[sdiy] Looking for OB-8/CEM3320 filter gurus

[jhaible]

> JH > It's remarkable that this is stable...
>
> Well, the OB-Sx two pole SVF filter is not. It honks at certain cut-off
> frequencies and resonances. You can't hear it honking because it is
> oscillating at several hundred KHz. At first I thought I had a bad 3320,
> but I have tried several ICs, from different batches, and all honk. This
> has the audible effect of making the filter appear to suffer from bad CV
> breakthrough as the HF oscillation comes in and out during a filter
> sweep. Putting a small cap on the input pin to ground controlled the
> situation well enough. (albeit a complete and utter bodge)

I didn't know that. Very interesting!

(Just to be sure: the oscillation was also there without the extra
capacitive
loading from the scope probe?)

JH.