Headphone Amp Ground Loop Buzz/Hum

Discussion in 'Computer Audio' started by GCTonyHawk7, Mar 26, 2008.

  1. GCTonyHawk7

    GCTonyHawk7 Limp Gawd

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    Hey guys. I recently ordered the ibasso P2. (http://www.ibasso.com/ShowProduct.aspx?ID=37) The device works great, although I've got one rather major issue with it.

    One reason I bought the P2 was because it came with the AC adapter to plug it into the wall. I don't want to use it as a portable device, and just want it to sit at my computer.

    [​IMG]

    Hooked up to my PC's sound card is a set of Logitech Z5500 speakers. These have a headphone port on the control center. I simply plug the P2 into that headphone port, plug the AC into the wall, and then plug my headphones into the P2. Seems like it should work and be great. Cuts power to the speakers, sends it to the headphones, and this works.

    The catch here is something I never knew about; ground loop. Apparently, because the speakers/computer/P2 are all plugged into the same power grounding, it creates some crazy electrical loop and this loop creates something called mains hum. This hum/buzz can be heard clearly in my headphones when using this setup. To solve this, unplug the AC adapter to the P2, and boom, gone.

    Now, this in turn means, it works fine with portable devices, like you'd think. iPod, PSP, DS, they all work fine without this issue. But I bought this for my desktop. Yes, sure, I could just charge it, use it, and then charge it again, but I did not pay $157 for an amp to have an inconvenience like that. I want to plug it into the wall, and not have to worry about that. Not to mention charging it like that all the time wears out the battery so it won't be any good for when I do want to use it portably.

    So, in the end, I am looking for a fix. I know I can buy some $80-100 power strips that create their own ground. Don't want to spend that much. Yes, I know there are devices like the following:

    PAC SNI-1/3.5 Noise Filter Helps eliminate ground loop noise from your portable music player! (3.5mm plugs) at Crutchfield.com

    Although, I fear that could alter sound quality, and again is nearly $30 shipped.

    I figure that you guys, with all your experience with this stuff have found ways to solve this. Any way to power the amp over USB? (It is a 12V DC Adapter)

    Thank you to anyone that can provide some incite.

    Various Info:

    - P2 uses a built-in 8.4V 470mAh Li-polymer Batteries or external power
    - External power supply: 12V DC
    - Battery Life: 11 hours
    - Battery Charge time: 3 hours
    - Both the Z5500 and the Headphone amp use a two-prong power adapter, so there are no grounding rods involved
    - The same thing happens when I plug my P2 directly into my computer, maybe it is the original source of the buzz/hum?
     
  2. sdgserv

    sdgserv [H]ard|Gawd

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    I know this is going to sound stupid..I had the same problem.
    On one side of the my wall is a set of outlets, they are connected different than the other side..Meaning in the fuse box. I just changed to a different outlet.
    and no more What the H**L is that noise
     
  3. GCTonyHawk7

    GCTonyHawk7 Limp Gawd

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    Tried all the outlets in my room, no luck. They are all connected to the same fuse. It would be stupid to run extension cords all the way down the hallway and your excuse to everyone else is; it is for my headphones. :-\

    Anyone else have ideas?
     
  4. Xyrax

    Xyrax Limp Gawd

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    Does touching the chassis of the amp weaken the hum or eliminate it (unless the chassis is plastic but the pics of that amp look like an alluminum chassis)?

    The reason unplugging the AC adapter eliminates it is because "mains hum" refers to the mains power (another word for the home outlet power is "mains" power). In the US, the AC power oscilates at 60 Hz so what you're hearing is that 60 Hz hum/buzz somehow "leaking" into your audio. Since unplugging the adapter removes the "mains" power source you no longer hear the hum.

    Antoher possibility is the ac adapter may be defective or have poor filtering.
     
  5. GCTonyHawk7

    GCTonyHawk7 Limp Gawd

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    Touching and moving the amp does nothing. Not sure if it is aluminum, but it is all metal.

    You're right, I still don't full understand the ground loop, but that i what I've read. I know it isn't the AC adapter, because playing my ipod with the P2 plugged in has no hum. So, it is for sure because of the loop.

    Any suggestions?
     
  6. Xyrax

    Xyrax Limp Gawd

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    What if you place one hand on the amps chassis and the other on your PC chassis? Try to bring both devices to a common ground level. Doing this will most likely not eliminate the hum but if it weakens it or alters it then it'll provide a starting point on finding a fix.
     
  7. GCTonyHawk7

    GCTonyHawk7 Limp Gawd

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    No go, didn't do anything. Hmmmm. :(
     
  8. Xyrax

    Xyrax Limp Gawd

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    Well my ground loop knowledge is limited and there isn't much more I can think of. If you don't get anymore answers here you may want to try heading over to the head-fi.org forums. The people that frequent the DIY forum deal with grounding issues all the time since they do alot of designing and building of audio components.