Not to be confused with the Roland MPU-401 MIDI interface for computers.
MPU-101 tech specs
The MPU-101 (short for MIDI Processing Unit) was, I believe, the second ever MIDI to CV converter, shortly behind the rather more obscure JMS CG-X. It was released by the highly influential Roland in 1985.
It can play four notes on one MIDI channel (perhaps for someone with a lot of System-100M modules), or one note each on four channels (to control four independent monophonic synthesisers, a more likely setup), or, I believe, anything in between. Note that for the latter, the four MIDI channels used must be consecutive.
While it has four complete sets of CV/gate pair and velocity, it only has a single set of pitch bend, mod wheel, aftertouch, and volume. (The pitch bend is not combined into the other pitch CV signals — as with the TB-303, Roland's engineers made a simple resistor-based DAC that can only output twelve-tone equal temperament pitches. As far as MIDI volume goes, I have yet to hear of any musician actually using it, making it a curiously obscure choice to include.)
There's no portamento option, although the manual points out you can attain this effect simply by buying the System-100M's rare 165 Portamento module.
The transpose switch is a nice touch you don't see on many converters, although it's usually made redundant by the synthesisers' oscillators themselves having a footing switch. It can also output S-trig as well as V-trig.
While it technically can convert the MIDI clock into a 4 PPQN clock (say, for your 182 Sequencer module), it can only do so instead of converting notes, using the same phone jacks. If you want to do both at once, or for that matter to output DIN sync, then you'll need to pair it with a dedicated synchroniser like the SBX-10. You might as well dedicate a MIDI channel to continually playing 16th notes — at least then you can swing them, and by extension, any step sequencers you're using.
So while the MPU-101 works fine, due to its age it's rather simple and has a few caveats. Whether it's still useful depends entirely on the complexity of your setup.
- "MPU-101 service notes" Roland, Jun 1985
- "The Shortest Route" Simon Trask, Electronics & Music Maker, Aug 1985, pp. 78—80
MIDI to CV converters: MCV-24 | MPU-101