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Earth loop blues

Discussion in 'Subwoofers' started by womblenuggets, Sep 11, 2005.

  1. womblenuggets

    womblenuggets
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    Hi. I just bought a VIBE Alpha II HC Subwoofer which I connected to my Yamaha RX-V1400RDS AV Receiver Amp via an unbalanced RCA to RCA lead. All was fine and I was pretty impressed with it.

    Then, a couple of weeks later, started a hum. It's really quite loud, so I got searching on the subwoofer forum and heard it might be an earth loop problem. The guy in work mentioned that if I disconnect my earth at the plug and the hum goes - it's earth loop. I did and it is. It's re-connected now - please don't flame me!

    Anyways, my reconnected sub still hums and I'm still looking for a solution.

    The two solutions I've read most are

    1. Series capacitor in a break in the RCA to RCA shielding, to break the loop and drain the RF interference
    2. A ground loop isolator in with the RCA to RCA

    I'm not keen on the first. Am not happy about cutting through the shielding on beautifully crafted cables to solder a cap in.

    The isolator solution seems reasonibly attractive, but I have heard they are expensive. Well the ones I'm seeing on Ebay aren't.

    My questions are 1) Will £10ish isolators from Ebay do the job or will they degrade the fidelity badly? 2) Are there other solutions I don't know about ( pulling the plug partially out at one end leads to a very loud hum btw ) 3) There must be an underlying reason why some mains sockets lead to this and others don't - is there a way of correcting the mains earth which currently goes down to my incoming supply shielding and water pipes ?

    Sorry this has been so long - thanks for reading this far!
     
  2. Nick_UK

    Nick_UK
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    If disconnecting the earth at the plug cures the problem, disconnect it. Simple as that. It's not interference, it's the movement of tiny earth currents in the shield of the co-axial cable which are being amplified. There is no danger in doing this - hi-fi people have been doing it for years - a sound system should only be earthed at one point. Many amplifiers have an earth post so a separate heavy earth wire is connected after all the other earths have been removed. As long as you disconnect your equipment from the mains before fiddling with the interconnects, there's no danger. If you're really worried, fit an earth-leakage device in the mains feed.
     
  3. Steve.EX

    Steve.EX
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    Nick UK

    So....we meet again :)

    People have indeed been "doing this for years", and it was as "french" then as it is now. It is usually the answer for most who cannot be bothered to locate the source etc.
    From a purely I.E.E point of view alone removing any earth from a non-class 2 device is not a great idea. This type of connection to common earth is refered to as functional and indeed it is.
    In real world terms what are the chances of internal gubbins going short circuit to earth? I don't know, but through my earlier career i have had enough nasty belts to know it certainly has implications.
    Rather than remove earth connections i would recommend bonding all chassis together if you not going locate and deal with the problem at source (presuming it is something other than the sub connected to the receiver - Sky boxes, pc's and other devices that may be being supplied from another ring etc are a good place to start). Simply connecting via a flying lead all metal bodied chassis will acheive the hifi equivalent of EEBAD commonly used in domestic/commercial/industrial electrical installations. This has the effect of negating any rise in potential across related components.

    Steven
     
  4. womblenuggets

    womblenuggets
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    Earth loop has as many solutions as people it seems.

    I'll admit - keeping the sub earth disonnected has a certain appeal. But I agree Steve.EX - I don't really want any disconnected wires in my sub shorting down my RCA to RCA shielding. The house has RCDs which would trip at some stage but after how many coulombs have done what they will with my amp.

    I had not heard of bonding all the chassis together. By bonding I'm reading bolting an unbroken and reasonibly chunky earth wire between the chassis? My sub has no external earth connector - are we talking drilling through the casing to expose a chassis connection here ?

    I'm also very interested in the "locate and deal with the problem at source" solution. Is the ultimate problem that there is poor conductivity in the mains earth wiring between my amp and sub that therefore supports potential differences ? Or could it be the from the earth pin to the chassis in one of the boxes ( my sub has 14 ohms between the plug earth pin and the outer RCA connection which seems high to me - haven't measured my amp's equivalent yet ).

    My sub and amp are on the same ring main and even when I plug them into the same Belkin PureAV 8 Socket Surge Protector - the hum persists. Would this imply it's poor earthing internal to my sub or amp?

