ASM-1 as an analog filter?

[Joe Farler]

The state-variable type of filter (which the ASM-1 has) is well known for
its raunchy sound when overdriven, especially as the Q is turned up. It's
the nature of the beast. If you want nice clean sounds with lots of
resonance with this type of filter, you will need to keep the input signals
down way below standard synthesizer module levels (like below a volt p-p).
This is usually discovered by accident as the synthesist creates a
perfectly normal patch at low resonance and then reaches out and tweaks up
the Q pot. Turns out however that the resulting grunge is pretty cool after
all!



It's not just a question of input level as you can also tweak the compensation capacitance - the ones across the input divider resistors.  On the Electronotes 2-pole I built , I had to tweak these values to get a good compromise between high Q settings and uncontrollable grunge.  With no compensation at all the filter bursts into loud and clipped oscillation at the high end - sort of like a burst of noise.  If you overdo it on the capacitance the oscillation will be down in the bass region.
I found a good compromise with just 36 picos on the first input stage only. (That's for 10K / 22R dividers.) This allows for higher levels of input and Q .

If you want grunge for industrial type stuff then leave the resonance circuit open 
 and you will get some crazy distorted sounds across the whole range.

Joe