Simple VCA

[patchell]

    If you want to do some experimenting goto :
http://www.synthfool.com/diy/hj_vc_hadsr.html

    You will have to do some disecting.  Remove everything that looks like it
controls an ADSR, what you will have left Q1, Q2, Q3, Q9 and U8C and associated
compontents.  The collectors of Q2 and Q9 are the output (you would feed this
into the summing junction of an opamp).  You CV input would go into U8C, and
the attenuation control would be done on the bases of the transistors.  Now, I
don't know how practical this would be.

    So here is a second suggestion.  Use an LM13700 or CA3280 (this is what I
use) and just a plain old 2n3906.  You get two attenuators per package and the
LM13700 is pretty darn cheap (unlike the CA3280).

    Using just descrete transistors would be tough.  The only way I can think
of off hand would require at least five.

    Take what I said with a grain of salt.  It is friday, I am tired, and these
just came spewing out.

    -Jim

Paul Maddox wrote:

> Dear all,
>
>   Im after a simple VCA, nothing fancy , 1 or 2 transistors/fets.
>
>   Its to scale EGs under CV control, so no audio is involved..
>
>   Suggestions? Ive tried lots of Transistor combinations but cant crack it.
>
>   Paul

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