[sdiy] Hum Problem Kaput

[harry]

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.

B at stards such as myself cut this third wire OFF... making the unsafe
adapters.

I also modify extension cords so that three wire plugs can be cheated into
two wire
cords... AND file the neutral plug down so it will fit with either polarity,
or fit the
original USA standard socket.


> You cannot buy
> anything similar here in Germany (but OTOH mains voltage is twice as
> high here).
> A safe way would be to disconnect circuit ground from mains ground
> (protective earth) but leave the connections between mains ground and
> anything that has to do with mains voltage (power transformer, front
> panel with mains switch etc.) intact. Not easy with a Mackie mixer...

Right... so you let the Mackie be the ground point... unground the other
gear...
then let the audio shields carry the fault current to the Mackie... and blow
the
fuse / breaker.

Its 'safe'... but allows a wider range of equipment destruction in a fault.
OTOH if
the gear is noisy it cannot be used for the purpose anyway... so in the
words of
Ian Pace (Deep Purple) "I bought it, I'll bloddy well boot it!"

Most ground problems come from shitty, ignorant design on the part of the
OEM.
Some can be fixed... some cannot.

> I have the slight suspection that the funny ground wiring scheme
> sometimes found in gear made in the U.S. is just because these
> "criminal" adapters are available there.

The adapters are legal. The use is questionable.

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.

> The main hum source here is an Ensoniq DP/4. The PCB ground is connected
> everywhere to the chassis, as is the power transformer...

Amen !

H^) harry

>
> OTOH in my Alesis RA-100 amp it was very easy to disconnect circuit
> ground from chassis.
>
> Ingo

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