AW: tomg LM13600 VCO5 mod?

[Haible Juergen]

	>Built this, couldn't get enough range,
	>replaced the buffer in the 13600 (the one connected
	>to the cap) with an op amp follower, now it is ok.
	>
	>Anyone else had trouble? or is it just me?
	>Also the triangle grossly asymmetric at very low frequencies..
	>has anyone built this with LM3080s instead?

Haven't tried this very circuit, but it sounds like a typical
LM13600 problem: Leakage from the buffer will cause
offset currents, i.e. limited range and asymmetry.
Opamp buffers work indeed, but they are a bit of a waste
of the internal buffers. If the rest of the circuit allows, I'm
normally using a discrete JFET between the OTA output
and buffer input. This makes a 3 stage buffer, and the 
FETs threshold voltage and the 2 BJT's  be voltages
even compensate partially. (Not that this is so important
in a closed loop configuration, though ...)
The greatest advantage of this method is that you can
easily retrofit it on PCBs that only use the internal buffers.
Had to do this on many of my projects to increase the
usable range on the low end.

JH.