voltage/current controlled amplifiers?

[Spasticteapot]

I need a voltage/current controlled amplifier for use in a synth project I'm building - or, rather, six of them. Can anyone recommend a good and inexpensive solution?

[mlloyd1]

some pointers to a few ideas:
1. there's the old reliable approach that can be seen in ota app notes - i think national's lm13700 is still available:
http://www.national.com/ds/LM/LM13700.pdf
2. that semiconductor makes vca devices:
THAT Corporation Blackmer IC Voltage-Controlled Amplifiers
3. analog devices has at least a couple of devices that might be worth a look as well:
http://www.analog.com/static/importe...s/SSM2018T.pdf and
http://www.analog.com/static/importe...ts/SSM2164.pdf
the lm13700 is fairly inexpensive i think. the others, i have no idea about. since you need more than one, the ssm2164 may be more interesting.

ok, more than a few :-)

4, 5, and 6. you can visit almost any diy analog synth site and see more ideas, including approaches to build a discrete transistor vca or use analog multiplier devices (good ones cost $$).

as for recommendations, i have used other (older versions) of item 1 (the no longer available CA3080A and NE5517) in analog synth vca modules and been happy with the result.

good luck!
mlloyd1

[tomchr]

An analog 4-quadrant multiplier like the AD633 would work. Depending on your requirements for THD, etc.

~Tom

[Spasticteapot]

Originally Posted by tomchr

An analog 4-quadrant multiplier like the AD633 would work. Depending on your requirements for THD, etc.

~Tom

The AD633 costs a mint - someone named "Audiosector is selling 'em cheap on eBay, though.

I found an IC called a CA3080 sold by Small Bear Electronics for $2.50. It seems to be the cheapest option, and has been highly recommended by other synth builders.

VCA-1

It seems that to use it as a VCA, all you need to do is add a highly linear FET to convert voltage to current. Can anyone recommend one?