[sdiy] Multimode filter topology

[George Hearn]

This topic was discussed at some length a few months ago under the thread
"XPander VCF" I think.  One thing I found when trying out multimode filters
was that you can't quite get the stop band attenuation in the HP and BP
modes you might like due to component variations.  
I've built an implementation of a multimode VCF constructed from an SSM2040
(equivalent).  The schematics are at
http://sites.google.com/site/hearnmorley/synth-diy-resources

George

-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of KA4HJH
Sent: 18 August 2009 02:01
To: synth-diy at dropmix.xs4all.nl
Subject: RE: [sdiy] Multimode filter topology

At 4:22 PM -0700 8/17/09, David G. Dixon wrote:
>For instance, I can find no reference to the aforementioned allpass mode on
>the web or in any of the books on my shelf; the only reference to it is in
>Grant's webpage given above.  One thing I can do, given that my 4-pole VCF
>has + and - outputs available from every stage, is to test every
combination
>I can think of to see if they are any good.

This could save you some time:

http://www.crowncity.net/ratcave/Electro/MIF/mif.html


John Blacet had a similar device (Phasefilter?) years ago that only used
the more "interesting" combos.

-- 

Terry Bowman, KA4HJH
"The Mac Doctor"
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