So here we go, it’s part 2 of the Sequential Circuits Pro One CPU/MIDI upgrade!  I had ordered some parts and was waiting for them to arrive when I left off in the previous tech post here.  I got the cables I ordered and they worked out just as I had hoped.  I broke this tech project into 2 parts because I had some intense and somewhat stress inducing decisions to make about the second half of this affair.  The CPU upgrade was pop and drop and non destructive but the MIDI part of the project required drilling!

I believe the saying goes something like “measure twice, cut once”.  I tend to  measure by eye 3 times and then cut later after measuring one last time.  It seems to work for me this way.  Here’s a breakdown of what it entailed:

1, Holes were drilled in the bottom plate of the synth to add the MIDI daughter board.

2, Holes were drilled in the back ( this is the scary part! ) of the synth to add MIDI in out and through jacks.

3, I made a wiring harness out of RC servo cables to attach the MIDI board to the new CPU and to the MIDI in out and through jacks.

4, The wiring harness was done so that there’s connectors between all the boards which makes future work easier to accomplish.

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I was most concerned with making the MIDI jacks I was adding look good on the back of the synth.  I also wanted to mount them on the 45 degree angle so that they would underline the Pro One logo.  I used a small drill bit to make pilot holes for the 3 jack locations and a larger stepped drill bit to enlarge them to the final size.  The MIDI board was placed on the opposite side of the instrument to keep it away from the audio path and closer to the power section.  I flipped the orientation of the RC cable harness wires so they wont get confused if the synth is disassembled in the future.

PS: In case you are wondering why I only attached 3 of the 5 connections for the MIDI jacks, The only connections actually used on a MIDI cable are 2/4/5. 1/3 don’t do anything!  I believe that under the original MIDI specifications there was 5 cables allotted for future implementations.  There was probably supposed to be a MIDI II convention that never got written or adopted.  Those last 2 wires could have allowed faster parallel data transfer or maybe a separate sysex / note transmission bus implementation.  Many manufacturers like Motu made MIDI interfaces for computers that would stream MIDI much faster between the software and the interface than the interface would stream to the MIDI devices.  This allowed individual MIDI in/outs to actually be more in time with each other as the MIDI interface multiplexed the data stream from the computer to the individual hardware outs.

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Resources:

MTG

Winecountry

Vintagesynth

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