monosyllabic
Joined: 06/04/07
Posts: 491
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What's a ground loop?
#450005 - 20/04/07 04:50 PM
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I've noticed the signature on Martin Walker's posts and am interested in what exactly a
ground loop is?
I assume it's interference of some sort (like when you run a
cable near to an AC mains current and you get a hum at 60hz, 120, 180 etc...). Does it
usually affect turntables also?
If someone could explain it that would be
great!
SJ.
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TAKEN.BALL.GONE.HOME
posting's fun
Joined: 16/09/02
Posts: 1638
Loc: Manchester, UK and Den Haag, N...
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Re: What's a ground loop?
[Re: monosyllabic]
#450014 - 20/04/07 05:22 PM
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Rather than rewrite what has been written many many times (!), here's a link to an
explanation by our esteemed Technical Editor... Hugh on Earth Loops
-------------------- TAKEN.BALL.GONE.HOME
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monosyllabic
Joined: 06/04/07
Posts: 491
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Cheers!
SJ.
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monosyllabic
Joined: 06/04/07
Posts: 491
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Re: What's a ground loop?
[Re: monosyllabic]
#450043 - 20/04/07 06:52 PM
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I think I understood that. Seems like the lesson is not to mess with the earth in guitar
amps.
SJ.
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Martin Walker
Watcher Of The Skies
Joined: 28/02/01
Posts: 16381
Loc: Cornwall, UK
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Re: What's a ground loop?
[Re: monosyllabic]
#451108 - 23/04/07 05:28 PM
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You shouldn't mess with the earth in any mains appliance Simon  The largest number of ground loop problems nowadays seem to occur with laptop computers
when running on mains voltage (I set up a dedicated sticky thread about this topic in the
PC Music forum, which you can read at www.soundonsound.com/forum/showflat.php?Cat=&Number=222392 ). Unlike the previous more typical 'analogue' ground loop problems which result in
continuous regular low-level hum/buzz, ground loops in digital/computer systems give rise
to rather more annoying high-pitched 'hash' which can vary when you move your mouse, when
your screen graphics get updated, and when your hard drives are accessed. Martin
-------------------- YewTreeMagic
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monosyllabic
Joined: 06/04/07
Posts: 491
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Re: What's a ground loop?
[Re: monosyllabic]
#451205 - 23/04/07 08:41 PM
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I run an Apple laptop set up and I've never noticed anything. Though, I have found that my
laptop is building up a lot of static in the metal case. Could that be an earth
problem?
SJ.
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Martin Walker
Watcher Of The Skies
Joined: 28/02/01
Posts: 16381
Loc: Cornwall, UK
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Re: What's a ground loop?
[Re: monosyllabic]
#451570 - 24/04/07 04:23 PM
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If by static you mean that the laptop's metalwork feels furry/tingly when you stroke it,
it's not earthed at the mains and the metalwork is therefore 'floating'. As long as its
PSU is double insulated then you should be perfectly safe, but that feeling should
disappear as soon as you connect the case to any other grounded object. Martin
-------------------- YewTreeMagic
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Jeraldo
Joined: 10/09/05
Posts: 2131
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Re: What's a ground loop?
[Re: monosyllabic]
#451689 - 24/04/07 09:16 PM
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Quote Simon Mitchell:
I've
noticed the signature on Martin Walker's posts and am interested in what exactly a ground
loop is?
SJ.
Open
a beer and drink to your good fortune of not having to know what a ground loop is! Many
would consider you fortunate!
And besides, Martin will trace it for you.......
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monosyllabic
Joined: 06/04/07
Posts: 491
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Re: What's a ground loop?
[Re: Martin Walker]
#451930 - 25/04/07 12:12 PM
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Quote Martin Walker:
If by static
you mean that the laptop's metalwork feels furry/tingly when you stroke it, it's not
earthed at the mains and the metalwork is therefore 'floating'. As long as its PSU is
double insulated then you should be perfectly safe, but that feeling should disappear as
soon as you connect the case to any other grounded object.
Martin
That's exactly the feeling I
mean. The feeling actually disapears when I disconnect the main adaptor. Sometimes it's
not there as well when it is connected to peripherals like USB hard drives. Is it worth me
taking it to an Apple shop? It needs to go anyway because the CPU whines all the time and
the DVD drive has started doing silly things. Thank got for warrantys.
SJ.
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Martin Walker
Watcher Of The Skies
Joined: 28/02/01
Posts: 16381
Loc: Cornwall, UK
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Re: What's a ground loop?
[Re: monosyllabic]
#451993 - 25/04/07 02:06 PM
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That feeling will disappear when you disconnect the mains adaptor, because the metalwork
is no longer even vaguely connected to the mains supply. It will also disappear when your
laptop is connected to any peripheral (such as a USB hard drive) that is itself earthed
via its mains lead. I doubt that taking it to the Apple shop will prove
fruitful - my PC laptop does exactly the same thing, and as I said previously it's
perfectly safe as long as your laptop's PSU is double-insulated (look for the square
inside a square logo). In fact, some musicians dream of having 2-wire mains leads on their
laptop PSUs, as this removes a major cause of ground loops! Martin
-------------------- YewTreeMagic
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*INACTIVE USER*
Joined: 01/09/04
Posts: 1217
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Re: What's a ground loop?
[Re: Martin Walker]
#452135 - 25/04/07 08:05 PM
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Actually that feeling means that the EMI caps are putting a very high impedance 127V on
your case. It isn't dangerous But it means that the psu is designed to be connected to the
earth and it isn't.
In the psu EMI filter, there are capacitors that are
connectoed to earth from live and neutral. If the earth isn't connected, you get a
capacitive voltage divider that puts about half the line voltage on the unconnected earth
terminal. Since in most laptops this is connected to circuit ground and case you get the
feeling of static.
I doubt those psu's are double isolated.
--------------------
Expert in non-working solutions
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