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What materials block RF interference?

  1. Nov 30, 2008 #1
    My interest is in reducing RF interference in electric guitars in RF-noisy environments by shielding the body cavities with sheet metal.
    Would copper sheeting block RF?
    Or would it need to be some ferric material?
    I imagine aluminum alloy would be RF-transparent - is that true?
    Ideally, I would like some material that comes in thin flexible sheets and is easy to obtain.
    Any suggestions?
    Thank you in advance.
  2. jcsd
  3. Nov 30, 2008 #2
    Any conductive material will reduce stray RF interference. Depending on the frequency of the RF, the 'box' does not even need to be solid.

    See Faraday Cage: http://en.wikipedia.org/wiki/Faraday_cage" [Broken]
    Last edited by a moderator: May 3, 2017
  4. Dec 2, 2008 #3
    If you're just trying to filter the RF out of the audio then you could also use a RF filter circuit on the audio out line.
  5. Dec 2, 2008 #4


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    Stewart MacDonald Sells copper foil tape and conductive paint for that purpose. Make sure that your guitar's bridge is connected to the shielding, too.

  6. Dec 2, 2008 #5
    audio was never really my thing, but i don't think most of your noise will be coming from "stray RF". those frequencies are mostly too high for you to even hear. most of it should be directly coupled in from the AC power supplies (60 and 120Hz noise) and inductively and capacitively coupled to the system through cabling. things like ground loops may give you more grief than RF.
  7. Dec 2, 2008 #6
    I agree. See my other thread here about an AC problem I'm having in an audio circuit of my own. the interesting thing is that right now that project is a bare PC board on my desk, with long, untwisted wires (i.e. antennae) to the control and gain pots, running under flourescent lights. Doesn't get much more exposed than that. I get almost no observable audio noise at all, even with the gains maxed out. (I do get some strange rogue AC artifact injected, but that's a different issue...)
  8. Dec 2, 2008 #7


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    The noisiest bars that I played in usually had lights on dimmers. Turn those lights off or all the way up, and the interference went away. And yes, it was 60-120 cycle stuff that can get really grating, especially if you're using single-coil pickups. Grabbing a guitar equipped with humbuckers helped, but some of my favorite tones come from Gibson soap-bars and Strat single-coils.
  9. Dec 2, 2008 #8
    I have to disagree, I've done audio work before, I've heard line voltage and other noises in that range after amplification. The circuit for filtering it is pretty simple.
    Last edited: Dec 2, 2008
  10. Dec 2, 2008 #9
    What filter specs do you suggest? Ckt Diagram? Thx.
  11. Dec 2, 2008 #10
    Well there's two ways of doing it, with an IC, and with an Inductor.

    The schematic for the inductor style is at my school, I'll fetch it and post it up here. In the mean time here is a site that has several IC schematics.


    I suggest going with the inductor style, so much simpler.
  12. Dec 4, 2008 #11
    Thanks for the suggestion, but I'd rather BLOCK as much RF as possible rather than filter it out after it's been picked up. Also, I apologize but I was using "RF interference" rather sloppily to refer to any Electro-Magnetic Interference, which includes mains hum, which is 50 Hz here in Australia, so that makes it "audio-frequency RF" if you will forgive the apparent contradiction. And 50 Hz is well within the range of the notes output by a guitar, (I think a bass guitar goes down to about 12Hz) so a filter would be counter productive.
  13. Dec 4, 2008 #12
    That "copper foil tape" suggestion is a great idea. I'll give that a shot. Thank you.
  14. Dec 4, 2008 #13
    Ok, well then if it's in the 50Hz range then you'd be better trying to block it in the first place. Shielding the guitar would be a start, but if possible you might consider trying to also shield your amp and any other devices in the room, so less interference leaves the device.
  15. Dec 11, 2008 #14
    if the foil tape doesn't work then build this really simple circuit http://www.radio-electronics.com/info/circuits/opamp_notch_filter/opamp_notch_filter.php" [Broken] it even gives you the values to use for the capacitors and resistors to block 50Hz.
    Last edited by a moderator: May 3, 2017
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