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Voltage Trimming

Hi is there a way to adjust the voltage trim of the outputs?

I noticed melodies on my osc were slightly flat as the rise up the scale, not to a great degree but noticeable in certain situations, I’m only talking about a shift of around 15-30cents over four octaves.

Obviously it was different with each of my osc due to their subtle differences in calibrations but quite consistently going flat as it rise up the octaves. So I checked the output from track 1 and 2 with a multimeter. 0v from 101 is giving me a tiny positive voltages in 0.008v (pretty standard I’d say) but at 4v from 101 it is outputting 3.987v (probably quite normal too). However, I was wondering if there was a global way of trimming this, so that I can get 4v to output say 4.008v (or something nearer to that anyway).

I had a look for trimmers on the board but couldn’t see any.

I appreciate I can fix it in the indexes but that would mean calibrating each note slightly off the perceived exact value.


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Btw sorry for being a royal pita with all these posts! :smiley:

But that’s the whole point of the indexes i.e. that is the solution… surely?

You only have to do it once :slight_smile:

Actually, you should NEVER have to calibrate the ER-101. So something is wrong. What is the accuracy of your voltmeter? What is your voltage measurement of the VREF test point on the back of the module?

Good to know!

Sorry if I misunderstood; I wouldn’t ever think to do this or think there was anything wrong with the ER-101; I’d just adjust the indexes because I don’t have test equipment that sensitive, it’s really not cheap when you need that level of accuracy.

Sure, it’s a laborious process, not entirely unlike tuning a piano, although probably technically a lot simpler, but once done, you have a perfectly tracked scale that you can reference using the index and never really have to look at the adjusted values again.

Actually, my post was directed at @iPassenger. Nothing wrong with your suggestion accept that it should never be necessary to compensate for an inaccuracy in the ER-101. The displayed voltage should be the one that is produced at the output and if that is not the case (to say within +/-0.004V, except for 0V) then there is probably something wrong. On the other hand, using the voltage tables to adjust for the tracking inaccuracy in a VCO is an expected use case.

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It’s just a relatively cheap multimeter so it is possible it is at fault. I can’t remember the model but I’ll have a look when I’m home.

How would I test vref on the back if the module?

Totally disagree on this. You should have all your voltage sources outputting the same scaled signals and try to get the calibration on your osc as accurate as possible. Then the adjustment in cents or shift say with the er101 index can be used musically rather than to fix bad tracking and the fine tune on the osc can be for sound sculpting.

That being said some osc cannot be calibrated that well and in those cases then using the fine tune of voltage tables is a good workaround, similar to how the expert sleepers or Reaktor stuff works

There is a very accurate voltage meter built into the ER-102 (+/-0.001V). Perhaps you could try verifying the output of the ER-101 like this:

  1. Have Track 1 output 4.000V on CV-A.
  2. Patch CV-A to the CV input of the mod-X channel on the ER-102.
  3. Place the GROUP MODIFIER switches to slope and X.
  4. Press the GROUP MODIFIER focus button.
  5. Set the scaling factor for CV-A to 1.0.
  6. Read the voltage in the VOLTAGE display.

I’ll try that

My multimeter is a victor vc921. Had it recommended for calibrating my rubicon.

What range setting were you using on the VC921?

mV - smallest one so I could see the difference with the least amount of rounding

Unfortunately the mV setting is only valid up to 4V on the VC921. So perhaps use 3V (safe distance from the edge of its range) as your test case if you are going to use the VC921?

Also, make sure the batteries are fresh.

Ok yeah I’ll try that I was actually testing octaves at first but then settled on 0v and 4v.

I’ll try both methods, with the 102 and the vc.

@iPassenger Indeed, but I very rarely bother :smiley:

It all goes to pot with FM anyway - as an aside, how do you tune when you’ve got 2/3 or more ‘operators’ modulating something?

You know I like the wiggly stuff :joy:

@odevices Didn’t make the connection about the voltmeter in the ER-102 but it seems really obvious now you say it! That’s awesome and super useful - better than my little hand held machine for sure!!

FM is indeed a nightmare, even if your ratios are all bang on, tuning a perfect and your using linear fm, still the slightest dc bias in a modulator waveshape will upset the tuning on deep fm patches.

Some folks don’t bother, make the chaos fm sound they want then cheat with a sample of it and tune the sample, certainly an option if your doing melodies with it etc.

OK, yep! It’s very rare these days that I don’t use FM to some degree… so…

The third way is just to fine tune everything until I get the sound and tuning I like - no samples or cheating, everything I do is real time live recorded!

At which point, the original tuning is far less critical.

I fully acknowledge that this doesn’t work if you have a specific intention, but I’m into bootstrapping the system and letting it guide me, and with this approach it works a treat :slight_smile:

Argh no wiser!!

The multimeter maintains the same readings even with brand new batteries, voltages are lower than they should be.

However, according to the 102 the voltages are ever so slightly higher but only by .001v per couple of octaves, so bang on basically.

:(. So possibly my multi is wrong or the 101/102 combo is wrong!

It seems probable my multimeter will be at fault but I’ll borrow another and see if I can get a “second opinion”.

Will be annoying as it will probably mean I need to recalibrate my osc!! :frowning: