For example, if I tune my VCO to C2 and press D2 it is offset 15 cents higher, on E2 30 cents higher, F2 40 cents etc. If I press C4 I am 10 cents below C # 4. I don’t get it tuned right. I use the Beatstep pro for the 1V / oct and have also set 1v / Oct correctly so NOT Hz / volt to exclude that immediately. So where is the error, where can I start to solve it. Now I finally have enough modules to make some music and then they don’t work … With the first VCO I built, I have the same problem, but exactly the other way around. So with one VCO too much arrives and with the other too little. I think that’s called offset, but how do I get it under control?
Edit: The VCO is Sams 3340 Stripboard Core here is the Layout:
are you sure that C2 is exactely tune with C1 / C0 / C-1 …
with the trimmer pot there are several point that seems to be in tune but in the precision not really.
No, it doesn’t work at all. If I tune it to C0 and press D0, it is 15 cents higher, as I wrote above. I can’t even get it to tune it so that, for example, c0 and c1 or c3 and c4 match. Maybe I would have to make an attenuator between the beatstep and VCO. But the problem with the other VCO is the same, but there are always a few cents missing, so I think there is apparently too little power.
The first question is, do you really have 1V/Oct control voltages going in? Measure the CV while playing C0, C1, C2 etc. and see if it changes by 1V exactly. Ideally measure it while the CV is plugged into the oscillator. Depending on the circuitry in the controller and the oscillator, you could see 1V/oct coming out of the controller when it’s not plugged in, and less than 1V/oct when it is. (I think there’s a 100k input impedance, so a 1k output impedance on the controller would give a 1% tuning error, i.e. 0.99 V/oct meaning 12 cents mistuning per octave. But it sounds like you have worse problems than that. Edit: Not sure about that impedance, hard to tell without a schematic.)
Once you’re sure you have 1V/Oct control voltage, the trim pot should allow you to adjust the oscillator’s response so the frequency changes by 1V per octave. If you can’t get 1V/oct regardless of the trimmer setting then something’s wrong.
Problem solved, you can call me a jerk … I thought the trimpot is something like a fine tune knob. So I set the frequency knob roughly to one note and then fine-tuned it with the trimpot, which of course didn’t work because it’s a scale knob … Well, in any case, both VCOs are now tuned and I’m happy again because I’ve learned something and it’s nothing worse.
Sometimes I misunderstand your approaches because my English is not that good. You have already written me the solutions … thank you again for that. Possibly. could someone write instructions for tuning and pinning them somewhere
I have a follow on from this. I used the trim pot and I got it to work 1V/ Octave no probs, the problem is even with the main tune pot turned all the way down the lowest note I can get is basically mid to high range, if i go up octaves then it goes into dog whistle mode. If I have a larger corse pot value will I get lower frequencies or is there something more involved ? Thanks Matt.
