Capacitorless filters (was:Re: [sdiy] polivoks filter)

[jhaible]

No idea what's inside the russian parts.

But the Farfisa Synthorchestra had a 4pole VCF that was built
without capacitors. It used a quad opamp with
adjustable internal current sources. And of course there *are* capacitors:
The silicon-made phase compensation that's on chip.

Basically the same structure as an OTA + cap + buffer, only
scaled down to very small capacitors and very small currents.
Doesn't work too well at low cuttoff frequencies, no surprise.
But it's remarkable that it works at all!

JH.

-----Ursprüngliche Nachricht-----
Von: Karl Dalen <karldalen at yahoo.se>
An: <uzs159 at uni-bonn.de>
Cc: <synth-diy at dropmix.xs4all.nl>
Gesendet: Samstag, 11. Oktober 2003 01:52
Betreff: Re: [sdiy] polivoks filter


> Exactly, listen here to what designer Vladimir Kuzmin
> says at http://www.muztech.ru/eng/history.php
>
> quoute; VCF doesn't have any capacitor at
>         all and use only two op amps.
>
> Now, that's interesting! I wonder how this is done!
> Another interesting thing is the VCA, it has
> differential outputs!
>
> KD
>
>  --- René_Schmitz <uzs159 at uni-bonn.de> skrev: > I wrote:
> > > The filter caps are not on the filter board, but on the connector
> > board.
> >
> > Oops, no they're not.
> >
> > --
> > uzs159 at uni-bonn.de
> > http://www.uni-bonn.de/~uzs159
>
>
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