    Thanks for your opinions guys! :thumbsup:
     
  5. Steve.EX

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    It is simply another option. A flying lead of an absolute minimum csa could be used, we are after all (usually) talking about milliamps. Bell-wire or the like will be sufficient. Simply loosening a casing screw and attaching lead by an open lug, or even placing conductor directly beneath the screw-head if you want to be crude, will suffice.
    This is not a universal fix and ELH's can be an absolute nightmare but in many instances it will cure said hum.

    Steven
     
  6. Steve.EX

    Steve.EX
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    If indeed it is the mixture of sub/receiver that is the cause.
     
  7. Nick_UK

    Nick_UK
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    If an ELCB is used, there is no fear of shocks, because the power would be removed before any lethal earth leakage could be reached. There is no need for any "disconnected wires" shorting anywhere - merely remove the earth wire from the pin in the 13A plug, put some sleeving over the wire, and put it back. The other option would be to break the earth sheath of the co-axial cable between the sub and the amplifier, but that's more messy to do.

    There's no mystery here - the two earth connections to the 13A plugs, and the earth braid of the interconnect is forming a "loop", into which small currents are being induced. The sub is amplifying these small currents, and the problem is increased because the hum is 100Hz, which the sub is tuned to. Somehow and somewhere you have to break the loop to stop the hum. It's not rocket science.
     
  8. Steve.EX

    Steve.EX
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    I will presume you mean RCD or RCBO.
    Installing an RCD/RCBO is no substitute for removing earths imho.
     
  9. bilba

    bilba
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    I worked with Owain Thomas some time back to look at ways of fixing his earth loop problem. That turned into a marathon thread:
    http://www.avforums.com/forums/showthread.php?t=170017
    Owain did eventually go for the "bond all chassis together" approach, which worked. :)

    I was advocating either the "open shield with capacitor" solution or the "isolating transformer" solution.

    Searching for isolating transformers on the net, I found that there seems to be a range of prices available. For isolating the sub, you only need 1 transformer (mono into the sub), and because the signal is low frequency, a cheap one would surely suffice. If you go for this approach, let us know how it turns out.

    PS even with an ELCB, disconnecting the earth lead from the power plug is just not on. Remember, an ELCB uses the current flowing through your body to earth, to trip the circuit! It is sensitive enough to trip out before the current reaches a lethal level, FOR MOST PEOPLE. What if it is your dear old mum that completes the circuit? :suicide:
     
  10. Steve.EX

    Steve.EX
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    An RCD works on a simple L/N differential type basis. A connection to earth IS required (here in the U.K at least) for provide a path for fault currents regardless.
    I believe current (I.E.E) requirements are something along the lines that if an RCD is to be used as the primary device for disconnection then the resistance to earth (supply transformer usually) must be less than 100ohms to ensure a touch voltage of less than 25 volts or so. IIRC correctly this has been the standard requirement for a number of years now, although i am happy to be corrected.

    Steven
     
  11. womblenuggets

    womblenuggets
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    Were I to disconnect the sub earth, it would still be sort of earthed since the incoming ( amp earthed ) RCA feed is connected to the sub chassis. So loose wires in the sub touching its chassis would inject lots of current down the RCA lead and through the amp earth, tripping the RCA ( ie I don't have to wait for a passing grandmother to lick my sub or whatever ).

    Anyhow, I'm not keen at all on any of that happening. RCA leads just weren't sent to this planet to pass large currents.

    I've just popped downstairs and connected some mains flex to the amp earth point on the back and pushed the other end into one of the sub screws. The hum went and I think I woke my girlfriend with the corresponding yelp of glee!

    This solution is to my mind sonically and IEE friendly - cake and eat it stuff. Will pop to Maplin tomorrow to get some crimped connectors to do a good job of it.

    Thanks for your opinions anyway guys - have leant a lot about earth loops, hope I can help someone else out one day. :clap: :clap: :clap:
     
  12. womblenuggets

    womblenuggets
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    p.s. "tripping the RCA" was meant to read "tripping the RCD" in my last post.

    p.p.s. had no idea RCDs had so many other acronyms!

    p.p.p.s. am very happy now. :D <- me
     
  13. Steve.EX

    Steve.EX
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    Top banana.
     
  14. Nick_UK

    Nick_UK
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    There are several names for these devices (ELCB = Earth Leakage Circuit Breaker)

    Who said it was ? However a 20mA ELCB/RCD/RCBO.... will make the arrangement safe, whilst providing a simple and cheap solution.
     
