If all else fails you could still try increasing the value of C1, admittedly this is probably not the most elegant solution.
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I haven’t forgotten about that cap, either! I intend to put an end to the click. 
When I first read Craigyb’s post (post No 9) I wrongly assumed he was talking about dc offset on the actual lm13700 's inputs. I Did consider that to be a pausible cause of the clicking issue.
I see on Ray Wilson’s VCA he made provision for this very problem, see bellow the extra components inside the green box:
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I think Richard redressed this as well for the electric druid suggestions, except he made the point that he thought it was to the cv mix input not the ota input, but I’m definitely going to go down the list until I get an agreeable result.
I was looking at the schematic for the AD/AR envelope generator and noticed that there is no resistor in series with the pots, so when the attack pot is at minimum resistance there is nothing to limit the charging current into the 1uF cap, Im wondering if the opamp is freaking out a bit due to being presented with a large capacitive load, Im not sure as I havent built it, but it is another possible cause of the clicking. Worth considering if none of the other fixes work.
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I considered that the problem might be in the envelope. I do have to reduce the attack significantly to get rid of the click, so it doesn’t only happen at full attack (that would be bottomed out on the attack pot I think). But I am not ruling anything out. I will definitely try this out if I can’t figure it out. I’m planning to do all this tomorrow ( my day off work). I haven’t tried anything yet, but I did make some in line attenuators today so I can try it and other solutions.
Have you made much progress with the clicking problem?
I feel like I have made some progress, but I can still here some clicks for sure with full attack and no release (immediate release). I have only so far implemented the bias offset and the attenuation of the envelope. Im still gonna try the capacitor switch. It’s probably just because I have the cheapest most non regulated power supply possible. 
Do you hear the click at the start or end of the attack? If the release is minimal then you have an abrupt change in the amplitude which could result in a click sound. Can you get it to go away by turning up the release time slightly?
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Yes. It behaves as you described. I wanna say it clicks at both ends with full attack, but reducing it a little and adding a little release clears it up. I was wondering if that would be a factor. It has mellowed quite a bit with your suggested trim pot though. I put a couple more 10n caps across the power rails too. Thought it couldn’t hurt. Not sure if I had adequate decoupling. Its not so bad now. And with a little release it isn’t there at all. Im satisfied. Thanks for the support Kosomonauts!
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Kosmonauts or Kosmonuts!
Seriously that is a great collective noun to describe our tribe, did you just come up with that just now?
Congratulations on fixing the click, I think I’ll build that AR envelope gen but add say 2k2 ( I seem to have an awful lot of those ) resistors in series with the pots
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Nah, that’s been around for years, e.g. this link.
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I got excited as there appeared to be another Kosmonaut about 2-3 miles from where I live. It turns out it is me, so the location info is a bit approximate!
Definitely not mine. I borrowed it from the link Rich (@analogoutput) posted. 
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Yeah — I’m looking at a circuit that has one comparator triggering four different envelope generators. They had fixed 200Ω resistors in series with the pots but even so the op amp couldn’t supply enough current to keep the trigger voltage (and hence the envelope amplitudes) up when one envelope was turned to minimum. The datasheet doesn’t seem to say how much current the TL07xC can supply but for the (generally better) TL07xH they show the output voltage swing cratering at about 25 mA. Using that and a 10 V envelope says the load has to be at least 400Ω. Or presumably 1.6k for four envelopes — I ended up going with 4.7k, which still gives me envelopes that are short enough, I think.
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I’d say 4K7 is a good choice with a 1M pot (roughly 200:1 range) if you need a bigger range a coarse and fine pot would be better in series with say 470R corresponding to approx 20mA max charging current
Hi Dogstar.
I solved this by replacing the 10nf capacitor on the trigger side (2 transistor schmitt trigger) with a 100nf capacitor.
Hope this helps.
Are you talking about the envelope circuit or the vca circuit?