I glanced at a search for this topic and didn’t see much said about it. I have been putting off building this circuit. I tried it when I first started building circuits a couple years ago and I didn’t get it working right. I figure after the last couple years of experience I should try it again. Especially after my success with my first round on the Thomas Henry 555 VCO (the second round did not work LOL). Despite the failure of the second round I decided I want to give another exponential vco a shot so I put the Shapes circuit on breadboard with thermistors and coarse tune and CV input and only the sawtooth out. I was very surprised at getting 8 octaves in decent tune (a few cents out on the top and bottom octaves) all while on the breadboard. Looks like I’ll have time this week to make a strip board out of it and hook it up to go with my Thomas Henry setup. 
Thanks again to @moritzklein for this great and very simple volt per octave vco!
Best of luck with your stripboarding.
This was my take on the same VCO, trying to squeeze it into 8HP Eurorack:
Well, then I will share my built as well 
I don’t get eight octaves out of it, but it still has a very usable range.
Has anyone tried to get the thermistors tied to the transistors? I haven’t seen anyone do it, not even the Erica Synths PCB, and I wonder whether it could improve the tracking.
I did that in my MFOS VCO
but didn’t attempt to measure the effect on tracking. But in principle it should improve stability. You can see the PCB has a footprint for putting the thermistor on top of the dual transistor chip, as well as one (vacant here) for if you’re not coupling it to the transistors.
I was going to make at least an attempt, but I remembered reading about the Erica pcb so I figured it wasn’t that necessary. I really wouldn’t know, but mine is gonna be in a small case full of other modules. Shouldn’t be too drafty in there…
It’s not the drafts to be concerned with, it’s the heat generated by the circuit itself, and the circuits nearby.
It’s like the 3340 oscillator chip’s well known problem of changing pitch slightly when changing the pulse width CV, which seems to be related to changes in the temperature of the chip with different CV values (if I understand correctly).
In the old days, Moog oscillators were infamous for going out of tune within minutes due to self heating. ARP was able to take away a chunk of Moog’s business by designing oscillators with features to reduce and compensate for temperature sensitivity — presumably including tempco resistors bonded to the transistors.
Well I have a working module on stripbaord with 5 in tune octaves, 1 a little off but usable, another going a little more but it’s C1 so I don’t really care and C0 is halfway to sharp and I really really don’t care. Six usable octaves is more than I expected out of my work. Lol. I worked a shift and made the module start to finish panel and all.
With C1 you mean 32,7 Hz?
I also couldn’t have that in tune with the higer octaves in my Moritz Klein build, but that note is important to me. The way I made it better it was by using a 10nF capacitor instead of 2,2nF.
My theory is that the voltage corresponding to C1 in his design is too low at the base of the transistor, which means the transistor’s curve is not yet truly exponential in that region. With a larger capacitor you can “go up” in that curve. Meaning, the same current at the collector of the BC548 will have to charge a larger capacitor, which in turn will take longer to discharge, producing a lower frequency. That way you need to increase the voltage at the base of the transistor to produce the same C1 frequency as before, which brings that low note more within the exponential region of the transistor curve. The consequence is that my C5 is now very slightly flat, but still acceptable to me. I find the low notes more important anyway. =P
I’m not sure of the Hz, but i like your rationalization. The note was just not important to me. I have other synths for my bass lines. I want to try some lead melody lines, so I went for the solid higher ranges. Still pretty stoked to have 6 totally useable octaves!