Also now I have one unused opamp on the output board. Anyone have ideas what to do with it?
Why not doing a simple voltage follower on the output? It could help with the stability of the VCO when you’ll plug it into another module.
The outputs are already buffered. Here’s the current state of the output board:
I could also try to replace U5B with some passive CV mixing circuit and then replace U5 with a TL072… But I’d prefer to keep it like it is and figure out something useful to do with U5D
This is a really cool looking project. Spitballing a few things you could do with an extra op amp stage: I sometimes mod my oscillators with an extra pulse wave sub oscillator, or a white/pink noise generator, or you could buffer an additional copy of something like the triangle wave and send it off on a bus to a tuner - I have one tuner on a rotary selector switch so it can tune all my oscillators one at a time. Or perhaps you could do some kind of sine wave output like the AI synthesis oscillator, here’s a link to the schematic:
I’ve built a few of those and I thin kthe since wave output is nice.
Another random thought - it seemed like you were deciding on how to handle the PWM attenuation - I’ve messed around with having a dedicated PWM bias control and then a single CV input+passive attenuator connected to a switch that links the CV to either PWM or FM. Then you can have the PWM bias as well as a CV in. I tend not to modulate FM and PWM at the same time since it tends to sound over-modulated to my ear, so I don’t mind too much having to choose just one or the other.