Help! Ground Feedback? RFI? EMI? Monitor problems
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  1. #1
    Tech Wizard Bruiser Smith's Avatar
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    Default Help! Ground Feedback? RFI? EMI? Monitor problems



    Here is a video with sound so everyone can see what I am up against. There has always been a bit of a high-pitched noise from my monitors, but just recently it has increased exponentially (in both monitors).

    This happens every time I power on my VXT-6 studio monitors. I have tried a number of remedies that haven't worked:

    1. Changed power cord
    2. Plugged into different outlets in my house
    3. Unplugged other electronics that would cause interference

    First off, I can't tell if this is noise is actually ground loop feedback, radio frequency interference, or electromagnetic interference. However, since it seems to go away when plugged in at a friend's house, I can only assume that it's a problem with a ground loop? From my understanding ground loops typically have a low-pitched hum, rather than a high pitched whine like this.

    What gives me hope is that these have sounded great in other people's houses, and so I am aware that this is most likely specific to my electrical system. I am considering purchasing a Tripp Lite ISOBAR for surge protection as well as possible power conditioning. If anyone has any experience with these as far as in a studio environment I would like to hear about it.

    If anyone can offer any suggestions regarding this, I would really appreciate it!

  2. #2
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    So I've experienced this issue and there are a couple of things you can try:
    If this is a grounding issue
    1) look into getting a 'power conditioner' power strip (there is a possibility you've got 'dirty power' in your house, and that is giving you the feedback (this is expensive to fix when it comes to changing the wiring of your home)
    2) Follow me on this one, get 2 new power cords for your monitors (then break off the ground prong on both). I know it sounds crazy, but I had the same issue, and this solved it right away!!

    If it's not a ground issue.
    3) do you have anything in your setup that is analog? For instance I have a turntable amplifier that my Technics 1200 is plugged into, and then that goes into my Saffire, Audio interface. Whenever it's actually plugged in, I get feedback/interference. This is sometimes more of a high-pitched feedback, but I can (at times) hear an audio signal (possibly radio, tv, who knows!?)

    Try those things and see what you get. I feel your pain though, I actually bought 2 new sets of monitors, moved my setup to 2 different places in the house, and had an electrician come out and give me an estimate on getting a dedicated grounded outlet (which was astronomical). I did all of that before trying the breaking off of the grounding prong on my monitor power cords. That worked like a charm. I hope this helps!!

    ** I said to get 2 new chords, in case you (for some reason) need/ want to go back to the cords with ground plugs
    Last edited by complete93; 11-24-2012 at 12:54 AM.

  3. #3
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    Typically ground loop manifest themselves by low freq noise. It is usually a 60HZ freq. Your noise is high freq around 2KHZ or higher. What changed in your system recently? Any chance you added a turntable or started using Traktor or Serato with your turntable? It sounds like the same 2.5Khz tone that comes off the control vinyl.

  4. #4
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    First, for crying out loud, don't ever cut the ground pin from your cords. - Jeebus.
    If it is a ground loop, plugging everything into a single grounded power strip or the same outlet should eliminate this. Also, try swapping your interconnects with a known good pair. Sounds like AC line noise, though. Perhaps your interconnects are lying across a power supply for another device or a video monitor?

  5. #5
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    That is a ground loop. Full stop. It's not AC line noise, which is the low frequency noise that DJ Aaron is associating with ground noise. Listen to it here... http://en.wikipedia.org/wiki/Mains_hum

    Bruiser, go to a Home Depot or other hardware store and buy a gray 3 to 2 prong adapter. It should cost about a dollar, and it will keep you from cutting the grounds off your cords. Set everything up and plug the adapter into one grounded device at a time, starting with your computer mains cable (if it's grounded). Remember to have your volumes turned down and power off between plugging so there are no pops.

    When the noise stops, you've found your ground loop. Now you can address the issue a couple different ways. You should first try plugging everything into a decent power strip INSTEAD of different outlets (as HigherFi suggested). If that works, you're done. If not, then you have a few options. My favorite way to kill ground loops is with an Ebtech HumX. Great little device. http://www.ebtechaudio.com/humxdes.html Super handy, and it MAINTAINS GROUND, so you'e still being safe. You can also address the ground through the USB connection with this... http://electronics-shop.dk/galvanically-usb_isolation This has the same kind of galvanic isolation that's built into the Rane audio interfaces. Also very handy.

    Both of those address ground issues without interfering with the audio signal path. That's preferable, but it's also more expensive. You can also use these... http://www.radioshack.com/product/in...ductId=2062214 and go the cheap route. But know that your audio quality will suffer slightly. You can also use a line lever DI box that has a ground lift (like http://www.seismicaudiospeakers.com/...FYF7Qgod_RIAQg ) .

