[sdiy] OTA Iabc feeding

[Guy McCusker]

There's a decent discussion of various control circuits for the Iabc
in Thomas Henry's book "Making Music with the 3080 OTA". At least, it
seemed decent to my beginner's mind.

On Sat, Sep 2, 2017 at 9:56 AM, Olivier Gillet <ol.gillet at gmail.com> wrote:
> The voltage at the Iabc pin is V- + 2 diode drops.
>
> So if you want to only use a resistor between your CV source and the
> Iabc pin, your CV source must be offset so that its minimum level (the
> value that will, for example, completely shut off your VCA) is exactly
> V- + 2 diode drops. That's not a very convenient voltage to deal with!
>
> It's more convenient to provide a current to the Iabc pin with a
> current source circuit - a circuit that is able to source a current
> proportional to the voltage at its input, irrespectively of the
> precise value of the voltage at the Iabc pin.
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