[sdiy] Linear VCF control

Quincas Moreira quincas at gmail.com
Fri Nov 9 21:15:31 CET 2018


AND there's a tempco :)

On Fri, Nov 9, 2018 at 1:01 PM <mskala at ansuz.sooke.bc.ca> wrote:

> 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/
>


-- 
Quincas Moreira
Synth Diy Guy
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