Noise traveling through power circuits

Discussion in 'Recording/Live Sound' started by ari, Feb 24, 2006.


  1. ari

    ari Member

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    I need an affordable solution for cleaning up my power supply. My monitor is constantly buzzing, and I can hear other things plugged into the circuit -- for example, when the washing machine is going, the monitor has a buzz corresponding to the washer's spin cycle. :eek: My laptop's power supply also sends out hard drive noise into the circuit as well.

    Any good power conditioner/filters that can solve this problem? Ideally for <$100?

    Thanks!

    ari
     
  2. LSchefman

    LSchefman Supporting Member

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    First off, sadly, there are no cheap conditioners that will solve this problem; in fact, some expensive ones won't, until you get to the level of an isolation transformer, and that costs a bunch (I have one, I have been around the block on this stuff).

    However, there are two fixes:

    1. If it's an AC problem, a dedicated line can be installed by an electrician for not a ton of money.

    2. You probably don't have an AC problem, you probably have a ground loop problem - ground loops can pick up all kinds of noise, such as hard drive noise, and even electromechanical noise from appliances.

    The clue in your case is that you say your monitors always buzz. If they buzz when the appliance isn't running, and when you shut down your hard drive, I think your problem is a ground loop.

    It is not difficult to solve a ground loop problem, but it is fairly time consuming if you have a lot of gear.

    There are lots of resources on the web, Rane's website has stuff on solving cable-caused loops, but you can also solve some ground loops by running a central inexpensive grounding block to your board's power supply, and then experimenting with running smaller ground wires to the chassis of certain pieces of gear. And sometimes rack rails cause loops, and there are fixes for those as well.

    You can discover the cause of loops by simply unplugging one piece of gear at a time, and seeing if the hums and buzzes stop or are reduced. I do this with headphones on, so that I can check if there are hums and buzzes associated with the monitors and unlpug them (or their power amp). If a hum stops or is reduced when you unplug, that piece of equipment has a ground loop, and you need to apply a fix to it, and move on to the next piece of gear until all the hums and buzzes are gone. When you replug the offending piece of gear in, TEMPORARILY use a 3 into 2 plug adapter (get em at radio shack), and do this to identify further problems. Often more than one piece of gear is creating a loop, and you want everything plugged in for each test.

    I don't have a single hum or buzz in my studio, but it took me a lot of experimenting to get things to what I consider a quiet level, and I even went to the trouble of installing balanced power throughout my studio.
     
  3. ari

    ari Member

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    Les, thanks for pitching in. What you're saying makes sense. It's probably a ground loop.

    Now, assuming it's a ground loop problem, I was wondering if something like this (http://www.ebtechaudio.com/new.html) can solve the problem. All I need to do is to isolate the monitors so I won't hear any noise that's running in the circuit (though I've been reading about how excessive line noise can cause computers and A/D/A converters to perform poorly).

    What about power conditioners from likes of Furman and Monster Cable? Don't they claim to have RF filter/isolation? Do they do anything?

    Thanks again.

    ari
     
  4. zenpicker

    zenpicker Member

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    I've got a Monster and it helped some in a rural house where I sometimes record, but the problem there was different--bad wiring causing a lot of just plain static and crosstalk on the line. This was improved by the Monster for sure. Think I paid something like $60 for it, if memory serves. Of course, it's no sub for a real power conditioner, but as Les says that's a lot of dinero.

    Also, computer monitors do add hum, although laptop LCDs can have their own problems. Don't know if you're on a laptop, but sitting here at my desk I have a laptop connected to a nice big flat-screen monitor and also to my two Behringer Truth studio monitors (via a TurtleAdvantage USB audio plugin). If I switch the display to the flat screen alone and run off battery, it's pretty darn quiet. If I activate the laptop's screen it gets noisier. If I then plug in the laptop it's almost intolerable, with the greatest buzz being, without a doubt, from the laptop's own power circuit. So, it depends on your gear and who's connected to what.
     
  5. LSchefman

    LSchefman Supporting Member

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    The Ebtech plug can lift the grounds; you might want to test the system out with the much cheaper adapters, and then go to the Ebtechs for your permanent solution. That way you only need to buy as many as necessary.

    Power conditioners don't solve ground loops. All they do is filter out electromagnetic and radio frequency interference, and some of them also regulate the AC voltage. Voltage regulation is good for computers, by the way.

    A balanced power isolation transformer will operate to lower system noise, but is unlikely to solve ground loops. It lowers system noise like a balanced cable does, by inverting the polarity of one leg of the AC line, which cancels out AC-induced noise, especially when signal cables and power cords are close together. The noise in my system was reduced by about 6db, which is significant, when I made the switch to balanced power. My transformer is a 2 Kilovolt Sola isolation transformer my tech modified, but you can buy premade systems from Furman and other companies.
     
  6. LSchefman

    LSchefman Supporting Member

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    >>If I then plug in the laptop it's almost intolerable, with the greatest buzz being, without a doubt, from the laptop's own power circuit.<<

    If it makes more noise when you plug the computer in, you have a ground loop, though it's possible that your computer power adapter is adjacent to signal cables and generating additional noise. This is a perfect example of a power conditioner being ineffective against ground loop problems, and also being pretty ineffective against electromagnetic/rfi interference generated by wallwarts, etc. Kinda tells you something about the limitations of these power conditioners!

    What the Monster solved was typical radio frequency or electromagnetic interference, and these boxes do a fine job on that.

    However, it won't solve serious AC noise problems that aren't EMI and RFI, such as those generated by big appliances or nearby power lines, and it certainly won't cure a ground loop, as you can see.
     

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