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LPG --> bandpass, highpass response? multimode gate
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author LPG --> bandpass, highpass response? multimode gate
Hi all,
does anyone know of a way to obtain a bandpass or highpass response from a Buchla 292 -style LPG?

Specifically I have a quad thomas white LPG that I am wondering if I can mod somehow.

I have heard that inverting the LPG output and mixing with the source signal yields a highpass response, is this true? (My polarizing mixer is in the shop right now so I haven't been able to check since reading this).

And then a bandpass would mean highpass -> lowpass in series?

Does anyone know how the boogie filter obtained BP and HP modes, or is this a different filter topology from a 292-style LPG that just happens to use vactrols?
This might be a good resource to start with:
its a sallen key filter so basically you should be able to get high pass by swapping the place of the two resistors and capacitors in the filter circuit, this could be done with a switch. bandpass by just swapping one resistor with one cap IIRC. Google sallen key filter and check your lpg schematics, should be relatively easy. If I have understood this correctly, never tested it, just thought about doing this at some point ....
Yeah, I came across that page searching google. The Mutant Vactrol was several 292c LPGs wired into a Sallen-Key filter topology (in theory anyway).

I was thinking with a quad LPG you basically have 4 separate "poles" that could be patched into various filter responses using polarizing mixers and a lot of patch cables. How to actually do it, or whether its possible, is eluding me at the moment.

Dead Banana
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