Power Adaptor causes loud audio output jack hum?

Discussion in 'MacBook Pro' started by ciaronm, Jul 27, 2007.

  1. ciaronm macrumors newbie

    Jul 27, 2007
    Hi all, a spot of advice please.

    I have just had my MBP SR 2.4Ghz delivered today, in many ways im delighted with it but in others in a little dissapointed. Most annoying is the problem i have when plugging in headphones and or any external audio device into the headphone jacks. I realise that this has been discussed at some length here in the past but there are a few points that i would like cleared up.

    1) Is it normal for a load hum to come through the jack just when the power cable is connected?

    2) Is it normal that when i earth the computer in the above situation by touching the case that the hum disappears completely?

    I dont seem to be really exhibiting other problems with the audio that other people have mentioned when not running off of the charger. When detected they are minor, as is the static.

    The problem only occurs when running off of the power adapter, and produces a steady but loud hum!

    What should i do? Is it more faulty than the standard problem? Should I send it back?

    Many thanks,
  2. Tweak3D macrumors regular

    Jul 17, 2007
    what your hearing is known as a ground loop gum. its will run at either 50 or 60 hz depending on the country you live in. All electronics can have this happen. Your best bet is to purcahse a good power filter for your power adapater. they make small portable ones that will not only further protect your computer but also eliminate the ground loop. do a quick search on google for ground loop and you will find more information.
  3. ciaronm thread starter macrumors newbie

    Jul 27, 2007
    Thanks for the advice it is really much appreciated.

    However i have a further questions.

    -On a product that is worth £1599 is it really acceptable that i have this problem?
    -How common is this problem within the MBP community?
    -What in the machine is allowing this ground loop hum to occur(poorly earthed, poor magnetic shielding)?
    -Is this an issue that could equally be resolved if i were to replace the MBP using my 14 day return clause?

    Many thanks once again,
  4. Tweak3D macrumors regular

    Jul 17, 2007
    from my experience, it is typically a combination of things which leads to this particular fault. A poor ground can do it though. When I had my powerbook it would do the same thing when I had it hooked up via DVI to my TV which was also hooked up to my surround sound system. Come to find out aftersome trouble shooting, it was the coax (cable for the tv) causing the hum because it was not grounded properly. I ended up purchasing a basic monster powerfilter and surge protector and the problem went away.

    You can try exchanging it for another one but I do not think personally it will help you. Does it still hum if you use headphones or the built in speakers? if not the only thing I can suggest is power filters. If it does hum on speakers and headphones and grounding makes it go away, you can make a cheap permanant ground/security device which may help aswell. ill explain that if you want too.
  5. Alloye macrumors 6502a

    Apr 11, 2007
    Rocklin, CA
    -I don't believe it's common. At least I don't have it and I haven't seen any other complaints about it in the forums.

    -This one is difficult to answer. Since it doesn't appear to be a common problem, it's possibly something unique to your environment. Have you tried using the power adapter with different outlets? Perhaps even outlets in another building? That may help isolate the problem.

    -Depends on what's causing the problem. A replacement will only make a difference if your computer is defective. If the problem is external to the computer, the replacement will suffer the same fate.
  6. Marky_Mark macrumors 6502a


    Sep 30, 2005
  7. ciaronm thread starter macrumors newbie

    Jul 27, 2007
    Thanks again for the help,

    ill test it out on some different power supplies to see if it makes a difference. Its also i believe something to do with th impedance of my headphones, i tried some old budget Sony headphones (massive on head types) they seemed to work well enough. The cables are a bit thicker than the others that i was trying so i assume offer more resistance. It's not ideal though and i would much rather have an out jack that works properly!

    The sound only effects headphones etc, not the speakers. We shall see what happens.

    Not to sure how i could get it exchanged either, its complicated as i had my MBP in part funded by my local education authority and thus they provided it. I think they have sub contrated out the apple care to a company called Microlink.

    Hope i can get it sorted out though as it is rather disappointing.
  8. fwhh macrumors regular

    Aug 11, 2004
    Berlin, Germany
    This is, as said before, a quite common problem with audio equipment, which contains components that are earthed, called "ground loop". (You can look it up in wikipedia)
    It appears most often when you connect a computer with a power supply (so not running on battery) to a stereo set that is connected to another earthed device, such as any device that is connected to cable tv oder satellite dish. You can resolve it using a transformer for your computer-audio-line oder using a small adapter for your cable tv, which breaks up the ground connection using a capacitor. Your local electronic store will sell you such devices for a few bucks (should be <10$).
    So this is not a problem of you MBP.
  9. ciaronm thread starter macrumors newbie

    Jul 27, 2007
    Thank you all for your advice. I have managed to resolve the issue and am now a very happy user. Everything is working well and im coming around to the world of OSX as well.

  10. Megatron macrumors regular

    Nov 19, 2005
    What did you end up doing to get rid of the noise?

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