[sdiy] very simple VCA circuit

[David G. Dixon]

> > why not the CA3080 of LM13600/700 ?
> > OTA have reasonably low component count, good to very good performance.
> 
> Sorry, but I can't accept this w.r.t. the CA3080. That chip doesn't do
> anything that I'd qualify as "good performance". If you're lucky, it'll
> stretch to "acceptable performance". Mostly it's noisy with obvious
> feedthrough.
> 
> Still, it probably compares pretty favourably to the one-transistor VCA
> that Justin suggested, though I've never tried that. And I do agree with
> Harry that the question is "how good does the VCA need to be?".

First of all, thanks for all the great responses.  Definitely food for
thought.

The deal is, I'm working on a new VCA design which has 8 VCAs in it (all
2164), and I need a ninth, so I didn't really want to add another 16-pin
chip just for a single VCA.  This VCA only needs to vary the gain of a
control voltage from 1 to 2 depending on a certain other voltage.  The
control voltage itself will control the depth of FM modulation, so it
doesn't need to be too high-performance.  Also, since it is going into a
linearized 2164, it's confined to positive voltages, so one transistor would
work well.  I'll definitely check out the "one tranny" solutions in the
WP20, etc.