VCF design using OTAs

[Grant Richter]

> 
> 2) What is good value for the input potential divider pairs? I've used
100k
> and 1K, but circuits using 3080s seem to use lower values. Any reason?
> 
A 3080 is only linear over about 10mv thats why the 100K-220 divider. You
can drive a much higher voltage into the CA3280 and LM13600 with
linearizing diodes. Electronotes had practically a whole issue  comparing
the 3080, 3280 and 13600 and showing how to upgrade their old designs to
the new OTA's.

> 3) How good are the buffers inside the LM13700, some designs use TL074s
and
> they work fine for me, but is there anything wrong with the darlington
> pairs provided?
> 
The darlingtons introduce a 1.4 volt voltage shift which could limit your
output voltage range. The closed loop compensates for the internal voltage
shift. If your running 5v pp it shouldn't be a problem.