[sdiy] SSM2164 VCA

[David G. Dixon]

> Why use a switch at all? Why not use a summing amp (or even just a pot) to
> allow both exponential and linear at the same time? Looks like it wouldn't
> be too difficult to do with Marc's circuit. I built some VCAs using an
> SSM2022 chip that allows both linear and exponential CVs at the same time.
> Sometimes I'll use 60% linear 40% exponential, sometimes 80% linear and
> 20% exponential, depends on the patch.

That's definitely doable.  In fact, I could use my board either way with no
changes, and simply replace the SPDT switch with a pot.  Of course, one has
to be cognizant of the 5k input impedance of the 2164 VC pin, which will
give all but the smallest pot a pretty non-linear response (damn you,
Thevenin!).  I wouldn't even have to change my panel layout: I could just
ream out the switch holes a bit and put 16mm pots there instead with those
cute little "small Boss" knobs from Small Bear.

However, notwithstanding all the fuss, I must confess that I use the linear
setting about 95% of the time, since I'm almost always using an
exponential-decay ADSR to gate my VCAs.