[sdiy] Linear VCF control

mskala at ansuz.sooke.bc.ca mskala at ansuz.sooke.bc.ca
Fri Nov 9 20:02:23 CET 2018


On Fri, 9 Nov 2018, Quincas Moreira wrote:
> Matthew Skala (North Coast Modular) has designed the Leapfrog Filter, which
> does indeed have Lin FM, as well as Expo.https://youtu.be/akMwn7jVV6A

True.  It's AC-coupled, and really intended for modulation rather than as
the main frequency control; I'm applying the linear modulation input
through a capacitor to the collector of the reference transistor in a
standard exponential converter which drives LM13700s.  Voltage changes at
the reference transistor collector translate linearly into changes in the
reference current, and the exponential control of the converter is all
scaled proportionally to the reference current.  If someone wanted
the main frequency control to be linear, they could dispense with the
exponential converter entirely and just do linear voltage-to-current to
drive the OTAs.

-- 
Matthew Skala
mskala at ansuz.sooke.bc.ca                 People before tribes.
http://ansuz.sooke.bc.ca/



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