[sdiy] SSM2164 VCA

[David G. Dixon]

> > All the designs I've seen based on the Mike Irwin design change
> > Vref to whatever they want the CV range to be. Is there a reason
> > why you couldn't just use -15V and scale the resistor connected to
> > Vref to suit? Wouldn't the 2164 just be seeing a current input, and
> > not care what voltage is on the other end of the resistor?
> 
> A couple of quick observations:
> 
> 1/ What happens if my "+15V" is not actually +15V, but perhaps +14V?
> Or is someone wants to run your module from +12V?

Then he should either a) invest in a second PSU if his first one is
overtaxed, or adjust the PSU trimmers if they are out of adjustment, or b)
learn to live with the resulting VCA control range of 0 to 4.67V.

> 2/ Any noise on the rails (and they are generally noisy, shared
> across all modules) will couple very easily into your signal path.
> Unless you consider this desirable I'd say save up your pocket money
> and splash out on, at the very least, a 5v1 zener or even better a
> proper voltage reference diode.

That is undeniably true.  Probably best to leave the -5V source in.