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More-MIDI

A low-cost MIDI expander box

By Jim Rowe

IF YOU’RE REALLY INTO electronic music, odds are that you now have quite an array of synthesisers, MIDI instruments, sequencers, keyboards and other controllers. And that probably means swags of MIDI cables, daisy-chaining around from this box to that box to the other box, and so on.

Click for larger image
Fig.1: the circuit uses OPTO1 to isolate the input stage plus a 74HC04 hex inverter (IC1) to drive the four output stages and the signal indicator LED.

That’s OK, but daisy-chaining introduces cumulative delays into the MIDI system and sooner or later those delays can become audible and irritating.

The simplest solution is an expander box like More-MIDI. It "pumps up" the number of MIDI outputs from your sequencer or computer and lets you run more signals directly out to the instruments, in "star" fashion. You still need just as many cables but at least the instruments are all driven with just one short delay – ie, the minuscule 5μs or so introduced by the circuitry in More-MIDI itself. That’s really not significant in MIDI terms.

Best of all, More-MIDI is cheap and very easy to build. It uses just three low-cost ICs plus a handful of passive components and literally everything mounts on a small PC board which fits in a compact low-profile instrument case. Power comes from a standard 9-12V DC plugpack.

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