VCO tuning and scaling issues

#1

I tried playing my 400 VCO from Elektron A4 and noticed that the scaling is way off, can barely get 1 octave in tune on any of the VCOs.

Has anyone had any luck getting theirs to play in tune? I allowed it to warm up for 30 minutes after the first unsuccessful attempt, and obviously I was using a correctly rated power supply.

I know the VCO’s have trimmers on them but I’m reluctant to take it all apart if they are not going to solve the issue, also they are very small smt trimmers so pretty difficult to adjust.

#2

Is there no calibration procedure ?

#3

No, just a separate sheet which shows the trimmer labelled tune, no details in main manual.

To be honest it isn’t a deal breaker for me personally, as I have plenty of other oscillators that track well, but I think it will be a problem for some people, so I hope TE sort it.

BTW - Elektronauts down? @LyingDalai

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#4

Mine appears to track about 2.5 - 3 octaves well - then it starts to get a bit wonky tuning wise. I haven’t touched the trimmers assuming it was set up correctly at TE.

Ide email their support to determine the procedure for the trimmers - but be prepared to wait a few days for an answer.

Have you also checked the A4 CV offset for tuning? - I’ve found mine all messed up before which prevented modules from tracking properly.

EDIT: I’ve noticed that upon firing up the unit, the tracking is pretty bad - understandably being an analog synth. After a few minutes of warmup, I find the tracking to be much smoother/steady across about 3 octaves.

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#5

The saw wave has a second frequency running though it. Making it almost impossible to get one straight note out. The square and sine seem to track better because they are more stable. I was using an Agilent Technologies O-Scope and I did upgrade the power supply. But now that it stays on I can scope it and say that try playing with square and sine for things you want in tune, and the saw for more percussive or stuff you don’t mind about the tuning. That may help.

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#6

Time for a tune up with a trimmer?

#7

its a bit more complicated.

There is a second frequency somehow running through the saw. I don’t believe it was intentional.
There is no way to get rid of it. My guess is a cap would do the trick somewhere on the board to
even out power supply ripple. But I’m not a for real EE so thats a guess.

Its like you always have something Sync FMing the Saw Oscillator.

#8

Could be some kind of balance thing with internal trimmers, but i do not have the system 400.

#9

The two trimmers are the center tuning frequency and Volt Per Octave.
There is not a third trimmer and it is a single oscillator. If it were a complex
oscillator like a Buchla 259 or Hertz Donut then I could see why there is
a second frequency floating in an oscillator path, but on a single oscillator
there should only be one frequency.

#10

Maybe it is saw width modulation :slight_smile:

#11

it sounds really cool and its not that bad its just not 100% stable with the saw.
This little modular has a lot of character. definitely a nice DIY project.
the square and sine seem to be pretty in tune over three octaves. Its
what I would expect from a small simple modular. Wish there were faceplates and
a way to get them out of this yellow thing and into a case. the back of the manual
has some info that says some type of chassis, but I dunno?

#12

And after a while it doesn’t stabilize? Cause the osc are not heat regulated probably.
Well it can be a thousand things. Maybe a pot that is not well aligned. It sounds like something simple.
Good luck finding it.

#13

I‘m experiencing the same problem with my saw module. One octave is in tune, the higher and lower ones get out of tune.
It is no problem when I‘m using the PO170 alone. But in combination with the OP-Z the difference in tuning is annoying.

Does anyone of you ( @darenager @fallen_lassen @josepailo ) used those screws on the module to calibrate?

And if so, how does it work?

Thanks.

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#14

I believe it’s not the scale note root so it’s the space between the Expo converter. You should get the OpZ and play c2 and tune your tuner to C2 with the saw oscillator. Then play c5 on OpZ and see how off it is. One direction with that little trimmer should make it flatter or sharper. That would be my guess. I haven’t done it with mine but it’s so basic that would be my guess. It should be very easy but again turn the trimmer slowly so you don’t hurt anything.

Try it and let me know, but be careful pushing that little trimmer. You will need a small screwdriver for sure.

#15

These are the little screws for calibration:

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The way I calibrated my oscillators was to cycle through the octaves - play C1 - C6 from the OP-Z, send the audio to my DAW and use a tuner and look at how much the tuning is off on each octave, then keep adjusting until you’re as close as possible (=/- a couple of cents). It took me a while to do though definitely worth it.

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#16

Thanks. Where did you get the manual from?

#17

This isn’t my pic but I had the same thing - came as a separate sheet from the manual with the 400.

#18

Hi @5StarNomad @josepailo, thanks for both of your help. I tuned the saw module with the tiny screw. Now all te octaves play in tune, wich is really satisfying to listen to, when the PO170 is in combination with any melodic sequences from the op-z and op-1. I didn‘t touch the filter screws yet.

What I‘m experiencing now is a fluctuation sending cv from the oblap module. Maybe this is a result of the nearly empty battery.

#19

Sounds like uncommon grounding. Any fluctuations I get in the Buchla is typically a result from two things not sharing a ground. Like when I accidentally forget to ground both cases to each other. The idea here is find ground on the PO170 and somehow ground it to the ground on the cable of the OPZ. Make sure you use mono cables from OPZ pitch and gate. Do not use the stereo cables included or you will have a floating ground.