[sdiy] Formant 24dB filter

[Brown David]

This sounds plausible, although I've not come across this phase reversal
effect before.  Can anyone suggest an opamp that DOESN'T suffer from phase
reversal?

-----Original Message-----
From: jhaible at t-online.de [mailto:jhaible at t-online.de]
Sent: 06 June 2001 12:22
To: cfmd at swipnet.se
Cc: synth-diy at node12b53.a2000.nl
Subject: Re: [sdiy] Formant 24dB filter



> Sure, it has non-inverting buffer on the output, but the input is
> inverted. What was you hinting at? Incorrect feedback-sign or what?
> Please speak up on the full story...

Phase reversal. Once your signal is strong enough to go out of
the allowed common mode range, negative feedback turns positive.
As somebody else pointed out, use opamps without phase reversal,
and the problem should be cured.

DC offset has nothing to do with it. Causes a little CV
feedthru, but won't latch the circuit up.

JH.
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