the total. Never, never turn up the volume control fully or you may overload the speaker units and burn out delicate, expensive-to-replace voice coils.

Protection of tweeters against bass pulses: strong, sudden bass pul ses may occur when the power amplifiers are turned on and off, and these could damage the tweeters. As a protection, a capacitor of approximately 6 - 12pF should be inserted (in series) between high range amplifier and tweeter.

Setting of crossover frequency controls: start with the settings recommended by the speaker manufacturer or, lack ing these, start with 200Hz for low/medium and 2,000Hz for medium/hi gh. Then play your favorite tape or record and slowly ad just the controls in either direction unti l the sound becomes most satisfying.

(Leave tone con trols flat.) Finally, let us reveal one of the great joys of owning

a multi -amplifier system: the advanced amateur or semi-professional can do away with ready-made speaker systems and can instead buy individual loudspeaker units and have these installed in custom-made enclosures. This provides a new dimension of freedom in sound­engi neering one's home.

chapterS

Four-Channel Sound The development of 4-channel comes close to solving

the biggest problem inherent in conventional 2-channel stereo, that is the fact that all sounds- both direct and indirect, and of different phases - are heard from the two speaker systems placed in front of the listener. To improve this, 4-channel employs four speakers, usually two in front and two in the rear of the listener as illustrated.

The two major advantages of 4-channel are: (7) The listener can enjoy in his own home a musical environ­ment often comparable to a concert hall, since the two rear speaker systems reproduce the natural sounds of the concert hGII - mainly the indirect sounds. And (2}, a new world of sound, one heretofore inconceivable, is created. What one hears is music that has been com­posed, arranged and recorded with the effects of 4-channel in mind, i.e., two orchestras in position, one in front, another in the rear to enable switching back and forth between the two; surrounding the listener with music; or enjoying the movement of sound.

FOUR-CHANNEL SYSTEMS There are today a number of different forms and

types of 4-channel program sources. Bu t general ly speaking, they can be cl assified into the fol lowing three categories. (Discrete, Regul ar matrix, SQ)

(I) DISCRETE SYSTEM Th is system is the most authen tic in terms of sound quality, and also the most expensive, since it not on ly requi res 4-channel equipment, but also 4-channel tape recordings. When the sou nds are reproduced, four independent playback amplifiers are used, so that optimum 4-channel effects are achieved. This system is often referred to as the 4-4-4 system. Conceivable

63

program sou rces for discrete 4-channel include open reel, 8-track cartridge, or cassette tapes, or disc record­ings and FM broadcasts. Today open reel , 8-track cartridge tapes and discs are al ready on the market.

1 Discrete Four-Channel Tape The illustration below shows the functions in discrete 4-channel open reel tapes and 8-track cartridge tapes. They provide the best tonal quality reproduction, as well as the most distinct separation of sou nds, since independent signals can be recorded on each track, so that the pl ayback effects provide the same ri ch and abundant sounds of the concert hall for classical or popular music. Additionally with this system, other unusual effects are possible, such as switching back and forth between sounds of two orchestras or the move­ment of a sound field at very high speeds.

Fig. 8- 2 Four-Channel Tape System

Conventional 2-channel Stereo 4-channal Stereo

) i f ~ ~ )~l~~~gg OPEN-REEL 4 TRACK TAPE

CARTRIDE 8 TRACK TAPE (1 3 5 71

l'lllllll~ g::: lj ]'2:

4

:

6

:81

13.11 I (4, 8) ~

track 2·channel Stereo 8 track 4-channel Stereo

Fig. 8- 3 Open-Reel and Cartridge Four-Channel Tape

2 Discrete Four-Channel Disc (CD-4 Disc) The CD-4 disc record is a unique 4-channel discrete record that has compatibility with mono or stereo records. In the CD-4 disc, four independent signals are recorded by usi ng special modulation techniques. This disc mai ntains the conventional 45°/45° record groove, but on the inner groove wall the left channel sum signals (channel 1 + channel 2) are engraved, while on the outer wall the right channel sum signals (channel 3 + channel 4) are engraved. Additionally, important sign al com­ponents for the rear channels are transmitted by the inaudible subcarrier, the center of which ex ists at 30KHz. These signal components consist of the dif­ferential signals (channel 1 - channel 2) of the left channel s, as well as the differential signals (channel 3 -channel 4) of the right channels. These signals are frequency modulated and are then added to the walls of the record groove in addition to the above-mentioned sum signals. When we matrix these signals and the differential signals, four independent signals are ob­tained. Since this disc is the modulation type, a CD-4 demodulator unit is required for exclusive pl ayback in addition to a high-quality stereo turntable and phono cartridge.

