NEW Keyboard for SCI Pro One!

Posted on March 18, 2012 by grantb4

A long time ago I ordered a new 37-key Doepfer keybed and cable from in the USA. In fact I think Doepfer gets them from in Europe so there might be a better way to obtain one. The new keybed is make/break (velocity sensitive) style, but the Pro One does not have the pinning to make use of the break contacts, so I only used the make ones.

Long story short, after making a new cable out of the supplied Doepfer/Fatar one and a 16-pin DIP, my Pro One keyboard is like brand new! The new keybed will fit in the Pro One, but the hole pattern on the bottom of the synth need to be drilled. This is fantastic news for anyone that has the membrane style Pro One keyboard. Anyway it will work with either the original Pro One CPU or my new TurboCPU. I have a couple of photos, but will also upload a wiring pinout later when I get time.

http://www.musictechnologiesgroup.com/images/pro_one_keybed.jpg

http://www.musictechnologiesgroup.com/images/pro_one_keyboard.jpg

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MIDI Jack mounting

Posted on October 21, 2011 by grantb4

I have received some photos from users showing off their TurboCPU+MIDI installations, but don’t have them at hand right now. What I do have is an interesting photo from the old Oberheim DX or DMX that shows yet another way to mount the MIDI jacks. This might be an interesting option for the Sequential Pro One too:

Sequential Pro One MIDI

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USB 5 1/4″ Floppy Drive

Posted on April 19, 2011 by grantb4

I know it sounds off-topic, or that I have a fetish with all things vintage, but the reality is that a lot of my EPROM data and other files were kept on 5.25″ floppy disks back in the 80′s. Getting at these files has been somewhat painful. But now I have compiled the parts to built my very own USB Floppy drive for 5-1/4″ disks. And it works!

Now I just need an enclosure to make it a bit more transportable. So if anyone in OC-land or LA-ville needs to read a floppy, I can do it!

Or if you have extremely deep pockets, I can make one for you. ;-)

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MIDI Control Surface for Pro One

Posted on July 27, 2010 by grantb4


I just ordered a Behringer BCF2000 MIDI Control Surface and will be looking at creating a template that maps all the changeable parameters to the knobs buttons and sliders. Hopefully there are enough controls on this unit. I wanted the BCF for the motorized faders because I thought that would be way cool for programming the new soft LFO (LFO2).

I’m also going to experiment with making LFO2 sync the waveform start to user keypresses. I was playing with the negative ramp wave assigned to pitch control. This is, of course, the way synth drum sounds are often made — falling pitch.

I’m still a couple of weeks out on finishing the “CV” module (DAC and possibly A/D). So much to do … super exciting though.

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MIDI to CV, Pitchbend and More

Posted on July 5, 2010 by grantb4


Today I did some further experiments on the next little improvement to the MTG Turbo CPU for the Sequential Circuits Pro One: MIDI-to-CV. I’ve acquired a quad DAC (D/A or digital-to-analog converter) board that can be very easily hooked up to the CPU module in order to control a few more parameters in the Pro One.

For now I’ve tested controlling three parameters of the Pro One:

  • Pitch (Osc 1 and/or Osc 2)
  • Filter cutoff freq
  • Filter resonance
  • VCA ADSR/volume (I haven’t played around with this yet).

Therefore, taking input from MIDI or from within the CPU itself, here are some possible sources of data to control those parameters:

  • MIDI Pitch Bend, Mod Wheel, Aftertouch, Velocity
  • Other MIDI continuous controller(s)
  • The internal sequencer data
  • A soft-LFO that features a variety of waveforms including sample and hold (S&H)
  • MIDI Clock/Sync??

For now I’m thinking it would cost about $25 to add these features to and existing MIDI+CPU setup. And it would be very easy to install. Now coming up with a nice clean way for the end user to control it all — that will be a challenge.

Any other ideas or comments?

Posted in Pro One CPU | 11 Comments

MTG “Turbo” CPU for Sequential Circuits Pro One

Posted on June 29, 2010 by grantb4


What’s with the “turbo” you ask? Well my marketing persona determined that “replacement” CPU was not suitably catchy. I guess that was my engineer persona at work.  But turbo actually does mean something here. As in “faster” and “more”. The modern CPU is much faster than the old one, so I have (below) some numbers to back it up.   As far as more is concerned there are certainly more features (sequencer modes and memory, arpeggiator modes, MIDI in/out/thru and so on).

The metrics. Here are a couple of measurements that demonstrate the turbo-ness of the upgrade.

  1. Key scan rate.  The keys are scanned on the stock Pro One once every11.7ms and each set of 8 keys takes 1.32ms to read/analyze. On the MTG CPU the key scanning is programmed at a rate of once every 5ms and it takes a mere 20us to read/analyze. So 2x the scan rate (and 66x the read/analyze time).  The scanning could probably be done even faster, but with the crappy contacts on most Pro Ones this could lead to contact bounce noise in the output.
  2. Key press to DAC enable. This indicates how long, once a key has been read in the “down” state, until the new control voltage is set by the DAC.  The stock Pro One takes 1.7ms. The MTG CPU takes 200us, an 8.5x speed increase.
  3. Gate-in to gate-out. The LFO signal is read by the CPU and then the CPU drives the DAC, the Gate and the Trigger signal as a result (for example when a sequence or arpeggio is running).  This metric indicates how fast the CPU picks up on the LFO signal and translates it into sound. The stock Pro One translates the positive going edge (PGE) of the LFO and turns it into a PGE Gate signal (or NGE DAC enable or PGE Trigger) in 2.7ms. The MTG CPU performs the same duty in 40us. That’s a factor of 67.5x faster.
  4. Finally NGE DAC Enable to PGE of the Trigger signal. This is mainly house-keeping and indicates how fast the CPU gets through the chore of updating the DAC and then sending the associated Trigger signal.   On the stock CPU it takes 144us. On the MTG CPU it takes 4us.  A 36x improvement.

So in summary moving to a processor 25 years hence improves the responsiveness considerably. And all this while taking on a bigger workload too (MIDI In/Out).

Posted in Pro One CPU | 9 Comments