[sdiy] Looking for 2164 12db/oct slopes bandpass filter design.. more detailed..

[David G Dixon]

The Intellijel Korgasmatron II does this as well, and it's made with 2164.
It is two independent filters, either of which can be any one of six
different filter modes, including 12dB LP and 12dB HP.  In fact, any pair of
12dB filters in series will do this.  Two bog-standard SVFs in series will
do this.  With a single 2164 quad VCA chip, they can both be controlled from
the same CV.  The only challenge with SVF design is to get them to
self-oscillate in a stable manner with low distortion.

A cascaded 4-pole filter (such as the Intellijel Dr. Octature) can also be
easily gain-blended to be a 12dB/12dB BP filter.  You simply add the second
(12dB) and fourth (24dB) outputs, and subtract two of the third (18dB)
outputs.  This is how we got the BP output on the Intellijel Atlantis.

> -----Original Message-----
> From: synth-diy-bounces at dropmix.xs4all.nl 
> [mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Roman Sowa
> Sent: Saturday, March 08, 2014 10:04 PM
> To: synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] Looking for 2164 12db/oct slopes bandpass 
> filter design.. more detailed..
> 
> why not take a look at "the classics", now almost 14-years 
> old design, which among other things, does exactly that - 
> chains 2 state variable 2-pole filters, one HP, one LP, with 
> control for the gap size.
> 
> http://sowa.synth.net/modular/vcf.html
> 
> just replace 2164 cell with other OTA in the feedback path so 
> to need only one 2164 for both filters.
> 
> Roman
> 
> W dniu 2014-03-08 17:46, Jean-Pierre Desrochers pisze:
> > In fact I should have been clearer on my needs..
> > I'm looking for a 2164 based  bandpass filter design Built with one 
> > separate 2 poles lowpass (12db/oct) (2164 section #1+2) In 
> series with 
> > one separate 2 poles highpass (12db/oct) (2164 section #3+4).
> > These 2 blocks in series  make it possible to feed 2 separate & 
> > different cutoff CV's Thus having the possibility to open 
> or close a 
> > 'gap' between the cutoffs Creating a variable bandwidth for the 
> > overall bandpass filter CV controlled.
> > That's why I cannot use a 'derivated' bandpass from a 
> lowpass design 
> > using pole mixing because the cuttof freq would be the same 
> All around 
> > the 2164 blocks..
> > I'm only looking for schematics of:
> > -2 poles 2164 based lowpass filter (12db/oct slope)
> > -2 poles 2164 based highpass filter (12db/oct slope)
> >
> > Your ideas are welcomed.
> > J-Pierre
> >
> >
> > -----Message d'origine-----
> > De : synth-diy-bounces at dropmix.xs4all.nl
> > [mailto:synth-diy-bounces at dropmix.xs4all.nl] De la part de 
> Jean-Pierre 
> > Desrochers Envoyé : 7 mars 2014 11:34 À : 
> synth-diy at dropmix.xs4all.nl 
> > Objet : [sdiy] Looking for 2164 12db/oct bandpass filter design..
> >
> > Looking for 2164 based 12db/oct bandpass filter design..
> >
> > Any web link ?
> >
> > Thanks
> > JP
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