~ {{ch.l+ch.2)t{ch.l -ch.2)}•ch. l ~{{ch .ltch.2)-{ch. l -ch .2)} •ch.2 ~{{ch .3+ch.4)t{ch.3-ch.4)}•ch.3 ~ ({ch.3+ch.4)- (ch.3- ch.4)} • ch.4

Fi . 8-4 The Principle of Discrete Four-Channel Disc

6

Fig. 8-S Four·Channel Disc (CD·4 DISC) System

3 Discrete Four-Channel FM Broadcasts The FM discrete system uses multiplex modulation techniques as well as conventional stereo FM broadcasts techniques, and also employs the wide carrier bandwidth. At present, various kinds of systems have already been annou nced, including the "Dorren" system. The futu re of FM discrete broadcasts is bright, but government regu lati ons regarding this system are still pend ing in the United States and other cou ntries.

(II) REGULAR MATRIX SYSTEM Four signals recorded in the form of 4-channel are fed through a special 'encoder' and converted into two­channel sign als. In the playback process, they are fed through a "decoder" to recreate the original 4-channel sound fie ld . This system is called "matrix", or "4-2-4" system, and, when used, does not require a special tape deck or turntable as is the case of discrete. All th e matrix systems avai lable today (except the SQ matrix) can be classified into this "regu lar matrix" group. All basically are compatible with each other.

(Ill ) SQ MATRIX SYSTEM The one matrix 4-channel system that has no com­patibi li ty with any of the others is called the SQ system. Its encoding/decoding process is dramatically differen t, and thus a special SQ decoder is requ ired in order to reproduce its program sources. Therefore, regular matrix and SQ decoding circu its are required for true matrix 4-channel versatil ity.

Model OX-949 (4-channel receiver)

Model OA-800A (4-channel integrated amplifier)

Model OL-600A (4-channel rear ampli f ier)

Model QX-747 (4-channel receiver)

Model QC-800A (4-channel preamplifier)

Model OX-646 (4-channel receiver)

Model QM-800A (4-channel power amplifier)

68

Chapterg

Of Dollars and Decibels A few words of pecuniary advice to the hi-fi novice

may be warranted here because an audio system re­presents a major investment and should be purchased with wisdom and care. As a convoy of ships can onl y travel as fast as its slowest vessel, so a hi-fi system will only be as good as its weakest link - th e catchword is "balance." It makes litt le sense to pair off a superb amplifier with a meek speaker system, or equip a top turntable with a so-so pickup.

To help avoid such pitfalls, we have drawn up the fo llowing illustrations which give approximate per­centages of the total avai lable budget to be spent on each com ponent of a hi-fi system. Absolute amounts cou ld not be quoted because prices differ greatly from country to country, manufacturer to manufacturer, but these percentages should prove about right in prac ticall y all cases.

chapter tO Dos and Don'ts Do read the operating instructions supp lied with each unit. Keep referring to the instruction manual when setting up you r hi -fi system, and keep the manual handy for future reference. Do read and compare the speci fications. These contain valuable figures for matching your components correctly. Most items are explained in this guidebook. Do fill out and mail the warranty cards, if required, to obtain full warranty protection. Do experiment with different speaker positions. No cover-all ru les can be given, but often a minor change in the speaker position can bring about a major improvemen t in sound. Do treat your phonograph records with utmost care. Always put them back in their jackets immediately after playing. Store th em either in upright position or horizontally in stacks of not more than 10. Do store tapes in their boxes and away from motors, TV sets or other electrical appliances. Do fo llow the manufacturer's instructions in regard to proper maintenance of all units - cleaning, lubrication, fuses, etc. Don't install any hi-fi component in a dusty, hot, moist or wobbly place. Do avoid direct sunlight. Don't accidentally drop the stylus on the turntable or record when making adjustments of the tracking force etc. Cartridges are eas ily damaged. Don't obstruct th e movement of a turntable or tape reel by hand. Don't ground the system at two or more poin ts. Grou nd connection should be made onl y from the ampli fier. Don 't run th e system at fu ll bl as t for extended periods. This may dam age the speakers and the nerves of your neighbors. Hi-fi is not synonymous with loud ness. Don 't call a serviceman immediately when you think your system isn' t functioning properly. Refer back to the in structions. Very often there is no defect at all , onl y an operating error. Don 't open or otherwise tamper with a hi-fi unit. This can be dangerou s and can invalidate your warranty. Contact qualified service personnel for repairs.

