Triangle Core VCO Schematic

[jaradical]

Looks super interesting - I’m going to have to take a deeper look when I have some more free time, that’s for sure.

@porl

Not sure if the temperature compensation will work well - there are so many variations out there that work with so many different circuit topologies, so I’m not sure if the combination I’ve gone for will function correctly or not.

One thing on the V/Oct trim. The way I did it, and have seen it done, is to put the trimming on the output of the inverting summer amp that has the thermal resistor in the feedback path which I think will buffer the CV inputs. I’m not sure but I think you may get different trimming interactions depending on what’s plugged in to your CV jacks with your current config.

Also check out http://www.openmusiclabs.com/files/expotemp.pdf - section IV. T HERMISTOR COMPENSATION
That shows a PTC in feedback. If you want to use an NTC - check out @jkb’s post with some references here;

Polykit Octo VCO

I mainly choose the NTCs because they are cheap and broadly available compared to tempco resistors. Kassutronics [1] and René Schmitz [2] have some background on the usage of the NTCs. PTCs should have the same effect when used in the op amps feedback path to change gain on temperature change (higher temperature = higher gain). I don’t know about the LM13700 regarding the VCAs, they are even to expensive for my taste. I think I’m going for a simple op amp/transistor solution. I’m very interest…

Cheers,
Jared