Why do some amps don't have a ground pin in the power cable? - diyAudio
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Old 11th September 2010, 11:39 PM   #1
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Default Why do some amps don't have a ground pin in the power cable?

I actually have two questions:

First one, why do some amps including mine doesn't have a ground
pin in the power cable that goes to the socket?
Is it ok that i already added a cable WITH a ground pin to my amp
while modding it?

Second question, how come my amp and many other devices can
work with the power cable connected either way and the polarity
doesn't matter?
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Old 11th September 2010, 11:59 PM   #2
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The amps without ground are specially made in a safe way called double insulated. Their purpose is so that you don't have ground loops in the sound. You are fine connecting the amp case to mains ground (earth) but you may find you get ground loops if you connect other equipment that is also grounded.

Because the mains just feeds a transformer which works the same whichever way round it is wired. Do however always observe the correct live and neutral wiring convention though as there may be an implication to the fusing which could be dangerous.
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Old 12th September 2010, 12:10 AM   #3
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Quote:
Originally Posted by rg12 View Post
Is it ok that i already added a cable WITH a ground pin to my amp while modding it?
Sure. Just don't actually connect it to anything.

se
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Old 12th September 2010, 01:06 AM   #4
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Thanks guys,
I still didn't get that thing with the ground loops though...
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Old 12th September 2010, 01:18 AM   #5
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Quote:
Originally Posted by richie00boy View Post
The amps without ground are specially made in a safe way called double insulated. Their purpose is so that you don't have ground loops in the sound.
This is certainly true at DC. But since mains is 50Hz AC then there's nowhere for the AC to go when the amp is ungrounded (transformers have capacitance to the mains). If you connect to all other ungrounded equipment that's fine, but as soon as one grounded piece is introduced you'll get current flow to the ground. The current is small, usually less than 1mA but isn't limited to being just 50Hz - it contains all kinds of RF hash too.


What was it about ground loops that you didn't get rg12?
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Old 12th September 2010, 01:58 AM   #6
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Quote:
Originally Posted by abraxalito View Post
This is certainly true at DC. But since mains is 50Hz AC then there's nowhere for the AC to go when the amp is ungrounded (transformers have capacitance to the mains).
Eh?

Quote:
If you connect to all other ungrounded equipment that's fine, but as soon as one grounded piece is introduced you'll get current flow to the ground.
Yes. So?

Unless you have another grounded piece in the system, what exactly is the problem?

se
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Old 12th September 2010, 02:28 AM   #7
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Quote:
Originally Posted by Steve Eddy View Post
Eh?
What did I explain wrong here? Just point it out and if I've made an error, I'll correct it.


Quote:
Yes. So?

Unless you have another grounded piece in the system, what exactly is the problem?
I didn't say there was a problem. Just something to be aware of, particularly when choosing cables - if your cable screen has appreciable resistance or inductance, there will be some noise in series with your signal.
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Old 12th September 2010, 02:36 AM   #8
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Quote:
Originally Posted by abraxalito View Post
What did I explain wrong here? Just point it out and if I've made an error, I'll correct it.
Just trying to figure out what you were trying to say when you said "This is certainly true at DC. But since mains is 50Hz AC then there's nowhere for the AC to go when the amp is ungrounded."

So what do you mean by "there's nowhere for the AC to go" and what exactly is the consequence of that?

Quote:
I didn't say there was a problem. Just something to be aware of, particularly when choosing cables - if your cable screen has appreciable resistance or inductance, there will be some noise in series with your signal.
How so? What exactly is the mechanism?

se
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Old 12th September 2010, 04:37 AM   #9
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SE, it's a simple matter of a leakage current or noise source having to be sunk remote. Even if none of the equipment is grounded, if you have one singing chassis, it's driving everything else, which could have the oddest loads including re-radiation points. The problem gets worse the higher frequency gets. When it gets to be a significant problem would be anyone's determination.
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Old 12th September 2010, 04:43 AM   #10
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Quote:
Originally Posted by Andrew Eckhardt View Post
SE, it's a simple matter of a leakage current or noise source having to be sunk remote.
Having to be sunk remote? What do you mean by "sunk remote"?

Quote:
Even if none of the equipment is grounded, if you have one singing chassis, it's driving everything else, which could have the oddest loads including re-radiation points.
What I was querying about was abraxalito saying that if you have one safety grounded piece of gear in the chain you'll get current flowing in the safety ground.

I was wondering how that would result in interchassis currents if none of the other components were safety grounded.

se
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