[sdiy] Formant 24dB filter

[Ian Fritz]

Burr-Brown has quite a few opamps that don't phase reverse. Check the BB/TI
website. Examples I have used are the OPA132 and OPA277. They're not all
that expensive.

  Ian


----- Original Message -----
From: "Brown David" <David.Brown at tms-ltd.com>
To: <jhaible at t-online.de>
Cc: <synth-diy at node12b53.a2000.nl>
Sent: Wednesday, June 06, 2001 7:26 AM
Subject: RE: [sdiy] Formant 24dB filter


> 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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