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>>>my amp tech could easily hook up 9 volt through one of the wires of the midi cable that is unused. My new Midi control device, a Kenton Spin Doctor, sais it needs 9V d.c. @ 250 mA.in the manual. Can the EDP supply this without getting into trouble? Can I simply try this out without coursing breakdowns? Matthias? Kim?<<<
andreas, I wouldn't recommend putting the extra load on any power supply like this, as you're straightaway inviting reliability problems & voided warranties & so on.
what I do with my midi rig (& I've written this up to the list at greater length before) is use the "spare" connections of the midi cabling to distribute + & - 12V from a /laptop/ power supply. this approach has the benefits that the power pack can be replaced easily, works anywhere in the world & has an absolutely flat output that won't put hum onto the midi data signal.
at very least, the 9V needs to be regulated. if it doesn't say "regulated" on the power supply, it isn't.
there are some more caveats for even the most experienced techs: quite a lot of midi devices, especially those from japan, don't have the midi din socket fully populated. that is to say, the outer pair of contacts are physically absent. many commercially available midi cables also lack these connections; though the pins are there in the plugs, there's no electrical connection to them.
I made my own midi cables with all the pins connected, & for certain bits of gear there's a second, shorter cable coming out the back of the din plug alongside the midi cable, to go to the power jack on the boss/roland/korg/whatever.
also, it's common practice to have the ground lifted at one end of a midi connection; this is usually achieved at the receiving end &, while it doesn't preclude use of the ground wiring for the power supply, one should take care not to create an unwanted midi grounding.
most small midi devices, like the kenton & doepfer controllers, carry the same spec on their cases- "must have 9V at 200mA" or whatever, & then you open them up & find a 7805 there every time. I can't remember the last time I saw a bit of gear that didn't have it's own internal voltage regulation, except for stomp-boxes.
but I have done this & made it work & now there isn't a single "wall-wart" in my live-rig.
duncan/r.m.i.
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