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Old 19th March 2007, 02:16 AM   #1
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Default Grounding questions

Hi all,

I know there are hundreds of threads on grounding, but I'm afraid I'm not sure how I should proceed with grounding my new setup.

I have the following:

- DAC with external double insulated SMPS
- AMP with external double insulated SMPS
- Preamp with external double insulated transformer
- Phono preamp with external double insulated transformer

None of these supplies are earthed, so am I right in thinking I need to run a mains earth to each component to ground the chassis and signal shielding?

My commercial CD player is also double insulated.

The only component I have with an actual earth connection is my turntable.

I know I'm not exposed to mains voltages, and the solution is probably extremely simple, but just want to make sure I'm doing the right thing before I connect things up.

Thanks in advance,

Andrew S.
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Old 19th March 2007, 05:39 PM   #2
AndrewT is offline AndrewT  Scotland
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Hi,
if all that equipment is double earthed to the ClassII standard then it does not need any safety earth lead back to the distribution board.
It is designed, built and tested to ensure the users are safe irrespective of what internal failure may occur.

If you have concocted some home built contraction that you think is double earthed, then take it to the dump before you kill somebody.
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Old 19th March 2007, 07:49 PM   #3
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Quote:
if all that equipment is double earthed to the ClassII standard then it does not need any safety earth lead back to the distribution board.
It is designed, built and tested to ensure the users are safe irrespective of what internal failure may occur
I'll just add, if the equipment is to this standard do not attempt to provide earthing - you will actually compromise safety. And audio is never worth that...
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Old 19th March 2007, 09:21 PM   #4
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Hi guys,

Thanks for the replies. The power supplies are all standards approved. I'm not crazy enough to try and home build double insulated equipment.

The power supplies are all in separate enclosures sitting on the floor, with low voltage output cables running up to my equipment.

So, in this situation with properly constructed double insulated PSUs and separately constructed DIY equipment, is there a safe way to provide signal and chassis grounds for the purpose of RFI shielding?

Or, is it dangerous to attempt to provide any grounding for the equipment connected to the double insulated PSU?

I haven't done anything yet, so I'm not compromising my safety at the moment.

Thanks,

Andrew S.
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Old 20th March 2007, 08:18 AM   #5
AndrewT is offline AndrewT  Scotland
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Hi,
leave all the standard ClassII PSUs alone.
You may find that shielding of the audio stages is not necessary.

You will need to create a floating audio ground for each channel. This has absolutely nothing to do with safety earth, having already confirmed that all your PSUs are ClassII.

Now the difficult bit, how do you plan to interconnect all the return legs of each channel back to source without creating hum loops. Omitting the shielding chassis makes this very easy.
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Old 20th March 2007, 11:09 AM   #6
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Hi Andrew,

I have connected a few components using a floating audio ground (not earthed), and without shielding the chassis. Hopefully I'm following your advice, please let me know if I'm not.

I have the following setup at the moment:

Turntable===phono stage===preamp===headphones

I can hear hum with the volume up.

If I do any of the following, the hum volume increases significantly:

- Place my finger on the insulated RCA barrel at the phono stage input.

- Disconnect the turntable.

- Place my finger on the chassis.

If you have any ideas how to eliminate this it would be great. If not I'll understand...

Perhaps getting rid of the external transformers, and setting up each component with a star ground scheme is the best thing to do?

Best regards,

Andrew S.
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Old 20th March 2007, 04:23 PM   #7
AndrewT is offline AndrewT  Scotland
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Hi,
riaa pre with it's extra 40db of gain or +66db for MC will be difficult to eliminate all noise/hum.
For this part I think you will need a shielding chassis.

With the input & output plugged in and yet you have sensitivity when you touch the return/shield indicates a mis-wire somewhere. The shield/barrel should be completely immune from a finger touch.
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