[sdiy] SSM2164 state-variable filter

[Neil Johnson]

Time for a quick update.

Ian Fritz wrote:
> At any rate, the answer looks to be what Harry said -- the clipping  
> is in the wrong place.  I suggest trying back-to-back zeners across  
> the the (+) input of the summer.

Good suggestion - moving the two zeners away from the third  
integrator improved the low frequency behaviour.

I now have a constant self-oscillation level from 0.14Hz (7s as  
measured against my wristwatch) up to about 2.5kHz, and then the  
amplitude increases steadily as the frequency climbs to around 33kHz,  
although further measurements needed to determine what the  
relationship is.

Neil
--
http://www.njohnson.co.uk