[sdiy] Buchla 295 10-band comb filter topology

[Mike Bryant]

They are just bandpass filters - one pot in the feedback changes the freq and one changes the Q.  And they both interact with each other of course.

But why he inverts every other band into the summing amplifier is a mystery to me.

________________________________
From: Synth-diy <synth-diy-bounces at synth-diy.org> on behalf of Lanterman, Aaron D via Synth-diy <synth-diy at synth-diy.org>
Sent: 22 November 2022 10:01
To: synth-diy mailing list <synth-diy at synth-diy.org>
Subject: [sdiy] Buchla 295 10-band comb filter topology

Does anyone recognize the topology Don is using here in the bandpass sections?

http://fluxmonkey.com/historicBuchla/buchlaFiles/Buchla_2950_200.jpg

The low and high bands are 3-pole Sallen-Keys, but I’m not sure what’s going on in the middle filters. It looks kind of like a multiple feedback filter, but instead of having a resistor to ground like in Figure 1 here:

https://sound-au.com/project63.htm

There’s some weirdness with a 3rd capacitor connecting to the resistive feedback back.

Aaron Lanterman, Prof. of ECE, Georgia Tech
My blog on Education and Innovation: https://edupocalypsenow.wordpress.com
My blog on Electronics and Programming: https://lantertronics.blogspot.com
My YouTube channel on Electronics and Programming: https://www.youtube.com/c/lantertronics



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