Earth/Ground Loops?

Hi Simon,

Not sure I'm up to Master Class standard! - but as a sufferer of earth loops I have learned a bit about it the hard way.

Earth loops are created when the signal 0-volt in the sistem is connected to mains earth in more than one place. This can easily happen when you are mixing and matching kit (eg for me with LP12 and an ArCam AV amp, other notable kit with an 0volt-earth connection includes all the NAIM CD players).

The effect is that at certain times there will be a current flow between these 0volt - earth link points - generally noticeable as a hum, but the main problem is that humming or not the music gets killed - dynamics are restricted, timing is off, top end is muffled or congested, very much like a really bad mains day.

To test for these conditions I resorted to a multi-meter (a few pounds from Maplins). I disconnected each of my bits of kit from everything else, stuck one probe on the mains earth pin of the power cable and the other on a visible signal ground to see if they were connected.

For me both my LP12 and my Arcam were 0volt-earth connected.

The solution should be to disconnect one of the earths, however in my case if I disconnect the Arcam earth it sounds rotten, and if I disconnect the LP12 earth, then it sounds rotten! So I have to disconnect the LP12 earth spade to 62 when AV-ing, and unplug the Arcam from my 62 and reconnect the LP12 earth spade to 'do' vinyl...

If anyone has better ways - I'd love to hear it!!! (my 62 is hard to get behind!).

Cheers!!!
Chris

Hi Chris,

Just trying to grasp this. As I understand it, merely uplugging one of the two pieces of 'problem' equipment, ie either the Linn, or the Arcam from the mains doesn't do the job; you have to actually unplug the signal line out/input?

Also, you note that even if there isn't hum, the main system sound may be negatively affected. Is this a huge difference, or something very subtle.

Lastly, I''m considering adding on a 3rd party piece of equipment in the form of a Sony AV processor, so as to be able to do AV.

I notice that the original plugs were 2 pin, and for local regulations have been replaced with a 3 pin plug; however the earth pin does not appear to be connected ie the new plug is semi transparent and I can see no earth wire present.

I also have one or two other pieces of equipment, ie a clock radio, and my VCR, that both have two mains pins only, ie no earth pin. So how are they earthed, and would such a piece of equipment thus wired give rise to the earth loop problems you've mentioned, when used in conjunction with my Naim HiFi.

Many thanks,

Cheers,

John.

Populist thinking exalts the simplistic and the ordinary

"To test for these conditions I resorted to a multi-meter (a few pounds from Maplins). I disconnected each of my bits of kit from everything else, stuck one probe on the mains earth pin of the power cable and the other on a visible signal ground to see if they were connected."

Is the kit powered when you are checking?

I'm asking because my DVD player has an electronic on/off switch. So it seems like the signal may *not* be connected to ground when the unit is off or unplugged buy *may* be connected to ground when the thing is on or running. So I might not have a loop when playing CDs on a separate CD player, but would when playing DVDs since my CD player stays on all the time.

Also...

"Also, you note that even if there isn't hum, the main system sound may be negatively affected. Is this a huge difference, or something very subtle."

When I checked this with my LP12 in a former setup, the difference was and wasn't (!) night and day. It was night and day from a timing standpoint. The music got "phasey" sounding and didn't sit right. But its not like the bass went south or anything.

- GregB

Insert Witty Signature Line Here

Colleagues,

Here's a few words about earthing and hum loops - hope it helps!

Electronics equipment does not require an earth. An earth is sometimes used for safety reasons, where adequate insulation is not possible between the primary and secondary windings of any mains transformer.

For electronic devices with only low power requirements a double insulated approach is used. For example the mains transformer is wound using a split bobbin. It is considered inconceivable that a short could occur between the primary and secondary windings.

Where this approach cannot be used, for example in a power amplifier with a toroidal transformer, an earth is required for safety. This does not mean that the earth need be connected to the signal ground. A good toroidal transformer will feature an inter-winding layer (actually another winding with only one end available). This inter-winding layer is connected to mains earth, this helps reject mains-borne noise but prevents the primary from shorting to the secondary, it shorts to earth via the inter-winding layer first and blows the fuse.

HiFi systems are a little different. It is customary to connect the signal common to mains earth where there is a phono input. The low signal level makes hum pick-up likely and the connection to mains earth makes shielding more effective.

I cannot comment upon any earth loop problems without knowing more about the equipment involved and having some sort of block diagram showing the connections. However, here's an approach I've used with a very complicated AV set up I used to have (I counted 20 boxes of electronics). I have since split this lot into three separate installations.

I decided where I was going to connect this lot to mains earth. Easy, the pre-amplifier (with the phono, input). All other units which had an earth connection were connected to earth via 100 ohm resistors (I made a mains distribution unit for all this with the earthing resistors, filters and mains-on control relay).

