resonance in

[Martin Czech]

> Hi all,
> 
> I would like to have a VCF I'm building have a resonance input, since I
> think it would lead to some versatile sounds. The res. feedback loop in
> most VCFs is basically just a volume knob to control feedback, so I was
> thinking I could replace the res. knob with a VCA, so that the "gain" knob
> on the VCA would control the intitial resonance, _and_ you'd be able to
> have a modulation signal in to control the res. I was thinking of using an
> asm-1 VCA for this purpose since it's a simple design... maybe (hopefully)
> it will overdrive the res. a bit at max res. and lead to an interesting
> overdriven sound.. Hopefully not _too_ noisy at low resonance, though.. 
> 
> Has anybody done this using the method I described? Is there an easier
> way? 
> 
When I toyed arround with my state variable filter, I used a N-JFET
voltage divider.  Of course the "feedback" in a state variable works
different from a cascade, but that should be no problem. I added a
little diode network in order to have an equal control scale, without
this most of the resonance happens in only 10 degrees of the pot angle.
So no need for fancy reverse log pots, just a linear. You'll need an
control voltage summing op-amp anyway.

m.c.

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