[sdiy] Later MS-20 filter with 2164

[David G. Dixon]

> I've just been simulating my 2164 Korgasmatron with adjustable zener
> limiters in the resonance feedback loop (as per the IC Opamp Cookbook, 1st
> ed., pg. 202, with 3.3V 1N4728s back to back and a 20k pot)...

According to simulation, with this adjustable limiter setup:

                                               33k
                                          |---/\/\/--- GND
                                          |
                                          /
                                          \
opamp neg --- 1N4728 >| --- |< 1N4728 --->/ 100k pot
                                          \
                                          /
                                          |
                                          |
                                       opamp out

I can adjust the sine waves at self-oscillation from +/-7V all the down to
+/-1.75V, or just 25% of their full amplitude.  The 33k resistor between the
pot and ground eliminates a "dead zone" in the pot rotation.  This pot could
be put on the panel to dial in as much distortion as desired.

OK.  I'll won't talk about it anymore until I actually build it.