AW: VCS3 questions

[Haible Juergen]

	> 1) Exactly how does the shape control on oscillator 1 affect the
sine output?

The raw saw wave of the VCO is converted to a triangle. The triangle is then
fed into a sine shaper, which is built around a discreet opamp and a diode /
resistor
feedback network that does a soft limiting or "rounding" of the triangle's
corners.
If you build this kind of circuit (or similar ones with differential pairs
or overdriven
OTAs), you would normally need an offset trimmer to adjust for symmetric
rounding
on top and bottom of the triangle input. EMS increased the range of this
offset
voltage (it's just added to the summing node input of the sine shaper), and
used
a front panel pot instead of a trimpot. I can only guess about their
intentions to do 
so, but to me it looks like they hit two birds with one stone: no more
trimpot
to be calibrated, and you have a new "Shape" feature. Now, that's the
technical stuff.
The effect on the output waveform is that you have a nice sine wave when the
Shape
control is near center, and if you turn it to one side, one of the triangle
peaks gets
squashed even a little more, and the other one leaves the region where the
limiter
would be effective, thus you still have the triangle shape on this side.
It looks a bit like full wave rectified sine, but it is not.

	JH.