Exponentially Challenged

Despite my best efforts, I can't seem to get a working exponential converter hooked up. The majority of the designs I can find online use OTAs and have an output current rather than a voltage, so are useless. The one useable design I have found is this one on the EA site, but I can't seem to get it working. I'm using a TL084 quad op amp  for it rather than having an OP-7 for the final stage, so maybe that's the problem, though it does look like any standard kind of op amp should fit in there!


I'm considering a full redesign of the VCO now using OTAs. Saw a triangle/square VCO schematic in the LM13700 Datasheet that looks promising:

If I can make that work then I can keep my existing triangle-to-sine circuitry and find a new exponential converter design. Then I can design the PCB, get two of the damn things onto a board and be done with the VCO section! THEN I can finish my sequencer!