[sdiy] RE: [AH] Parametric EQ

[David G. Dixon]

> What did you do about the resonance response of the SSM2164? I found
> that getting a reasonably constant resonance out of it w.r.t cutoff
> was quite difficult. Did you bother with any compensation? In the
> end, I think I decided I didn't care that much (it sounded so *fat*
> and *good* anyway...yuummmm!) and I've just got a couple of back-to-
> back 4V7 zeners on the LPF output amp. This isn't shown on this
> earlier circuit diagram, but they're on IC2.2, in parallel with C4.
> 
> http://www.electricdruid.com/VCResonator.jpg

One thing that strikes me about this schematic is that the Res CV will have
an exponential effect on the degree of resonance feedback.  Of course, an
exponential response is desired on the variable resistors and the output
level.  However, I would have thought that a linear response would be more
appropriate on the Res CV.  Of course, that would require two 2164 VCAs (a
la Mike Irwin), thus raising the total number to five, which is pretty
darned inconvenient unless the output one is sacrificed, or moved to a
dedicated four-input mixer.  Also, that might not improve the problem of not
achieving constant Q with constant Res CV, but then again it might, and it
would definitely make it easier to "dial in" a certain Q with a pot.