69

70

J\ Glossary of J\udio Ternts

AC: Alternating current. An electric current with periodicall y changing polarity. In popular parlance, often used as synonym for electrical house (or mains) current.

Acoustic Feedback: Unwanted acoustic interaction between output and input of an audi o sys tem, usua ll y between speaker system and microphone or turntable cartridge. Can lead to "howl."

Acoustics: The science of sound . Also, the acoustical character of halls and rooms.

Active Filter: See filter.

Aerial: Sy nonym for antenna in British English.

AF (Audio Frequency) : Frequency within the range of human hearing -app roximately 20 - 20,000Hz.

AFC (Automatic Frequency Control): An AFC circu it of an FM tuner corrects for an inaccuracy in tuning by locking in the station being tuned .

AM (Ampli tude Modulation) : tude (in tensity) of the carrier.

Modulation accomplished by varyi ng the ampli-

Amplifi cati on: Increase in signal magnitude.

Amplifier: Unit providing amplification of signal, from low to higher voltage or current (pre-amplifier) or power (power or main amplifier).

AM Suppression : Characteristic of an FM tuner to suppress changes of ampli tude in received signals, thereby improving the signal-to-noise ratio by re jecting noise and interference.

Anechoic Chamber (Room) : A specially designed room, used for testing micro· phones and speakers, rendered acoustically "dead" by sound absorbing material.

Antenna: Assembly of metal bars, wires or loops for picking up radio waves. Dimensions depend largely on the wavelengths to be received.

Antenna Directi onality: The characteristic of certai n antenna configurations, includ ing most FM and TV antennas, to receive radiowaves reaching it within certai n defined angl es more strongly th an those com ing fro m other directions.

Antenna Gain : An indirect measure for an. antenna's output level, i.e. the strength of the signal supplied by the antenna when compared to a standard antenna and at a certain frequency. Expressed in decibels (dB).

Anti-Skating Device: Mechani sm exerting a small outward force on a tonearm to compensate the inward th ru st caused by groove/stylus friction and tonearm geometry.

Antistatic Fluid : A fl uid (or spray) used to prevent phonograph records from becoming electrically charged, as an electrical charge would attract dust.

Audibility Threshold : The minimum sound intensity that the average human ear can hear. Approximately 0.0002 microbar at a frequency of l ,OOOHz.

Automatic Level Control: A circuit which au tomati call y keeps the level of a signal within a certain range. Examples: automatic gain control in AM radios, ALC in portable tape recorders.

Automatic Record Changer: automatically.

Record player which can change from disc to disc

Aux (Auxiliary) Input: Inpu t on amplifier, etc. Accepts ex tra signal source such as cassette tape player, etc.

Baffle: The board on whi ch one or several speaker units are mounted. Separates the radiations from the front and back of the speaker.

Balance Control: Potentiometer used to adjust volume difference of left and right stereo channels.

Bandpass Filter: A circuit which will pass signals above (high bandpass) or below (low bandpass) a certain frequency whil e attenuating others.

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Bass: Low audio frequency range, below approximately 200Hz.

Bass Reflex: Speaker system enclosure with an outlet permitt ing sound from the rear of the speaker cone to be radiated to the front.

Beat: A pul sation caused by interaction of two waves of different frequencies.

Bias: In tape recordi ng, a high frequ ency signal applied to the tape to optimize its frequency response. Also, the side-thrust on a tonearm.

Bias Compensator: See anti-skating device.

Bi-Radial Stylus: See ell iptical stylus.

Block Diagram: A schematic diagram illustrating the mai n circuit blocks and signal flow in an electronic device.

Capacitor: A device which can store an electric charge. Permeable to AC, impermeable to DC.

