[sdiy] filter resonance

[crystal]

i think that you ~can~ usually make a voltage controlled resonance as an
add-on or designed into a circuit. why not?

i have modifryed 2 of my old radio shick moog mg1's, a moog prodigy, and
perhaps a few others. i  used the stock VCA as the OTA for Vc res and added
a nice SSM VCA IC  for the output VCA. wasn't that complicated, just took
some noodling around to get a good response.

unfortunately all my docs are at my ex's in AZ. next time i visit i will
have quite a haul of electronic stuff....


happy synthing,
crystal




>
> > Bzzzt.  (wrong)
> >
> > Some filters have resonant feedback as you suggest... but most do
> not.
> > The State Variable filter has feedback from a circuit point that is
> not
> > always accessible (the BPF output) and the Moog ladder has feedback
> to
> > the other side of the input differential pair, normally never
> accessible.
> > The Sallen-Key (MS-20 et al) have a very different resonance control
> > (basically the gain of the amplifier)
> >
> > Filters with cascaded integrator stages (like the CEM3320) could use
> the
> > technique you describe.
> >
> > Bear in mind that you might use linearized photocell methods to do
> the
> > resonant control (see National Semi AN-20 "analog multiplier")
>
> Thank you for the clarification, Harry. Always a fount of good
> information.
> --
> john
>