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The maximum length of a standard MIDI cable is given as 15m (50 ft). The cable for MIDI should be screened twisted pair. Cable with a braided screen is to be preferred for flexible interconnections, while foil screened cable provides good screening and is recommended for permanent wiring. Lapped screen cable is not recommended, as it provides inferior screening at high frequencies, and is often not robust if flexed. Ordinary decent microphone cable generally makes satisfactory MIDI cables.
For short runs, up to about 2m, you may very well get away with other cable, such as a tape recorder (that is, NOT reversal, mirror, or cross-connected) stereo DIN to DIN audio lead. Proper MIDI cables are, however, to be preferred.
On each end, the cable should have a five pin 180° (sometimes alternatively designated 45°) male DIN plug. For studio or performance use we recommend the use of robust die-cast plugs, as these will survive being stepped upon.
The screen (shield) should be connected to pin two (the middle pin) at both ends. The shells of the plugs should not be connected to the screen of the cable. Pins one and three (the outside pins) are not used for MIDI interconnections, and it is best to leave them not connected. Pins four and five should be connected each to one of the cores, and should be wired pin-to-pin: that is, pin four to pin four on the same core (eg. red), and pin five to pin five on the other core (eg. blue).
The signal on pin 4 is the current source, derived from a positive voltage in the driving MIDI output. The signal on pin 5 is the current sink, which is normally switched with the MIDI signal.
After soldering the wires to the pins of the plug, do your best to clean off the solder flux with a suitable solvent. The flux can easily corrode fine strands of wire, leading to eventual failure of the plug wiring.
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Author: Philip Rees.
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