Capstan: Drive spindle in a tape deck. The tape is pressed against the capstan by a pi nch roller.

Capture Ratio: An FM tuner 's abi li ty to re ject unwanted FM stations and inter-ference occurring on the same frequency as the desired station .

Cardioid Microphone: A microphone with a directional characteristic that resembles the shape of a kidney.

Carrier: Main radio signal from a transmitter. Can be modul ated in di fferent ways (AM, FM) to convey sound or picture information .

Cartridge: container.

Cassette: recorder.

(a) phono pickup; (b) endless loop tape in a packaged, standardized

Preloaded container with tape and spools for use on cassette tape

Center Channel: An output terminal found on some stereo amplifiers which supplies a monophonic mixed L+R signal.

Channel Separation: Degree to which left and right channel signals are separated in a stereo pickup, FM stereo tuner, amplifier, etc.

Characteristic: Refers to a characteristic curve which conveys in formation abou t an amplifier or other item.

Chrome Tape: A newly developed tape using the chromium dioxide particles, and offers excellent frequency response and wide dynamic range.

Coaxial Cable : A cable consisti ng of an inner conductor and an outer screen. Used as antenna leads and for interconnecting aud io units.

Coax ial Speaker: A loudspeaker consisting of a bass cone with a concentrically mounted tweeter.

Compatible: (a) FM MPX signal receivable as mono by a radio or tuner; (b) Stereo disc playable with a mono pickup. (c) Stereo pickup suitable for playing mono records, too.

Compli ance: The flexibili ty of phono cartridge. Th e un it of compliance is 10- 6 em/dyne.

Component System: An audio system consisting of separate units: turntable, tuner, ampl ifier, speakers, etc.

Condenser Microphone: A microphone utili zing the changes in capacitance caused in a condenser if one of its plates - the microphone membrane - vibrates in rh ythm with sound waves. Same pr inciple can be applied to a condenser type phono cartridge.

Control Amplifier: A preamplifier and amplifier combined in one unit.

Cost-Performance Ratio: A way of evaluating a unit's over-all performance by grad ing its characteristics with points, and divid ing the sum of accrued points by the cost. Naturally high ly individual istic.

Counter Weight: Weight fitted at rear end of tonearm behind the pivot to counter the weight of the arm/head assembly and to permit adjustment of the tracking force.

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Crossover Frequency: In loudspeaker systems and mu lti-amplifier audio instal­lations, the borderline frequencies between low/med ium range and med ium/high range spea kers or amp lifiers.

Crosstalk: Leak of right channel signal into left channel, and vi ce versa. Expressed as level of unwanted signal in relation to wanted signal channel, measured in decibels (dB).

Cutting: The process of engraving undu lating grooves in a rotating, wax-coated or lacquer disc. An important step in the manufacture of phonograph records.

Cutt ing Angle: See vertical angle.

Cutting Sty lus: Stylus used for cutting of phonograph records.

Cut-Off Frequency: The point at which frequ ency response is effectively limited, often determ ined as the point at wh ich level is reduced by 3d B.

Damping: Reduction of resonant effects by use of resistance or its mechan ical and acoustic equivalents.

Damping Factor : Ratio of speaker or speaker system impedance to amplifier's internal impedance. Denotes amplifier's ability to damp unwanted, residual speaker movement.

dB (Decibel): A logarithmic unit used to express the ratio between two power, voltage or current levels.

Mathematically: 20 log 10 ::~:: ~ or lO iog1o power1

power2

Decoder: In 4-channel , a circuit or circuit complex which translates matrix­encoded signals arriving in the form of two separate signals into four signals to be amplified and passed on to the speaker systems.

DE -E mphasis: Attenuation of high sound frequencies in an FM tuner, to counteract the boosting of these frequ encies ("pre-emphas is") done at the FM station.

Demodu lation : The process of "extracting" from a modulated high or inter-medi ate frequency wave the original audio signal which it was modulated with.

Demodu lator: In an FM stereo tuner, the ci rcu it that ex trac ts the left and right channel signals from a broadcast signal original ly modulated by the FM multiplex system. In a discrete 4-channel system, a demodulator is that unit which derives four signals from a CD-4 record.

Derived Center Channel: See center channel.

