MIDI Expander Box

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
Reply to
J.B. Wood
Loading thread data ...

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? 
 Click to see the full signature
Reply to
Gareth Magennis

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

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

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.

Reply to
asdf

When I built my MIDI pipe organ in '89 the boards I got for 8031 processor included MC1488 RS-232 line drivers. I ended up using the 1488s to drive MI DI which work better than the TTL chips. Add a diode to the output to preve nt the MIDI from going seriously negative. The 1488s have current limiting and do not over drive the optocoupler input. Most were using Sharp PC-900s but I used 6N137s because they were easier to get at the time and work fine also.

The box you describe would have zero latency and pass any MIDI data straigh t through. While it would square up the transitions it would not correct an y bit timing issues. A processor would clean up the possible timing issues but would have at least one byte of timing delay and more if you attempted to actually process the MIDI data. It's not difficult to do even with those old processors.

Reply to
stratus46

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.