repl pots with vc

[Haible Juergen]

	>3. Use ota. Better use 13700. Has anybody tryed to give a state var
filter
	>a ota resonance control ? I must try this.

I have, but Oberheim has done it decades before (;->)
The OB-X filter is very close to the SEM filter, with a 3080 for resonance
control. I've used the exact circuit for the 2-pole part of the filter in
the JH-4.

	>4. JFET attenuator. Problems with large signal amplitudes, much
	>distortion one is able to see on the scope, distortion changes
widely
	>with attenuation, ie. bias.

EMS used a FET in their VCS3 filter. Unlike the Moog filter, the variable
resistance is the lower half of the divider. No "reverese log" action
needed;
the FET works great here. As for noise and distortion, the differential pair
that is connected to the FET should contribute more to nonlinear behaviour
and noise than the FET. (There's a linearizing circuit around the FET
anyway)

JH.