[sdiy] SSM2164 to use as ring modulator...

[Roman Sowa]

I don't know how would actually sound the result of X*exp(Y) but you may 
definitely try.
For linear gain response of 2164, I'd recommend expo/lin converter using 
one of 2164 cells in feedback path of an opamp, so as a result you get 
voltage that when connected to another 216 cell control input, would 
control its gain linearly with the main input voltage.
You need 2 of such converters, because one will control positive control 
voltages, and the other negative voltages. And they both go to separate 
VCA cells, which outputs are simply tied together in summing amp. And 
one of those cells is supplied with reversed "X" signal.
So in fact you get 1 ballanced modulator (who knows how well or bad 
ballanced anyway) made of one 2164. Not a big bonus although I think 633 
quite expensive anyhow, when compared to 2164.

Why do you need separate VCA for positive and negative? One input, let's 
call it X, that is treated as attenuated input in typical 2164 
aplication, can go + or - voltages and that's how we leave it. But the 
other signal to multiply, let's call it Y, carries only information of 
the VCA gain, but not polarity. It vill never reverse the X signal, so 
we need 2 amps. One is carrying normal X signal, and the other one - 
reversed. When one VCA is working at + end of Y input, the other VCA is 
attenuated to -120dB, and vie versa.
I know a schematic would be recommended here, but I don't really have 
time for this today, sorry.

Roman

W dniu 2014-02-13 21:27, Jean-Pierre Desrochers pisze:
> Would it be a good idea to use the venerable SSM2164
> for a ring modulator project (dual, quad)?
> The modulation could be log (by default) or lin
> with some tweakings..
> I could also use the AD633 but I'm just wondering.
> I already have plenty of 2164 chips so..
>
> JP
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