While we're talkin' about SSM VCA's...

[Haible_Juergen#Tel2743]

>... awhile ago, someone besides myself (Juergen?) was talking about how 
they
>had used the SSM2024 (still available) in a dual-VCA + VC xfade / VC pan
>module.
>
>however, one signal comes up to full volume and the other one goes down, 
but
>never gets completely faded out. It's too low to hear when mixed with the
>other
>signal, but when it's the only signal, it's quite visible on the scope.

The control circuit with a single transistor pair is much less than perfect 
indeed.
I use it on my systems main (output) VCAs nevertheless, because using only
one VCA per channel is the optimum for the *audio* path. So I learned to 
live
with some of the CV circuit's problems.
My CV circuit is a little modified however. I don't route the balance CV to 
the
base of one transistor only, but I use a panpot-circuit (like in an audio 
mixer)
to route the CV to either of the two bases. This has some other drawbacks
(the threshold for the main VCA CV input varies slightly!), but I can make 
perfect
100% pans without problems.

JH.