Doepfer

> 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

Denis,

I don't think that a standard opamp can do the job unless you use a motor
that requires only a few milliamperes.
The next step would be to add a power output to a standard opamp. For motor
control 2 power transistors added to the opamp output (one npn and one pnp)
should do the job. I can send you the schematics directly if you want.
But this will not generate a RPM that's reasonably proportional to the
applied voltage. Each motor has an "offset" voltage. Below this voltage the
motor will not work, i.e. you have to apply e.g. 6V before a 12V motor will
begin to run. Only in the working range (e.g. +6...+12V) you will have a
behaviour with RPM reasonably proportional to the applied voltage.

Best wishes
Dieter Doepfer