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Old 14th May 2008, 10:32 AM   #41
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For completeness, do we need to discuss:

1. The cable gland. Are they still legal? If so, then the method of clamping the power cable is important and the earth wire must be longer than the active and neutral.

2. Should the fuses between the PSU and amp be shown.

3. Should the gender of the umbilical plugs and sockets be shown. Important if DC voltages are high.

4. What about countries with no earthing system?

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Old 14th May 2008, 10:35 AM   #42
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Although overkill is mostly a good thing

i don't think it's really necessary to have an extra earth wire.
Although a great option.

I feel that the earth connection through a capable ground wire should be ok.
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Old 14th May 2008, 10:41 AM   #43
AndrewT is online now AndrewT  Scotland
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Quote:
Originally posted by Greg Erskine
do we need to discuss:
........................4. What about countries with no earthing system?
could someone do a different diagram for supplies without the Safety Earth Wire?
Can it be done safely?
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Old 14th May 2008, 11:11 AM   #44
studiot is offline studiot  United Kingdom
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@AndrewT

As you are so hot on quoting (UK)regulations I am suprised that you are so selective in your choice.

The regulations only have legal force applied to articles offered for sale.

The word 'disconnect' has special significance in the regulations and that is not the 'disconnect network' discussed here.

@all

It is important to realise that a safety earth is intended to be 'an equipotential' system and should have no currents circulating in normal operation.

There are two ways that unwanted signal can appear at the output of a circuit via the ground or return line.

One is due to magnetically induced pickup which is avoided by the star system of grounding as the OP points out.

The other is for the output and input return ground to share a common line. The (large) return current from output generates significant millivolts variation along this common track or wire which is injected into the input and amplified.

Unfortunately the amplifiers, as drawn, appear to do exactly this second thing.
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Old 14th May 2008, 11:44 AM   #45
Nuuk is offline Nuuk  United Kingdom
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I've always done my two-box GC's with a separate wire for safety earth. It just seemed logical to do so, leaving the other wiring 'unmodified' and therefore simpler for me to understand.

Another thought - if you use two rectifier bridges and want to leave the grounds separated until the amp stage, you will need five wires in the umbilical, and will almost certainly need to make up a lead rather than using something off-the-shelf. Unless using fairly small wires, choice of plug/socket will be a bit limited too.
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Old 14th May 2008, 11:49 AM   #46
Nuuk is offline Nuuk  United Kingdom
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Studiot, AndrewT is not trying to 'sell' us anything, or mislead us. He is rightly concerned about the safety aspect of building mains-powered equipment, more so since many builders have little, or no training, in building this sort of stuff.

Although most of us will not be selling anything, it still makes sense to agree on a method of making these amps as safe as we can, if only for purposes of not invalidating our insurance.

It's not a court of law and he is free to quote what he likes.
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Old 14th May 2008, 03:59 PM   #47
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Quote:
Originally posted by AndrewT
Hi Gni,
your last diagram addresses all the issues I had. Excellent.

Does anyone else see any problem?

Do we need a dedicated fourth conductor between the chassis?
Can the audio ground lead going to the disconnecting network do the duty of carrying fault current back to the PSU?

If we get agreement on your diagram, then I suggest it becomes the Wiki standard for two box amp/PSU.

BTW,
your diagram can become a single box amp/PSU with just the removal of the extra box and the short length of surplus Earthing wire.
How about posting that once we see others' comments.
Andrew,

I think that the 4th wire for safety earth should go to both enclosures, if "the audio ground lead going to the disconnecting network does the duty of carrying fault current back to the PSU" then you could momentarily get a voltage difference between the 2 chassis, which would result in the bad kind of shock using 2 hands. Or, if the 2 enclosures were stacked or side by side and touching, you'd be shorting the disconnect network.

Questions I still have are if there should be any kind of connection between the amp chassis (safety earth) and audio ground in the amplifier, for example capacitors to the chassis from the shell of an RCA jack
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Old 14th May 2008, 11:22 PM   #48
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This is GREAT! Everyone working tohether to come up with a thorough, safe solution instead of just criticizing and dismissing somone else's attempt to help those of us not as knowledgable.

Thanks everyone.
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Old 26th May 2008, 04:13 PM   #49
ygg-it is offline ygg-it  Italy
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This tread has helped me a lot to find the final solution for my amplifier.


AD826 Grounding Design

Most are common considerations but you will find few different ground connection that I found sounding better
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Old 26th May 2008, 06:18 PM   #50
gni is offline gni  United States
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Thank-you for the further input. . .
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