[sdiy] Noninverting integrator / 2-opamp Biquad

[jhaible]

Hi Fabio,

no, I wasn't talking about a FDNR - this integrator is using
a constant (not frequency dependant) negative resistor, built
from an opamp with a positive and negative feedback loop.
See
ftp://ftp.orban.com/672A/672A_Manual.pdf
for details.

JH.



-----Ursprüngliche Nachricht-----
Von: fmg <1984 at softhome.net>
An: <jhaible at debitel.net>
Cc: <synth-diy at dropmix.xs4all.nl>
Gesendet: Freitag, 16. Januar 2004 03:48
Betreff: Re: [sdiy] Noninverting integrator / 2-opamp Biquad


> jhaible at debitel.net wrote:
> >
> > Remember the discussion a few days ago?
> >
> > Now I found that this odd little circuit
> > - NIC creates negative reistance to undampen
> > a passive RC circuit - has been used in the
> > famous Orban Equalizer 672A.
> >
> > That's a mix between graphic and parametric EQ:
> > Parametric, but with small sweep range for each
> > band. This is more than compensated with the
> > use of 8 of such parametric bands!
> >
> > (Absolute) bandwidth can be adjusted independent of
> > center frequency, and all this with ordinary pots
> > (no dual pots, as in a 3opamp biquad)
> > Center tapped pot for gain, but probably just to get
> > an exact 0dB detent.
> >
> > www.orban.com  - I think they have a download area.
> >
> > JH.
> >
>
> Jurgen,
>
> I don't know if we are talking about the same think (haven't the
> Orban schem), but for negative resistance I took a model from
> an Analog's application note and did some simulations with it.
> The sim showed a weird gain/phase response. I really would like
> to breadboard a few "cells" to see how it works with real components
> values and how useful it could be to keep torturing harmonics.
>
> For reference:
>  Analog Devices AN-281 "Passive and Active Analog Filtering" -
>  Frequency Dependent Negative Resistor (FDNR) - pag.4
>
> Fabio Gonzalez
>