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MS20 Mini Tuning
Old 8th February 2019
  #1
Here for the gear
 
MS20 Mini Tuning

My problem is that between C1 and C4, the tuning is out by almost a full semitone. (When C1 is tuned correctly, C4 will be closer in tune to a B).

So it seems to have been discussed on a couple of previous threads (linked below) and it seems that there is a fix, but I can't see it mentioned. I also can't find any service manuals for the MS20 Mini. I have one for the original MS20 which includes external trim pots that the Mini doesn't.

I've been advised by multiple people that there should be adjustable "trim pots" inside the MS20 Mini, and that this should fix my tuning issue. However, I can't find any specific information and don't want to go poking around blindly.

Please help!

(Threads this was mentioned in):

Korg Ms20 Mini Tuning Problems

MUFF WIGGLER :: View topic - MS20mini Calibration? NECRO THREAD: More issues

(Original MS20 Service Manual):

http://www.synfo.nl/servicemanuals/K...ICE_MANUAL.pdf
Old 8th February 2019
  #2
Gear Guru
 
Jamie munro's Avatar
 
🎧 5 years
Quote:
Originally Posted by kaidaw ➡️
My problem is that between C1 and C4, the tuning is out by almost a full semitone. (When C1 is tuned correctly, C4 will be closer in tune to a B).

So it seems to have been discussed on a couple of previous threads (linked below) and it seems that there is a fix, but I can't see it mentioned. I also can't find any service manuals for the MS20 Mini. I have one for the original MS20 which includes external trim pots that the Mini doesn't.

I've been advised by multiple people that there should be adjustable "trim pots" inside the MS20 Mini, and that this should fix my tuning issue. However, I can't find any specific information and don't want to go poking around blindly.

Please help!

(Threads this was mentioned in):

Korg Ms20 Mini Tuning Problems

MUFF WIGGLER :: View topic - MS20mini Calibration? NECRO THREAD: More issues

(Original MS20 Service Manual):

http://www.synfo.nl/servicemanuals/K...ICE_MANUAL.pdf
isn't the easy solution just to turn the master tune knob to the point it is perfect and leave alone?
Old 8th February 2019 | Show parent
  #3
Here for the gear
 
Quote:
Originally Posted by Jamie munro ➡️
isn't the easy solution just to turn the master tune knob to the point it is perfect and leave alone?
I can do this to tune C1 perfectly, but the notes above it are all slightly flat, to to the point where C4 (high C) is almost a full semitone out.
Old 8th February 2019 | Show parent
  #4
Gear Guru
 
Jamie munro's Avatar
 
🎧 5 years
Quote:
Originally Posted by kaidaw ➡️
I can do this to tune C1 perfectly, but the notes above it are all slightly flat, to to the point where C4 (high C) is almost a full semitone out.
i do apologise, i read straight over that

contact Korg would be my advice, they are always helpful in my experience and they will point you toward the area of the board you need if it is possible
Old 8th February 2019 | Show parent
  #5
Here for the gear
 
Quote:
Originally Posted by Jamie munro ➡️
i do apologise, i read straight over that

contact Korg would be my advice, they are always helpful in my experience and they will point you toward the area of the board you need if it is possible
No worries! Thanks for the advice- I have contacted them by email, and they suggested that I simply take it to a service place, and get charged for a service. Do you think I'd have more luck over the phone, talking to a technical advisor?
Old 8th February 2019
  #6
Deleted 859c1b8
Guest
Does it go out of tune both when midi controlled AND when played from the keyboard?
Old 8th February 2019 | Show parent
  #7
Here for the gear
 
Quote:
Originally Posted by Deleted 859c1b8 ➡️
Does it go out of tune both when midi controlled AND when played from the keyboard?
Yes, no difference
Old 9th February 2019 | Show parent
  #8
Gear Guru
 
