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Is it possible to magnetically shield your tv

Discussion in 'Televisions' started by Karma, Sep 21, 2003.

  1. Karma

    Karma
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    Hi all

    Apologies for posting in two areas, but I'm not sure how much people read two disparate topic headings

    An unusual problem for which I hope any of your experiences may help.

    I have just upgraded my Hi Fi to have two power amps. The sound coming off these is now magnificent.

    However, the tranformers in the power amp induces hum in the pre amp. The answer is not to have a power amp on the shelf directly below the pre amp.

    I use a metal rack (Apollo) that has five vertical, audio width, shelves permanently linked to each side of a large central shelf which houses the TV.

    Now without spending LOTS of money on additional cables (a metre run has already cost £295 just to match the existing cables) to split the amps up further, it seemed possible, with a little jigging around of the gear to have one power amp under the TV.

    Unfortunately it has induced staining on the TV. Using the TV's de gaussing circuit clears it, but as soon as the amp is switched on, the staining (which pulses) re appears.

    I feel that constantly de gaussing the TV may have a detrimental efect on the power amp.

    Knee jerk reaction is to place a sheet of metal under the TV. Will this work?

    Or does anyone have any other ideas on how to shield the TV from the amp.

    The equipment arrangement on the shelves is as follows.

    Left side of rack (five shelves) top to bottom

    CD Transport
    DAC
    Pre amp
    CD Recorder
    Power amp (Main stereo speakers - HF & Mid)

    Centre of rack (three shelves)

    Centre speaker
    TV
    power amp (Main stereo speakers - bass)

    Right hand side of rack

    DVD
    laserdisc
    Sky +
    Av processor
    power amp (centre speaker and rears)

    Whilst the AV gear is nice to have, the system has been designed so that when the AV side is not in use, there is no link (and hence no compromise) to the audio quality of music replay.

    Any help would be gratefully received, before I bankrupt the household on a two further lengths of cable will I can now ill afford, as I was "pursuaded" to upgrade to the Denon 2900 at the same time.

    Thanks

    Karma
     
  2. groundy

    groundy
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    Unfortunately No, this will not work.

    You could take a look at this stuff - careful placement may create a barrier or sorts but I've never used it so can't say for sure:

    http://www.lessemf.com/mag-shld.html
     
  3. LV426

    LV426
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    Either

    move the equipment

    or

    buy a Plasma or LCD TV

    are the only safe and sure ways of preventing magnetic staining.
     
  4. nathan_silly

    nathan_silly
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    CRT RP's are less prone to magnetic fields than normal TV's. I've got three speakers, plus seven items with large torodials right next to the TV.... no geometry distortion or purple banding etc.
     
  5. LV426

    LV426
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    CRT RPTVS suffer magnetic interference differently to direct view CRT TVs. It does not cause staining on CRT RPs. It can, however cause convergence errors. Typically, however, CRT RPTVs have user adjustments for this so it can be adjusted out more readily than the staining on a direct view CRT.
     
  6. Garrett

    Garrett
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    There is one thing that will shield against magnetic fields and that is some material caled Mu Metal (pardon if the spelling is wrong).
    Unfortunately it is hard to track a supplier down and if you did it is a little on the expensive side. I think one of its main uses is in avionics for shielding flight control instruments.

    EDIT Ops Just clicked on groundys link.
     
  7. Chris Muriel

    Chris Muriel
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    Mu metal is indeed expensive.
    It is commonly used as a shield for the tube (CRT) in oscilliscopes.

    Chris Muriel, Manchester.
     
  8. Karma

    Karma
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    Thanks for the replies.

    I did investigate Groundys link. But as has been said, mumetal is expensive, and can offer no guarantee of success.

    Looks like the equipment has to move back around the rack, which will add a cost in cables, but will save the bank balance from a projector and screen.......

    .......... for the moment!

    Thanks again.

    Karma
     
  9. flibb

    flibb
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    Hello just a comment that might be of use.
    We use NMR scanners at work that are basically large electromagnet filled with liquid He and N2, these produce a strong enough field to grab objects like spanners etc and attach them to the can, also wipes credit cards etc. Placed within 5ft are two 21" sun monitors and the only protection for them is what appears to be a sheet of metal covering 5 sides. Take a look at this

    http://www.acornnmr.com/appnotes/shielding.htm

    amd

    http://www.jitterbox.com/

    Bit about making your own shielding is about half wasy down the 1st link

    Might help might not
    Jon
     
  10. porker

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    Magnetic fields cannot actually be blocked, there is no such thing as a magnetic insulator, magnetic field lines MUST terminate at the opposite pole.
    The way "shielding" works is by re-routing magnetic field lines to the opposite pole, so the material used to do this has to have high magnetic permeability.

    Crap shielding material with low permeability would be things like lead, copper, aluminium, tin, air.

    Good material to use iron, stainless steel, nickel.

    Although Mu-metal (an alloy of nickel & iron) is very good it is certainly not the only material you can use, why not try a sheet of steel, it will cost very little?

    Porker.
     
  11. porker

    porker
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    Sorry, I have just followed Flibb's link, that explains things pretty well.
     

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