> Hi Dieter,
>
> thanks for the advice. The PWM-based circuit that Derek mentioned
> should help overcome that "offset" voltage in the motor, right (as in
> such a pulse-based circuit, you always apply the full 12V
> voltage.....just not all the time).
>
> Basically the idea is to use a CV to modulate the PW of a VCO (the
> a-111 goes from 0% PW to 100% PW IIRC), then use this VCO to drive a
> power amp as shown here http://solorb.com/elect/pwm/
> pwm1/ .....which basically is similar to controlling RPM with the CV.
>
> (omitting the comparator circuit, and plugging the 111 into R9).
>
> This is gonna be fun :-)
>
>
> Cheers,
> denis

I'm not sure if the PWM will solve the offset problem. After all the motor
works as a "low pass" filter for the PWM. Consequently e.g. a 25% PWM
voltage with 12V level should cause the same result as 3V DC. As far as I
know the main reason for PWM was the power dissipation of the control
electronics as switching causes much less unneeded heat than linear DC
control. It's the same for switching power supplies vs. linear power
supplies (e.g. smaller heat sinks for switching supplies). But I'm not the
motor specialist and maybe I'm wrong.

Dieter

btw. we did some VC motor applications for Kraftwerk but in this
appliactions servo motors were used and the CV controls the position of the
robot elements (via Midi-CV) rather than the RPM.