DESIGN AND IMPLEMENT A LOW COST AUDIO AMPLIFIER

AZMAN BIN Y AAKUB

Universiti Malaysia Sarawak 200t

TK 7871.58 A9 A995 2001

P.KHIDMAT MAKLUMAT AKAD!MIK

:ademt'kIIIIIIII OOO~IO'11182 RAWAK

DESIGN AND IMPLEMENT A LOW COST AUDIO AMPLIFIER

AZMAN BIN Y AAKUB

A Project Submitted in Partial Fulfillment for the Bachelor ofDegree of Electronit: Tdecolllmunication Engineering ",ith Bonors

in the Faculty of Eogineering t)niveniti Malaysia Sarawak

200t

Borang Penyerahan Tesis Universiti Mala sia Sarawak

BORANG PENYERAHAN TESIS

JuduJ: DESIGN AND IMPLEMENT A LOW COST AUDIO AMPLIFIER

SESIPENGAJIAN: 200012001

Saya AZMAN BIN YAAKUB

mengato membenatkan tesis .ini disimpan di .PosaI. Khidmat MakIumat Akadcmik., UniveJSiti Malaysia Saroll'ak deRgan syarnt-syarat lregunaan severo berilan:

I. Hakmilik kcrtas projek adaJab di bawab nama pennlis melainkan penulisan sdJagai ProP bersama dan &biaym oJeh UNIMAS, baIuniliknya adalab kqJlDJ)'3aIl lJNlMAS.

2. Naskbah salinan di dalam bentnk kertas ar.au mikro hllD)'a balch dz"buat dengan lcebenaran berrulis daripada penulis.

3. Pusat Khidmat MaJdumat Akademik, UNIMAS dibenarkan membuat saJinan uutuk pengajian mereka. 4. Keltas ptojd!. baD)'8 boleb ditestmkan dengan kcbeuaran JlCllUlis- Ba~-.uan.myalti adalab meDgoon.kadar

yang dipmetujui kelalc. 5. • Saya membe:oarkanltidak membenarkan Perpustakaan mcmbuat salinan kertas projek ini sebagai bahan

pertukanm di aDlarII institusi pengajian tinggi. 6. .. .. Sila taDdakaB ("-)

C]SULIT (Mengandungi makllDDa1 yang berdatjah keselamatau atau kepelllingan Malaysia seperti yang tennaktub di daJam AKTA RAHSlA RASMll912).

c=J TERHAD (Mengandungi 'maldumat TERHAD yang telab ditentukan oleli organisasiJ badan di mana penyelidikan dijalankan).

D TIDAl<. TERHAD

~Jz~PENmJS) LIA)

Alamat IClap: .~,

No 26, Lot 2626, JJn. Layang-Jayang, Semariang semerah Padi, 93050, Kuching ,SARAWAK

En. Kismet Hong Ping ( Nama Penyelia )

Tarikh: Tarikh:

CATATAN Potong YIIIIg tiM berUnall. Jib Kert. Projek jni SULIT _u TERHAD, Jib Iam,phkan JUl'lIa daripada pink 'berlmual 0I'pIIisaIIi benenllM ~~eJ1akaa sebti tftlllpob kertall projek. lni periu. IfiIidIDliaD sebagai SULlY .... TERHAD.

m (Project

APPROVAL SHEET

This project report attached here to, entitled "Design And Implement a Low Cost

Audio Amplifier", prepared and submitted by Azman B"m Yaakub in partial

fulfillment of the requirements for the degree of Bachelor of Engineering (Electronic

Telecommunication) is hereby accepted~

" /'0/:;.001E nJte

Lecturer Electronic T eIecommunication Engineering Depanment Facu1ty Of Engineering Universiti Malaysia Sarawak

~'I /fb5 I ~oo l AzmalfBiJlYaakub Date No 29, Lot 2626, .no. Layang-layang, Semariang ~merah Padi 93050 Kucbing, Sarawak. ~ ~

Dedicated to my parents, brothers,

loves one & friends.

ACKNOWLEDGEMENT

First of all, I would like to express my gratitude to Allah s.w.t, the God

almighty, of His gracefulness for allowing me to finish my final year project.

