Laptop grounding question

Discussion in 'OT Technology' started by ia_cox, Feb 20, 2007.

  1. ia_cox

    ia_cox Active Member

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    I have a Dell 9300 laptop, about a year and a half old, and I've noticed that when I have it plugged into a stereo, when the power supply is also plugged in, there's a lot of noise with the audio signal, like processor/fan noise or w/e. But I've learned that if I lift the ground on the power supply all that noise goes away. I don't really know why it does that, but i've been doing it pretty much since I've had the computer. I know desktops need to be properly grounded, but amd I fucking myself over with the laptop by leaving it ungrounded, since it runs off of DC power?:wavey:
     
  2. deusexaethera

    deusexaethera OT Supporter

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    When you lift the ground on the power supply...huh? Isn't the power supply grounded via the plug in the wall?

    As far as grounding goes in general, all connected devices must be connected to a common ground for best (and safest) operation. Professional audio patch cables, for example, use the standard 1/4" stereo headphone plug, but instead of using the third conductor to transmit a second channel of sound, they use the third conductor to connect the ground plates of the two devices being patched.
     
  3. ia_cox

    ia_cox Active Member

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    yes, but I put an adapter on the power supply (one of those gray ones) that lifts the ground before it gets into the wall. I know about TRS cables, just I have never seen them for home audio equipment. The amp I'm using isn't grounded at all; maybe I'm getting a loop going from that? Though it doesn't really sound like a ground loop; the noise is much more noticible when the processor is doing something (maxamizing a window, starting a program) which makes me think what I'm hearing is internal noise.
     
  4. deusexaethera

    deusexaethera OT Supporter

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    Using onboard audio, it's certainly possible that the signal is getting messed up by EMI created by other circuits on the motherboard. Are you using Headphone Out or Line Out? If you have the option to use Line Out, you should. Also, make sure that your stereo is powered by the same circuit as your laptop; otherwise there is the potential to have a ground voltage differential that can damage your equipment, white noise or no white noise.

    Ah, you know the right term for those kinds of 1/4" plugs -- very nice. I've never seen them for home audio either, but they're widely used in prosumer audio and recording.
     
  5. ia_cox

    ia_cox Active Member

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    ok, but why does the noise go away when i unground the computer?
     
  6. ia_cox

    ia_cox Active Member

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    and am I screwing my computer over leaving it ungrounded?
     
  7. dorkultra

    dorkultra OT's resident crohns dude OT Supporter

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    grounding is there for a reason, you should try getting cleaner power (UPS) or isolating the laptop power supply from the stereo (plug it into another outlet)
     
  8. deusexaethera

    deusexaethera OT Supporter

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    I'm pretty sure I just said that it's a bad idea to run his laptop from a different outlet than his stereo. Ground voltage differentials can do a lot of damage to electronics.

    Anyway, I doubt that it will do much harm to your laptop's power supply to disconnect the emergency ground (the third prong) because the only difference between the third prong and the second prong (the larger flat prong) is their shape -- they still both connect to a metal rod stuck into the ground behind your house. The emergency ground is really only there to catch electricity that gets drained into the metal casing of a device -- since the power transformer doesn't have a metal casing, the emergency ground will only do any good if the second prong on the wall outlet fails.

    If all else fails, you can always buy a Sound Blaster Extigy and use that to pipe music from your laptop to your stereo.
     
  9. ia_cox

    ia_cox Active Member

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    but why should grounding have anything to do with a laptop that's running off of DC battery power? The farthest i can tell is the grounding prong grounds the adapter, but now the computer. My computer's power supply has only two conductors (+,-) coming from the AC --> DC adapter, so the ground is not reaching the computer at all. But I'm still curious as to why lifting the ground on the power supply DOES make less noise in the system. Becuase like I said, I'm not picking up the abnormal frequencies from the grid, I'm getting processor/HD/fan noise from inside the computer. But it goes away when the ground is gone.

    o well, I've answered my own question at least as to if I'm frying my computer or not.
     
