[sdiy] VC Resonance

[David G. Dixon]

> Curiously enough, it was a desperate desire for
> voltage controlled resonance on my MS20 that
> led me to make the Frostwave Resonator Mk2.

I left that feature off of my 2164 Korgasmatron, opting instead to stick
(more or less) to the features available on other MS-20 clones like the MOTM
420 while offering two complete filters on one board.  Perhaps on the next
iteration (Korgasmatron Mk2?) I'll wedge it in.

(Tip o' the day:)  Of course, in LP mode (and particularly with square wave
input) with an MS-20 filter and two VCAs, you could just about have VC RES
anyway: put one VCA on the filter input, the other on the filter output, and
control one VCA with a standard envelope and the other with its inverse to
maintain constant overall signal amplitude.  Resonance will increase
(relative to the signal) when the input amplitude decreases.  This will not
work, however, in HP mode.

> As it happens, it has been very useful for the
> 'table top chaos/fractal' type of music, because you
> can effectively use the RES input as a trigger to
> throw the filter stage into resonance.
> 
> Or use a square wave as a gate, of course.
> It turned out that I never used it as I thought I would -
> but it was more useful than I expected!