SV: Re: [sdiy] midi optocouplers

[harrybissell]

Grant Richter wrote:

> >
> > You could just tie the synth ground to one side of the AC line (on
> > 120V)... its incredibly
> > risky and stupid. I did it once to drive some theatre marqee lights.
> >
>
> May you should mention that you tied the frame to neutral.

Actually I floated the whole thing (ground of the DC supply was connected to

neutral).  Its a wodden box so can you say "fire hazard" ???

If the circuit functioned well, there is no problem.  If there was a
failure,
DEVASTATING voltages would have been applied to the synth. This is where
isolation is really called for !!!

> The three wires to an US wall socket are:
>
> Hot - current carrying 117VAC power wire - supposed to be black,
> don't trust color codes, use a meter.
> Neutral - current carrying local ground - supposed to be white, don't
> trust color codes, use a meter.
> Ground - non-current carrying local ground - supposed to be green. ditto
>
> It is a good idea to verify that your electronic music studio wall
> sockets are wired correctly.
> I have seen strange things happen when neutral and hot are reversed.
> Even on transformer isolated equipment.
>
> Some guitar amps have a switch and a cap that ties to the AC line.
> Supposed to reduce hum, but mostly shocks people when they touch a
> grounded mic.

I have seen a guitar amp (an old Traynor) that had a chassis connected to
neutral.
I didn't find out until removing a rack mount effect. Once the hard
connection was
gone. I got the 'leakage current'.  So I had to decide... throw the unit and
save myself... or continue to burn.  I actually remembered the magic trick
with the tablecloth and moved my hands REAL fast... the unit dropped the one
rack space to
the next level down... only minor scrapes on the back of the knuckles.

The amp was banned from the studio, forever.

H^) harry