[sdiy] Hum Problem Kaput

[Ingo Debus]

Moho Disco wrote:
> 
> Well, this is for the benefit of anybody who
> would like to know how my hum problem
> got resolved...
> 
> I got my Echo Layla24 laptop adapter, and
> the hum reduced by a good 60%.

Perhaps it just has a higher output level, thus the signal to noise
ratio gets better?

> And then
> after that I plugged the laptop's power supply
> into a two-prong adapter disconnecting the
> ground plug, and bingo, all the rest of the
> hum was gone.

Exactly the same phenomenon my friend had with his Mackie mixer.

> So I have a question.  Does getting rid of
> the ground plug expose me or my laptop
> to any kind of electrical danger?  What
> exactly does removal of the ground do?

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. 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...

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

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

Ingo