Differential Amplifier: A type of ampl ifie r consisting of two transistors in wh ich the di fferenti al signal of the transistors' input signals is amplified. Because of th eir excellent thermal characteristics, differential amplifiers are used in the first-stage of OCL power amplifiers, FM limiter stage, etc.

DIN (Deutsche lndustrie Normen): German Industr ial Standards. In aud io, the German standard of plugs, sockets, etc. DIN is used as a standard in many European cou ntries.

Dispersion: Distribution of sound from a speaker through a room.

Distortion: Output signals not present in the origin al input. See harmon ic distor tion, intermodulation distortion.

Dolby System: A unique noise reduction system, which electronically eliminates the irritating noise (tape hiss, circui t noise, etc.) with out sacrifici ng the original tonal quality.

Drift: Tendency of a tuner to move away from optimum adjustment as its components warm up. Compensated by AFC.

Drop-Out: In tape recording and playback, the "holes" in the sound caused by thin or bare spots on the tape.

Dual Cone: Speaker consisting of separate bass and treble cones mounted concentrically and driven by the same coil. See also Coaxial. Mechanical 2-way speaker.

Dynamic Mass : The effective mass of the movi ng parts of a pickup cartridge. This is not simply the sum of the masses of each component, but rather the equi valent mass that determines the mechan ics of its behavior.

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Dynamic Range : In program material, the range of signal amplitudes from highest to lowest; the range (in dB) which a device will handle.

Efficiency: Ratio of output to input power in a transducer. In speaker systems, the percen tage of electrical input available as acoustic output.

Electrostatic Speaker: A loudspeaker utilizing the principle of a membrane vibrating in a strong electric field.

Elliptical Stylus: A pickup stylus shaped so that its width across the groove is greater than the width of its sides. Claimed to have better high frequency charac ter­istics than round styli.

Enclosure: The cabinet which houses one or more speaker units. Has great influence on bass response of speaker.

Equalization : Correction for frequency non-linearity of recordings. Phonograph records are cut with low frequencies attenu ated and high frequen cies boosted. Equalization compensates for this, producing a fl at frequency characteristic.

Equalizer Amp li fier: In a pre-amplifier, the circuit which amplifies and "flattens" th e phono input signal. Needed because phonograph records are not cut with fl at frequ ency response but accord ing to a standard "equali za tion" curve.

Feedback: Signal from output of amplifier or electronic network applied to input in anti-phase (hence negative feedback) to reduce distorti on and noise, and to flatten or otherwise shape frequ ency response. Also, unwanted acousti c feedback.

Ferrite Core Antenna: An antenna, used chiefly for AM reception, consisting of wire windings around a core of ferrite . Advantages are: compact size, good sensitivity and high directionality.

FET (F ield Effect Transistor) : Special kind of transistor consisting of metal ox ides. Amplifies voltage, not current. Used in audio equipment because of its good linearity and stable impedance.

Field Strength : The intensity of an electrical or magneti c field .

Field Strength Meter: See signal strength meter.

Filter: A circuit which attenuate signal s above, below, or at a particular frequency.

Flutter: Quick waver of pitch caused by speed flu ctuations in the movement of tape or discs. Heard as a so rt of quiver.

Flywheel: A disc of large mass which, when rotating, has the tendency to maintai n its rotational velocity. This effect is utilized in tape equipm ent and turntables to maintain constant speed.

FM (Frequency Modulation) : Type of modul ation of radio waves in which the frequency, not the amplitude of the carrier is modulated by the audio signal. FM broadcasting achieves higher sound qu ali ty.

Four-Channel: A new ly developed au dio technique using four (instead of two) channels for sound reproduction.

Frequency Response: respond to.

The frequency range which a unit will reproduce or

Front End: Section of a tuner that selec ts the wanted station from th e radio band and converts the RF (Radio Frequency) sign al to IF (Intermediate Fre­quency).

Function Selector: In an amplifier or receiver, the switch or knob which selects the different program sou rces such as ph ono, FM, AM, AUX, etc.

Gain: Degree of signal amplification achieved in an amplifier circuit. Expressed in decibels (dB). Opposite: negative gain or loss.

Gap: Vertical slit in a tape-head. In the gap, a magnetic field occurs during recording, and a magnetic signal is induced during replay.

