[sdiy] 3280 VCA question

[Kenneth Martinez]

Ok...looked at his pages...patchell_ca3280_5.html shows something similar,
except that the base doesn't go straight to ground.  Still a little unsure
of this - what's the math for its use - how do I set the resistors on either
side of the tranny so I'll know that 5V in will produce 1mA out to the OTA's
Iabc, for example?


The Old Crow wrote:

> On Fri, 30 Mar 2001, Kenneth Martinez wrote:
>
> > I was breadboarding a 3280 VCA, copied from the final voice VCA of the
> > Prophet-5...
> >
> > I've got it working, but I don't understand the function of Q410 in
> > controlling Iabc - what does it do, since its base is connected to
> > ground?  How does this resistor-transistor-resistor setup differ from
> > just connecting a single resistor?
>
>   That is a linear voltage to current converter.  The OTA is a
> current-controlled device; to control it with a voltage you want to
> convert the voltage to a current.  I think Jim Patchell has some pages
> about using the CA3280.
>
> Crow
>
> /**/