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Humm and Radio :eek:

Discussion in 'Subwoofers' started by AMc, Jul 15, 2005.

  1. AMc

    AMc
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    I had to replace my AV amp when my Yamaha A5 started to make a thump when you muted the amp and refused to output anything through the sub. I also seemed to have trouble with the sub refusing to 'wake' when bass kicked in. I've bought a Denon 2105. I'm using a cheap Eltax active sub - stop laughing it's all I can afford for now ;)

    I had the problem with the Yahama, but it seems worse with the new Denon...

    Connecting the sub with a phono lead produces a buzz that sounds like mains interference. Half disconnecting the input so the external connection isn't made but the central pin is, kills the buzz but the sub functions OK. The Yamaha was connected like that for about 9 months. I butchered a cheap interconnect so that the outer wasn't connecting but the plug was fully 'in'.

    Wiring up the Denon I hoped the ground loop or whatever it is might be gone but it did the same thing. Using the cludged interconnect allowed it to play and not buzz.

    I came home last night and discovered that the sub was running (normally it auto stands by) and was quietly, but quite clearly picking up radio from somewhere. The amp was connected but in standby. Powering up the amp killed the radio and putting it back into standby didn't bring it back so I assume it happened over time.

    My questions are

    1 - Is 'connecting' my sub like this responsible for the death of the Yamaha and likely to kill the Denon?
    2 - Could the sub output of the Yahama producing a DC thump have damaged the sub in some way leading to the radio interference?
    2 - is there a better/safer way to connect them that will prevent the A/C buzz and not pick up Radio Caroline?

    Any thoughts welcome, thanks for reading.

    AMc
     
  2. bilba

    bilba
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    Hi Andy,

    to answer your questions....

    1 - Using an "Open sheath" solution to earth loops won't damage your amplifier

    2 - A thump from the amp could eventually cause problems for your sub, but would probably not have caused the radio interferance

    3 - There is there a better way. Opening the earth sheath fixes the earth loop problem but can cause the lead to act as an aerial. You can either short the lead with a 0.01 mfd capacitor which will shunt away the RF, or you can use an isolating transformer in line with the lead.

    I researched and wrote up this article a couple of months ago, and posted a link on this forum. That thread has slipped well down the list now, so here it is again for anyone who is interested.


    http://www.users.bigpond.com/bcolliso/earth-loop.htm

    regards
    Bilba
     
  3. AMc

    AMc
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    That's a really clear explanation of the problem and the solution! Thanks.

    When you say a 0.01 mfd capacitor do you mean something like this "Mylar 0.01 WW18U"?
    http://www.maplin.co.uk/Module.aspx?ModuleNo=371&doy=18m7D
    Excuse my ignorance but it's been 14 years since I did any hands on electonics - is there a power rating or a capacitor type I need to check?
     
  4. bilba

    bilba
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    The Mylar cap should be fine. We are only talking line-level here, so power ratings don't really come into it. Use the cap to bridge the gap you created when you opened the sheath. :thumbsup:
     
  5. AMc

    AMc
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    Excellent. There's a Maplin just around the corner from work so I won't have to pay postage on a 4p part. Many thanks for your help.
     
  6. AMc

    AMc
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    Just to follow up I got hold of a couple of fat phono connectors and that capacitor from Maplin yesterday and put together the interconnect. The phono was wide enough to install the capacitor in the barrel which I was pleased about.
    Anyway my soldering skills have always been a bit ropey but I managed to put it together and it works well - no hummmmm no radio.
    I'll start a new thread for my new problem :( ...
     
  7. bilba

    bilba
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    I'm glad to hear my information was helpful. Thanks for the feedback :smashin:
     
  8. AMc

    AMc
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    Took delivery of new speakers and sub (CD50+CD100+CD1) from the Canton Power Buy in the speakers forum.
    I've found a new way to beat the earth loop problem - the sub from the CD1 set has a European 2 pin plug - no earth= no hum :)
     

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