vca: no CEM, no SSM (was: ssm-2040)

[Paul Perry]

At 01:36 PM 11/08/98 -0400, Andrew Schrock  wrote:
>I know this has been tossed around before, but has anybody come up with a
>good non-CEM, non-SSM VCA solution?

Jim Williams published one in EDN using 3 LF421 op amps and a LM394 matched
pair and a 2n2222. The hard part is bleedthrough, in his there isn't much,
even with 10v pp input. There is a separate "cancellation" part of the ckt 
with a phase shift and freq response tailored to match the multiplier
feed through.
It is reprinted in 'A Designer's Guide to: Innovative Linear Circuits' by
Jim Williams 1985 (also there is a high spec oct/v vco with the transistor 
heater trick)

But, if I had to do a good enough one with almost no parts I'd just use an
AD633 multiplier. Built carefully, I think it would equal anything (ducks!)

paul perry melbourne australia