Akai pitch bend fix

I have an Akai Synthstation 25, the one that was sold for the iPhone and iPod touch. Sturdy little unit and a great idea, until Apple declare something obsolete again after five minutes. Here’s the thing though, it still does the job it was designed to do really well. Just one small thing – the pitch bend.

Akai seems to have an issue with certain pitch bend units, I have to say on opening the Synthstation, I was very impressed with the build quality, but the pitch bend unit keeps spitting out random-ish values. It’s really quite good, apart from the fact that it doesn’t work properly.

I use Linux – so fire up Alsa Sequencer – GUI, with the quirky little interface and connect the keyboard to GMIDImonitor. Hmm… lots of bogus pitch messages. If I physically pull the wheel down slightly, they stop, and resets to zero, as soon as I let go – there they are. So a physical issue?, nope, the visual inspection says its returning correctly and there is no way this pot can slip. If I hold the wheel to make the messages stop, it is distinctly “off-centre”.

Ok, is there any kind of variable resistor on the board to set this value? Nope. Ok, so if the pitch wheel is a resistor, and it’s saying I have a value that says +234 or whatever, that must mean that the pot is not giving enough resistance to say – “hey – I’m at zero” hence the shouty values in the monitor.

Add resistance.

How much?

No idea, this electronic stuff is a bit daunting, but I have the idea of mounting another variable resistor ACROSS the pitch bend and change the value until the pitch bend shuts up.

Cue Cermet Trimmer 100K Ohms RS 186-772 (new very old stock) from parts box.

Experimenting starts. If I hold the two outer legs of the Cermet against the pitch bend, the messages stop.

Soooo…. if I get a standard 100K Ohm resistor, and solder it across 2 and 3 on the pitch bend?

Bingo.

Problem solved.

P.S. I’m pretty sure that the value can be a lot less, as the maximum value bending down is now -7616, and according to https://usermanuals.finalemusic.com/Finale2009Win/Content/Finale/Pitch_wheel.htmmax “it’s useful to remember that when the pitch wheel is at rest, its value is 0; when it’s as far down as it can go, its value is -8192; and when it’s at the top of its range of movement, its value is 8191.”

I just put the thing back together so more play on another day.

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