Hi all. Im new to building modular synth parts and I recently built the CEM3340 1v/oct VCO. It works nicely (after fixing some newbie soldering mistakes) and I even ended up getting a Midimuso MIDI to CV module because I wanted to properly test it out, but now ive discovered something that I dont really understand.
When I plug in a CV input, the pitch knob affects the pitch still, offsetting it and making it sound wrong…
As far as I can tell this is how it should work as the circuit uses a sum of the CV AND the pitch knob for the final sound, but then how do I make it so my pitch is accurate to the MIDI notes I send to the Midimuso? Is it just a normal thing that you have to set the pitch knob to a certain position when you use the CV? I really need someone to just explain this whole thing to me…
i’m also new and i dont know, if i understand your question correctly, but i hope i can give you some hints.
Think about the tuning knob like you are tuning any other Instrument (for example a guitar). You can use an external tuner and set the vco to the lowest note you want. (or use another instrument to eqal). When you use more then one VCO you have to tune them one by one to match.
After that, when you send 1Volt to the CV-in , th tone of the VCO is 1 Oktave higher. Every half note equals 1/12 V, because 1 Oktave have 12 halfnotes. You have to check the output of the Midimuso CV-Out. I dont know this Unit exact. I use a keyboard with direct CVout.
Yes, your vco is working like it should. You will need to calibrate it to get the result you desire as volt per octave. To do this you will need to adjust both the pitch potentiometer (knob) and the volt per octave cvscale trimpot on the circuit board. You will need to have tones to reference in order to tune it, but the method is not so straight forward. Sam can show you what to do! Here is a link to his video for this circuit. Around 8 mins into it you will get tuning calibration tutorial. https://youtu.be/4Kz8YopLTCQ?si=oKaxesuK8CYhysPF
Once it’s calibrated you just have to send it a C (or whatever) from the MIDI and use the pitch knob to tune the oscillator to actual C. From there on the MIDI notes should be in tune — well, more or less; analog oscillator pitch does drift, so you will need to retune (with the knob again) at times. But the calibration should be good long term.
Also, there’s a known quirk of the 3340 where if you change the pulse width CV it changes the tuning. There are fixes for that though (and maybe you haven’t even included the pulse width control in yours in which case it’s not a problem).
Thank you all for your amazing help, I think I see how it works now, and I have managed to properly tune my VCO now using both the trimpot and the pitch knob! I dont think I wouldve figured it out without your guys instructions
