CD transport earthing, help needed - diyAudio
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Old 27th March 2004, 02:11 AM   #1
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Default CD transport earthing, help needed

If you use a cd player (with no mains earth on the power cord) as a intergrated unit it gets it`s earth to the chassis via the interconect from the pre or power amp. However if you use it as a stand alone transport using the digital coax conection (without the analog conections attached) and a d/a converter, you do not get the earth to the transport anymore, because the digital standard is to only earth the digital coax sheild at both ends (transport and d/a convertor) through a .1uf cap. So what we have is a transport case that may as well be made out of plastic, forget all the exotic copper plating inside and metal construction if it is not earthed. I earthed the transport chassis and there is a big difference in sound, to being not earthed.
Can anyone give me a reason why the manufactures have overlooked this earthing, can it be they just did`nt see it or is it done on purpose.
Cheers George
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Old 28th March 2004, 05:58 AM   #2
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Few people looking at this problem, but no explianations yet, does`nt anyone have any idea on this?
As there is a major difference in sound between the two.
I think it could have a big effect on the caps maybe, as they have no reference to earth, so the zero side of the caps can float up and down and never get to true earth potential. Let alone shielding the innards.
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Old 1st April 2004, 07:49 AM   #3
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Comon, guys 114 interested lookers but no one has anything to say about this weird red book earthing?

Cheers again George
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Old 1st April 2004, 08:24 AM   #4
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Originally posted by georgehifi
Comon, guys 114 interested lookers but no one has anything to say about this weird red book earthing?

Cheers again George

Hi

Earth is a safety issue. If the isolation from the CD drive mains power supply to all touchable parts withstands 4kV or higher, earthing is not required. Check the transformer spec and respect design rules for safety.

A Boeing is not earthed either

cheers
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Old 1st April 2004, 09:30 AM   #5
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The earthing depends on what you are trying to do.

A faraday cage does not need to be earthed to have 0 electric field inside.

Edit: missing space
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Old 1st April 2004, 04:13 PM   #6
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The earthing depends on what you are trying to do.

A faraday cage does not need to be earthed to have 0 electric field inside.

Edit: missing space

dear all,

Indeed: earth is a safety issue and has nothing to do with screening at all, not electrically nor magnetically

cheers
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Old 1st April 2004, 07:50 PM   #7
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A faraday cage does not need to be earthed to have 0 electric field inside.



So why earth the sheild on inter-connects, at least one end to ground, to remove the r/f that the sheild catches to ground?

Why all the elaborate copper plating on my transports chassis?

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Old 2nd April 2004, 05:35 AM   #8
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Others might have a differnt opinion but my view is that the reason to for it is to extend the faraday cage to the other device since you are trying to transmit a signal out from the cage. You are basically extending the cage to the other device. This is since you are connecting their grounds anyway. With a digital device where you have, in theory at least, galvanic isolation. There should be no need.
There are however many simplifications made with these statements since you have other connections between the devices, parasitic capacitances via the power supply lines etc.

Copper plating is because the cage depends on the conductivity of the screen for higher frequency RF signals. There is still a point in screening the individual device.
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Old 2nd April 2004, 08:27 AM   #9
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Can you then tell me why the big difference in sound presentation when you earth the transport, when it has no earth to speak of when using only the digital coax conection,
(remembering that the digital coax does not supply earth to the transport itself)
Cheers George
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Old 2nd April 2004, 09:34 AM   #10
hjelm is offline hjelm  Sweden
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Default I'll stick my neck out and say...

No
I have no idea.
I do not know the design of the device, the actual earthing you did and even if i did i am not an expert on the subject.

Have you tried to measure the chassi with and without earthing?

A osciloscope might say something.

A guess might be that there is a capacitive coupling in the transformer and the chassi is grounded at the secondary side of the transformer.
The ground would then have a coupling to the ground in the electrical system. This and considering that the ground might then be oscillating relative to the outside world could cause the box to act as an antenna. With a loop that goes from the cdplayer via the powerplugs back through the amplifier and the caps through the coax shield.

Far fetched i admit but i do not know any better.
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