Ghost: In TV, the appearance of a secondary picture slightly to th e right of the main picture. Sim ilarly, ghost can be used to mean multipath FM reception. Also the "images" of the true station frequency that an FM tuner purports to receive. '

Harmonic Distortion : The sum of all signals in an output which are multiples of the inpu t signal frequencies ("harmonics"). The ir intensities are expressed as a percentage of the total output intensity.

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Head: a) the erase, recording and play back heads in tape equipment; (b) the shell-cartridge assembly of or attached to a tonearm.

Headphones: Small t ransducers, usually mounted in pairs on a bracket to fi t over the head and designed to make intim ate contact with th e ears.

Head Shell : The part of a tonearm which carries the cartr idge. Head shells in top-class equipment are usually detachable.

Heat Si nk : A device used to remove heat from electronic components such as tubes, t ransistors, etc.

Hertz (Hz): Uni t of frequency, equal to one cycle per second.

Horn: Speaker unit using a trumpet-bell shaped, fl aring funn el to couple its sound vibrati ons to the sur rounding air.

Hum: Unwanted low frequency tone. Usually caused by 50Hz or 60HzAC and its harmoni cs.

Hysteresis Motor: A motor used in high quality turntables. Characte rized by very constant speed regardless of power voltage flu ctuations.

IC (Integrated Circuit) : Solid circuit bl ock containing the functions of numerous transistors, diodes, resistors, capacitors, etc.

IF (Intermediate Frequency): The frequ ency which resul ts in a tuner when th e incoming signal from the antenna is mixed with the oscillator frequency.

1 F Transformer: Component in tu ner or radio receiver used to couple or feed IF signal between successive amplify ing transistors or tubes. Windi ngs usuall y tuned with capacitors to resonate at the fi xed IF frequency.

IH F (Institute of High Fidelity): Insti tute founded by American manufacturers of audi o equipment, devoted to the improvement of audio technology, standardiza­ti on of tes t and measuring methods, etc. " IH F" in audio specificati ons means that values were obtained in measurements accordi ng to IHF stand ards.

Image Rejection: The ability of a tuner to reject an RF signal which appears to be received, bu t which is actu ally a sum or difference frequency of the tuner's

oscill ator and intermediate frequencies.

IM Distortion: {see Distortion) Signals in outpu t caused by interaction of two or more input signals, but not harmonically related to them. Expressed as a percentage of total signal intensity. IM distortion is known to cause li stener fatigue.

Impedance: Resistance to th e fl ow of alternating current. Measured in ohms. It may vary with the frequency of the applied alternating current.

Induced Magnet Cartridge: A pi ckup cartridge in which both magnet and coils are fi xed. The moving part is a tiny iron sheet.

Infinite Baffle: Type of spea ker mounting wi thout an air path between front and rear of spea ker cone.

Integrated Ampli fier: Unit combining a pream plifier and power amplifier. Also called pre-main amplifier.

In terference: Unwanted in flu ences upon desired signal by extraneous signals, for example from electrical appliances, motors, automobiles as well as from un­desirable signals generated within the audio equipment.

LED: Light Emitting Di ode.

Limiter: caused by amplitude.

Circuits in an FM tuner that reject unwanted amplitude variations atmospheric or ignition noise, producing an FM signal of constant

Linearity: {a) Amplitud e linearity, di stortion of which produces harmonic distorti on and intermodulati on;

(b) Frequency linearity referr ing to the straightness of a frequency response curve.

Line Output: Output terminal of a preamplifier, tape deck, etc., providing a signal for monitoring, tape recording or suppl ying to a power amplifier.

Loudness Control (Contour): A circuit which counteracts the reduced sensit ivity of the ear to very low and high notes at low volume levels.

Low Filter: A filter circuit designed to remove low frequency noises (rumble,

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hum, etc.) from the program.

Magnetic Cartridge: A phono cartridge which derives its electrical output signal from change effected in a magnetic circuit by means of some mechani cal device such as a moving coil, moving magnet.

Main Amplifier (Power Amp lifier): power required for driving speakers.

Ampl ifier unit which produces the output

Monaural : One-eared. Sometimes erroneously used to mean monophonic.

Mon itoring: Listening to a program to judge or control the sou nd quality.

Monophonic: channel.

Recording, transmission and reproduction of sound via a single

MOS FET: An FET utilizing MOS (M etal Oxide Semiconductor) element.

