HJ2743 at denbgm3xm.scnn1.msmgate.m30x.nbg.scn.de
Mon Oct 16 18:23:00 CET 1995
> I have no idea what's inside the Odyssey module, so now I'm incredibly
> curious; what's the circuit like? How on earth do they use an LM3900
> in a VCF circuit? How did you get a schematic?
The ARP filters are very interesting designs. Not the first ones:
just a Moog ladder built of arrays.
But the later ones use discrete PNP pairs as variable gm stages,
and the Norton Opamps act as differential current-to-voltage
converters. Basically, it's a similar thing as those OTA-circuits,
only that the OTA has the diff pair inside the chip, and not the buffer,
and here it's just the opposite. And a PNP input stage ... and some
additional reference voltage/current paths are required externally.
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