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Interference on stereo from cable box

  • 31-10-2011 11:20PM
    #1
    Lennoxschips
    Registered Users, Registered Users 2 Posts: 1,772 ✭✭✭


    Hi,

    I have recently purchased a DVB-C box. Am very happy with the picture quality, hooked up to my computer monitor through a spare HDMI port.

    For sound I hook the red/white RCA ports on the DVB-C box into my stereo system.

    Only problem is, I hear a slight "humming" sound on the stereo system now, even when I turn the volume all the way down. This is also present when I select another source on the stereo amplifier (e.g. CD player).

    However, I discovered that if I disconnect the coax cable from the DVB-C box, then the humming noise goes away!

    Is this the case of a badly designed box? I.e. the signals inside the box not being properly shielded?

    Is there something I can buy to filter the signal from the coax? I have no knowledge on this subject. An attenuator or something?

    Any tips would be greatly appreciated. At the moment I have to disconnect my DVB-C box from the coax cable whenever I want to enjoy music on my stereo... and then reconnect to watch TV (with a humming noise in the background).


Comments

  • #2
    Lennoxschips
    Registered Users, Registered Users 2 Posts: 1,772 ✭✭✭Lennoxschips


    Do I need one of these??

    30490.jpg

    (And shouldn't it be built into my DVB-C box?)


  • #3
    Antenna
    Registered Users, Registered Users 2 Posts: 2,442 ✭✭✭Antenna


    Lennoxschips wrote: »
    However, I discovered that if I disconnect the coax cable from the DVB-C box, then the humming noise goes away!

    Its a ground loop problem.

    http://siber-sonic.com/electronics/GLoopwhatis.html

    Connect the coax cable through an isolated outlet to that DVB-C box.
    An isolated socket will have capacitors on the little circuit board on the back.

    There is slight signal loss with isolated (compared to non-isolated) sockets so only use them where its necessary

    The cable company might give you one for free if you explain the problem!

    not 100% sure if the thing in the picture will do what is required.
    If you have a multimeter - an isolater will have a very high or infinite resistance reading from input to output - for both coax outer and inner.


  • #4
    Lennoxschips
    Registered Users, Registered Users 2 Posts: 1,772 ✭✭✭Lennoxschips


    Thanks for the tip, but what exactly is an isolated outlet?

    Bear in mind I am renting so can't change anything...


  • #5
    Antenna
    Registered Users, Registered Users 2 Posts: 2,442 ✭✭✭Antenna


    Lennoxschips wrote: »
    Thanks for the tip, but what exactly is an isolated outlet?
    ..

    It is to block any mains (50/60Hz) current (as well as DC) on the cable, whilst passing VHF/UHF.

    Put one in-line on the connection to the STB (rather than change your outlet)


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