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Earthing amp case

Discussion in 'AV Receivers & Amplifiers' started by Stereo Steve, Jul 21, 2004.

  1. Stereo Steve

    Stereo Steve
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    I have a Pioneer AX5 which I'm delighted with but this evening it gave me a buzz, literally. I brushed my arm against the case (it was off) and felt a bit of a shock. I figured it was static so I did it again with the same results. I checked the mains lead and it only has 2 terminals so I assume the amp is not earthed through the mains.I can't imagine an electrical field in the amp casing is doing much for performance.

    Questions are:

    1. Is my amp faulty or do some amps do this. How come it's not earthed? I'm concerned with kids strolling around that someone will get fried.

    2. My Russ Andrews mains block has an earth terminal which he recommends you use to connect to all components via a case screw. Should I get a bit of wire and connect this up?


    I'm assuming it's due to a build up of static in the case but I can't understand why it's not earthed by design. Any electrical bods have an idea? Your help would be much appreciated.
     
  2. Brogan

    Brogan
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    Steve, I have experienced this several times in the past with other equipment.
    My AX5 however is OK - nothing at all on either the front or side.
    I did replace all of mains leads/plugs though but I can't remember if the AX5 lead is hard wired into the case or if it's a kettle type plug.
    If it is then it's likely that I earthed it when I replaced it.
     
  3. Stereo Steve

    Stereo Steve
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    Hi, it's the kettle type but with only 2 prongs. I image the electricity I am feeling is more static than anything. I tried earthing the chassis to the RA mains block and the problem went away. I did actually think I detected a marked 'tightness' in the sound afterwards as well, a less boomy bass. I am however, willing to accept this is all in my head and am just happy that the amp is now earthed and safe. Can't detect any hum after doing it either.

    I have never experienced this before but have done a bit of research and it seems common. I guess there's a lot of electricity buzzing around the chassis so it's not suprising.
     
  4. davehk

    davehk
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    Hmm... If the amp doesn't have an earth, it must be classed as "double insulated" - there will be a symbol with two concentric squares on the back near the mains inlet.

    If this is the case, then something has to go very wrong for the amp case to be live (since there are TWO layers of insulation between the case and any live parts).

    It is much more likely that you have a bad earth on some other piece of equipment connected to the amp. Most earthed equipment will have interference suppressors on the mains input, which include capacitors across all three (L,N,E) conductors. The Earth is linked to the case, and to the screens on the I/O sockets in most cases. If the mains earth on this equipment is missing, then the case and screens will float at 1/2 mains voltage, due to the two capacitors that link to the L and N acting as a potential divider. This is probably the source of your buzz.

    I suggest that you disconnect all other equipment from your amp, then use a mains tester screwdriver (or better, a multimeter) to check each item of equipment. You should find one of them where the case/screens are at 115V relative to earth. This is probably just a matter of tightening the earth terminal in the mains plug - but if that isn't the problem, you'd best get the unit to a service engineer.

    NOTE: EQUIPMENT THAT IS PROVIDED WITH A THREE WIRE MAINS CONNECTION MUST BE EARTHED FOR SAFETY. Is it NEVER acceptable to remove a mains earth to fix an earth loop (hum) problem - in the event of a fault developing, the equipment could become live and deliver a lethal shock to anyone who touches it. There are other ways to fix earth-loop problems safely.
     
  5. RTFM

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    Steve,

    This is very common on kit that is not earthed. I've noticed it a lot with Pioneer DVD players. With those it normally goes away if you reverse the figure of eight plug on the back of the player. With IEC connectors you can't do this.

    Jeff
     
  6. Stereo Steve

    Stereo Steve
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    Thanks Dave,

    I certainly would not remove an earth from any equipment that is supposed to have one. I'm suspecting that my new Panasonic digibox may be the culprit if anything. I only hooked it up yesterday via phonos. It has a plastic case though so may be difficult to test. I guess there will be screws on it somewhere.

    I have a cheap multi meter. Can you tell me what I'm testing for? I use it purely for resistance testing for making speaker cables etc. to make sure I don't get shorts and am not really up to speed with the rest of it. I guess I'm looking for DC voltage? Or is it AC voltage or DC current????

    If I set the meter to the highest setting on the relevant test and connect one probe to the amp case and the other to the wire I have attatched to the RA earth point (disconnected from amp obviously) then I should get a reading yes?
     
