Tag Archives: Audio Repair

Sequential Circuits Pro-One Restoration Part 2

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Although I had seen photos of the Rev 1.2 mushrooms (mine was made prior to Rev 1.2), I didn’t expect to see Chenrezig, the Tibetan Buddha of Compassion, silk screened onto the circuit board of my Sequential Circuits Pro-One, or the Buddhist mantra, “Om Mani Padme Hum”, etched into the board in Tibetan characters. Even better, Sequential Circuits founder and MIDI pioneer Dave Smith initialed the circuit board twice in the upper left hand corner.

I should mention that this is my second Pro-One. The first one was stolen, and I bought the second one to replace it since I needed that exact sound for the band I was in at the time. The new one was missing a mod wheel. Later one of the knobs was broken off at a show or studio session, so I’m pretty excited to have it restored to it’s former glory.

Checkout the gallery to see the photos of the restoration process. The second and final session of the restoration happened the moment I received the missing parts. These included a replacement modulation wheel (although I think it turned out to be a pitch wheel), a replacement potentiometer, and a missing knob.

The first thing I did was install the mod wheel. Then it was time to swap out the broken pot. I had to remove the circuit board to do this, so while I had it out I thought it would be a good idea to clean things up a bit, so that was the majority of time spent. Finally I removed the old pot, replaced it, and reassembled everything, cleaning things up along the way. Before I put all the screws in I gave it a quick listen to make sure it still worked and the new parts were functional. It was an evening’s work, but more like fun to be honest. Enjoy the pics.

Sequential Circuits Pro-One

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I have finally started restoring my Sequential Circuits Pro-One. My plan is to get it as close to mint condition as possible and start using it again for recording and perhaps performing. Once I started using the Korg MS2000, I neglected the Pro-One and it fell into disrepair. Over time the key contacts became dirty and inconsistent. At some stage one of the knobs was broken off and lost, leaving a stub of potentiometer protruding uselessly from the control panel.

The first thing I did was clean the pots. For you laymen, pots is short for potentiometers. In other words, I wasn’t diverted by dirty dishes. To clean the pots I removed the knobs and then squirted a few drops of a greaseless lubricant called LPS-1 around the post. The stuff works wonders on crackly volume knobs and was recommended to me by the electronics experts at AEI Electronics in Minneapolis years ago. I’ve been using it ever since. After applying the LPS-1 I made thirty or more rotations of the pot from zero to maximum so that the dirt particles were worn away by the fluid.

I put the thing back together and did some tests. The knobs no longer had anymore crackling going on, so that was fixed, but the keyboard was horribly inconsistent. The Pro-One uses a J-wire keyboard with open air connectors that are prone to collecting dirt (or residue from malted beverages spilled over the keys). For a close up view of the Pro-One J-wires check out this post on MaxtrixSynth. Another problem is that the J-wires can become less springy, making the connections a bit weak. I used used q-tips with a drop of LPS-1 to clean each J-wire and the metal bar that they connect to when the key is depressed. I also bent the J-wires slightly to improve the tension. After all that I tested it again to find it working flawless, although still a little difficult to tune. Next up I’ll be replacing the missing mod wheel, the broken potentiometer, and the missing knob.