I've been using this PWM circuit to run motors:

http://solorb.com/elect/pwm/pwm1/

Main thing is to use a transistor to do the actual PWM instead of
running too much current through the opamps themselves. You could
replace the potentiometer for the PWM with a vactrol of some sort and it
should work fine for VC. It's something I mean to try myself. I run six
of these circuits and six 12V cassette player motors from a 12V 0.3 amp
wall wart, so the draw isn't that heavy at all. You don't want the PWM
mixed in with your synthesizer grounds however, since it's super noisy!
So yes, use another PSU, but it doesn't need to be so heavy duty.

Unfortunately, this circuit doesn't do reverse. For that, you will need
to investigate an IC called an H-Bridge, which can switch from positive
to negative. Most datasheets of an H Bridge will give a simple app for
this. You should also look at the documentation of the Arduino project
for simple PWM motor control circuits, there should be one with an H
Bridge in there as well.

best!
Derek

Denis Gökdag wrote:

> Hi all,
>
> i want to build myself a little VC electro motor, you know, one of
> these little model-plane 12V motors but with VC RPM. It's not supposed
> to track V/oct cleanly, just be somewhat predictably controllable via
> a CV.
>
> I'm not much of an electronics genius, but i figured that i would use
> a non-inverting amp based on an OP-amp to buffer the CV, then use the
> output as the voltage to drive the motor (the second connector of the
> motor being connected to ground). Obviously, the Op-amp would be
> powered by the a-100 +/-12 V, so the design should be able to output
> -12...12V to drive the motor (with the negative voltage reversing
> direction).
>
> Does that sound about right
>
>
> cheers,
> denis
>
>
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--
derek holzer ::: http://www.umatic.nl ::: http://blog.myspace.com/macumbista
---Oblique Strategy # 137:
"Repetition is a form of change"