Hello Nick

The A-101-2 contains a exponentiator circuit, but an opto coupler does
not have an exact response curve. That means: the A-101-2 will be
"something similar as exponential".

But there is another reason why you should have a OTA based VCA: Opto
couplers are slow. You never will get that fast response, that a OTA
base VCA like the A-130/A-131 can provide.To be honest: I'd recommend a
A-132-3, then you have a linear and an exponential VCA. Usually you need
a linear VCA for the envelope modulation and a exponential VCA for LFO
modulation. In the A-132-3 you have both.

Florian