Hey I have a question regarding stable and consistent tuning/ calibration on a vco I made using the schematics on LMNC’s performance vco. I made and tested one made from the same schematic and components as Sam’s, and it works fine. Same with the one I also built today. The issue I have with them is calibrating them and keeping them in tune. With the first one, I have it where the center note (in this case C) shows up on all octaves and sounds fine. The issue is that when I adjust the track and move up an octave to tune it, go back down an octave to retune down, and go back up, it’s a never ending back and forth. No matter how many times I retune them on either the trackpot or fine tune knob, none of the octaves would stay in tune. And its the same issue with the second one I built, except I can’t get the center note at all in any of the octaves, its always going to completely different notes and would not even stay as those notes. I’ve already set them to 4v on the reference trimpot and sat the vcos in room temperature for about 30 minutes, so I’m out of ideas on how to keep them in tune. Any ideas?
I fiddled with that last week, for at least an hour. The poor trimpot still works, but man…
I can’t give you a definitively good answer, but think of it this way:
At every octave, the note goes up or down a bit, according to the next octave.
Start at the lowest Octave, you see (hear) that, naturally, there’s a limit how low you can go, if you’re too low, you get a zero, instead of a note.
Use the track pot and turn it right. If you have the feeling it doesn’t go any further, switch to the next octave. When you are at the highest octave, you realize that every other octave below that, drops in tone if you turn track back to the left. Turn the middle octaves to a high note if you have to, like F or E. That will be your starting, or, orientation point.
Don’t turn it too far, only like…40-50 degrees or so…like 1-2 cm at once, switch back down, turn, switch, turn, switch, turn.
If you are at zero again, the “orientation-note” was too low.
You don’t need “hf” until the end. For the most part, only use track, and if you can, try to center the center octave to C. If it works, it somehow is easier.
Even if that’s an incredibly bad explanation, if the other fine folks here don’t shed another light on the issue, keep trying. I sometimes thought that this will never work. But all three of mine do now.
Oh yes, only plug in the 1222 into your power source, and a mixer if necessary. My Midimuso interfered with the 1222s while plugged into the same power supply. The 1222s still worked but the LEDs were constantly flickering like if the pitch was constantly changing. Who knows what else might cause such or any problem. Drove me nuts and never knew the issue until recently.
Watch this (again?), it might help:
I’ll definitely try your advice and I used that video and his other video on the calibration as references but man somehow they make it seem so easy. Granted what I have is not the exact same PCB and is just built off the same schematic but uses SMD components instead, but I assumed that it’ll work about the same
I was actually wondering, are there some components that could potentially affect calibration/tuning?
That could point to poor quality trim pots (they could move and change value due to vibrations or temperature changes) or bad solder joints (the IC is designed to be minimally affected by temperature, but in theory anything can happen on a bad solder joint).
How well matched are your “precision” resistors? Mismatched resistors will not give the required 1.0V difference for each octave on the rotary switch.
Everything looks fine for the most part, I even swapped chips around to see if theres any difference and even after building two of the boards, double checking the resistor values, connections, wiring and the whole 9 yards, I have the same issue on both of them. 2 out of the 5 VCOs I’ve built are properly calibrated and stay in tune while the others all have the same problem where one octave would be C, then another D, the next would be E or something and no matter how much I try adjusting the track, they wont change or properly calibrate
Edit: Im sorry for blowing this thread up but this has been an issue I’ve been having problems with now and really want to get to the bottom of this. I’ve noticed as I try to calibrate using the track trimpot, the notes pretty much don’t change between octaves no matter how many times I go back and forth adjusting them. Say on my lowest octave I have 32 Hz and when I go up an octave, it’ll be at 72 Hz or something, and I adjust it to 65. Go back down, readjust and repeat. Thing is after a minute of doing this over and over, the frequencies don’t change what so ever after I switch octaves. Is there something I should look at in the schematics or check?
This is by far the absolute best guide on calibrating ever! Saved me so many hours and nights of frustration all done within an hour or less for all 4 oscillators! I really hope this guide is more accessible and known because it is some of the best tips on calibrating I can find! Thank you so very much!
Excellent write-up. (20)
This is excellent! Perfect timing, as I’m building a Timo Rozendal 3340 AND the Polykit-X! My builds have been going great, although I’m a little nervous about some of the harder surface mount stuff I have coming. Anyway. This is a wonderful explanation of something I found VERY intimidating! Thanks again!
Actually I do have one sort of final question when it comes to the calibration of these sort of as3340 based VCOs. I finally got all of my VCOs calibrated with the help of the wonderful guide provided, but I ran into a sort of small problem. When I plug my midi to cv converter into the 1/V input of the VCOs, they go way out of tune, with each octave on the octave switch outputting a random note at a random octave and everything being out of tune. I would even play middle C on the keyboard and bring the center note down to C3 and from there it’s all out of tune again. Like I mentioned, I already calibrated the oscillators by using the guide with the octave switch on the VCOs which worked fine for me when getting the 4.000 frequency ratio. However, I have no idea if I have to calibrate them using the alternating 0V and 2V on a keyboard method if I plan to use a midi keyboard or what the work around is when I already calibrated them with the first method then wanting to use a keyboard on them. If I have to recalibrate them, would I have to still aim for the 4.000 frequency ratio with the alternating 0V-2V on a keyboard method? If so, would I need to calibrate them with the octave switch on the lowest position or does the position of the switch not matter? Or is there a work around this? I’m really curious because I am in love with these types of oscillators but I always bump into something I only overcomplicate more
Update: It’s definitely been some time since I’ve been on here, and recently decided to see if I can solve this problem once and for all. Sadly, I have not yet and am still running into the same issue that I have said in my last post. Even changing the precision resistors on the octave switch, the 100k resistors on r19 and r22 to 0.1%, the octave switch still does not go up or down octaves and instead goes into a sort of chord shape. For instance, I would calibrate the vco on the 2v position using a midi to cv converter with a midi keyboard and have it perfectly calibrated on that position. But when you turn the switch on the lowest position, instead of a low c, it would give me an F, go up one, an A, go back to the 2v, C and finally the last octave would be an E or something. I’m not sure if there’s a proper way to calibrate these vcos using both the octave switch and keyboard at the same time, or if it matters the position you have the switch while you calibrate using the keyboard. Anyone have any ideas?