Polyfusion HPVCF Trouble

R.Fahl 8brain at spiritone.com
Mon Jun 30 21:02:36 CEST 1997

I recently finished building a copy of the Polyfusion Highpass VCF that's
on Kevin Lightner's Synthfool page.   I'm having trouble getting it to work
properly - when I pump audio into it, it works sort of like a highpass
filter, kinda buzzy and I can sort of sweep through the cutoff range,
though it is limited.  I have no control over resonance, but it seems like
it is resonating on its own.  When I have no audio going into it, it puts
out a high frequency oscillation that's barely audible.

One change I made was that I substituted 2N4392s for the E-112s that the
circuit calls for.  Is this a good substitute?  If not, what would be?
Would changing the biasing resistors fix the problem?

For those of you who are interested, here's the URL for the diagram:


I appreciate any advice that might help me get this stillborn module


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comprise its diagnosis. Synesthesia is "abnormal" only in being
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