Matching 3080s?

[Martin Czech]

> I want to go back to a couple of Polyfusion VCFs that I built and make them
> work.  I think part of the problem is unmatched JFET buffers, but I think it
> might be a good idea to match the 3080s.  Does anyone have a circuit for doing
> this?
> 
It is described in one of the formant books, most likely No I.
Just feed the ota with some Iabc (pot and resitor). Connect the output
to a resistor, apply some differential voltage to + - inputs. Now you
can measure the output current depending on Iabc. Maybe it is a good
idea to overdrive the differential input, this should be checked. If
you have a scope, just apply a sine or tri to the diff input, and look
at the output. So you get gm.

If gm is known, it should be not neccessay to match, instead you can
change to respective cap so that the product gm*C is constant.

m.c.