[sdiy] Expo converter tempco placement

[Olivier Gillet]

> Wouldn't the current output requirement potentially vary depending on the VCO circuit that the current source was driving?

Yes, but irrespectively of that, you still want it to double every
time the note increases by one octave.

Because your expo converter produces a current proportional to
exp (-Vb / Vt), it'll be halved every time Vb increases by Vt log 2 =
18mV octave - so that's the scaling in control voltage you aim for.