MIDI Expander Box

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J.B. Wood 12 years ago

For those who use MIDI-capable musical instruments: I've got a nearly

25-year old MD 80 MIDI expander (thru) box that works fine but I've noticed that connecting the MIDI out from some devices to an input on the MD 80 doesn't always result in a signal at any of the MD 80's 4 output (thru) ports as there should be. Yet connecting a different MIDI device the same way works. I'm a bit puzzled as to this incompatibility given the relative simplicity of a MIDI connection. Your comment and time is greatly appreciated. Sincerely,

J. B. Wood e-mail: arl_123234@hotmail.com

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Gareth Magennis 12 years ago

For those who use MIDI-capable musical instruments: I've got a nearly

25-year old MD 80 MIDI expander (thru) box that works fine but I've noticed that connecting the MIDI out from some devices to an input on the MD 80 doesn't always result in a signal at any of the MD 80's 4 output (thru) ports as there should be. Yet connecting a different MIDI device the same way works. I'm a bit puzzled as to this incompatibility given the relative simplicity of a MIDI connection. Your comment and time is greatly appreciated. Sincerely,

J. B. Wood e-mail: arl_123234@hotmail.com Perhaps the MD80 doesn't like MIDI active sensing? A device with active sensing will send sense data every 250 mSec I think. Anyway you can find out which devices do and don't do this by inserting an LED into the two pins either side of centre of the MIDI out socket, and see if it flashes regularly. (The LED has to be connected the right way round) Gareth.

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J.B. Wood 12 years ago

Thanks for taking the time and providing the tip, Gareth. Sincerely,

J. B. Wood e-mail: arl_123234@hotmail.com

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asdf 12 years ago

That device looks suspiciously similar to the old Yamaha YME8 thru box I bought in the late eighties and used for decades. A thru box is usually a very simple circuit: one optoisolator at each input followed by a buffer, say one or more 74ls04 or the like with their outputs wired as a current loop. There is not much that could fail, other than maybe the power supply filtering capacitors both on the device and the wall wart. I would check those first.

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MIDI Expander Box

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