ESD, was : RE: [sdiy] midi optocoupler isolation voltage?

[Neil Johnson]

> If the conncetor shield and/or mesh must not be connected to chassis
> ground, where is it connected to?

Careful here: read the words:

> >From the MIDI 1.0 Specification:
> >"The grounding shield connector on the MIDI jacks should not be connected
> >to any circuit or chassis ground."

So, the "grounding shield connector" must no be connected at either end,
but referring to the schematic in the MIDI Spec, the shield of the cable
is connected to pin 2 of the MIDI Out and MIDI Thru jacks:

> >"Pin 2 of the MIDI In connector should also be left unconnected."

So, the cable sheild _is_ connected to ground, but only at one end (at the
MIDI source).  They specifically mention the grounding shield connector as
it is usually harder to isolate this from the chassis than one of the
signal pins.

> There would be only a major loop problem, if both devices have a plug
> with mains ground. I think only my Atari computer could have something
> like that. The current loop was chosen bcause it has no common mode
> problem,

Most things in a studio seem to have some path to ground these days, be it
through a mixing desk, effects unit, synth, computer, etc etc.  Murphy's
Law will ensure that no matter how careful you try to be, there will be a
ground path in something you thought otherwise.  Example: a classic ground
path is through the 19in rack frame.  You can buy plastic insulators that
separate the rack ears from the rack sides and mounting screws.

Cheers,
Neil

--
Neil Johnson :: Computer Laboratory :: University of Cambridge ::
http://www.njohnson.co.uk          http://www.cl.cam.ac.uk/~nej22
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