[sdiy] SSM2164 state variable filter

[Paul Perry]

Tom, I haven't been following this closely so I don't know whether the zener 
goes to ground..
but if so, here is an "adjustable zener" circvuit, possibly:
http://notes.ump.edu.my/fkee/e-Magazine/Elektor%202004/Articles/E/e047017.pdf

I expect it is also possible to make an adjustable zener from a transistor -
relying on the bias - this would be much 'softer' than a real zener, but who
knows, that might be better, in this application.

paul perry Melbourne Australia