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Old 19th January 2009, 01:07 PM   #1
diyAudio Member
Join Date: Dec 2008
Default question about amplifier earthing.

I have an early audiolab 8000A which had a 3 wire mains lead with earth. And a late model which has the IEC 14 type mains plug and socket (kettle connector) but only 2 pins - no earth. I have two 8000Ps on top which also have 2 pin mains connectors.

The strange thing is the later setup actually has no mains noise with no signal, the volume on full and your ear right up against the drive unit - with no earth connections, whereas the earlier integrated amplifier with earth connection had a slight buzz audible under the same conditions. The cd player and hard drive player (and in the past DAT machine etc) all do/did not have earth connections.

I know the earlier amp probably needs the supply caps changing (again) due to age which might be a factor in the very slight buzz. It's only used in a secondary system now.

But I was in the impression that one box in the system should have an earth and the rest of the connected boxes should "star" earth though the interconnects to that box to prevent ground loops. The logical earth box is the preamp or integrated?

What is the current thinking on earthing equipment and is it safe to have several hundred watts of amplifier capable of supplying many amps not earthed?
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Old 19th January 2009, 01:26 PM   #2
AndrewT is offline AndrewT  Scotland
diyAudio Member
Join Date: Jul 2004
Location: Scottish Borders
all the equipment without the third Earth wire/pin should have the double insulated symbol on the appliance (double concentric squares).

An all doubled earthed system should never have mains voltage on any exposed part.

The problem is that in a mixed system where some are doubled insulated and others are conventional, requiring a Safety Earth to blow the fuse if the mains ever leaks to an exposed part, is that a fault in the Safety Earth can cascade through the system and appears at any disconnected interconnect and/or speaker cable. That's the danger, system turns itself (apparently) off. First thing you do is start fiddling with interconnects. That's precisely what you should not do.

The grounding in the older Safety Earthed amp will have been changed to make the double insulated version. It is almost certainly that grounding change that has eliminated the buzz. But, be careful, you cannot just copy the new grounding to the old unit in case you compromise the effectiveness of the Safety Earth.

the Safety Earth is not required for effective audio. It is only there to protect the user and the house.
regards Andrew T.
Sent from my desktop computer using a keyboard
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Old 19th January 2009, 10:17 PM   #3
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Join Date: Dec 2008
Originally posted by AndrewT

the Safety Earth is not required for effective audio. It is only there to protect the user and the house.
Hi, thank you, that's the answer to my question. I suppose it's time to put some new caps in the older amp power section again - can't but help
thanks again.
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