Humming Speakers & Sub

Discussion in 'AV Receivers & Amplifiers' started by ibrady, Aug 14, 2002.

  1. ibrady

    ibrady
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    OK I'm new so shoot me down if the question is stupid.

    I have just finished connecting my system -

    Pan TV (TX-32PL30D), Denon DVD 1600 and Denon 3202 with KEF HTS2001 & PSW2000.

    System works perfectly until I connect the cable antenna to the TV, afterwhich the humming on the speakers&subs begins.

    I suspect it has something to do with earthing, having read through someof the threads - however I have no clue how to resolve it.
    Most of the threads refer to 'earthing the amp' - how is this done ?

    Is it possible to resolve this problem alternatively - with a better cable for the TV ?

    Need some help .............

    :confused:
     
  2. M.Joshi

    M.Joshi
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    The problem mostly occurs due to a difference in potential between the earth of each piece of equipment. There should be a connection labelled {See Attached File!} on the back of the receiver.

    If you connect this to the mains earth (Preferably via a large value resistor - Mega Ohms), this should solve the problem.

    The other cause could be a poorly constructed / screened lead - If the cable box just uses standard connectors and not TNC type, you could easily try testing another lead. Try the earthing option first to see if this solves the problem.
     

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  3. ibrady

    ibrady
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    Ok I have found the connector - but the resister bit I didn't catch.

    If I put a wire on the receiver ground connector and put it directly in to the ground of the wall socket - will that do ?
     
  4. mickey moo

    mickey moo
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    yes that will earth the amp ok

    the problem is almoast certainly because you have an aerial booster in the loft which is powered from a different mains ring (eg upstairs lighting circuit) and the only piece of equipment earthed with the AV stuff is the sub.

    If earthing the amp doesn't cure the problem you will have to do something clever with the aerial like using a booster which is in two parts having the power supply with the AV gear.
     
  5. M.Joshi

    M.Joshi
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    Am I missing something here....ibrady did not mention anything about signal boosters in the loft in the original post.

    With regards to the resistor, it is there for safety - You do not necessarily need it. Connecting the earth pin on your receiver will also work.
     
  6. mickey moo

    mickey moo
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    No I was making an assumption - If the humm only happens when the aerial is connected then the aerial must be at a different earth potential - most likely from a booster. If the co-ax went straight up to the aerial there would not be a problem. OK perhaps I should not have put 'almoast certainly' and said 'possibly' or 'might'. The only other possibility is that the aerial splits off to other rooms where it may be earthed there, but few electrical items are earthed these days.
     
  7. ibrady

    ibrady
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    I have earthed the receiver - no joy !

    Although after applying the earth there is a reduction in the noise volume ?

    What I have noticed is that disconnecting my subwoofer cable removes the humming ?

    Regarding boosters in the loft - I am not sure - if this is the problem then I'm screwed. As I live in an appartment I have no access to the loft.

    Maybe some other ideas ?

    Tomorrow I am going to try a surge arrester on the coax - let's hope...............
     
  8. mickey moo

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    Didn't think it would. What you need is a balun - a device (basically a transformer) which will allow the aerial signal to get through but with no direct electrical connection. You are going a little outside my area of expertise. It may be that some aerial boosters do this and I have a vague memory of something like this being used for car hi-fi. I will see what I can find out and get back to you but it will probably be Tuesday at the earliest.

    Mike

    (the other possible solution involves disconecting the earth from the sub but I cannot advise you to do that unless KEF say you can).
     
  9. mickey moo

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    Here is something you could try:

    From Maplin get two baluns (order no. FD78K @£199 each)

    These are really designed to turn one aerial impedence into another (75 ohms into 300 ohms) but if you connect your incoming areal into one end, use two short bits of wire to join one balun to the other using the screw terminals (you will understand if you look at the picture,then connect your tv/vid aerial to the second balun. this will turn 75 ohms into 300 and back again. you will loose some signal but there will be no DC continuity with the apartments aerial booster. I have never tried this (never had to) but in theory it should work and doesn't cost too much.

    http://www.maplin.co.uk/products/details.php?CartID=0208181323141453461&moduleno=5145&modulecode=

    regards - mike
     
  10. guyb

    guyb
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    Hi ibrady

    Did you manage to solve the problem. I have just bought a Kef PSW2000 and have the exact same problem - a very loud noise coming from the sub at all times. The only way to stop it is to unplug the sub cable from the back of the receiver.

    Thanks

    Guy
     
  11. guyb

    guyb
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    Hi Ben

    Thanks for the info. I will have a play tonight to see if I can solve this by pluging then into the same surge protected power strip.

    Thanks

    Guy
     

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