Moog filter fun

Tony Allgood oakley at
Sat Nov 22 14:22:32 CET 1997

Hi all,

In my quest to find the ultimate moog ladder design, for my Rack'd VCF
module, I've been looking to eradicate any sign of CV breakthrough. Now
this I have done to a good degree, but one thing still puzzles me. If the
resonance pot is wired as a variable resistor and ac coupled to the output
of the diff amp, the CV breakthrough is small and can be ignored. But the
law of the pot is terrible, ie. sound rapidly changes only in the last 50%
of travel. This is usual for any Moog designs I have heard. It can be
avoided by using a potential divider instead of a variable resistor. The
law is great but... the CV breakthrough is higher, not bad but higher. I've
ac coupled and buffered but the VR wins every time. WHY? Its feedback
reducing the CV but why am getting it anyway... my hunch is that a VR
design always applies a small feedback signal to reduce breakthrough.

Any help would be greatly received. 

Tony Allgood

Cumbria, UK

e-mail: oakley at

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