MTG “Turbo” CPU for Sequential Circuits Pro One

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).

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3 Responses to MTG “Turbo” CPU for Sequential Circuits Pro One

  1. I am starting to install one of these in my Pro-One. Looks fairly easy and I expect to have some great fun with this project. It appears as though all the parts I’ll need have been included and the documentation looks great! Right On!

  2. Jeff says:

    Hey there, my tech had recommend this update for the Pro One. I am interested in adding MIDI and the rest is a bonus. Does this new chip allow the internal arp / sequencer to sync to MIDI beat clock?

    Lastly, does this have any effect on how good the Pro One sounds? I’d hate to add this at the cost of making the Pro One more ‘civilized’. I quite like how organic it sounds.

  3. Jeff says:

    That’s great news. Thanks for getting back to me.

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