The whole lot must be fed via an ELCB or RCCB (if you prefer that term). The 100 ohm resistors have a value low enough to trip the ELCB if there is a short to signal ground in the corresponding unit but high enough to prevent high earth loop currents flowing.

How does an earth loop current cause hum to be heard together with the signal? The loop acts as a pickup coil for the 50Hz electromagnetic field which is everywhere where there is mains. This loop has a low resistance and so quite a high current flows. Should this current flow through the ground tracks of an amplifier, in particular a phono stage, it will develop a small voltage due to the resistance of the printed circuit tracks. This voltage is, effectively, in series with, and so adds to, the signal voltage, hence you hear hum.

When I design amplifiers I put a lot of effort into defining the grounding configuration. It is possible to design amplifiers to be extremely tolerant of earth loops. I am surprised to hear of hum problems these days. I design amplifiers just for fun, but I used to design industrial electronics for a living, in particular power supplies.

Just as an aside, I recently bought and returned a load of Linn equipment which hummed (turned out to be a short-circuit). What bugged me was that Linn refused to give me any information about how their equipment is earthed and refused to give me any electrical safety information. They said the dealer is responsible, but he was unable to help.

Before adopting any unconventional earthing arrangement, information about how the units in question use their earth connection is important to verify that the set-up will be safe. I have been following some of the discussion about mains spurs, I do hope that people are keeping electrical safety in mind.

Regards,

Paul.

I would have thought that a high percentage of people on this form (me included) have a turntable and Naim CD player connected to their Naim pre-amps. How many people disconnect the earths on one before listening to the other, I certainly don't.

Hi John,

My room layout has the mains plugs buried deep behind the equipment racks and various cupboards – so its easier to unplug signal inputs than muck about with the mains plugs.

The differences in sound are very noticeable – Singers are so slow they sound drunk! Transients and bass notes lose power - drums sound soggy and bass notes sound like they are coming from 2 streets away!

If your prospective equipment has no earth connection in the mains plug I’m sure that it cannot create an earth loop and should be fine to connect in (unless its from the likes of Krell, M-L, Quad etc – obviously !!!).

One other bit of advise I can offer you is that the different inputs on the pre-amps can sound different – on my 62 for example the tuner input is noticeably ‘nicer’ than the Aux or Tape inputs – so that’s where I connect my CD.

Hope this helps
Chris

Hi Greg,

I didn’t have the power connected to measure for continuity – I really did completely disconnect everything before going in with the probes!

My DVD has no mains earth connection – the AV culprit is my Arcam 5.1 amp (used to power my centre and rear speakers, and provide a volume control for the whole 5 channel sounds).

In my system, with the earth loop ‘made’, the LP12 sounded like a transistor radio! – well, maybe not quite that bad, but you wouldn’t ever want to listen to it like that – I honestly thought I’d trashed the cartridge!

Cheers!!!
Chris

Mr Greeny,

I have read various forum comments on having Naim CDP’s and turntables within the sistem, and you can either: unplug the earth spade from the turntable to pre-amp, or I think it is possible to isolate the CDP signal to earth connection.

However, since the Naim CDP 0v-to-earth is connected inside the box, I think most folks just leave their turntable earth spade off the preamp and allow the CDP to provide the single 0v-earth connection.

I’d urge you to try it – in my experience the result was dramatic!
Cheers!!!
Chris

Chris

I currently have LP12, CDX and an AV receiver connected to an 82. I have tried listening with various combinations disconnected etc but heard no difference. However I wonder if this could be the ABX effect (see One reason AB or ABX etc
,testing does not work ).

So bearing in mind there must be 100's of people on this forum with an LP12 and a Naim CD player I genuinly want to know if people actualy do this (and heard a difference).

Greeny,

depending what lead you have on the Lingo, the Linn may not be giving an earth loop. Conn 401/E is (ISTR) the one to have if you also have a Naim CD player.

cheers, Martin

E-mail:- MartinPayne at Dial.Pipex.com

I have a naim system and an AV system consisting of an AV amp with TV, STB, sub and 2 dvds.

Only the sub and the stb are earthed in the AV system.

When I connected the AV pre out to the naim and select that input on the 42.5 the naim starts to buzz with the volume around 10 oclock. When selecting the cdx there is no buzz when the volume is up (and the cdx is not playing).

After disconnecting all signal cables and antennas from the AV amp the buzz is still present. Note that the AV amp is not earthed.

when I connect the two earth plugs of the AV amp and the 42.5 together all the humming stops.

Strange, I have no idea where the hum came from. Maybe it didn't like the floating earth of the AV amp. But at least it is fixed.

I'll hide my Shane Mcgowan CDs next and check if any musos on the cdx sound drunk

cheers
Gus