AW: MS-50 filter

[Haible Juergen]

	>I had a look at the MS-50 VCF/VCA schematics at Music Machines.
	>Here are a couple of questions for those in the know:
	>Do the diodes in the CA3019 need to be thermally coupled? Or can
the CA3019 be replaced by matched >1N4148s?
	>Two 100k resistors in the VCA are corcled. Does that mean that the
should be matched? Or something >else?
	>What control characteristic does this filter have? 1 V/oct or
something else?
	>Is the VCA linear or exponential?

I'd say the VCF is V/oct, with low impedance drive of the diodes, the diodes
themselves providing
the expo function. Current thri diodes is limited by the resistors in the
supply (!) connections of the
driver opamps. Themperature compensation is done by D28. CV feedthru would
be minimized with
VR9.
The VCA is linear, with an exponential tail at the lower end of its range.
(Or exponential, with a linear
part at the upper part of its dB range, depending on the way you look at
it.)
High impedance drive. Not a current source, but 100k resistors as an
approximation. Matching
these resistors would be important to avoid CV feedthru here. (As well as
VR13)
The upper end of the CV dynamic range needs no temp compensation. The lower
(nearly expo
part) uses one diode of the array for tempco.

Anybody knows a source of 3019's ?

JH.