AW: Re: AW: Re: Analog Devices VCA ???

[Haible_Juergen#Tel2743]

>...but Juergen, one of the VCA's doesn't shut off all the way when you pan 
to
>the opposite side.
>Did you ever fix this problem?
>I even tried using matched transistors, and still had the same problem...
>
>I've built two of them and they both worked the same way - same problem. 
Only
>on one side (I forget which one), the other side does shut off 
completely...

I am quite sure that mine shut off completely. Quite, because I rarely use 
such
hard 100% pans, but I think I have tested it once when I built it. OTAH, I 
have
the circuit slightly modified, so I can't give guarantees for the original
SSM application.
But why would you think that you couldn't shift the current distribution of 
a
long tailed pair from 0% to 100%? Isn't this just a question of CV signal
strength at one of the bases? I am sure that with +/-1V you can completely
turn either of the transistors completely off. For reasonable attenuations
(80dB) this CV would even be much smaller.

There *is* a different problem, however, with the simple SSM application
circuit: With zero VOLUME CV and an extreme PAN position, one of the
VCA's will bleed thru. This is because with the PAN CV, the common emitter
voltage is altered, and so is the reference point for the VOLUME CV. But
you should be able to fix this, if you replace the resistor by a voltage
controlled curren source (i.e. another simple transistor stage).

JH.