Re: [sdiy] State Variable Filter self oscillation

[Roman]

All SVFs I ever made (all 2 of them) oscillate. One uses CA3080, second SSM2164. You have to add some nonlinearity in the circuit to get stable oscillation. Otherwise the opamps will clip into wild square wave. In one SVF I added diodes over the pot in feedback (Q) loop, something comonly seen in many SVF designs. In the other I added back-to-back zeners in the feedback of second integrator. All works well enough for me - oscillation from fraction of a Hz.
But then again, I may have not build a classic SVF, but that's the only one I know.

Roman

---- Wiadomość Oryginalna ----
Od: John Blacet <blacet at blacet.com>
Do: synth-diy at dropmix.xs4all.nl
Data: Tue, 01 Apr 2003 19:41:23 -0800
Temat: [sdiy] State Variable Filter self oscillation

>Has anyone built a classic state variable that can oscillate?
>
>I have a few versions of this filter that get close but do not sustain
>an oscillation.
>
>Still poking around the breadboard, but any comments?
>
>Regards,
>--/////--
>John Blacet
>Blacet Research
>http://www.blacet.com
>
>
>