Need help my monitors hum!!!

Discussion in 'Recording/Live Sound' started by 60HzShuffle, Nov 6, 2004.

  1. 60HzShuffle

    60HzShuffle Member

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    When I attach my monitors to anything connected to my pc, it hums really bad. I realise that this is probably a ground loop but I have tried everything.

    I have had them hooked to the speaker out on my PC and directly out of my Tascam USB unit (which is connected to the pc via USB).

    Anybody have any ideas??

    I have had them connected to the outs on a PODxt in the past with no problems.
     
  2. LSchefman

    LSchefman Member

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    Without knowing the exact cause of your ground loop, it's impossible to suggest a fix for the problem.

    Am I correct in assuming that the monitor output on your Tascam unit is balanced?

    Are your speakers wired with 3 prong grounded plugs? Your other gear?

    The usual procedure for sussing this problem out is to use 3 into 2 ground lift adapter plugs one piece of gear at a time to figure out what's causing the loop. Do not lift more than one ground at a time, and do not consider a ground lift adapter a permanent fix. Use it only to determine the source of the ground loop.

    Once you have determined what is causing the loop, there are two fixes, since you want the power cord ground to stay connected to AC ground.

    Fix 1: A grounding wire is attached to a known earthed ground, and then to the offending piece of gear. Sometimes this works, sometimes it doesn't solve the problem. If it works, you can attach it to the offending piece of gear and the problem is solved.

    Fix 2: Sometimes, especially in the case of powered monitor speakers, the loop can be eliminated by cutting the shield wire of the audio cable at one end, if the connection is on balanced audio cables. Do not do this, unless you know what the shield wire is, and unless you are running a balanced (XLR or TRS) cable.

    Fix 3: You can use something like the Ebtech isolation stuff to break the loop. They have a box that is usefull for two way stereo connections, for nominal money. They also make a lift adapter with a switch, but I haven't tried it.

    Fix 4: Sometimes rack gear with metal chassis on metal rack rails can cause a loop. The fix for this is to use plastic tabs or washers to isolate the gear from the rack.
     
  3. 60HzShuffle

    60HzShuffle Member

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    The Tascam outputs are unbalanced rca. The inputs on the monitors are that I am using are rca and unbalanced. There are also 1/4 inch and xlr balanced inputs, which I have used before and also hum. I'm not sure whether the pc sound card speaker out is balanced or unbalanced.


    The monitors have 3 prong plugs and plugged into the same power strip.

    I wonfer if it has to do with the pc power supply....






     
  4. TAVD

    TAVD Guitar Player Gold Supporting Member

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    Try one of those little 2-prong ac adaptors on the monitors to lift the ground. If the monitors still hum, it's not a ground loop.
     
  5. LSchefman

    LSchefman Member

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    >> If the monitors still hum, it's not a ground loop<<

    It could still be a grounding issue, tho it's less likely.

    As anyone who has had ground loops with a 2 prong pedal adapter on a pedal board knows, you don't need a three prong plug to have grounding problems.

    There are many pieces of gear in my studio that actually needed an additional grounding wire to stop a hum.
     
  6. TAVD

    TAVD Guitar Player Gold Supporting Member

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    You'd know better than I, but I was thinking if you lift the utility ground and plug the power in one way, than the other, you'd rule out a ground loop problem.

    With 60HzShuffle's setup, the likely case is a ground loop through the sheild of the rca cables.

    Also, I've lost count of the number of soundblaster cards I've thrown away over the years because of noise issues. I'm sure they've improved in the last few years.
     
  7. Bassomatic

    Bassomatic Silver Supporting Member

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    Have you tried changing your TGP name?






    (sorry, couldn't resist) ;)
     
  8. 60HzShuffle

    60HzShuffle Member

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    :) haha, very funny docta jones....
     

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