  10. ia_cox

    ia_cox Active Member

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    Viginia might wire up differently then we do here...both our grounds and neutrals typically go to a common bar in the Q/O panal and then to the common on the transformer. I can't see the neutral entering the ground...isn't that dangerous?

    Anyway, like I had said, the stereo is just a common houshold stereo that't not grounded, so there's really no way to get a loop going anway. I'm fine just living with it; if I were using this computer for more intense audio applications (like DJing) I'd definately look into an outboard card. However I don't need to spend something like that just for personal use.
     
  11. deusexaethera

    deusexaethera OT Supporter

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    You could still damage your equipment by not using the AC adaptor. You see, the AC ground still affects the DC voltage's neutrality -- that is to say, compared to the stereo's ground voltage, the terminals on your laptop battery could be +8V / -6V instead of +7V / -7V (or some other values of the sort). The difference in "0V" between your laptop and the stereo will still cause current bleed through your audio cable, whether or not you can hear it -- and I'm guessing either your stereo or your laptop doesn't like dealing with that.
     
    Last edited: Feb 21, 2007
  12. ia_cox

    ia_cox Active Member

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    ok, so live with the noise and keep it grounded? or buy an isolation transformer to put in the line from the computer to the stereo? or case ground the stereo to the outlet? I see you're in IT so I'm not going to argue too much; I've had plenty of experience with grounding and ground loops in theater audio systems, but I've never really gotten into the effects dirty power and grounding has on computers.
     
  13. P07r0457

    P07r0457 New Member

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    light pipe ftmfw!
     
  14. deusexaethera

    deusexaethera OT Supporter

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    First of all, your stereo's outer shell is almost certainly already grounded -- the issue is that the laptop isn't, thus causing the GVD. As such, you could be passing (relatively) substantial wattage through circuits not designed to handle it for long periods of time, roughly the equivalent of blasting the audio signal through at full volume constantly.

    The free option would be to change the power management settings on your laptop so you can plug it into the AC without it switching to full power mode and forcing the fan to turn on. Failing that, I'd go with the isolation transformer. It's a clean solution that you'll be able to use for the rest of your life, so long as adaptor plugs are available for whatever future stereo connections come along.

    Fiber cable is certainly an attractive option, but it requires that both ends have SPDIF hookups; they're pretty common on stereos now, but not so much on laptops. If you wanted to go that route, there's a company called Xitel that makes basic USB-driven sound cards with a single fiber cable socket -- I used to use one to copy music to my MiniDisc player, and all I can say is it made the player's already clear sound even better.
     
    Last edited: Feb 21, 2007
  15. ia_cox

    ia_cox Active Member

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    yet if I were to ground the computer I'd have a much noiser signal. It's not the 60Hz AC hum, it's not a steady hum at all. When the computer's grounded it's a very high frequency noise that comes in short bursts, usually when putting the computer under load. When the ground is lifted the noise is still there but is much quieter. I have noticed this while wearing headphones as well, so I don't think it has to do with different potential between the two devices. Whatever, it may be just something particular to Dells. my roommate has an HP and doesn't have problems and I know macs are pretty quiet when comes to audio as well
     
  16. deusexaethera

    deusexaethera OT Supporter

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    Then all I can think of is there's EMI inside the case when the computer is under load. That's the problem with Dells -- they always cut corners in places you don't notice until the warranty expires.
     
  17. P07r0457

    P07r0457 New Member

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    Dell *used* to be great. I had a 433/L that was amazing... That thing had a steel chasis with copper paint sprayed on the inside -- a very effective faraday cage. Unfortunatly, they are now among the worst on the market.
     
  18. ia_cox

    ia_cox Active Member

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    I have extended warranty with this POS, but I doubt it would do any good in this example since it is a design flaw and not necessarily something "wrong" with the machine. O well, I didnt' buy this to be a media center computer, I bought it for gaming and for programming, which it has held up very well for. I was just more curious as to why it does what it does and if I'm fuckin myself over with it
     

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