[sdiy] So just what *is* the Buchla 291?

[Aaron Lanterman]

I first heard this in person, thanks to Charles Cohen. It sounds pretty wicked.

I had a student build it, but I don't understand it.

I've heard it called a state variable filter, but when I look at the schematic I can't quite map it to any particular state variable arrangement I am familiar with. I don't see obvious variable gain integrator structures, and the "business capacitors" (i.e. the ones that look like the appropriate values for doing audio filtering) actually all seem to be in the feedback loops.

Here's the schematic:

http://rubidium.dyndns.org/~magnus/synths/companies/buchla/Buchla_2910_150.jpg

and here's the schematic redrawn by Marjan Urekar:

http://urekarm.tripod.com/synth/buchla_vcf_b.pdf

- Aaron