LM13600

[Haible Juergen]

	>I have read here of using a FET either between the buffer or in
place of
	>it.  Does this compensate for this effect in any way to make it
more
	>acceptable?

Using a FET instead of the internal buffer works if you don't load the
outputs too much.
Some early Roland Filters were built from OTAs and FET buffers. Or check the
recently published OB-1 vcf circuit: FET only where no load is applied, and
a
nFET / pnpBJT composite darlington where a lower output impedance is
needed. (http://www.haint.com/synth-diy/ob1filt.pdf - thank you Sean !)
Using a FET + the internal Buffers is a good thing for new designs. I do it
all
the time. But it will shift the levels between the OTA output and the buffer
output.
Normally the closed loop around the OTA will compensate for the buffer
output
voltage, just shifting the OTA output where it is needed for the right
buffer output
voltage. But obviously this affects the internal clipping levels of the
whole 
circuit. This might or might not make a difference in a specific design.
That's
why I say it's good for new designs, but maybe not to reproduce the sound of
a
vintage circuit to 100%.

JH.