AW: sorry meant VC crossfade ckt

[Haible Juergen]

	>>Have you tried to use two VCA's with the outputs summed and their
CV ins
	>>controlled by inverted voltages? A 13700 (two VCA's) and opamps to
invert
	>>the CV's and sum the outputs will do.
	>
	>this will work, but I am looking for something much simpler, based
around 
	>say an op amp with signal A run to both pos and neg inputs, and sig
B to
	>one input only, with a resistor network including a fet to ground
so that
	>as the fet resistance is changed the op amp output goes from A to B
	>(or likelier A to -B).
	>Pretty sure this is 'doable'.

Two OTAs with outputs connected together.
A pnp pair with the two collectors going to the two
OTA Iabc inputs. Emitters tied together, and connected
to positive supply over a resistor to set the max Iabc.
One base at GND, other base receives crossfade CV
over resistor divider. (approx +/-100mV)

Works fine. (I tried it.)
You can even use the common emitter of the pnp pair
for level control of the OTA pair, i.e. one OTA pair for
both crossfading *and* normal VCA (Envelope ...) function.
It works decently just with an ADRS output connected
to the emitter resistor (where the ositive supply voltage
was, see above), but you'd get a slight dependency 
of the crossfade and ENV function.
(I have this circuit twice as the main VCAs in the JH-3.)
Improoved solution: ENV goes to voltage controlled
current source, this current source drives emitter
of differential pair, rest as before.

This was probably more than you asked for. So
for the crossfade alone, just two transistors
and a few resistors.

JH.