New (old) VCA design

[Harry Bissell]

I got the idea from an old Casio (PT-30???) where they had only one
analog switch and got the timing from a processor output, and made the
envelope with a PWM out...

My refinement is the bipolar design... It looks hokey... but in my
design (for other reasons) I had two spare analog gates, the flip-flop
already there (with 50% duty square wave), and one "envelope follower"
so all I added was the inverter. Works great !!! There is no DC thump as
long as the envelope inputs are matched. If you don't use a 50%
duty cycle you will have DC offset (but that's what a pulse does
anyway...) .

It can be a 4-quadrant multiplier....  only one input is always a square
wave (or pulse...)

The DG444 could be anything... except a 4016/4066... unless you run
bipolar 7.5V supplies (not unheard of)

I present this circuit for those who might need an ultra simple VCA.. It
works great for my application....

H^)   harry
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