Quasimidi Polymorph – knob jitter hell

Quasimidi Polymorph
Quasimidi Polymorph

The unapologetically boring-looking Quasimidi Polymorph is a very powerful VA polysynth from the early 2000s that allows you to sequence and play back 4 parts on 4 different synth sounds, recording and playing back all the parameter edits you make along the way, and send them out on 4 individual outputs.  So basically it is 4 sequencing polysynths in one. 

Unfortunately it suffers from the same terrible “knob jitter” problem as many, many other pieces of gear that were made in the late 90s and early 2000s, but with 43 potentiometers, it’s just about as bad as it could possibly be.

A lot of gear made around this time used poor-quality, normal analog rotary pots encoded into digital increment/decrement data for all their controls. Unfortunately, as these pots get dirty, they start to send out a constant stream of arbitrary digital (usually MIDI) values, meaning all your settings just constantly jump around. The problem will inevitably spread to all the pots on the unit and cannot be solved by cleaning them. This happens with endless digital encoders too.

This one really did have all 43 of its pots jittering. The only solution is to replace them all.

Service Tips: The pots in here are 10K linear taper with side tabs to snap into the board.  It is tedious to find the right ones on an online catalog, as you have to make sure that the measurements of all dimensions of the pot are correct, and since I already went through that I don’t mind telling you what they are. If you are comfortable desoldering 43 pots, go for it.

TT Electronics pot
Bourns pot






The ideal replacement is TT Electronics P120PK-Y25BR10K, which is listed on both Digikey and Mouser but currently backordered on both. Hopefully it is not going out of production. Fortunately, my client found some on Ebay.

Bourns PDB12-M4251-103BF also has the same value and dimensions, but has a D shaft; I believe it should work, but I can’t promise that the knobs would fit.

If you are experiencing this problem with any of your gear, feel free to inquire whether we can fix it for you– it may not always be worth the cost and parts that fit may not always be available, but I’m always willing to take a look.  

Meanwhile, I am preparing to replace all of the pots and encoders on my own Korg Electribe ESX-1 🙁

5 thoughts on “Quasimidi Polymorph – knob jitter hell”

  1. The last time I used my Polymorph was in 2014 just before I tripped over the wall wart wire that broke the internal dc pin connector. I just got it out of storage and note that it sounds like something came loose as if the unit fell while it was in the closet in my camper (while in storage I did some work on the camper and think it fell by mistake at that time). After reading your recent post I remember the led display jump around a little in 2013 and I chalked it up to the cold weather it had endured after being in my car for a while during winter. Maybe the controls were getting sludged but I am worried that I have nothing but an expensive paperweight now. Please contact me if you think you can help. I realize you can’t get parts anymore but I was thinking all I had was a small problem until today.

    1. It was nice talking with you David, I’m glad it looks like I’ll be able to help you out. To anyone with one of these: the potentiometers have been restocked! I can work on these now 🙂

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