OTA question

[Haible_Juergen#Tel2743]

> 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.

JH.