Simple VCA

[John E Blacet]

One of the simplest VCAs to implement is the old reverse diode, organ
keyer trick. Built a top octave chip keyboard using these years ago; one
VCA per key. This only works with + to com waveforms and consists of a
couple resistors, a diode and a cap for the A/D ramp.

These days, you can get four very nice expo VCAs in one chip, the
SSM2164. One op amp section to scale and invert the CVs for each channel
and an op amp on the output. Parts count wise, this is the way to go. 

The 13600 is cheaper and you can do linear or expo control depending on
the way you do V to I conversion on the control input. Lot's of extra
parts though...

I think Mouser has the 13600 back in stock, but if anyone is needing
some, let me know.

Regards.
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John Blacet
Blacet Research Music Electronics
http://www.blacet.com
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blacet at metro.net
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