Sequential Circuits Pro One

::: Sequential Circuits Pro One MIDI Upgrade :::

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

::: IF :::

::: Sequential Circuits Pro One CPU Upgrade :::

This is part one of a two part series on the Sequential Circuits Pro One.  The Pro One is a classy sounding and nicely laid out mono synth from the same lineage as the SCI Prophet 5.  It was released during the era of Big Expensive poly synths and their more compact Mono brethren of the late 70's and early 80's.  Its sound is versatile and can cover any ground between Lead and Bass and all the way to great drums and percussion. :::

There's a limited CPU on board that can record basic, i mean BASIC, sequences and a decent Up/Up Down arpeggiator that is fun to use.  I happened upon a site for MTG, Music Technologies Group, that offered a replacement CPU that adds MIDI note in out plus other controller input to this classic synth.  This is the first part of the process.  I plan to complete the MIDI in outs and other CPU routings later but i found that i wanted to get some extra parts first.  The MTG kit includes the CPU, MIDI in out jacks, a MIDI daughter board, and some connecting wires.  I felt that i wanted to have connectors to and from the jacks and MIDI board so that the Pro One would remain easy to service and modular in layout.  I decided to get some RC servo extensions as they are 12" long and have 3 conductors in a nice small package with male and female receptacles.  I will complete this project as soon as I have all the parts from Amazon!

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While i had the machine apart i found that there was a broken pot that had been carefully repaired.  I re-repaired the shaft of this pot and cleaned the others to help improve the function and performance of the face plate controls.  It looked like someone had used superglue the first time.  I used epoxy this time so it will last longer!  I also noted that this unit has the power transformer mounted to the chassis and not the board.  In early versions the board mounted transformer tended to snap off and destroy the inside of the synth!

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Many people lament the construction of the Pro One and accuse it of being flimsy and shoddily made.  I think it could be better as well, but i have seen worse too!  The pots are all plastic shaft and are prone to breaking off if you abuse the instrument.  Especially because they are not secured to the faceplate.  I think that the faceplate is a cool design, but it is plastic and tends to flex more than it should considering it is the support for the board that is underneath it.  I have considered attaching a bar of some kind under the front lip of the top plate to strengthen it for the future but i don;t have a clear idea as of yet on how to make that happen.  Maybe for a future post!

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The CPU just pops in and it's ready to go.   Here's a list of features from the site: Features:

  • Plug-n-Play! No soldering required!
  • Supports the original functionality including the sequencer and arpeggiator.
  • Each sequence can be up to 256 steps (compared to total of 40 steps on the original).
  • Sequences are retained in memory even after power-down. The CPU module does not use a battery.
  • Power-on settable parameters for clock start mode, arpeggio up/down end notes, arpeggio down mode and arpeggio gate time.
  • Sequence Tie mode allows for a variety of note lengths.
  • Sequence End mode lets you chain the two sequences.
  • Optional: If you want to make your own MIDI interface, instructions are in the manual. If you want MIDI hardware included, see CPU+MIDI.

::: IF :::