New Stuff

[Haible Juergen]

	>>This is what I mean. Substituting opamps will most probably change
the
	>>bahaviour of the circuit.
	>
	>I'm not an expert at circuit theory, so excuse me if this is a
stupid question:
	>Wouldn't it be possible to omit the FETs in the Buchla BP VCF when
you use FET input >opamps like the TL071?

I haven't analyzed this (slightly exotic) circuit yet.
If you want to replace the FETs, you'd probably need FET input opamps
instead of
the FET buffers (not instead of the bipolar opamps!), and then you will
certainly
add some unpleasant delay in the loop, and you might have to fight phase
inversal
of JFET opamps (when the common mode is exceeded), too.

	>Another question regarding this filter:
	>There is an FM input that it AC coupled. This has a cutoff
frequencu of approx 7,2 Hz (47k, >470n). But with the slow response of the
Vactrols, how useful is this input?

No idea about this filter, but in other filters (MAM and MOTM Resonators,
various phasers)
you just get an attenuation at higher modulation rates (LPF, though slightly
nonlinear),
which can be quite pleasant; attenuating a LFO signal at higher frequencies
to prevent
exaggerated pitch modulation effects. 
This effect, combined with a 7Hz HPF, looks strange indeed. Maybe the BPF
that is formed
by tis HPF and the Vactrol's slew rate will just emphasize the most
interesting Vibrato
fequency region ?

JH.