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|   *Please check out the BLOG for latest news and notes:   ~ MTG blog ~    |    *How to buy: ~ Shop ~   |

* MTG Pro One Turbo CPU *
The ultimate upgrade for one of the world's most loved monosynths!
sequential circuits pro one 8021 CPU

Turbo CPU

The MTG Pro One Turbo replacement CPU Module is a drop-in replacement microcontroller for the Sequential Circuits Pro One's 8021 CPU (AKA P8021/8021H/P8021H).


  • Plug-n-Play! No soldering required!
  • Non-destructive FLAT pins. We don't use square pins that destroy the CPU socket.
  • 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.
  • Non-destructive FLAT pins. We don't use square pins that destroy the CPU socket.
  • Optional: If you want to make your own MIDI interface, instructions are in the manual. If you want MIDI hardware included, see CPU+MIDI.
sequential circuits pro one midi

Turbo CPU + MIDI

The above plus a MIDI In/Out interface board that adds the following features*:

  • Firmware update (“re-flashing”) over MIDI (using MIDIOX or similar).
  • Settable MIDI channel.
  • Receive MIDI note data.
  • Monophonic MIDI output of arpeggiator and sequencer data.
  • Polyphonic MIDI output of keyboard data.
  • Arpeggiator and sequencer sync-able to MIDI Sync In (settable clock rate).
  • Load/Save sequence data over MIDI.
  • MIDI In, MIDI Out and optional MIDI Thru.
  • Optional MIDI In/Out activity LEDs.
  • Location for optional DAC chip (see CV option below).
  • Soldering and installation are required for MIDI.
* - If you make your own DIY MIDI interface it can do all this too!

sequential circuits pro one MIDI plus CV DAC


"View" images to see a larger version.

Turbo CPU + MIDI + CV (Beta)   New

For the handy DIYers, add a tiny MCP4728 daughterboard to the Rev D MIDI board (and a few wires) and analog control over MIDI will be yours! Simply connect 2 additional wires from the MTG TurboCPU and then tie into the Pro One using 4 CV wires. No trace cutting or case butchering!

See the firmware and manual(s) below.

  • All you need is the MCP4728 daughterboard, some wire and solder.
  • Four 12-bit digital-to-analog converters.
  • Supports MIDI Pitch Bend receive including setting the range/sensitivity using RPN.
  • Control of Filter Cutoff and/or Resonance.
  • LFO2 with multiple waveforms (Square, Saw, Triangle, Sine, including Sample & Hold).
  • LFO2 range from 0.1Hz to 10Hz (10 seconds/cycle to .1 seconds/cycle).
  • ... and more!?
You can order a DAC board from me using Paypal when you order your TurboCPU+MIDI off of eBay and I will install and test it for $25 USD. For this, contact me by email (it's at the very bottom of this page).
Alternatively, you can order a similar one yourself here: MCP4728 Breakout Board

Manuals pdf

The User and Installation manuals can be found here. See also the Release Notes in the Firmware section below.

 *  USER manual                     Version 1.41

 *  INSTALLATION manual       TurboCPU and MIDI Installation

 *  CV/DAC Installation           DAC (CV) Installation

Finally, any updates and comments I post about the TurboCPU on my BLOG can be found here:

Ordering Information


Please note: I am building these by hand for now. Quantities at any given time are limited.

Please order off my eBay page (and see this notice).

(As mentioned above, if you would like the CV/DAC option pre-installed email me at the address shown at the bottom of this page).

Firmware Sys Ex

Please read these Release Notes.

The absolute latest information is on the MTG Blog (link at top).


Some sample .SYX Sys Ex files for reading and writing the settable parameters (zipped). These files are for MIDIOX (or a similar app) but the included text file lists all the commands and you can cut and paste them into your favourite application/tool.

Free Software

Pro One Editor App

The software below is a Windows "Editor/Librarian" that I use for development and testing of the TurboCPU+MIDI. It allows you to setup the various parameters more easily as well as manage sequencer files. I have also included a feature for easy firmware upgrading of the flash. The CV/DAC page is a work in progress.

Download TurboCPU.exe v1.41 here (includes v1.40 firmware upgrade file).

It's just a basic Sys Ex application so anyone out there is welcome to make a prettier one. This is now a signed installation package (setup.exe). If you would prefer just a standalone ZIP please ask.

"It came today and it's now in my Pro-One. Everything works perfectly! Thanks again!" - Ed (Canada)

"This is GREAT! Thanks. - J.L. (Canada)

"Thank you, item as described, my Pro One is singing again." - A.N. (Australia) via eBay

"GRANT you are a genius, this is so much fun. Support this guy, its essential for a pro-one and expands its so much beyond." - D.B.S. (USA)

"I got the CPU and it's now installed. It's absolutely perfect!!! - R.K. (Finland)

"As someone who's been repairing Pro-Ones for ten years, I can testify that this new CPU is definitely a "plug and play" replacement. It also offers increased sequencer options, and has a built-in MIDI interface that is the EASIEST and most functional of all such devices I've seen applied to the Pro-One over the years. Definitely worth the purchase (I've bought several for repairs -- no complaints)." - GMM (USA)

Partial list of experienced installers:
  • http://www.thisoldsynth.com (USA, California)
  • Cantos Music Centre (Canada, Alberta) AKA National Music Center
  • http://www.analogsynthservice.com (USA, California)
  • Digital Audio Service (Germany)
  • http://www.synthwood.com (USA, Washington)
  • http://www.audiorehab.net (USA, California)
  • http://www.theanaloglab.com (USA, NewYork)
  • https://abellrepair.com (USA, Ohio)

Sequential Circuits Pro One Manuals by Stanley Jungleib

with OCR and bookmarks


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