Earth loops

[tony sayer]

In article , [e-mail] scribeth thus

The earth connection .. where exactly then are you removing that?...

[Dave Plowman (News)]

Please describe these 'hifis' One make and model will do.

[Dave Plowman (News)]

And where to connect it? Some amplifiers do have an external ground connection - but I've not seen a PC with one.

[John Williamson]

The 1990s Marantz 50 watt per channel amp I use in the small transcription room for one. It's not professional gear, it was just cheap enough and good enough for checking there's a reasonable signal coming out of the computer. If you wish, I can get the model number when I get home. It's the amp for a range of audio equipment they made which all shared the same IR remote control protocol via a separate data connection.

[Dave Plowman (News)]

Tell me about this re-routed earth connection it has?

[meow2222]

asstd contributors wrote

Your pc case has no screws? Most have several cover screws, 4 psu screws an= d several expansion card screws to choose from.

I already did, separates systems. Its standard practice for record deck cha= ssis connection to go to the amp, and has been for many decades. This has b= een true of both class I and class II goods, lots of both of which were sti= ll in service until vinyl bit the dust.

Pretty much all separates systemsincluding a vinyl deck made by all the mai= n manufacturers. Eg Pioneer, Thorens, Dual, Garrard, Sony, Technics, and nu= merous others.=20

Many no-vinyl systems also have similar provision, though not all.

These are very basic questions.

Sounds challenging

NT

[dennis]

I remember having to mod a Gerrard (SP25?) deck and a Coniser BD2 (sp?) deck to remove the earth loops in my youth. It made a lot of difference.

[Dave Plowman (News)]

Yes - that generally because the pickup cartridge ground(s) isn't connected to the turntable chassis. However, neither will the mains lead ground of the turntable either. Otherwise you'll get a hum loop.

I'm waiting to here of a CD etc separate which gives you a choice of how it's earthed.

[Dave Plowman (News)]

None of which will make a reliable mains safety earth connection. You really do sound like a right bodger.

[John Williamson]

The case is earthed through the mains lead, and there's a screw connection on the case to use as signal ground for anything you connect to it. At the moment, the only connection that needs it is the phonograph input. It's probably only approved for use with double insulated equipment. The entire chain uses the amplifier chassis ground for screening and return. The system could include a matching CD player, cassette deck, radio tuner and video player, if I bought them

The sound card is an unbalanced external PCMCIA interface on a normal laptop with a three core mains lead connected via RCA plugs. The hum is hidden below the noise, which is pretty low anyway.

[Dave Plowman (News)]

It's for a turntable.

No - the phono input is grounded via the screen of the cable. The metalwork on the turntable is grounded via that stud.

None of which would be grounded to that terminal. They will all be double insulated with no mains ground. If not they would have to have metal parts grounded via the plug and a ground loop would result. Which did indeed happen with some early Jap gear.

Basically, each separate has to be safe in its own right - not left to the user to connect an external ground. Which means in practice double insulated with no ground connection the chassis. The signal leads provide this.

[The Natural Philosopher]

bo catridge has an earth. Its the arm which is the screen which needs to be a continuation of the amplifier ground -

[meow2222]

I'm perfectly capable of making a sound earth connection via the amp or the= computer, and so are a vast number of end users. If that's challenging I'm= sorry to hear it. If this standard practice for the past around 2/3 of a c= entury is a bodge, that's your opinion. I don't think its a significant ris= k. And life is certainly filled with significant risks.

NT

[Bill]

In message , [e-mail] writes

We seem to have drifted fractionally here from audio earths to safety earths.

Case screws, card screws etc would give you an earth that would be suitable for audio screening purposes. BUT if it was to be a safety earth then it should be to a dedicated fixing point that is unlikely to be disconnected when simply removing a card or case part. That has been standard practice since Noah wired up his Ark.

[Adrian C]

Or use s/pdif (optical or coaxial) and a DAC. Some mid to hi-end Sony Minidisc recorders (available for next to nothing on ebay etc) make good DACs.

[tony sayer]

Consider if you will the cartridge as a generator with a PD appearing across its pins.

Now one side of that is connected to the live, if you will call it that to the unbalanced input on the amplifier.

The other side is then carried via the screened cable covering back to the same amplifier there is no connection to the earth of the turntable at all.

Hence the earth "loop" cannot exist.

Of course you can earth the gram metalwork back to the amplifier if you want and no problem will ensure with that as the pickup wiring is not part of that earth at all.

Unlike the other situation in use discussion...

[tony sayer]

Good point:)...

[The Natural Philosopher]

Except that the cables were not screened in the arm itself, to save weight.

If the arm is NOT earthed, there is hum. If its earthed TWICE - once to an earthed turntable chassis and once to the local mains it hums as well

[tony sayer]

No, but a lot of the time there either tucked inside the metalwork of the arm or on some decks inside the metal tubing that forms the arm..

So screened to an extent;!..

There may be some due to Capactive coupling..

Why should it do that?, where's the voltage developed thats getting into the cartridge connection wiring?..

How exactly are you saying thats going to be done in practice?..

[The Natural Philosopher]

exactly. so you had to connect the ARM to the screened cable outers, and the ARM was connected to the DECK which was EARTHED..