[sdiy] OTA Iabc feeding

[sleepy_dog at gmx.de]

 >  Thomas Henry's book "Making Music with the 3080 OTA"

Argh! I bought that book years ago, then had an electronics fiddling 
hiatus, and completely forgot about it.
I better have a look at that then, thanks for reminding me!

Guy McCusker wrote:
> 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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