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

[HOSHUYAMA]

Hello List,

There are theories called "Active-R filter" and "Active-R oscillator" 
which directly use the dominant pole of a opamp to form a filter, 
though their main applications are RF.  Of course, it's a modern 
technique and I don't think it was used in Polivoks.  

Sam Hoshuyama
Kawasaki, JAPAN

Karl Dalen wrote:
> 
>  --- jhaible <jhaible at debitel.net> skrev: > 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.
> 
> I had that in mind to but quickly realising that having
> a production line for 20-25 000 made units relying on
> the phase compensation capacitance wich would in a FET
> amp be in the units of pF region i suppose was a bit
> hair raising at first thought!
> 
> Small capacitors and leakages and temperature shifts
> does not sound healty. Well, i dont know much about
> silicon process but anyway!
> 
> KD
> 
> > 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
> > >
> > >
> > > Höstrusk och grå moln - köp en resa till solen på Yahoo! Resor på

> > adressen
> > http://se.docs.yahoo.com/travel/index.html
> > >
> >
> >
> 
> Höstrusk och grå moln - köp en resa till solen på Yahoo! Resor på adressen http://se.docs.yahoo.com/travel/index.html