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monosyllabic



Joined: 06/04/07
Posts: 491
What's a ground loop?
      #450005 - 20/04/07 04:50 PM
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
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Re: What's a ground loop? new [Re: monosyllabic]
      #450014 - 20/04/07 05:22 PM
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
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Re: What's a ground loop? new [Re: TAKEN.BALL.GONE.HOME]
      #450039 - 20/04/07 06:43 PM
Cheers!

SJ.


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monosyllabic



Joined: 06/04/07
Posts: 491
Re: What's a ground loop? new [Re: monosyllabic]
      #450043 - 20/04/07 06:52 PM
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 WalkerModerator
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Re: What's a ground loop? new [Re: monosyllabic]
      #451108 - 23/04/07 05:28 PM
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

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YewTreeMagic


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monosyllabic



Joined: 06/04/07
Posts: 491
Re: What's a ground loop? new [Re: monosyllabic]
      #451205 - 23/04/07 08:41 PM
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 WalkerModerator
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Re: What's a ground loop? new [Re: monosyllabic]
      #451570 - 24/04/07 04:23 PM
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



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Re: What's a ground loop? new [Re: monosyllabic]
      #451689 - 24/04/07 09:16 PM
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
Re: What's a ground loop? new [Re: Martin Walker]
      #451930 - 25/04/07 12:12 PM
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 WalkerModerator
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Re: What's a ground loop? new [Re: monosyllabic]
      #451993 - 25/04/07 02:06 PM
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
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Re: What's a ground loop? new [Re: Martin Walker]
      #452135 - 25/04/07 08:05 PM
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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