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Earthing of phono amp

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Wilki View Drop Down
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    Posted: 02 Oct 2013 at 9:33pm
As a mechanical engineer I'm seeking clarification on an electrical matter as follows.
I notice that all phono amp mains plugs have no earth. However, the phono amp has an earth stud for connection of flying earth from tt tone arm.
Because the phono mains has no earth does this mean the tt tone arm is not earthed?

Sorry if this is a daft question

Regards
Ian
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Fatmangolf Quote  Post ReplyReply Direct Link To This Post Posted: 02 Oct 2013 at 9:52pm
It is a good question Ian. There are two parts to the answer:

1) the turntable is probably double insulated so a mains earth is not needed for safety.
2) the tone arm may already be earthed via the cartridge as some have metal bodies with one of the earth pins (green or blue) connected to them and thus to the tonearm via the mounting screws.

Without a record playing please turn the volume up on your amp, if you hear a buzz or hum I suggest dropping the volume and try running a cable from your turntable's earth stud to the preamp's earth terminal. If there is less buzz/hum tidy it up. If more buzz/hum remove the cable.
Jon

Open mind and ears, whilst owning GSP Genera, Accession, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote phildent Quote  Post ReplyReply Direct Link To This Post Posted: 02 Oct 2013 at 10:05pm
Interesting Ian.Made me curious enough to open the mains plug on a couple of phono amps I have here at the moment.Solid state seem to be unearthed and both valve ones are earthed.Maybe its because the valve phono stages have internal power supplies.
I'm sure Graham can enlighten us.

Phil
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Wilki View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Wilki Quote  Post ReplyReply Direct Link To This Post Posted: 02 Oct 2013 at 10:19pm
Thanks and interesting.
TT is sondek Majik so psi is onboard. The tt psu/motor is earthed through normal 3 pin mains plug. So I think that covers tat safety earthing.

Focusing now on the tone arm earth:
The tone arm is project carbon and cart is linn adikt with plastic body. So both are insulators meaning no insulation from cart to tone arm.
On a practical viewpoint hum is only apparent when the tone arm nears the centre of the tt spindle and even then can only hear hum when no record is playing but tat is rotating   
It's not. Big issue. It just seems the cart is picking up some hum from motor and onboard psu as it nears proximity of motor etc

Nonetheless this got me thinking that the tone arm flying lead does not seem to be earthed because the ore amp is not earthed to mains.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 02 Oct 2013 at 11:11pm
No mains earth is necessary.

The "earth" wire should be considered as a "grounding wire".

By connecting the grounds, the casing of each item, when subjected to interference, are both subject to the same interference and therefore cancel out that interference.

An analogy: the earth rotates at 1070 mph, but as far as we're concerned it's still.

Imagine interference as a "vibration" on the metalwork close to the cartridge: connecting the grounding wire means that the phono preamp does exactly the same "vibration", so inside that "connected world" no vibration exists.

It needs no connection to the outside world - no mains earth (provided it's class 2).

If the phono preamp is earthed to mains (class 1), such as a valve amp (for safety - but not necessary as I know plenty of old un-earthed units), then the turntable metalwork being joined to the phono stage is effectively earthed, although not in the legal sense.

Class 2 unearthed is better for the simple reason it can be used where no mains earth is available.

Also, the "grounding" is continued via the interconnect to the integrated amplifier or preamp/power amp, so to that system there is no differential, and so mains hum cannot exist...

...unless the cartridge which is inductive, comes into the proximity of another inductive device, such as a motor... or transformer... where hum is induced into it...

...not the fault of the phono stage.

However, nowadays EMC laws exist, and I find it odd that turntable and arm manufacturers seem as if they're allowed to flout the law!

We can make phono stages, with which properly designed turntables and arms, would never suffer hum or interference noise, and by careful positioning of inductive devices, hum would be a thing of the past.

But, we're the only one! It wouldn't do for our rivals to be put out of business, would it?


Not simple enough for Google-Bot to understand...
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