  15. Steve.EX

    Steve.EX
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    That'll be a 30ma then. :)
     
  16. Nick_UK

    Nick_UK
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    I'm not sure you understand how an ELCB works. It doesn't measure earth currents at all, in fact it's not even connected to the earth in any way. An ELCB compares the incoming live current with the outgoing neutral current very accurately, and any imbalance over a pre-determined level causes it to trip. If you have less current flowing out than you have flowing in, then obviously it has to be flowing via another earth path.

    For your dear old mum to receive a fatal shock from the disconnected earth, several things would have to happen......

    1. She would need to remove the co-ax cable from the sub, and grasp the plug in one hand.

    2. The sub would need to be switched on.

    3. She would need to touch some exposed metal on the sub with her other hand, or other bare metalwork that is connected to earth.

    4. The sub would need to be faulty, to pass lethal leakage currents to earth.

    5. The ELCB would have to be faulty, or she would have to have a heart condition which made her sensitive to currents less than 30mA.

    Pretty remote possibilities, I have to say :) Tell your mum to keep her hands off your gear :D
     
  17. Steve.EX

    Steve.EX
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    For what it is worth, for some, 30ma will be enough to stop your heart, commonly acting as an anti-defibrillator (if you like). Although a standard BS61008/61009 will generally operate between 15-25mA and rarely no later than 200ms, unless time delayed.
    Installing RCD's into an installation has some sometimes far reaching effects. What may have seemed like a good idea to start with can, to the uninitiated become a voodoo science.
    In another thread i have posted about the effects switched moded supplies can have upon the mains quality. It is oh so common to install these 30ma devices onto a ring main or radial that has no (real world) measurable interactions between conductors (which is good). Commoner garden Electricians refer to this as Insulation Resistance. So armed with the knowledge that you have more than 10,000,000 ohms of resistance between all conductors, why does the RCD keep tripping in a non-linear fashion?
    What tends to happen is that more or less anything will leak minute amounts of current. PC's are particularly notorious here with a net figure of some 3 - 5mA of leakage normally being associated per PC. It is the sum of all these appliances that causes problems with the net effect being all is well until you plug (i.e) your sub in and the RCD goes. You unplug it and the RCD will reset. You assume something is amiss with your sub and return it for service. Whilst it is away you plug something else in and it happens again, s**t! you think.
    An electrician turns up and tests the operating parameters of the RCD (with no load) and the unit is performing within normal spec........................ and so it goes on.

    If you want to offer your offer your kit the best service you can for sensible money install a radial of large csa conductors, with as large a CPC as your outlet earth terminals can allow, install a stake local to this circuit in addition if you like. It is the size of the CPC in particular and the lowest possible path resistance to common earth that allows for the dissipation of these noisey currents. If you want to be pedantic use a rewirable fuse (of a known material content) for circuit protection over MCB's and the like. If you stick with the more obvious and basic electrical circuit design, including common path earthing rather than chopping out conductors willy-nilly then you're off to a noise free start.

    A little off topic i realise but you live and learn.

    Steven
     
  18. Supersonic

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    I've been reading this thread (and the other one re. Owain's earth loop problem) and the solution was to bond the chassis' together.

    So here's my really dumb question - how exactly do you do this? Owain said he bonded his htpc power supply to the other components, which kind of confuses me as they don't have GND points on them.

    Is it simply a matter of connecting a lead (e.g. copper mains lead wire) from one component to the other(s)? And how do you connect to the chassis as distinct from the case? Or is that how it's done?

    I get very cautious when it comes to mains electricity supplies so I'd like to be absolutely sure of what I'm doing! Cheers.
     
  19. Steve.EX

    Steve.EX
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    Yes.
    By chassis i would, in the normal course of events mean casing.
     
  20. AMc

    AMc
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    womblenuggets - in my thread further down http://www.avforums.com/forums/showthread.php?t=227297
    I had a similar problem and soldered up a lead using these plugs
    http://www.maplin.co.uk/Module.aspx?ModuleNo=1006&doy=12m9
    and a capacitor (verified by Bilba as the man for the job) soldered in-line with the sheild.
    The cable is a short length of double sheilded satelite co-ax because I had it to hand and it had a nice solid copper core and good sheilding. It worked and sounded fine to my ears - I'm not a professional cable manufacturer or anything but I believe the workmandship is OK.

    You are welcome to it for the cost of the plugs and the postage donated to the charity of your choice (about a £5) if it works because I can't be bothered with cashing a cheque etc. and it will pay back some of the good advice I've had here over the years I've been a member.

