[sdiy] Buchla 295 10-band comb filter topology

[rburnett at richieburnett.co.uk]

It's a strange arrangement.  It looks a little bit like a twin-T notch 
filter, but not wired in the usual active topology.

I suspect that the inclusion of the additional capacitor might be to 
alter the way in which the amplitude of the bandpass response changes 
when the other two resistors are varied to alter the cutoff and Q.  Have 
you tried simulating the circuit in LTspice?

-Richie,



On 2022-11-22 10:01, Lanterman, Aaron D via Synth-diy wrote:
> 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
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