  7. davehk

    davehk
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    Steve,

    No problem with plastic case - you can use the phono sockets themselves
    Set your multimeter to 240V (or greater) AC voltage range.

    Put one probe on a known good earth, put the other on the OUTER connector (ie screen) of the phono sockets on the unit. There should be no voltage indication (or at most only a couple of volts - which on a 240V scale you won't notice).

    Dave
     
  8. lowrider

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    I disconected the earth on all my kit but one, it doesnt matter wich, otherwise I had hum...

    Same with all my friends that have more than DVD, Receiver, TV...
     
  9. davehk

    davehk
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    That is dangerous - this can increase the earth loop impedance so that in the event of a fault, the fuse does not blow and the equipment case remains live. The fault current flowing through the interconnecting cable screens can cause a fire

    DON'T DO IT!!!
     
  10. lowrider

    lowrider
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    Could be, but everybody I know does it, my dealer just disconnects the earth at the wall sockets, wich I did to all but one for a subwoofer...

    Never heard of any one eletrocuted, some static once in a while yes...
     
  11. Stereo Steve

    Stereo Steve
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    OK, done a bit of fiddling. Disconnected everything and did some testing. The amp and dvd are double insulated and display no voltage on the chassis. The voltage is coming from the scart lead from the Panasonic DVD-r, my PS2 and also the composite monitor cable from the TV, all appear to display about 50v on the earths. The TV airial lead also displays similar voltage although I assume this is from the booster unit I have.

    Am I reading the meter wrong? it has a scale for ACV and the needle stays around 25-40 when I switch from 50 to 500 on the main selector. It tells me to add 14 for 50 and 34 for 500 which comes out roughly the same.

    I get voltage on the earth of the composote video input of my TV with everything else (including RF) disconnected. I also get this on my DVDR with nothing connected.

    Is all my gear faulty? It's all virtually new. The one common link is that they are all Panasonic devices that are doing this. Not bought from the same shop, or at the same time. Is this a Panasonic thing? Is my meter faulty or am I using it wrong? Am I going mad?

    For now I have reconnected the earth to the amp chassis as a safeguard so it should be safe. Any ideas, should I get a sparky to come have a look?
     
  12. Stereo Steve

    Stereo Steve
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    Maybe I am measuring DC voltage instead. The meter has two sections one says V and then a wavy line and the other says V then a solid line with a broken line underneath. I've been using the wavy line as I couldn't get a reading on the other side.

    Is it possible that I am picking up the 12v DC that my TV booster sends up the coax to power the masthead amp? When the amp shocked me I had just got out of the shower and my arm was maybe damp. It felt like the tingle you get from a 12v battery placed on your tongue.
     
  13. Falp

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    I also sense some electrostatic once in a while...

    My equipmente doesn't have earth sockets, but I think my amp has a earth terminal in the back...

    Link it to the earth may solve the problem?
     
  14. Stereo Steve

    Stereo Steve
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    Yes, that's what I've done. I suspect that my lack of knowledge in the area is not providing enough information for anyone to really help me online. Maybe I should get a spark to have a look. What confuses me is that all these devices are nearly new, in good order and all seem to be displaying this effect. So, I deduce that my testing is somewhat lacking.
     
  15. Reiner

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    Is that lead grounded somewhere? It should be, for lightning protection & equipotential bonding.

    AC is the one with the wavy line, so you measured correctly.

    Reconnected to where? Didn't you earlier say it did not have an earth connection wire?
     
  16. Brogan

    Brogan
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    Does the kettle socket on the back of the amp have an earth pin?
    If so, why not just make a new lead with an earth?
    I think that's what I did but I can't be sure and I don't want to pull everything apart to check...:rolleyes:
     
  17. Stereo Steve

    Stereo Steve
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    No, it's double insulated. I earthed it using a wire from a screw on the amp chassis to the earth bracket on my RA surge strip.

    Still at a loss. Maybe I am testing wrong. With the TV, I disconnected all scarts, RF etc and just left the composite video cable connected and the mains on. I connected one probe to the earth on the cable and the other to the earth connection on my RA surge strip (the ring main earth). I set the meter to ACV 500 and it measured about 25. Switching to 50, the measurement went up to 35.

    I'm going to test the DVDR next with nothing but the mains connected.