    PM me your postal address if you're interested and I'll drop it in the post this week.
     
  21. Nick_UK

    Nick_UK
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    Yes, I know that 30mA will stop the heart. As an (ex) TV engineer, we were always taught to work one-handed when working with anything over 30V, because current passing from one arm to the other crosses the heart and stops it.

    RCD's are like fuses - they are not much use for protecting multiple devices. When I was an apprentice, I worked on Britain's first electronic telephone exchange which was eventually installed in Leighton Buzzard. The individual transistor circuits were made up in a plastic cube with electrical connections at the corners, and the cubes were wired together in a frame. The big problem that they came across was that nobody thought about fusing the things until the last moment. The whole rack ended up with a 5A fuse, but it only took 100mA to destroy a transistor !

    PC's are notorious for generating earth leakage currents, and so are devices which have mains filtration built in. RCD's are pretty useless at protecting whole ring mains, especially offices where there are 20 or 30 PC's on one ring. RCD's are also notorious for tripping on mains transients (spikes).

    Anyway, back to the topic, I still think that the technique of removing the earth wire to remove earth loops is not very high on my list of hazards. It certainly would not keep me awake at night if I had to do it in my own house.
     
  22. Steve.EX

    Steve.EX
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    This remains pretty much the norm.
     
  23. womblenuggets

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    Hi AMc. I had read your thread and considered the inline cap as an option. Thanks for the offer of your lead - unfortunately my sub is a good 4 meters from my amp.

    Last night I soldered some loop connectors to each end of some bell ( ok - Big Ben ) wire I had lying about and it's cuting out about 90% of the hum - which seems to be about as good as I'll get ( momentarly diconnecting the earth didn't improve this - which makes me say that ).

    I must say it's remarkable how many threads in these forums end up with people illustrating their command of the subject with a life history :boring:

     
  24. Troon

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    I once had a shock problem caused by *everything* being double insulated and thus floating at what ended up being the TV internal earth, about 55V above house earth.

    This was easily fixed with a dangerous-looking cable: 13A mains plug at one end, phono connector at the other. A length of speaker cable (single cable, not twin pair) was soldered on the earth pin of both plugs. To make the thing properly safe, I put heatshrink over the internal live and neutral connectors and removed the fuse altogether.

    I plugged this into a spare input on my receiver to pull the whole system's ground to house earth potential, and no more problems.

    If you're going to try this, please don't die or blow anything up. :nono: :lesson:
     
  25. Steve.EX

    Steve.EX
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    Humble apologies, i guess.
     
  26. Nick_UK

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    Some people learn from the experiences of others - sorry if it has had a soporific effect on you

    :boring: :lesson:
     
  27. IronGiant

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  28. Steve.EX

    Steve.EX
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    In trying to avoid any life stories :)
    If you have TNCS/PME or TNS as a supplied earthing arrangement then under most circumstances, presuming a cpc of at least 1.5mm exists within your ring main/radial and max Zs for the circuit protective device (fuse or mcb NOT RCD) is not exceeded then i believe there is no requirement for rcd protection (out of equipotential zone sw/skts not withstanding) An electrician of merit would confirm this for you i am sure.
    The first thing i would do is have someone test your rcd's with a meter capable of ramp tests that will indicate exactly at what current they operate. It is not uncommon for older devices to become overly sensitive, although breaking down is the norm. IIRC an rcd should not operate at below or less that half of it's rated operating current.
    This takes no time at all to test but make sure that it is tested with no load connected.
    If you can establish that the device is or is not working correctly then you know in which direction of actions you are heading.
    6 PC's is (IMHO) pushing it a bit. I personally would not recommend this. I believe that (long-time standing) current requirements are for circuits of this nature additional/larger cpc's are required to help dissipate these currents.
    Hope this helps and was not too self indulgent. :)

    Steven
     
  29. Steve.EX

    Steve.EX
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    Sorry, it reads a bit better now.
     
  30. IronGiant

    IronGiant
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    Not at all self indulgent :D, We can take this thread to DIY if required.

    So you say:

    1) No way can you use 6 Pcs with an in line RCD in/before the fuse box, particularly an old one, it will keep tripping.

    OK, now I'm aware modern equipment is incompatible with RCDs I'll take the old one offline and see how we go.

    If it keeps tripping on the new one I'll move the main ring off the RCD in the fuse box as well.

    Everything will still be protected for electrical safety by MCBs.


    Dave
     

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