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If the user-accessible part of the chassis is metal then that has to be bonded to mains earth.

2 core is only allowed for double insulated kit in the UK. Its not a quality of sound issue but a health and safety issue first and foremost.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

Some of the older 'pro' Yamaha power amps are 'double insulated' in that the mains tranny is toroidal and totally isolated from chassis and all mains potential is contained within double sleeving and neoprene boots over the switches etc. The ground connection is provided via the signal leads.

Ron(UK)

**Personally, I won't do those jobs, UNLESS the cable is an approved type. Examine the cable and I'll bet you won't find any of the relevant electrical authority markings. It has probably not been tested nor approved. Some of the leads I've exmamined barely have insulation suitable for 12 Volts, let alone 240VAC. As for your earth question, yes, I'd earth it.

Trevor Wilson

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Posted via a free Usenet account from http://www.teranews.com

LMAO !

So, the equipment is Class II (double insulated) and doesn't require an earth.

It might introduce 'hum loops' for sure.

It would be just desserts I think for the owner if that happned. It would serve him right for being such a crackhead as to believe in magic cables.

What does the website of the cable manufacturer say about how its product works ? They may have some special magic view about the role of grounds !

Graham

It is indeed a 'double insulated' item - as indeed most domestic equipment these days is, irrespective of whether it has a metal chassis / case accessible to the punter, or not. It of course carries the double insulated symbol to show this to be the case. So what I was asking was not primarily a health and safety issue, but a sound one, as the owner believes it to be. As I said, I don't think that connecting a mains earth to the metalwork of such an item - double insulated or not - represents any kind of safety issue, but as the equipment was originally designed to operate without a connection

*directly* from the chassis to the mains power outlet, then it might in fact make the noise performance worse than 'as-designed', rather than better, as the nutcase who owns it, believes ...

Arfa

Good point.

To attach an unapproved cable would strictly be illegal. You could be held liable for any consequences too.

Graham

"Arfa Daily" hath wroth:

Wrong class of customer. Such things tend to be purchased by people with more money than technical abilities. Did you notice that the cord is rather stiff? That's intentional as no self respecting audiophile would hide such an expensive purchase behind their equipment. It's made to be hung out the front of the rack or shelf, where all can admire it.

Ouch. One of these cables perhaps?

Be sure to check out the $1,080 power cable.

There was an article in EDN on the topic a while back. Digging... "OFC madness: Facts, not fantasy, regarding power cables for high-end audio equipment."

If it was 2 wire, it would need to be double insulated. Grounding the chassis is always a good thing (unless it's a 40 year old AC-DC power supply). Yeah, I would ground it.

Only if the AC power line noise were fairly high level (several volts) and the power supply design was relying on the common mode rejection of the AC power cord to remove the noise. A rather crude power line noise filter will remove all of that.

Don't give them any ideas, or we may be plagued with $200 replacement power cords.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Skype: JeffLiebermann     AE6KS    831-336-2558

Sounds like you're opening up a can of worms.

I've never seen a piece of consumer A/V gear with a grounded power cord, regardless of what the case is made of, but it certainly won't hurt anything to ground it.

Maybe you ought to manufacture some of these obscenely expensive power cords yourself, obviously suckers will buy them.

Hooking up mains plug ground to all audio equipment produces very nice ground loops. So I hope the customer is going to enjoy the nice 50 or 60 HZ hum and its harmonics....... A cluster of audio equipment should be grouned at one point only to avoid loops.

It MAY create problems. A grounded case will almost certainly ground the outers of the RCA jacks. That will provide a path to ground for any leakage currents and in turn that may result in 'hum' as currents flow where they weren't intended to.

Graham

On Thu, 27 Sep 2007 08:50:58 GMT, "Arfa Daily" put finger to keyboard and composed:

This month's Australian Silicon Chip magazine has an article on the hum and RF noise produced by 2-pronged DVD players. The author(s) tested quite a few of these players by connecting them to an old

3-pronged amp. They found that audible hum was introduced when earth current flowed from a player's switchmode PSU to the amplifier's earth via the analogue signal leads. Additional radiated interference was attributed to the digital noise produced by the main decoder chip, and to the 100kHz switching frequency of the PSU.

The only solution recommended by the author(s) was to replace the SMPS with a linear one. Doing so eliminated the hum and PSU noise.

- Franc Zabkar

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Please remove one 'i' from my address when replying by email.

100% predictable. The usual cuplrit is the Y caps in the SMPS of the 2 wire equipment which results is significant (but legal) leakage current of up to around 2 mA. Of course, this won't happen if the amplifier is a 2-wire type too since there's no earth for the current to flow to.

So, adding an earth to a Class II amplifier is likely to add 'hum'. Simple really.

Graham

On Sun, 30 Sep 2007 00:49:12 +0100, Eeyore put finger to keyboard and composed:

The same article measured the chassis potentials of the various devices. One measured 81VAC with respect to earth, others measured

115-117VAC. In some devices the A-E and N-E RFI suppression caps were not installed. However, all appeared to have a coupling cap between the AC and DC sides of the switching transformer. One end of this cap appears to be connected to the case, while the other end probably goes to the negative side of the bridge.

I would think that it would still be possible for a noise current to flow from one case to another if the chassis potentials were significantly different.

- Franc Zabkar

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Please remove one 'i' from my address when replying by email.

too

That one's a killer. The idea of it is to return switching noise on the output to the low impedance of the bulk filter cap. Of course it also results in the high frequency content of rectified AC being passed to the secondary side.

Or positive. Doesn't matter which especially but returning it to the negative side can interfere with the regulation circuitry operation.

I suppose that must be possible but maybe it'll be of a smaller magnitude.

Graham

Not so. If the power supply and mains wiring etc within the amp conforms to the standard there is no need to earth the metal chassis. Otherwise every single metal cased amp etc would have the casing earthed and hum loops would abound.

--
*Born free - taxed to death *

    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

Lots of Far East gear in the early days had grounded cases to pass UK regs without going to the cost of double insulation. And when you plugged separates from the same maker together using the provided leads you got a ground loop...

Grounding an amp case only may well be ok since that will be the 'master' part of any system. But doing the same to other separates will almost certainly create hum.

--
*In "Casablanca", Humphrey Bogart never said "Play it again, Sam" *

    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.