repl pots with vc

[Martin Czech]

> 	>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.



Thanx. I'll give it a try... if I can tidy up my appartment till Friday..
Looks like bomb explosion, totall mess.

> 
> 	>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)
> 

Perhaps my mail wasn't too clear, it is ok for the VCS3 filter, because
it's allready there, ie. a clone can do this, because it's in the original
drawing.

OTOH the distortion, even with anti distortion bias network, is also there,
it is so much that you can even see it on the scope. This means, that adding
a FET attenuator to any kind of filter might change the sound. But the aim was
just to add control eg. to the wasp filter clone, and not to change the
sound at all, because this isn't a clone any more then.

m.c.