YuSynth VCO - Frequency Range of output

[JPA]

Hi Forum,

I just had a go at this VCO as my second VCO build. It seems to be working ok, with all waveforms produced and looking good.

https://yusynth.net/Modular/EN/VCO/index.html

Im using the Matched BC547 Variant.

I wanted to ask if anyone knows what the output frequency range should be when you rotate the Coarse tuning Potentiometer?

At the lowest setting (-5) Im getting 30hz, mid setting (0) Im getting around 1khz, full (+5) Im getting 48khz. This seems rather wide and mostly unusable for human hearing!

I have checked many component values, tried swapping out chips, adjusted trimmers but dont seem to get a more usable range from it.

Does anybody know what range this VCO "should" produce?

Any tips of where tips look next?

Voltage at Pin 1 of u7a is 5.04v

Coarse tuning provides a range between +11.87v to -11.73v depending on position

Values were adjusted for the 12v supply (R7, R50, R36, R51, U1, U2)

Any thoughts would be appreciated.

[Hubaswift]

I have built a number of Yusynth VCOs and out of the box all go well beyond the audible range, and don't go too low either, so your results seem to align with mine. The 220k trimmer next to the LM311 is for setting the initial frequency so you can get somewhat lower by adjusting that. Otherwise you can change the value of C8 to something a bit higher in capacitance. I experimented with polystyrene capacitors up to about 680pF for C8 and found that the oscillator still operated as expected and allowed me to get lower into upper-LFO ranges. I can't recall how the upper range limit was effected by this change though. I imagine using a 470pF for C8 on your VCO will get you the lower frequencies you are looking for.

If you find that the coarse tune knob has too much range you can increase the value of R7 slightly. Maybe from 270k to 300k-330k. (EDIT: Just realized you are running on 12v, so an increase to 300k might limit range too much, I'd honestly just try increasing C8 and only change R7 to something round 240k or 270k if you deem it is still necessary, alternatively you could put a resistor on the side of the potentiometer that goes to +12v to limit the upper range while still allowing for the lower range to be unaffected)

Something I've actually never tested, was whether the indicators on the coarse and fine knobs actually align with octaves and semitones respectively. If that is the case changing R7 would of course cause the coarse tune indicators to no longer line up. I always tune by ear anyways so I've never cared.