Major ground loop that I can't seem to isolate.

Discussion in 'Mac Basics and Help' started by Kingsly, Apr 14, 2007.

  1. Kingsly macrumors 68040


    I just recently made a change to my office's sound system. My old setup: Minijack-to-RCA out to a 8 channel mixer, from there RCA out to some M-Audio studio monitors and minijack out (via the mixer's headphone port) to some other monitors with a sub.

    I also ran my iPod into the mixer, via 1/4" TRS. The mixer, Sub and M-audio are all powered (no ground).

    I got some big Bose speakers so that I can get the full range (high from the small monitors, mids from the M-audio, and lows from the Bose) and needed a way to power them. So, I dug up a aiwa receiver (simple, six input stereo, also not grounded) and ran the RCA out from my mixer into the receiver, looped the M-audio speakers through the receiver's OUT, and powered the Bose with aiwa's amp. The top-of-the-range speakers remained connected via the mixer's headphone out.

    Everything seemed to work okay and I was pleased with the range I was getting.

    Today I plugged in my external monitor, a cheap :Hansol 15" LCD. It's grounded. Buzzzzzzzzzzzzz!

    I cant, for the life of me, figure out why the monitor is causing feedback, when my old system worked perfectly fine. The only thing I can think of is since all the audio cables and the VGA and power for the monitor run together (they say not to do that...) that that would be causing a problem, but it was like that before and was okay.

    Help? :(
  2. bleachthru macrumors member


    Nov 13, 2003
    Try ground lifting the monitor, or plugging it into it's own breaker. This should resolve your issue.
  3. Kingsly thread starter macrumors 68040


    That's the odd part. The monitor is plugged into a different place on the wall.

    EDIT: reread your post. Yeah, they're all on the same circuit. I guess I'll have to lift it. Is that safe and all? :confused:
  4. faintember macrumors 65816


    Jun 6, 2005
    the ruins of the Cherokee nation
    You should have the monitor on a different circuit period, as the pre-monitor setup was more than enough for one circuit (in most household instances) IMO.

    If that is not a option you can try something like this instead of trying to lift the ground. I have had some success with this type of product in the past. And yea, lifting a ground loop can fry your gear.:(
  5. bleachthru macrumors member


    Nov 13, 2003
    If you cannot easily move the plug to it's own breaker, groundlifting can be done safley, here is a link that explains more:
    Also, if this is something that you run into often, or you need to do this as a permanent thing, you might want to look into the cost of an isolation transformer. As Ground lifting should only be done safely and as a temporary solution. Good Luck!
  6. stroud macrumors newbie

    Apr 25, 2007
    Ground Loop

    I too had this ground loop problem when using a LCD monitor (Acer 21" Wide) with my KRK monitors. The hum would only surface if I powered on the monitor.

    I tried everything in my studio to try and find the problem with no success until I started playing with the mains cable attached to the monitor. It was the earth wire in the mains cable! So I disconnected it and the hum went away instantly. I had previously tried powering it from ALL the different circuits in my house but with no success so I have removed the earth! This may seem dangerous to some, but the power supply is very similar to the one I use for my laptop wich only has a two prong lead so (as it is only 12v), I found this the best solution.

    It does worry me a bit that it is not earthed but I unplug it at night, and ocassionally connect it back to the earth to discharge any built up electricity, if there is any.

    I have searched the web also for the dangers of operating a 12v power adapter without an earth connection but have found very little.

    I will post agin if my monitor explodes but it has been two months now and anything is better than that annoying buzzing hum!!! :)
  7. ElectricSheep macrumors 6502


    Feb 18, 2004
    Wilmington, DE
    I found This to be a very informative read.

    In summary:

    Best and correct way to get rid of th hum: Use balanced lines and tie the shields to the earth-grounded metal chassis at the point the signal enters the chassis, and at both ends of the line. Do not use the signal ground.

    Second best way: Use isolation transformers on all unbalanced signals.

    Least best way: Use special cable assemblies that let you lift one end of the shield.

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