My most sincerely thanks to people who have contributed towards the

preparation of this project. Firstly, 1 wish to thank my supervisor~ Mr. Kismet Hong

Ping for his guidance, advice, comments and encouragement throughout this project.

Thanks also to an lecturers and staffs in the Faculty of Engineering of Uoiversiti

Malaysia Sarawak, for their supports.

I would also like to thank my family, especially to my parents, En. Yaakub

Abd Rahman and PD. Ramlah Bte. Bakar, and also my brothers, Azehar, Azlan and

Azrullah for all the help and motivation along the way to completing this project.

Acknowledgement will not be completed without mentioning all my friends

especially Saufi, lsaruddin, Mohd. KhairulMizay, Shaiful, Ahmad, Irwan, Sulaiman,

and my colleagues who have giveMeir constant supports and eocomagemeots.

1

ABSTRACT

Nowadays, the high perfo:rmance steroo audio amplifiers have been wide1y used

according to the technology. The system am be found in the market in various fODDs

and advantages. The considerable advantages of this 5o)'stem are in terms of its output

sound and application to many sound input SOIIDd devices. The purpose of this thesis is

to build a low cost audio stereo amplifier. The Characteristics and factors that have

effect on the specifications. of the system are discussed.. Method and problems that arise

in consttucting it are also discussed.

11

ABSTRAK

Pada masa kini, system penguat audio stereo berlruasa tinggi yang berlandaskan

telmologi terkini telah banyak diguuakan. Sistem ini boleb. didapati di pasaran da.lam

pefuagai beotuk dan kegunaan. Kelebihan yang dimiliki oleh setiap sistem dikira dari

segi keluaran outputoya dan aplikasinya bersama dengan sistem lain Tujuan laporan ini

dibentangkan adalah untuk menerangkao pembuatan sebuab penguat audio stereo kos

reodah. Kriteria-kriteria dan factor yang mempengaruhi spesifikasi sistem tersebut

dtbincaog. Metod dan masalah yang dihadapi semasa pembuatannya juga dibincang.

111

List of Contents

Chapter Page

Acknowledgement Abstract ii Abstrak iii List OfContenB iv List Of Figures vi Preface vii

Power Amplifier 1

1.0 Introduction 1.1 The Characteristic of Ideal Amplifier 2

2.0 Literature Review 2.1 Amplifier Classes and Advantages

2.1.1 Class A amplifier 4 2.1.2 Class 8 amplifier 5 2.1.3 Class C amplifier 6 2.1.4 Class D amplifier 7

2.2 Stereo Sound 8 2.2.1 Basic Stereo Signal Formats 10 2.2.2 A, B, M and S signals. 10 2.2.3 Effects of misalignment on stereo signals. 11

3.0 Components That Support The Amplifier 3.1 Transformer

3.1.1 Operation Of a Transformer 14 3.2 Power Supplies & Voltage Regulators 14

3.2.1 Rectifiers 15 3.2.1.1 Half -wav!ltectirJer 15 3.2.1.2 Full-wave Rectifier 16 3.2.1.3 Full-wave Bridge Rectifier 17 3.2.2 Filters 17 3.2.2.1 Capacitor Filters 18 3.2.2.2 RC Filters 19 3.2.2.3 LCn Filters 19

3.2.3 Voltage Regulators 20

4.0 Methodology 4.2 ApprOKh 22 4.3 The Design 22

LV

4.3.1 Initial Stages 22 4.3.2 Final Design 23

4.4 General Specification For Power Amplifier 24 4.4.1 Sensitivity 24 4.4.2 Power Output 25 4.4.3 Power Bandwidth 25 4.4.4 Frequen~y Response 25 4.4.5 Distortion 26 4.4.6 Signal-to Noise Ratio 26 4.4.71mpedan~e 27 4.4.8 Damping factor 27 4.4.9 Phase Response 28

5.0 Implementation 5.1lntroductioo. 29 5.2 PC Board Construetion Process 30

5.2.1 Printed Circuit Board Constru~tiOD 30 5.2.1.1 Method of Produ~ing Circuitry 30 5.2.1.2 Througb-Hotes For Components 31 5.2.1.3 Types of Printed Cir~uit Boards 31 5.2.1.4 Mounting 1'be Component 31 S.2.1.5 Soldering Components Leads In PC boards 32 5.2.1.6 Wiring Components 32

