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

Christopher List Christopher_List at sonymusic.com
Fri Apr 12 16:47:19 CEST 1996


... 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. 
I built the same thing (no VC panning in mine, just xfade). The VCA's work 
great. Here's the problem... The x-fade circuit I got from the data sheet. 
Without describing the whole circuit, it basically uses two transistors to 
exponentially split a current (derrived from the gain CV) between two OTA's. 
When I put a + CV in for the fade, it works fine, great in fact. With a - CV, 
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.
Has anybody else built this circuit? 
Have you noticed the same thing?
How did you compensate? - Did you even bother compensating?

The data sheet with the circuit I'm talking about is available in PDF format 
from:
http://www.analog.com/products/index/21.html

- Chris

ps.
Gene, are you staying away from the in-production SSM chips as well? - For fear 
that they might be discontinued? BTW, thanks for the VCF posts....



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