[sdiy] MIDI phantom power...over 5 pin MIDI connector ?

[rsdio at audiobanshee.com]

There are two kinds of current limiting.

Passive current limiting, like the 200 ohm resistors, is really only good for avoiding the "infinite" current that would try to flow if there was no resistance. But this option can only do so much.

Active current limiting is expensive, so it's not reasonable to expect all MIDI gear to have active current limiting.

The problem is that the cheap passive current limiting allows about 5 times as much current to flow as an active current limiter that would strictly enforce 5 mA and not allow much more. The reason this is a problem is that not every MIDI device can afford to provide 5 times as much current as is specified by the standard. Thus, passive current limiting may not be sufficient to protect the internal 5 V supply, at least not if the supply was designed to only handle 5 mA.

But, you're right in the sense that a turbo-powered MIDI probably won't destroy ALL MIDI gear - just some of it (and maybe only the really cheap stuff).

Brian


On Sep 10, 2015, at 9:39 AM, Ove Ridé <nitro2k01 at gmail.com> wrote:
> You're right, it's a current loop protocol and there are different ways to skin the cat. Nevertheless, I expect all reasonably designed MIDI gear to have current limiting of one kind or the other, on both the inputs and the outputs. Thus the claim I was responding to, that this hypothetical special high power device will by default destroy ANY regular MIDI gear if connected by mistake, is patently false.