Home studio - cable shielding?

Discussion in 'Recording/Live Sound' started by ajchance, Jan 29, 2012.

  1. ajchance

    ajchance Member

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    I searched for this topic and didn't find any suggestions specific to my need:

    I just added some KRK powered monitors to my system and am now having trouble with 60 cycle hum and obvious noise from my PC (the noise changes with screen changes from the computer). I'm running a very basic system with sound coming from the back of my computer's sound card, through a cheap mP3 extension cable (converted to RCA plug inputs), into a home stereo EQ, and into the monitors.

    I had some noise previously with my setup using an amplifier and Bose stereo speakers, but now it's significantly more pronounced.

    Troubleshooting so far:
    1. the cables from the EQ to the speakers don't seem to be the culprit - no noise if I unplug the input from the computer to the EQ
    2. Even though it sounds like it should be monitor related, when I turn off the monitor, I'm still getting exactly the same noise.

    My best guess is that I need some sort of shielded cable to run from my computer to the EQ. Any ideas?
     
  2. loudboy

    loudboy Member

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    It's from you computer's crappy soundcard - they're poorly shielded from the internal processer noise and this is typical.
     
  3. jb4674

    jb4674 Member

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    I agree. What kind of motherboard is it?
     
  4. LSchefman

    LSchefman Member

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    It also could be a ground loop. It may having nothing to do with the sound card or the shielding.
     
  5. '58Bassman

    '58Bassman Member

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    Is all of the equipment plugged into the same outlet strip and outlet? If they're on different outlets, it's probably a ground loop, caused by resistance on the wiring.
     
  6. LSchefman

    LSchefman Member

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    Ground loops can occur on the same outlet, if two pieces of gear have the wrong path to ground. The problem is often with the design of the equipment; some gear is not designed with sufficient attention to creating a solid grounding scheme, and this includes some expensive stuff.

    However, it's a very good idea to use the same outlet to eliminate that possibility when you're tracking down gremlins.

    Sometimes, one ground on a piece of gear needs to be isolated via an isolation transformer and that's the solution; sometimes, a ground needs to be lifted with something like a hum-x. Sometimes, a ground wire needs to be ADDED and attached to the chassis and an earth ground via a grounding block. Sometimes, lifting the shield on one end of a cable does the trick. And there are times when simply using nylon washers both front and back to isolate the chassis of your gear from metal rack rails and from each other does the job.

    You can use a ground lift adapter (GLA) - one of those 3>2 plugs TEMPORARILY to find which piece of equipment is causing a ground loop. But DO NOT leave it in place. When you find the offending piece of gear, deal with the loop in a safer way!!! If you do use a GLA to find the ground loop, what you do is unplug each piece of gear, one at a time, with everything else plugged in. TURN YOUR MONITORS OR HEADPHONES DOWN WHEN YOU UNPLUG EACH PIECE OF GEAR! LOUD POPS CAN MAKE YOU GO DEAF AND BLOW YOUR MONITORS. Then turn the monitors up, and see if the noise changes. When you have isolated the offending gear, you can then deal with it.

    There is lots of good info on ground loops on the web. A good place to start used to be the RANE website, as they had several technical papers on the subject at one point that could be downloaded. Rane tends to favor lifting the shield at one end, however, and that doesn't always solve the problem.

    Of course, as with guitar pedalboards, a good place to start eliminating noise is to move any wall warts far from signal cabling, as sometimes these will radiate noise into a system's signal.

    Hums and buzzes can be very difficult to track down, even with a tech and an oscilloscope. Back in ancient pre-software times, my studio had racks of hardware, and a 64 input console, and every time a new piece of gear was patched in, you'd start the whole procedure over again.

    Ground loops tend to pick up and recycle all kinds of hums and buzzes, from computer monitors, from lighting dimmers, and from nearby appliances. They can mimic all kinds of noises.

    Once you have moved any wall warts you may have, the place to start is to eliminate any ground loops. IF, with ground lifters, you find that you have no ground loops (which I doubt), THEN look at your sound card or other possible sources of noise.
     
    Last edited: Jan 29, 2012
  7. ajchance

    ajchance Member

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    Thanks for all the input! I'll address the ground loop issue first and try power the monitors via a different outlet. I thought that I had it hooked up that way, but I have a couple of power strips piggy-backed, so they are via the same hookup.

    The soundcard is hard-wired via my motherboard (which I can't remember the make). If the ground loop issue doesn't fix things, adding a better soundcard would be my next try.
     
  8. LSchefman

    LSchefman Member

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    Hang on, you don't want the monitors powered by a different outlet. You want them powered by the same outlet as everything else, if that's possible.

    I think I mentioned that it's a good thing to use the same power outlet.
     
  9. ajchance

    ajchance Member

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    Just re-read your post and missed a major tenet of your instructions. I'll do just that. Thanks again.
     
  10. ajchance

    ajchance Member

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    Bingo, we have a winner: Got lucky on the first try - I am powering the EQ and monitors via a power strip piggy-backed to the rest. I used one of the 2 prong adaptors to eliminate the ground and the noise is gone.

    Now to research the GL filters.

    Thanks again!
     
  11. LSchefman

    LSchefman Member

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    Excellent detective work! Now that you know it's a ground loop problem, it can be fixed using one of the many safe methods.
     
  12. headstack

    headstack Member

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    Excellent work cracking the ground loop!

    Les is a wealth of information, but you didn't hear it from me...

    Wouldn't want him mad at me when the phone starts ringing off the wall!:omg

    Happy New Year Les *wave*

    John Chase
     
  13. ajchance

    ajchance Member

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    The available knowledge on TGP never ceases to amaze me. I will have to admit that I'm in awe of Les and his 13k+ posts!
     
  14. LSchefman

    LSchefman Member

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    Well, ten years of posting here, and most of my posts are just BSing...

    I got a lucky strike on your question, that's all. ;)
     
  15. Motterpaul

    Motterpaul Tone is in the Ears

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    Funny...

    I have a ProTools system with a Digi 002 and I shocked when I realized the monitor feeds were analog (1/4" no less) rather than digital.

    Well, I just lost my home computer speakers so I borrowed my powered Roland monitors from my Protools system, and this computer has optical digital output. My home computer has GREAT sound now.
     
  16. headstack

    headstack Member

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    We know it's mostly BS, but the depth, resolution, psychoacoustic image and feel are truly top notch Les!:rotflmao

    Sincerely,

    Your crusty old brother in analog grudgingly turned digital...

    John Chase
     

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