[sdiy] Buchla 291 analysis?

Walker Shurlds walkershurlds at gmail.com
Fri Aug 28 17:12:53 CEST 2015

I think I changed my mind: the first op-amp doesn't seem to have a pole that actually moves with the control voltage, so probably not a SVF.

On Fri, Aug 28, 2015 at 9:47 AM, Walker Shurlds <walkershurlds at gmail.com>

> I'm looking at this one: http://www.synthfool.com/docs/Buchla/Buchla_200/291/Buchla_2910.jpg Is it different than the one you're looking at?
> It looks like SVF to me, but you have to remember than the "states" (I'm about 90% sure I'm really abusing the control systems terminology here, but bear with me) include all three possible outputs, all three possible inputs, every possible branch...
> So to me it looks like *both* the input and output are in different nodes than in the common tow-thomas and KHN topologies. And there seem to be extra branches added for stability. And C6 is making everything unnecessarily complicated, analysis-wise. Really tempting for me to analyze it instead of listening to my assembly coding professor lecture for the next hour.
> Hope that helps,
> Walker
> On Fri, Aug 28, 2015 at 1:52 AM, Pete Hartman <pete.hartman at gmail.com>
> wrote:
>> Are there any analyses anyone's aware of about how the 291 works?
>> Looking at the Dustin Stroh schematic, it looks *sort of* like a state
>> variable filter, but not quite, so that throws me off a bit.  Maybe it's
>> just that the schematic is oddly drawn, I think the last time I asked a
>> question like this it was a matter of re-arranging the bits to see it :)
>> Trying to determine if what I'm seeing with one is "normal" or not, and
>> with Buchla circuits, I can't just fall back on "does it behave like all
>> these other filters I have". :)
>> Thanks
>> Pete
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