Hi all! I just built my first VCO using LMNC’s schematic and it’s sounding great! (HUGE THANKS TO YOU, SAM!) I started with the basic, core design.
So, I plugged it all in to start tuning it, and I just can’t seem to get it to tune across one full octave, let alone 4 like he’s doing in the video. I’m using a MINIBRUTE for CV IN as well as pitch reference…I can get it to be in tune only to about a major 6th and then it starts getting really pitchy.
Should I be tuning it with the coarse knob all the way down, or in the middle, or somewhere in between? Should I be starting on a particular note?
I was planning on using it to play along with other synths, but it just doesn’t seem to want to cooperate!
Any help or ideas would be greatly appreciated.
Thank you!
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Sounds a little like a problem I had with the Befaco VCO I built, it seemed to calibrate okay but then was out of tune when I used the CV out from my Mother-32. What eventually occurred to me to do was to measure the CV, and though it was 1 V per octave coming off the M32 when it wasn’t plugged into anything, when plugged into the VCO it sagged a little, just enough to account for the problem. In other words the VCO was fine but the M32 CV output wasn’t behaving. (Turns out to be a problem other M32 owners have reported.)
So you might try measuring the CV at the input to your VCO and see if it’s really 1 V per octave.
What I ended up doing was putting the M32 CV output through a buffered multiple channel which I intentionally “miscalibrated” to be a little above unity gain, just enough to compensate for the sag. Kind of a kludge but it works.
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I know you probably did, as you stated you watched the video, but did you make sure to set the Reference Voltage?
Huh…that’s interesting. I wonder if that’s what’s happening with the MINIBRUTE. I’ll try to check the CV OUT level! Or use a different CV OUT source. Thanks!
In the video for the 1V/oct VCO here: https://youtu.be/4Kz8YopLTCQ
there’s no mention of a reference voltage? Are you talking about the one availalbe on his site as a PCB?
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Whoops, I missed the DIY part of your Thread Title, Ignore me, my comment would be in regards to his PCB and Panel version with the Tuner.
My bad lol
Hey, all of my VCOs are stripboardie types. Its a bit dodgy to tune, im seeing that as well. I hooked mine up to an oscilloscope and looked at the frequencies to get somewhat in tune. I think part of the issue stems from the trimmer pots im using are not up to the job, they dont have multiple turns. i feel if they did i would get more precision.
Hey Caustic, thanks for the info…I have a multi-turn trimpot on there, so I would think I could get finer resolution…I did notice it tends to be a bit dodgy if you press on the board a little too hard while tuning though! LOL
Maybe it’s just part of the charm of a DIY VCO!
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Yeah, make sure all the connections are solid on the board, etc.
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yeah, sometimes if you touch the board or you come close to wires it can cause interference. Have fun!
I am planning on building this, where should the main pot be set during tuning???
Rob
Hey twinturbo, I’m still not sure yet…I’ve found that plugging in a CV signal and playing the keyboard while tuning is the most direct way to do this, but as I stated above, I haven’t been able to tune it completely within an octave…I’ve put the coarse tune all the way down and in the middle while adjusting the fine tune to see what works best, but one doesn’t seem to be better than the other.
I know the chip allows for several different tuning pots to optimize the tuning, but this specific schematic only has one. And, as LMNC points out, you usually only play within a few octaves anyway!
I plan on using this specific module as a bass synth, so as long as I can get at least one octave out of it, it’ll be useful! Still working on that…
The datasheet suggests tuning the “scale adjust” trimmer (the 10k trimmer) at around 200 Hz (G3). The “coarse tuning” just adds a voltage to the CV, so set that so you can tune around that frequency with the CV source you’re using.
(you can probably go a bit lower for a bass synth, the idea is to tune the scale somewhere near the center of the range you plan to use it for)
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Thanks fredrik, I’ll try setting the 10k trimmer to G3…I have a feeling I’ll get the same results though. G3 - E4 will probably be in tune and then start drifting…at least based on my experience.
I meant that you should set the coarse tuning so you can get to G3 or nearby with your keyboard (or whatever you’re using to generate the CV in), then trim the scale pot around that point. The coarse tuning is an offset, the scale a multiplier.
OK…I think I understand. So, if that particular trimpot is meant to tune around the 200Hz range, I should maybe get better results in tuning if it’s set there?