nonlinearcircuits

andrewF http://www.sdiy.org

http://nonlinearcircuits.blogspot.com/

veena build doc. 11 Jan 2012 updated 26/02/13

This circuit was inspired by a paper called An Electronic Musical Instrument which accurately produces the spaces

of the Indian Music published by two fellows from the Hellenic Naval Academy? really! The article gives a

thorough description of the circuit, although this version has been changed to suit life in a modular synth, the core

concepts are the same.

Relevant thread on muffwiggler - http://www.muffwiggler.com/forum/viewtopic.php?t=50129

Due to the choice of passive filters cello, violin and viola, it does sound a bit like a stringed instrument. Calling this

module veena is somewhat exaggerated but its a time-honoured tradition in the synth industry. Have you ever

tried playing piano mode on a casio keyboard? That sounds as much like a piano as this module sounds like a veena.

The module is a mix of raw simple circuits S&H, VCO, Envelope generator, VCA, frequency dividers and passive

filters.

To operate it requires a CV signal and a gate. When the gate is high, the sample&hold circuit samples, the VCO is on

and an envelope is formed to turn on the VCA. When the gate ends, the S&H holds the CV signal so the VCO stays at

the same pitch and the envelope starts to fall, reducing gain until the sound stops. There is another envelope that

will turn off the VCO but this is set to be approximately the same length as the maximum setting for the VCA

controlling envelope. The VCO also has a vibrato input which accepts and AC signal and is independent of the S&H.

The output of the VCO goes to two frequency dividers. The outputs of the frequency dividers are ANDed together to

adjust their duty cycles. The 1st has the VCOs frequency and 50% duty cycle, 2nd is and 75% duty cycle, third is

1/8 and also 75%. One set of these are transistor buffered and sent to outputs (2nd, 4th, 8th, 16th) (16th is 50% duty

cycle). These signals will be turned off when the VCO is inhibited but otherwise run all the time.

The outputs from the other frequency divider are fed to the previously mentioned passive filters, via attenuating

pots. Filter outputs are mixed and into the VCA then to the output.

Inputs & pots CV and gate are as described.

Vibrato expects an AC signal and will convert anything that isnt into AC, the Vibrato pot attenuates this input.

Freq is a preset the frequency for the VCO. This is a 4046 PLL VCO so there is also a 470k trimpot on the PCB. You

may want to adjust the resistors/pots associated with these to increase the range of tuning. Generally increase the

values to get more range, try 1M pots. (untested). For the values given on the PCB it plays in a decent range. It is not

V/oct, not even slightly.

VCA Gain as the name implies, set it too high and the thing never turns off (sometimes necessary). This pot and the

Envelope Length pot are the main controls for setting up this module, they have the greatest influence on how it

works.

IMPORTANT MOD READ THIS BIT!

Envelope Length this is the one mod that needs to be done. On the PCB is a space for a 5k6 resistor. DO NOT

INSTALL THIS RESISTOR. Instead wire in a 1M pot (log type is probably best) and a 10k resistor in series. This is your

Envelope Length pot. I am not sure why the original design called for a 5k6 resistor herepossibly a typo?

Filter 1, 2 & 3 -These pots attenuate the divided signals for each filter. Use these to set up your sound as you like.

2nd, 4th, 8th & 16th outputs use as audio sources and feed into other filters. On my panels, the veena is intended to

sit next to a bank of passive mixers cloned from the Polymoog. Try feeding them back into the vibrato input?

Building it Do you really need a BOM? Dont you have everything in stock??

Probably there are mistakes; Id suggest you get a few extra of everything.

SMD components

100k - 4 on the bottom, 2 on top. These are unmarked SMD resistors.

There are also three SMD capacitors to be installed on the bottom of the PCB, these have 47n printed

next to them. These are for decoupling so any value from 10nF to 100nF will work fine, or leave them

outno biggie (the caps that is, you must install the resistors).

All SMD are 1206 size

You should install these first

If you have no experience soldering SMD, check out some how-to vids on youtube.

1206 size is very easy, although a set of tweezers is required.

Thru-hole Resistors

10 2

330 1

1k About 10

10k About 7

12k 1

22k About 6

47k 1

470k 3

680k 1

10M 1

Capacitors

The seven unmarked caps are for decoupling, 100nF is good, 10nF to 100nF will do. The spacing is 2.5mm. An

example is here - http://futurlec.com/Capacitors/C100UC.shtml

10u 6

2u2 1

4u7 2

47n 3

10n 2

4n7 1

Diodes

1N4148 5 (regular thru-hole signal diodes).

Take care installing the diodes. The silkscreen is not too clear. The triangle points towards the cathode

Pots

100k Linear 6

To mount on the PCB. I use 100k pots from Song Huei - R0903N-B100k, L-25KC (the 25 is the length L).

It seems a pretty common footprint. Another pot that fits is this Alpha from Altronics -

http://www.altronics.com.au/index.asp?area=item&id=R1948

If mounting the pots on the PCB, the spacing is 1 inch apart. If you want to try to increase the range of the VCO try a larger size

for the Freq pot, for me 100k is fine.

1M 1 for the Envelope Length, as described above. I used a linear pot but a log is usually more suitable in this

situation.

Trimpot one 470k, you may want to try a 1M here to increase the range of the VCO. I was happy with 470k.

ICs

TL072 2

TL074 1

4011 1

4520 1

4046 1

usual 4xxx cmos series. dont use 74xxxxx

Connectors

Holes for Power connector suit 3.96mm 3 pin Molex.

The connectors for the two 3 pin terminals and one 2 pin terminal are the standard 4 Pin .100" Header Connectors.

The connections are marked on the PCB.

Ground/0V connection

You might notice there is no ground/0V hole.

If using minijacks, you will need one, bananas dont need one (I got nanas)

You could solder a ground wire to the pad of the ground terminal for the power connector, under the PCB.

Transistors

BC547 NPN 4 Any general purpose NPN trannie will work, just be sure to get the pinouts correct. These are

unmarked.

BC547 pinout (top view)

J108 FET transistors 2

The original circuit uses BF256 (maybe a different pinout). The PCB is designed for J108. The GSD pinout is marked on

the PCB which will also indicate where to install the two FETs.

This circuit works on +/-12V.

+/-15V is untestedprobably okay with no mods.