    How should I ground the RF curcuit? All the RF leads meet at the booster which is in the cupboard with the consumer unit.
     
  18. Stereo Steve

    Stereo Steve
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    Disconnected all leads from Panasonic DVDR except power lead. Tested with meter hooked up as above, one probe on chassis screw, one on earth clamp. I get a reading of around 50v AC. Same as the TV earth. The dvdr has a small power plug with two terminals so assume it's not earthed either. If I pull the power lead out the voltage dissapears.

    Any idea why my Panasonic components should do this?
     
  19. eviljohn2

    eviljohn2
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    Is everything plugged into the same block of sockets? It sounds like there's definitely a ground loop somewhere.
     
  20. Stereo Steve

    Stereo Steve
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    Not everything. Surely though, the power lead to the dvdr doesn't contain an earth. It's one of the small shotgun/ kettle plug type things like you used to get on tape decks and stuff. I would have thought there is only live/neutral in there. So, I'm getting voltage from that into the chassis of my dvdr. Same with the TV, that has a transformer though.
     
  21. eviljohn2

    eviljohn2
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    OK, are all the leads comparatively short? Ground loops are often developed through long interconnects.

    For those that don't know, a ground loop is where the Earth potential is different in different places. The earth is best regarded as 0V with every other voltage in the system worked out as the difference from that. If the earth on various connected equipment is different then a potential difference (voltage) is established between them which often leads to a build-up of charge (as in this case causing a build up of charge on the amp casing) or it can manifest itself as noise, often noticed as a hum in subwoofers.
     
  22. Stereo Steve

    Stereo Steve
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    I do have some long leads, yes. Some up to 10m to the TV and sub.

    I still can't see why I should get voltage on the case of my DVDR with nothing but the mains connected to it, or am I missing something?

    Should I be content with the solution I have worked out? It seems fine and if anything, the sound is audibly better! I notice without the earth wire connected I get crackiling on my speakers.
     
  23. eviljohn2

    eviljohn2
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    My wild guess would be that the problem is because of the 10m lead to the TV. I'd just stick with your solution though (possibly grounding all of your equipment to the same point!) it doesn't do any harm and seems to eliminate your ground loop.
     
  24. Stereo Steve

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    Thanks John. I will make up some more earth leads and hook up all the stuff to the earth clamp. I really can't see that all 3 Panasonic items are faulty so it must be a one off effect, as you say.

    Thanks for your help.
     
  25. eviljohn2

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    Just bear in mind that grounding everything to the same point may introduce more of these problems. Especially if an item is earthed to a different mains socket (particularly some distance away).

    If you've got some old wire then have a play (as you seem to have found, there are improvements to be had) but you're just as likely to cause the problems you're trying to avoid so be careful :thumbsup:
     
  26. Stereo Steve

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    My situation is that all the source components are on one surge strip ina cabinet. The TV is about 9m away, as is the sub.

    So I guess maybe I should leave at just the one earth wire to the amp as it seems to cure the problem and there is no measurable voltage on any of the other source items. So, I guess I'll leave it alone now it's all working fine.
     
  27. eviljohn2

    eviljohn2
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    Good plan. These things are usually easy to fix once you know the nature of the problem. :)
     
  28. dynamic turtle

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    Stereo Steve,

    Sorry for stating the bleeding obvious, but have you tried connecting ground-loop isolators between your equipment? IME they work a treat, are cheap and easy to install.

    I used to get electric shocks everytime I touched my amp (in fact, such was the concentration of charge near my radiator, that it became electrified and would ZAP me every time I touched it!!). No problems now though.

    Oh, and try minimising the number of interconnects between your equipment. I removed a pair of redundant RCA's between my tv & amp (which were connected just for the sake of it) and managed to stop interference that had been bugging me for months!

    DT
     
  29. Stereo Steve

    Stereo Steve
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    Hi Turtle,

    What are those exactly and what do they do? Have you got a link? I seem to have cured the problem just by earthing the amp chassis (and hence all the other chassis) to the ring main.
     
  30. dynamic turtle

    dynamic turtle
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    I can't tell you exactly how GLI's work (electrical engineering is not my forte!), but they seem to absorb & nullify electrical interference very well. The ones I use are from www.Maplin.co.uk and are designed for use in ICE systems (where GL's are a common problem). They're only £8 and are marvellously effective. At that price, its worth just having one around anyway, just in case!

    DT
     

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