[sdiy] Calling all Buchla lowpass gate fans

[Aaron Lanterman]

On Jun 14, 2009, at 12:32 PM, David Ingebretsen wrote:

> It's a combination of VCA and/or low pass filter, I believe.

I figured it out. In filter mode, there's a feedback cap that's  
switched in to form a Sallen-Key. In gate mode, there's a resistor to  
grown that's thrown into the network right before the op amp in a  
Sallen-Key.

In "both" both, both of these are actually switched OUT. You get an  
attenuating filter with real poles (unlike the complex poles of a  
Sallen-Key.) "Both" mode i its own unique thing; you won't get the  
same sound by cascading a LPG in "filter" mode with an LPG in "gate"  
mode.

At least I think. Interpreting Buchla schematics is always daunting. I  
half expect Lovecraftian creatures to start crawling out from a vortex  
in the floor when I'm reading them.

- Aaron