Jamie munro's Avatar
 
🎧 5 years
Quote:
Originally Posted by kaidaw ➡️
Yes, no difference
so you definitely need to get inside then, seems odd for ms20 mini but i am sure it is possible to adjust

you could keep it or sell it as vintage soul in a modern style
Old 9th February 2019
  #9
Gear Guru
 
Jamie munro's Avatar
 
🎧 5 years
is it when using two osc or one also?
Old 9th February 2019
  #10
Lives for gear
 
ArtFluids's Avatar
 
🎧 5 years
Did you try and see if it tracks its own keyboard CV properly?
Patch KBD CV OUT to VCO 1+2 CV IN and see if it still works.
You should see no difference when you do this if things are calibrated right.
Old 9th February 2019 | Show parent
  #11
Here for the gear
 
Quote:
Originally Posted by Jamie munro ➡️
is it when using two osc or one also?
I just did a bit of testing- the two VCOs stay parallel to one another no matter what.

I put them to the same wave type and scale setting, tuned them to each other, and there was no variation across the octaves.

Whatever the tuning issue is, it's affecting them both equally.
Old 9th February 2019 | Show parent
  #12
Here for the gear
 
Quote:
Originally Posted by ArtFluids ➡️
Did you try and see if it tracks its own keyboard CV properly?
Patch KBD CV OUT to VCO 1+2 CV IN and see if it still works.
You should see no difference when you do this if things are calibrated right.
I just tried this- I'm not sure exactly what I'm supposed to be listening for, but it sounds the same with and without this patch to my ears.
Old 9th February 2019 | Show parent
  #13
Gear Guru
 
Jamie munro's Avatar
 
🎧 5 years
Quote:
Originally Posted by kaidaw ➡️
I just tried this- I'm not sure exactly what I'm supposed to be listening for, but it sounds the same with and without this patch to my ears.
well the kbd generates a voltage level or pitch if you like, this test is to see if the kbd is doing its job which then narrows down the process of elimination and ultimately points to the osc

edit : you already said this happens via midi so it cannot be kbd related anyway. hmmm.
Old 9th February 2019 | Show parent
  #14
Here for the gear
 
Quote:
Originally Posted by Jamie munro ➡️
well the kbd generates a voltage level or pitch if you like, this test is to see if the kbd is doing its job which then narrows down the process of elimination and ultimately points to the osc

edit : you already said this happens via midi so it cannot be kbd related anyway. hmmm.
I posted this on Reddit and a few responses indicated that the original MS20 had trim pots on the exterior that could be adjusted to fix this:

http://www.synfo.nl/servicemanuals/K...ICE_MANUAL.pdf

(at the bottom under adjustment procedure)

However the Mini doesn't have these, so it was speculated that they might be internal.

I have taken a look inside the case, but there are no clear labels on the circuit board, and I can't find a service manual for the mini.
Old 9th February 2019 | Show parent
  #15
Here for the gear
 
Quote:
Originally Posted by Zaphod Betamax ➡️
All the controls for Hi/Lo octave set should be accessible from the front
through the grommets. It is like this on the MS-20Kit.
I'm not sure what you mean- the only controls I have on the front of the MS20 Mini to adjust this are for adjusting the octave scale (which works fine), the VCO2 tuning (which works fine) and the master tuning (which works for one note, but the notes around it are not in tune with it).

Sorry if I'm being dense- I'm a little bit in over my head with this.
Old 9th February 2019 | Show parent
  #16
Deleted 859c1b8
Guest
Don't heed me, just looked online at the MS-20 mini.
No grommets on the front for tuning.

Add that to the differences between OG, the mini, and the Kits.

In my picture of my MS-20kit, you can see the removable
grommets to get at the Hi/Lo tuning.



Quote:
Originally Posted by kaidaw ➡️
I'm not sure what you mean- the only controls I have on the front of the MS20 Mini to adjust this are for adjusting the octave scale (which works fine), the VCO2 tuning (which works fine) and the master tuning (which works for one note, but the notes around it are not in tune with it).