5.3 Circuit Analysis 32 5.4 Cir~uit Function 35 5.5 Frequency Response 37 5.6 Frequency Response Curve Analysis 38 5.' Bandwidth Of An Amplifier 39 5.8 Fa~tors Affecting Frequency Response 39

.~,

6.0 Discussion 6.1 Discussion 40 6.2 Typical Amplif'rer Faub 41 6.3 Recommendations 42 6.4 Conclusions 44

Bibliograpby 45 Appendices 46

v

List of Figures

Figure 1.1 Symbol of Operational Amplifier 3

Figure 2.1 Class-A amplifier 4

Figure 2.2 Class-B amplifier 5

Figure 2.3 Class-C amplifier 6

Figure 2.4 Class-D amplifier 7

Figure 2.5 Two Channel Stereo 10

Figure 3.1 Half-wave Rectifier 15

Figure 3.2 Full-wave Rectifier 16

Figure 3.3 Full-wave Bridge Rectifier 17

Figure 3.4 Capacitor Filter 18

Figure 3.5 RC Filter 19

Figure 3.7 LC1tFilter 20

Figure 4.1 First Design Diagram 22

Figure 4.2 Final Block Diagram 23

Figure 5.1lDput Waveform 33 9i1o

Figure 5.2 Output Waveform . 33

Figure 5.3 IC's Pin Waveform 33

Table 5.58 Voltage Gain and Frequency 38

Figure S.Sb Frequenc:y Response Curve 38

VI

Preface

Power Amplifier

The purpose of power amplifier is to deliver a large amount of power to a load.. The

load here is most often a loudspeaker, which requires considerable power to convert

electrical signals to sound waves.

For a power amplifier to work or to perform its ftmction, it must be capable to dissipate

Jarge amount of power so that the heat produced from high current and voltage is

released to the SUITOlDldings quickly. This is important to prevent temperature buildup

before it disrupts the amplifier's operation.

That is why the author design the circuit in such a way that the surface areas is large to

enhance beat transfer to the surroundings, even though the amplifier's component is

bulky.

Power amplifiers are widely used in audio components such as radio, television audio

receivers, stereos and recording-studio equipment. Power amplifiers are also used in

electromechanical control system to drive electric motors. Examples are computer disk

and tape drives, robotic ~ators, autopilots, antenna rotators, ptUDpS and

motorized valves, and process controllers ofall kinds.

In this report, the author focused on only one thing, which is an audio power amplifier.

Vll

CHAPTERl

INTRODUCTION

In this chapter explains about the basic concepts ofamplifiers.

1.1 The cbaracteristk Ofldea1 Amplifier

An ideal operational amplifier bas the following attributes:

1. It bas infinite gain

2. Ithas infinite input ~

3. It has zero output impedance

Although no real amplifier can satisfy these requirements-. most modem amplifier bas

large gains and input impedances, small output impedances and negligibly small error

results from assuming ideal characteristics.

1

r

A detailed study of the ideal amplifier · is beneficial in terms of understanding bow

amplifiers are used as well as building some important theoretical concepts that have

implications in many areas ofelectronics.

Figme 1.1 shows the standard ~bol for an operational amplifier. Note that symbol

shows (+) for noninverting and (-) for inverting.

I'

( ,

I

Figure 1.1 Symbol Of Operational

2

----

r

CHAPTER 2

In this chapter, we will discuss on classes of amplifiers which are Class A, Class B,

Class C and Class D.

2.1 Audio Amplifier Classifications

lot.l Class-A Amplifiers

CJass-A amplifiers are amplifiers that are biased and during operation, the output never

satunItes or cuts off. The characteristic of an amplifier in class A is its output remains in

1he active region during a complete cycle (one full period) of a sine wave input signal.

Figure 2.1 shows a typical c1ass-A amplifier and its input and output waveforms [1).

+Vee

Vee (C\Aoff)1-----'-- - -------- - ­

Vcd2

Rc ~ Ic Vcc12 ---1-----­

J vanl _L\_ -----:lll~-'--

Vo

· --f-1/"

p-"""t (S1iI!ilJRI'm)• t

Fi2ure 2.t Oass-A anmlifier

3

,

•

The output of a class-A amplifier remains in the active region during a full period

(360°) of the input sine wave. From the figure, the transistor output is biased midway

between saturation and cutoff.

The efficiency of a power amplifier is defined to be

average signal power delivered to load 1]

average power drawn from de source( s)

Advantage of c1ass-A amplifier is that it generally produces less signal distortion than

some efficient classes of amplifiers. Disadvantage of class-A amplifier is it is less

efficient, which is approximately only % of total power consumed by the circuit is

delivered to the load, under optimmn conditions.

2.1.2 Class-B Amplifiers

CJass..B amplifiers are amplifiers that their output current varies dwing only one half-

cycle of a sine-wave input. It means that amplifier is active during a positive half-cyde

or only during a negative half-cycle of the input This operation is illustrated in Figure

2.2 [1].

Fitwre 2.2 Class-B amolifier

4

,... ,.

The principle of class-B, a push-pull operation. Output amplifYing device 1 drives

current k through the load in one direction wbi1e 2 is cut off, and device 2 current in the

opposite direction while 1 is cut off.

CIass-B operation produce an output wavefonn that is only half-wave rectified and this

makes it highly distorted. The waveform is not suitable for audio applications.

There are two transistors that are operated class B. One is to amplify positive signal and

the other one is to amplify negative signal. The output is the combination ofboth of that

waveform. These amplifiers are more efficient IUld more widely used in power

applications than class-A amplifiers.

The advantage of class..B amplifier is that it can achieve higher efficiency than can be

attained by class-A amplifier.

1.1.3 CIass-C Amplifier

CJass.C amplifiers are amplifiers that their output conducts load current during less than

me-balfcycle ofan input sine wave. Figure 2.3 shows a class-C amplifier [1].

I: Fi21ll'e 2.3 Class-C anmlifier

5

-------~ ~~----------------------------------------..

: I I

j '_Dc

A class-C amplifier bas a highly distorted input. It could not be used in an application,

such as an audio amplifier. Class-C amplifiers are used primarily in high-:power, high

frequency applications, such as radio-frequency transmitters.

The advantage of c1ass-C amplifier is that it has a very high efficiency compared to

other classes ofamplifiers before this.

1.1.4 Class-D Amplifiers

Class-D amplifiers are amplifiers that their output is switched on and off The output is

in its 1inear range for zero time during each cycle of an input sine wave. The only time

that a clw-D output device is in its linear region is dming that short interval. It required

switching from saturation to cutoff, or vice versa.

C~D amplifiers and its application is ideally suited for VMOS transistors. Figme 2.4

is the block diagram for Class-D [1].

- HL...--..----J=-H'------'~fl-<J041UI

-~f=-,r~-----,I Fiswre 1.4 Class-D amplifier

6

A fundamental component of a class-D ' amplifier is a pulse-width modulator. It

)I'Oduces pulses, which are proportional to the amplifier's input signal. When the signal

Ie¥eI is smaIL a series of narrow pulses is generated, and when the input level is large, a

lilies ofwide pulses is generated.

The adY8Dblge of a class-D amplifier is it bas a VeIy high efficiency, nearly lOO%. The

disadvantages are it needs a very good low-pass filter and a high-speed switching of

· . heavy currents generates noise through electromagnetic coupling, called

dectromagoetic interference.

1.1 Stereo Sound

Since this project is to build an audio power amplifier then we must observe some

filets about stereo s01md techniques. The true meaning of stereo comes from the Greek

word meaning 'solid', or 'three dimensional'. Since this audio power amplifier is

using two channels with two loudspeakers then we are considering about a two­

c:Mmel stereo reproduction principles.

In most cases stereo reprodu~ from two loudspeakers can on1y hope to achieve a

modest illusion of the original sound field, since reproduction is from the front

quadrant only. lt is possible to state that the best illusion will be created when the

!OUDd signals present at the two ears are as similar as possible to those perceived in

oaturaIlistening, even if one cmmot entirely rationalize psychoacoustics mechanism

involved.

7

It is possible to create this illusion using either time differences between the speaker

outputs or using level differences between them. It is also possible to use a

combination of the two, although there is a problem with 'time difference' stereo in

1hat contradiotions may arise between transient and continuous sOlmds. The main

point to be considered with loudspeaker reproduction is that both ears receive the

sigoa1s from both speakers, which is different from headphones where both ears only

aceives one signal channel.

