[sdiy] Hum Problem Kaput

[Ingo Debus]

harry wrote:
> 
> Ingo Debus wrote:
> <snip>
> 
> > The ground plug is for electrical safety, so interrupting that
> > connection of course affects safety. I'm wondering all the time why
> > these adapters are available at all in the United States.
> 
> History. The USA old standard was two wire 120V (hot and neutral... no
> ground).  Then they went to a combination of three wire (hot, neutral,
> ground) and
> polarized two wire... Neutral is larger and cannot be reversed... or plugged
> into
> an original two wire system.
> 
> The original system would allow you to reverse plugs... so you might have a
> short
> to hot in one chassis, and a short to neutral in another... and when you
> ToUcH ThEm
> BoTh YoU gEt iT !!!!   Musicians have died of this....
> 
> The "ungrounding" adapters are really "grounding" adapters... they have two
> prongs
> plus a wire or tab, which the user is expected to connect to the grounded
> electrical
> box... usually through the screws holding the cover plate.

Aah, new insights on U.S. wall outlets :-)
The two wire outlets that were used here in the fifties or so are almost
extinct (we still have one in our cellar, the house I live in was built
in 1907). So no need for adaptors.

> Try these adapters on test equipment (like a scope). I will not work with a
> scope
> that has both a ground clip on the probe... and a three wire plug at the
> same time.
> Cannot make proper measurements because of the ground loop. If it is
> reasonably low voltage, I float the scope. High voltage... i ground the
> scope and use a differential
> probe.

Hm, I never had a ground loop problem with a scope when using the ground
clip of the probe.

Ingo (more comments in another mail)