Newsgroups: rec.audio.tech
Subject: Re: low frequency "buzzing noise" emitting from subwoofer (part2)
References:    <[email protected]> 
"flint"  writes:

> "Don Pearce"  wrote in message
> > Have you tried disconnecting the mains earth from the subwoofer? I
> > know people will be howling that this will cause the premature end of
> > life as we know it, but really, there is no danger involved. I have
> > done it to my sub to cure exactly this problem. Even if you chicken
> > out of leaving it that way, at least it will tell you if a ground loop
> > is (almost certainly) the problem.
> 
> I've known two people who tried this and did actually shock themselves bad
> enough to warrant a rush to the hospital and dozens others who learned there
> lessons without any medical attention.
> 
> I do NOT suggest lifting the AC ground on the subwoofer or any device. I
> have seen the bad results first hand.

I do NOT suggest lifting the AC ground on the subwoofer or any device 
by cutting the ground wire/ground pin or using some "cheater plug" or 
similar. This does not generally kill you if you do this, but 
posses you to a safety risk. The grounding is there for safety 
reason to keep out to get into mains voltage if some of the insulation 
inside equipment fails, some wire becomes loose and touches case etc. 

There is another way adequate safety can be guaranteed withotu ground. 
Those quipment what are designed to operate safely without grounding 
use doulble insulation layer approach. There are always two insulation 
layers between the user and the mains voltage, so one of them damaging 
does not cause any damage. The equipment of this type are either 
built entirely to insulating plastic so that there is always the 
plastic case (plastic buttons, controls etc.) between the electronics 
and user, in additional to normal safety insulation inside equipment. 
Or the equipment that has metalli case has been built in such way 
that the metallic case can't get into touch with the mains voltage 
in case of some failure, meanign generally using two insulation layers 
wires inside equipment, transformers with special construction 
to withstand very high surge voltages, wire connections secured 
and some plastic around them so that even if wire on connection 
becomes loose it can't touch the case etc.... With those things 
taken into consideration, it is possible to design equipment 
that are safe to operate without ground in normal operating conditons. 

If you want to lift the ground of a grounded equipment, there is 
one proven to be safe way to cut the ground connection: 
you power the equipment through a safety isolation transformer 
that does not have connection from input to output grounds. 
This kind of safety isolation transformer cuts the ground connection 
safely when one isolation transformer powers only one equipment.

-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/