The result of this is that the loudspeaker listener sited in a center seat receives at his

left ear the signal from the left speaker first, followed by that from the right speaker,

and at his right ear the signal from the right speaker first, followed by that from the

left speaker, the time t being the time taken for the sound to travel the extra distance

ftom the more distant speaker. Figure 2.5 shows the principal of two-channe1 stereo

[2].

1f1he two speakers differ only in level and not in phase then it can be shown that the

wctor summation of the signals from the two speakers at each ear results in two

tipals, which, for a given frequency, differ in phase angle proportional to the relative

amplitude of the two signals.

8

Left Loudspeaker

., Leftear \.

..""...... ,:"

- Right ear

Listeoet:'s h~~rl

Figure 2.5 Two-channel stereo

2.2.1 Bask Stereo Signal Formats

In a basic stereo signal, we must consider about the nature of the stereo signal

together with the definitions of the tenns used to describe the various formats of

stereo sound.

2.2.2 A, B, M and S signals.

In broadcasting technology, the e (L) channel is always refer as the'A signal' and

the right (R) channel as the <B signal'. In some of the stereo microphones they are

caned ~x signal' and the 'Y signal' respectively. In a two channel stereo system the A

signal feeds the left loudspeaker and the B signal feeds the right loudspeaker.

9

It is sometimes convenient to work with stereo signals in the so-called 'sum and

difference format', since it allows for the control of image width and ambient signal

baJance. The sum or main signal is denoted by 'M', and is based on the addition of L

and R signals, whilst the difference or side signal is denoted'S' and is based on the

subtraction of R from L to obtain a signal which represents the difference between the

two channels. The M signal is that which would be heard by someone listening to a

stereo program in mono, and thus, it is important in situations where the mono listener

must be considered, such as in broadcasting.

2.2.3 Effects 01 misalignment on stereo signals.

Differences in level, frequency response and phase may arise between signals of a

stereo pair, perhaps due to losses in cables, misalignment and performance limitations

of equipment. It is important that these are kept to a minimum for a stereo work, as

interchanneJ interference result in various audible side effects.

Differences will also result in poor mono compatibility. The differences and their side

effects are discussed as below .

•a) Frequency response and level.

A difference in level or frequency response between A and B channels will result in a

stereo image biased towards the channel with the bigher overall level or that with the

better high-frequency response. Also, an A channel with excessive high-frequency

response compared with that of the B channel will result in the clear movement of

sibilant sound towards the A loudspeaker.

10

Level and response misalignment on MS signals will result in increased crosstalk

between the equivalent A and B channels, such that if the S leve1 is too low at any

ftequeocy the AB signal will become more monophonic (width narrower), and if it is

too bigh the apparent stereo width will be increased.

b) Phase

Interchannel phase interference will affect one's perception of the positioning of

sound source, and it will also affect mono compatibility. Phase differences between A

and B channels will result in 'comb-fihering' effects in the derived N signal due to

cancellation and addition of the two signals at certain frequencies where the signals

are either out of or in phase.

c) Crosstalk

An intercbannel level difference of only 18dB is required to give the impression of a

signal being either fully left or fully right. Crosstalk between A and B signals is not

therefore usually a major problem, since the performance of most audio is far in

excess of these requirements. Excessive crosstalk between A and B signals will result

in a narrower stereo image, while excessive crosstalk between M and S signals will .. result in a stereo image increasingly biased towards one side.

11

CHAPTER 3

COMPONENTS THAT SUPPORT THE AMPLIFIER

This chapter will be discussing on units that support the amplifier.

3.1 TRANSFORMER

Tnmsformer is a device that can be used to increase or decrease the input voltage.

GateraIly transformers are divided into two types, which are;

1. Step Up transformer

2. Step Down transformer

The functions of these transfonners are simple. The function of step-up transformer is

to increase input voltage and the function of step-down transformer is to decrease the

input voltage. Other important function of transformer is to separate the amplifier

cin:uit from the power source, as a voltage supply circuit. In this project. the author uses

astep-OOwn transformer to get a small amount of voltage.

12