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Old 22nd November 2007, 02:41 PM   #1
AndrewT is offline AndrewT  Scotland
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Default connecting audio ground to Safety Earth

Hi,
direct connection of audio ground to Safety Earth can give rise to a grounding loop causing hum.

Connect the safety Earth to the audio ground through a disconnecting network to break that loop.

But is it safe?

The main purpose of the Safety Earth is to ensure the chassis and any exposed conductive parts can never electrocute anyone if the Live side comes into contact with any internal parts.

I advocate a disconnecting network between the Safety Earth and Audio Ground that consists of a 25A or 35A bridge rectifier with optional 10r power resistor, power thermistor and/or ceramic cap all working in parallel.http://sound.westhost.com/earthing.htm fig3
The bridge rectifier must be able to pass fault current (>=1kA) to earth until the mains fuse ruptures.

But does it work?
http://www.diyaudio.com/forums/showt...94#post1357794

Comments?

Will 6A diodes and T8A fusing pass this test?
Who wants to join the testing panel for 110/120Vac?
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regards Andrew T.
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Old 22nd November 2007, 05:30 PM   #2
jcx is offline jcx  United States
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more "must read" info on safety gnd and audio in Bill Whitlock's Student Seminar Handout:
http://www.jensen-transformers.com/apps_wp.html
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Old 28th November 2007, 09:09 PM   #3
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Default Earthing system

Hi Andrew,
Quote:
Originally posted by AndrewT
...direct connection of audio ground to Safety Earth can give rise to a grounding loop causing hum...
I agree with you, this is a common idea.

One year ago I made this try. Examining my Marantz CD 94 pcb, I saw that designer allow more than one ground connexion to chassis. Common product, and Marantz CD 94 was, use only one connexion between electronic ground and chassis. I try to connect this second ground to chassis. Listening test were very good. Sound quality increase, more bass, less fog, more precision... First good point.

Marantz CD 94 use a two pole main plug (without heart). I extent my test and link chassis to earth. Listening test give better sound too. Second good point.

I renew test to plug CD player on earth on other systems (friend's systems) and obtain always same conclusion. Earthing devices increase sound quality. Examining system connexion, with multiple earth, you create multiple ground loop. Exactly the opposite you are testing!

In fact, each time you connect a source to earth, you win, even if this source in not powered on (just link to the overs).

Bill Whitlock's Student match with this test. He gives good description about unwanted current flowing across audio cable. I don't try to use his isolator transformer. Earthing material reduce parasitics current flowing across audio cable.

Eric
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Old 29th November 2007, 08:55 AM   #4
AndrewT is offline AndrewT  Scotland
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Default Re: Earthing system

Quote:
Originally posted by Eric Juaneda

Marantz CD 94 use a two pole main plug (without heart). I extent my test and link chassis to earth. Listening test give better sound too. Second good point.
I think you are saying that you modified your Double Insulated equipment by making a non standard connection to chassis.

If I have interpreted your statement correctly, then you would be breaking the law and exposing yourself and other users to danger.
I suspect your EC consumer law mirrors ours.

If you are breaking the law then posting this information here also contravenes the Forum rules.
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Old 29th November 2007, 10:49 AM   #5
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Quote:
breaking the law
I'm glad, that we have been spared from such laws here.
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Old 29th November 2007, 12:02 PM   #6
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I don't think he is breaking the law. He does void the CE certification from the manufacturer though and takes over the responsibility. How could it be dangerous?
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Old 29th November 2007, 12:14 PM   #7
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Default Re: Re: Earthing system

Hi Andrew,

Quote:
Originally posted by AndrewT
I think you are saying that you modified your Double Insulated equipment by making a non standard connection to chassis.

If I have interpreted your statement correctly, then you would be breaking the law and exposing yourself and other users to danger.
I suspect your EC consumer law mirrors ours.

If you are breaking the law then posting this information here also contravenes the Forum rules.
I modified my double insulated equipment by adding a connection to Safety Earth. I add a double security!

Eric
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Old 30th November 2007, 01:10 PM   #8
JPV is online now JPV  Belgium
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Join Date: Dec 2006
Default Re: connecting audio ground to Safety Earth

Quote:
Originally posted by AndrewT
Hi,
direct connection of audio ground to Safety Earth can give rise to a grounding loop causing hum.

Connect the safety Earth to the audio ground through a disconnecting network to break that loop.

But is it safe?

The main purpose of the Safety Earth is to ensure the chassis and any exposed conductive parts can never electrocute anyone if the Live side comes into contact with any internal parts.

I advocate a disconnecting network between the Safety Earth and Audio Ground that consists of a 25A or 35A bridge rectifier with optional 10r power resistor, power thermistor and/or ceramic cap all working in parallel.http://sound.westhost.com/earthing.htm fig3
The bridge rectifier must be able to pass fault current (>=1kA) to earth until the mains fuse ruptures.

But does it work?
http://www.diyaudio.com/forums/showt...94#post1357794

Comments?

Will 6A diodes and T8A fusing pass this test?
Who wants to join the testing panel for 110/120Vac?

As I understand you tested the safety aspect of this connection and it works.

Let me add two remarks that could improve the otherwise good approach.

First from an EMI point of view:
The incoming shield should be connected to the chassis at one end AND should be connected to the chassis via hf capacitors AT the entrance of the other end. A classical way is to provide a so called clean ground which is a conductive strip connected to the chassis ground and running at the entrance of incoming lines. The shields or the decoupling and filtering caps should be connected to this clean ground.
In this case, the noisy currents picked up by the shield will be diverted to earth via the chassis without flowing in the audio signal ground. This is what will unfortunately happen in the example shown by your reference.

If the hum voltage is higher than a few volts the diodes will operate and the loop is still existing. Then you cannot avoid the use of balancing techniques.

In any case, it is better to use shielded twisted pair even with unbalanced connection and connect the shield as described.


Second, inrush current

The use of ground loop breaker would require fast acting primary AC fuses which is in contradiction with high surge current in case of toroidal transformer.
A good solution is the use of a special AC breaker that controls the magnetisation of the transformer by sending pulses at switch on avoiding the high surge. see http://www.emeko.de/index.php?id=29&L=1

With this device fast fuses are OK.


Cheers

JPV
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Old 6th February 2008, 09:05 PM   #9
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I just publish result of my test on my web site. Ground and (safety) Earth

Eric
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Old 6th February 2008, 10:38 PM   #10
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if the circuit has a earth leakage detector on it then not much current has to pass to earth at all before it will trigger, some as low as 5ma. so loop breaking circuit doesent have to pass current for long at all in order for the power to be cut due to fault condition.
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