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Crackle Through USB Audio Devices When Plugged In To External Power

Discussion in 'Computer Audio' started by collinc, Jan 20, 2015.
  1. CollinC
    So first off, I have a Dell Inspiron 15 3542. I got this second hand from an acquaintance for basically nothing without the HDD. I use a UCA202 USB running to a UB1202 mixer , and acts the same way with my Xenyx 302USB mixer (haven't tested mic interference, nor care to; what matters is it has the same sound) with different cables. So when I plug in the power, even without a battery in the laptop, there is a loud crackling interference that changes when both the mouse or touchpad moves the cursor around and such (the mouse is not causing any issues, so it's out of the question). When running direct output to my headphones (HD439) and monitors (HR824), I can hear it more when I turn it louder. Now, when I run it to a Lexicon MPX 100 processor just as volume control for the monitors, it has the same amount of static going to the output, no matter what i do on the board. It's as if the board is cranked to max volume, but it's turn all the way down. The noise is also in my mic inputs no matter the volume. All this happens when I run the power form a Dell power adapter. I have two of the same, and both give the same results. It's a 90w-AC brick adapter that sends 19.5v 4.62A(4,62A) DC. So I'm very confused. Any of you sound engineers know how to get rid of this? I have a feeling this has something to do with grounding from what I've read, but I'm still VERY confused.
  2. dmbr
    This might help:

  3. CollinC
    Anything that wouldn't cost the same as 3 of my USB device?
    Also, note that it does the same thing with all USB ports.
  4. cdsa35000
    First power the laptop with the battery only, noise should be gone because the mains and the usb earths line is causing groundloop.

    Then power the laptop with the DC adapter and then connect 1 usb device only uca202 or 302usb and hear which usb is causing the noise.

    Either lift the earth/ground pin of the powerbrick plug or cut the USB cable shielding to get rid or the ground loop.
    You can use a usb extention cable or test with different usb cables, maybe some cable don't have the usb shielding connected to usb ground.



  5. CollinC
    I was thinking about cutting the ground off, but if there was a power surge, could it fry my laptop?
  6. cdsa35000

    Buy groundlifted powerplug dongle or buy usb extension cable or usb hub then cut the shield cable.
    Read this:
  7. cdsa35000
    THIS is posible mistake also, check it:
    Common TOO small audio buffersize mistake cause:
    If you hear clicks & pops during playback, try to adjust Audio Buffer Size somewhere in the config settings.
  8. CollinC
    As a quick fix, I think I'll just cut off the ground pin from the cable, or pick up a cheater plug. I've never had a power surge in the 16 years I've been at this house, and I'll buy a piece of gear the really fix the grounding loop. Thanks a ton!

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