Sorry if I'm being dense- I'm a little bit in over my head with this.
Attached Thumbnails
MS20 Mini Tuning-img_20190208_201422503.jpg  
Old 9th February 2019 | Show parent
  #17
Here for the gear
 
Quote:
Originally Posted by Zaphod Betamax ➡️
Don't heed me, just looked online at the MS-20 mini.
No grommets on the front for tuning.

Add that to the differences between OG, the mini, and the Kits.

In my picture of my MS-20kit, you can see the removable
grommets to get at the Hi/Lo tuning.
Ah I see the confusion. Thanks for putting this there though- even if there aren't external controls, surely the fact that there's something there for adjusting on the kit AND the original MS20 means that the mini must have something somewhere!
Old 9th February 2019
  #18
Here for the gear
 
Fixed thanks to Sovietpop!

I'll copy/ paste his fix for future reference so anyone else with the same issue can resolve this:

Here you go !

Remove the screws from the endcaps and pop them off.Remove the three screws along the top edge of the back.Flip the panel assembly forward (gently, as some of the cords are a bit taut) and unscrew the bracket that props it against the back of the case.Remove the four washered screws that hold the panel cover to the main board's spacer bracket/cover. Remove all the knobs. Unscrew the nut from the headphone jack (it's the only real nut on the outer panel) and remove it and the washer behind it. Lift off the panel cover and set it aside.Remove the screws holding the spacer bracket to the main board. Remove the nuts from the pots that have them (VCO1/2 waveform and octave, HPF/LPF cutoff, main volume.) Gently lift off the spacer bracket. You now have full access to all the trimmers. You can safely set the main board in place on the back of the keybed, angle it against the back of the case, and operate the synth as normal without shorting anything.Reassembly is a simple reverse order. The only minor gotcha is that the volume knob is mounted on a separate mini-board and placed in a hole in the main board, so you'll want to make sure it's all properly aligned in its hole before replacing the nut that clamps it to the spacer bracket.
The trimmers for tuning are the ones down in the lower-left corner of the board. (To the best of my experience) the top-leftmost is the keyboard CV adjust; the one below it is VCO1's coarse tuning. The top middle trimmer is VCO2's coarse tuning; the one below it is VCO1's fine tuning, and the bottom-rightmost trimmer is VCO2's fine tuning. No, it's not a very intuitive arrangement, but whaddya gonna do.a
Old 5th October 2019
  #19
Here for the gear
 
🎧 10 years
My friends.

Had the same problem, fixed it using the inner pots.

However, i may add that you can access the pots from the back of the main board, if you use a screwdriver that's thin enough. So you just need to remove the back plate or the plastic left side.

Should save you tons of time.

Have fun.
Old 5th February 2021
  #20
Here for the gear
 
Hey guys,

Just thought I’d add my experiences with this issue in to here just for anyone still having the same problem. So after spending a few hours investigating this, I can confirm the potentiometers in the bottom left are as follows:

Top left: Osc 1 pitch
Below (slightly right): Keyboard tracking
Upper middle: Osc 2 pitch
Lower middle: Osc 1 tracking
Lower right: Osc 2 tracking

I was having tracking issues with mine, both from an external source, midi and from the keyboard. The way I solved this was as follows (I’m going to assume you know how to use a tracking potentiometer to calibrate/tune an oscillator):

Connect an external Hz/Volt pitch source you know is accurate to the OSC 1+2 CV IN jack (this will disconnect the MS20s own keyboard so you can tweak the tracking of oscillator 1 and 2 independently of the synths keyboard)… I used my Keystep Pro for this. Play a few octaves on your external source and see how well the pitch tracks with each octave. If it’s going flat or sharp with every octave, tweak each oscillators tracking potentiometer until it tracks nicely. Repeat for second oscillator.

Once you are happy both oscillators are tracking nicely with the external source, disconnect the external Hz/Volt source and play the MS20s keyboard. If it’s tracking nicely you’re done, if it’s not, you need to tweak the Keyboard Tracking potentiometer until it tracks nicely.