    Now go fix your stuff.

  6. #6
    Tech Wizard Bruiser Smith's Avatar
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    First off, thank you everyone for all of the suggestions. I forgot to mention in my first post that I had already tried the 3-2 prong adapter but that didn't change anything as I only used it with the speakers themselves. I also tried plugging into different outlets throughout the house, as well as testing connections by killing my breakers one by one to see if that changed anything. I didn't think though to use the adapter to test everything else though, and so I will do that next. I will keep you guys posted as to what I find.

    I've been looking at ways to kill ground feedback easily and was looking for something that would be easy to use. I also have a bunch of stuff plugged into my power strips in my studio/office, and was looking into possibly getting a rack power distributor/conditioner by somebody like Tripp Lite, APC, or Monster (yes, I'm aware that they make overpriced cables but I like their PDUs and have read a lot of bad things about Furman's) just so it looks relatively nice. I'll keep the HumX in mind though! I don't think that my issue is with USB ground as the speakers have this issue with only the power cords plugged into it rather than any audio coming from the computer.

    Just another note - I've also read about this model of monitor being particularly sensitive to RFI, but at this point I am not willing to open them up and shield them from the inside just yet.

    Also, as a side note, I'm not using anything analog in my setup. No turntables - just a DN-X1600 and an ipad (and the noise was there before I got the mixer).

  7. #7
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    Just another note - I've also read about this model of monitor being particularly sensitive to RFI, but at this point I am not willing to open them up and shield them from the inside just yet.
    If you want to take a look at the insides of those KRK VXTs, the backplate is easily removed. But this isn't an RFI issue. If you had your cellphone right on them, then maybe. But it would sound different.

    If you plug one of the speakers into the wall and don't attach any of the signal wires (so it's just the mains cable), is it still making that sound? Also, with your existing connection, does the "chatter" that's mixed with the high pitch tone correspond to hard drive access or mouse activity?

    EDIT - Please also understand that power conditioning stuff like an ISOBAR or a JuiceGoose won't necessarily fix your problem. But if you get a HumX, you can use it at the end of a power strip and plug multiple things into that power strip and it will all play nicely.

  8. #8
    Tech Wizard Bruiser Smith's Avatar
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    Quote Originally Posted by nem0nic View Post
    If you plug one of the speakers into the wall and don't attach any of the signal wires (so it's just the mains cable), is it still making that sound? Also, with your existing connection, does the "chatter" that's mixed with the high pitch tone correspond to hard drive access or mouse activity?
    That's how they were when I shot the video - no other cord connected other than power. The chatter has always been there although it may have something to do with the wireless router maybe? However, from what I can tell it doesn't correspond to a hard drive access or mouse activity.
    Quote Originally Posted by nem0nic View Post
    EDIT - Please also understand that power conditioning stuff like an ISOBAR or a JuiceGoose won't necessarily fix your problem. But if you get a HumX, you can use it at the end of a power strip and plug multiple things into that power strip and it will all play nicely.
    O sure. I know that these may not necessarily do anything. I was reading about the ISOBAR having noise reduction and for my setup just thought it would look nicer than a power strip with everything plugged into it. But I understand that depending on what you get it can basically be a glorified power strip and nothing more, although what I have found is that there are at least a few reputable manufacturers. I've also been doing a bit of research regarding power conditioner units such as these.

    I think I'll just need to start testing by trial & error and see if I can find out where the problem lies, and then go from there. If it were a ground issue, though, any idea if killing the breakers for whatever was making the noise resolve it (such that no power in means no grounding to be done)?

  9. #9
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    OK that changes things quite a bit. If these aren't connected via audio and only plugged into power, and you're still getting that sound - but only at your house - then it may very well be an RFI issue. But I've never heard of such a nasty case as yours. Do you have any transmitters close to the speakers? Does the chatter correspond to data transfer for example? Do you have a MiFi in your house, or wireless speaker system?

    Also, to eliminate the possibility of your ground being corrupted, have you tried the 3 to 2 adapter on a single speaker's power cord?

  10. #10
    Tech Guru antifmradio's Avatar
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    would you believe i spent 4 years trying to find out where this same noise was coming from in my home dj setup

    and when my monitor died, so did the noise?!!

    i was from the monitor attached to my desktop..


    point im making is,
    You can try removing one dj piece at a time but yuo can also try actually unplugging things from yuor computer

    in my case i needed to detach the monitor
    in your case, you can also try removing anything else connected to your laptop (external, change the power strip) dude really
    i mean ANYTHING is game

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