Hurray a question!

[René Schmitz]

At 20:43 09.04.00 -0400, Harry Bissell wrote:

>1) Normal resonance (the usual)
>2) Abnormal resonance (the MS-20 is self-oscillating and locking and
unlocking
>in sync with the input waveform
>3) Over-Resonance (the wave has a single overshoot, whose width varies
with the
>filter
>cutoff frequency...
>
>This is a NASTY filter design... I can't stand to listen for very long in
modes
>2 or 3...
>kind of like listening to a ring-mod all night for kicks... Maybe I'm too old
>(or too laid back).

I have done my own version of that MS-20 filter, which is more like the
original, it has the diode-limiter inside the feedbackloop. 

But it still is nasty in a way, it can lock onto the input, especially with
high input amplitudes.

There is selfoscillation only inside the voltage range where the diodes 
(I used a pair of green LEDs, btw.) don't clip, above and below 2.2V the
feedback gain is lowered to unity, giving a normal saw above and below
that, with the resonating between that. Quite different to any other filters.

But my conclusion would be that this part of the circuit should be included
after the resonance VCA, to make its response more MS-20-ish.
Or rather, bridging the whole VCA with a string of diodes. 

>I have you build a nice smooth filter next... maybe a Moog ???

Sounds like the SSM2040 is something for you!

Bye,
 René


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