Moving Coil (MC) Cartridge: and the magnet is fixed.

Moving Magnet (MM) Cartridge: moves and the coils are fixed.

Magnetic ph ono cartrid ge in which the coil s move

Magnetic phono cartridge in which the magnet

Mu ltip lex: Transmission of two or more channe ls on a signal carrier so that can be independently recovered by the receiver. In FM stereo: transmission of L+R (sum) signal and L- R (difference) signal on main carrier and subcarrier, respective­ly.

Multipath Reception: Arrival of FM or TV signal vi a several path s of different length, due to obstructions, reflecting objects, etc.

Multipl ex Demodu lator: See demodulator.

Music Power: The maximum power avail able temporari ly from a power ampli fier. Also cal led "dynamic-power."

NAB: (Nati onal Association of Broadcasters). Most widely used standard of tape recording techniques.

Network: In au dio, a frequency divid ing network in a speaker system, or an electronic crossover network in a multi-amplifier installation.

Noise: Unwanted signal consisting of a mixture of random electrical agita tions. Also, the sum of all unwanted signals such as hu m, hiss, rumble, interference, distortion, etc.

Omni- Directiona l: Equ al sensitivity or output in all directions. Said of an tennas, microphones and speaker systems.

Osci lla tor: An electron ic circuit which generates an alte rnating current, e.g. the oscillator in a tu ner produces the freq uency used to mix wi th incoming radio signals.

Output Impedance: the load .

Impedance at output te rminals of a device as "seen" by

Output Stage: a loudspeaker.

Fi nal stage of a power amplifier which supplies power to

Output Transformer: tubes to loudspeaker.

Transformer in tube power amplifier to couple output

Overtone: A tone accompanying the fund amental in a musical note. May or may not be harmonic.

Phasing: Connections between power amplifi er and speakers in a stereo system must be made in such a way that signals representing a central sound sou rce cause the speakers to move equ i-d irecti onally, i.e. in phase.

Phase Shift: As a signal passes through a tuner, amp I ifier, etc., some frequencies may lag beh ind others. In a tuner, th is phase shift can, in extreme cases, cause loss of channel separation of FM stereo broadcasts. Phase shift in an amp li fier resu lts in blurring of stereo spati al localization and, in serious cases, can cause unstable amplifier performance and distortions.

Polarity: Positive and nega ti ve te rminals of a battery or power supply, or the north and south poles of a magnet. Sometimes refers to phasing of cartridges and loudspeakers.

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Power Amplifier: See main amplifier.

Power Bandwidth: The frequency range over which a power amplifier will produce at least half of its rated output power (according to IH F standard) .

Power Handling Abili ty: into a speaker system.

Maximum amount of power that can be safely fed

Preamplifier: A circuit unit which takes a small signal, e.g. from a tuner or turntable, and amplifies it sufficiently to be fed into the power amplifier for furth er amplification.

Quietening: Term som etimes used instead of " muting" in FM tuners.

Quieting: See lim iter.

Rated Output Power: The maximum power that an amplifier will deliver continu ously without exceeding its specified distortion rating. Also called con­tinuous power output or RMS power output.

Ratio Detector: Circuit in an FM tuner for extracting audio signals from modulated radio or intermediate frequency sign als.

Resistor: Circuit device which offers resistance to the flow of electric current. Resistors may be made from wire, metall ic fi lm, carbon and other materials.

Resonance: The tendency of a mechanical or electrical device to resonate at a particul ar frequency.

Response: See frequency response.

Reverberation: Reflection of sound from walls or ceilings. Echo. Can be created artificially by electronic or mechan ical devices to imi tate the effect of large halls.

RF (Radio Frequency) : The frequency of a radio carrier wave. AM (MW) covers 535 - 1605kHz, FM occupies 88- 1 08MHz.

RIAA (Record Industry Assoc iation of Am erica): Usuall y refers to the disc recording and replay frequency response curves established as standards by this association.

RMS (Root Mean Square): Abbreviation for Root Mean Square; the effective amplitude of an AC voltage waveform (RMS); equ al to the DC current or voltage that in any given load wou ld produce the same power dissipation.

Ro ll -Off: The frequency at which an equalizer, tone control or filter begins to attenuate.

