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Mains hum

Discussion in 'AV Pre-Amp/Processors & Power Amps' started by Jackam, Nov 2, 2004.

  1. Jackam

    Jackam
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    Hi, I have an annoying mains type hum from my Sony AV amp that remains constant regardless of the volume setting. It can be heard equally through all 4 speakers and the sub (I dont have a center).
    I have tried the following without success:
    - Re-routing signal cables away from mains cables.
    - Unplugging the coaxial digital input and switching to an optical digital input.
    - Unplugging the subwoofer LFE phono and turning off the subwoofer.
    - Unplugging the front L/R pre out phono's.
    - Attaching an earth lead from the AV amps ground post to the earth pin of a plug.
    Does anyone think I have a faulty AV amp? I only use the AV amp to power my rears. The fronts pre-out to my main 2ch hi-fi amp.
    Thanks.
     
  2. alexs2

    alexs2
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    You say you're only using the AV amp to power your rear speakers.....I assume the hum,from what you've said is unaltered by anything that you've done so far,but given that it only powers the rear speakers,the fault must lie in the preamp stage,and after the volume control as well.

    If it's in warranty,it would be worth taking it to your dealer,and either having it checked out,or better still,loaning another and seeing if the problem persists.
    Hum or other mains borne interference can be one of the most difficult things to eradicate from a system,but you seem to have gone through just about all of the usual ways of clearing it,including removing some of the other sources to your amp.
    Have you tried running solely an optical digital input to it,and physically removing all of the others?
     
  3. Jackam

    Jackam
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    Thanks for the reply. Yes, I bought an optical cable as I thought I had isolated it, but the hum is still there.

    It still hums if I mute the speakers via the remote, but stops if I switch them off via the a/b/ab/off selector on the front panel. Strangely, it does not hum through the headphone socket.
     
  4. alexs2

    alexs2
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    All very odd!.....I suspect the remote mute simply lifts the input relays or similar,whereas the speaker selector physically disconnects the speakers.

    A trip to it's maker sounds in order.
     
  5. Jackam

    Jackam
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    I seem to have fixed it, well, temporarily anyway.

    I took the lid off and re-seated every connector I could, and found/cleaned 8 fuses. I also cut the horrible 2 pin to 3 pin mains plug converter off and fitted a decent MK plug. It has stopped humming for the time being...
     
  6. andy_pandy

    andy_pandy
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    I know I'm a couple of days late for this thread but I had constant 'hum' on my system and after contacting a couple of manufacturers we came to the conclusion it was due to the mains power ring in the house.....very common with pre/power amps due to the power...and usually caused by fridges/freezers etc in the kitchen as they are all on the same ring main for downstairs in the house. All sorted by ensuring the whole hi-fi system is at the same earth level - ie using the same plug sockets. I have a Belkin Surgemaster single filter with built in earth in one socket for the amp (due to the 1000W it consumes) and the rest of the system is on a Belkin 8way filter with built in earth (about £20-30 in Argos/Comet) both plugged into the same twin outlet socket.
    All 'hum' gone and everything is OK.....I think taking your unit apart was a bit over the top... :eek:
    Anyway if the 'hum' comes back try that.
    Andy.
     

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