A few things to note:
The MIDI in converts the MIDI notes to voltages and sends them to the oscillators via the synths keyboard. This means that if your MS20 keyboard tracking is out, it will also be out if you plug in an external MIDI source. If you don’t have an external HZ/Volt source, MIDI will not stop the MS20s keyboard from influencing the oscillators pitch, and you won't be able to establish if the oscillators or keyboard tracking is the issue. The only way to do this is with the OSC 1+2 CV IN. I would not recommend attempting to tune/calibrate this instrument without an external Hz/volt source you can use to get the oscillators tracked first.

You shouldn’t need to adjust each oscillators master pitch too much, if at all, but if you do just make sure you tune them to C (with the master tune knob set to the middle), so a C note on the keyboard plays a C note out of the synth. Otherwise you risk getting your synth tracking well, but the pitch shifted so the keys don’t play the right note (and you may be beyond the range of the limited Master Tune knob).

Well there you go, good luck with it. My MS20 mini had sat unplayed for years and i finally decided to fix it. Thanks to kaidaw for the original fix post, although i found out the potentiometers locations are not quit what he posted.

I’ve attached a picture of the PCB with the potentiometer locations.

Good luck!

http://ibb.co/fNFmRkq
Old 5th February 2021 | Show parent
  #21
Lives for gear
 
hcppp's Avatar
Good info to be had!


It also explains why there are no removal grommets on the front for adjustment like on the MS-20Kit.

So indeed, add this to the differences between the two.


Quote:
Originally Posted by Hetrodyne ➡️
Hey guys,

Just thought I’d add my experiences with this issue in to here just for anyone still having the same problem. So after spending a few hours investigating this, I can confirm the potentiometers in the bottom left are as follows:

Top left: Osc 1 pitch
Below (slightly right): Keyboard tracking
Upper middle: Osc 2 pitch
Lower middle: Osc 1 tracking
Lower right: Osc 2 tracking

I was having tracking issues with mine, both from an external source, midi and from the keyboard. The way I solved this was as follows (I’m going to assume you know how to use a tracking potentiometer to calibrate/tune an oscillator):

Connect an external Hz/Volt pitch source you know is accurate to the OSC 1+2 CV IN jack (this will disconnect the MS20s own keyboard so you can tweak the tracking of oscillator 1 and 2 independently of the synths keyboard)… I used my Keystep Pro for this. Play a few octaves on your external source and see how well the pitch tracks with each octave. If it’s going flat or sharp with every octave, tweak each oscillators tracking potentiometer until it tracks nicely. Repeat for second oscillator.

Once you are happy both oscillators are tracking nicely with the external source, disconnect the external Hz/Volt source and play the MS20s keyboard. If it’s tracking nicely you’re done, if it’s not, you need to tweak the Keyboard Tracking potentiometer until it tracks nicely.

A few things to note:
The MIDI in converts the MIDI notes to voltages and sends them to the oscillators via the synths keyboard. This means that if your MS20 keyboard tracking is out, it will also be out if you plug in an external MIDI source. If you don’t have an external HZ/Volt source, MIDI will not stop the MS20s keyboard from influencing the oscillators pitch, and you won't be able to establish if the oscillators or keyboard tracking is the issue. The only way to do this is with the OSC 1+2 CV IN. I would not recommend attempting to tune/calibrate this instrument without an external Hz/volt source you can use to get the oscillators tracked first.

You shouldn’t need to adjust each oscillators master pitch too much, if at all, but if you do just make sure you tune them to C (with the master tune knob set to the middle), so a C note on the keyboard plays a C note out of the synth. Otherwise you risk getting your synth tracking well, but the pitch shifted so the keys don’t play the right note (and you may be beyond the range of the limited Master Tune knob).

Well there you go, good luck with it. My MS20 mini had sat unplayed for years and i finally decided to fix it. Thanks to kaidaw for the original fix post, although i found out the potentiometers locations are not quit what he posted.

I’ve attached a picture of the PCB with the potentiometer locations.

Good luck!

http://ibb.co/fNFmRkq
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