Rumbl e: Low frequen cy noise resultin g from vibrations in platter and motor of a turntable and from record warp.

Selectivity : The ability of a tuner to receive only the desired station while rejecting stations which are not requ ired. Measured in decibel s (dB).

Sensiti vity: The input signal level required by a tuner, amplifier, etc., to be.able to produce a stated output. The lower the necessary input, the higher the sensitivity.

Separation: See channel separation.

Signal-to-Noise Ratio: Ratio of desired signal voltage to unwanted noise and hum voltage. Expressed in decibels (dB).

Solid-State: Circuits using semi-conductors, e.g. transistors and integrated circuits (ICs).

Speaker System: Enclosure containing two or more speakers and a crossover network. Speake r box.

Stereoph onic : Recording transmission and reproduction of sound via two or more independent channels.

Stylus: A fine ly machined piece of sapphire or diamond . The part of a phono pickup that traces the record groove.

Synchronous Motor: Type of AC electric motor in which rotor speed is related directly to frequency of power supply.

Tape Deck: Tape equipment comprising complete tape transport system, with motors, drive pu lleys, linkage etc., as well as pre-ampli fiers for recording and play­back, but no power amplifier or speakers.

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THD (Total Harmonic Distortion}: See Distortion.

Time-Constant: Product of capacitance and resistance in a circuit of resistors and capacitors (R/C circuit); ex pressed in mi croseconds (J.Ls) to specify response curve shapes such R/C circu its achieve.

Tone Control : in the sound.

Control ci rcu its used to vary the proportion of bass and treble

Trackabi lity: Ability of phono cartridge to track record grooves o f high amplitude and velocity. Also, see compliance.

Tracking Error: Deviation of center-line of phono cartridge from tangential of record at point of stylus contact. Caused by tonearm geometry.

Transducer: Device for converting energy from one form to another; e.g. a speaker converts from electrical to acoustic, a tape head converts from magnetic to electrical.

Transient : Abrupt change of state; sudden change in signal ampli tude as caused by percussion instruments, "attack" of plucked strings, etc.

Transient Response: The abili ty of an amplifier, phono cartridge or speaker to follow sudden changes in the level of a sound.

Tuner: The part of a receiver, or a separate unit, which receives rad io broadcasts and converts them into audio frequency signals.

Tuner-Amplifier: Unit combining the functions of a tuner, preamp li fi er and power amplifier. Also cal led "Receiver. "

Turnover: The frequency at which a response curve changes its shape or slope or at which an audio system undergoes change in operation mode.

Tweeter: A speaker designed to reproduce the high part of the sound spectrum.

Vent : Opening or port in a bass reflex speaker system enclosure.

Voice Coi l: A coil of wire attached to a spea ker cone. When placed in the field of a magnet, the coi l responds to the alternating signal from the ampli fier, moving

the speaker cone back and forth in accordance with the frequency and intensity of the signal.

Weighted : Appl ied to a noise-level figu re or wow and flutte r, etc., which takes account of the human ear's sensitivity character istics.

Woofer : A speaker designed to reproduce the low part of the sound spectrum, e.g. organ, bass, etc.

Wow: Slow variation of pitch caused by speed fluctuation in tape or record movement.

WRMS: Weighted Root Mean Square.

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DECIBEL CHART

100000

10000 · 0 .;;-

«:-'~~

.Q 1000

... "' a:

100

q} ~,o

o.:i- ~'I>

« ~'\.\ ~\e

\c-> '!o."-'l>~e

~0

20 10

5

2 1

0 4 10 20 30 40 50 60 70 80

Decibels (dB)

Decibels Power Rat io

Decibels V oltage or

(dB! (dB ) Current Ratio

0 1 0 1 1 1.26 1 1.12 2 1.58 2 1.26 3 2.00 3 1.4 1 4 2.5 1 4 1.59 5 3.16 5 1.78 6 3.98 6 1.99 7 5.0 1 7 2.24 8 6.31 8 2.5 1 9 7.94 9 2.8 2

10 10 10 3.16 20 100 20 10 30 1,000 30 31.6 40 10,000 40 100 50 100,000 50 316 60 1,000 ,000 60 1,000 70 10 ,000,000 70 3,160

80 100,000,000 80 10,000 90 1,000,000,000 90 31,600

100 10,000,000,000 100 100,000

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