[sdiy] Buchla 295 10-band comb filter topology

[Donald Tillman]

On Nov 22, 2022, at 2:41 AM, Mike Bryant <mbryant at futurehorizons.com> wrote:
> 
> 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.

The phase response of each of the filters lags below resonance, and leads above resonance.  

And when you mix'm together, the phases of neighboring filters will work against each other, and generate notches between them to some degree.

So inverting alternate filters eliminates those notches.

  -- Don
--
Donald Tillman, Palo Alto, California
https://www.till.com