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Old 18th June 2013, 04:19 PM   #1
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Default mU-METAL GOOD SOURCE AT DECENT PRICE...searching desperately....

HIall,
I want purchase some MU-METAL for shielding my phono cables and phono chassis and maybe also all the "REST".

I want know a good source of layer or "band" as like as "scotch", possibily in EUROPE.

thanks for reading

Paolo VENEZIA ITALY
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Old 18th June 2013, 05:19 PM   #2
DF96 is offline DF96  England
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Do you have facilities for re-annealing it after bending or drilling?
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Old 18th June 2013, 05:25 PM   #3
jcx is offline jcx  United States
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Default mu metal is over-hyped

hobbyists have little need for mu metal shielding - usually don't understand the real problem(s) and most won't know how to apply mu metal if needed in the correct manner

I have designed scientific and industrial instrumentation professionally - gains up to 4000 in strain gage amplifiers, 50+ ft cable runs to sensors - and I have never used mu metal in any instrument design

even in phono pickups twisted pair in the arm to RCA phono coax is normally all that is used - hum/buzz is more likely to enter as ground loop noise than to be introduced from magnetic field coupling to the signal wire's internal loop area in home environments

and “ground loop noise” is often chassis leakage currents flowing in common “ground reference” impedances – not so much power frequency magnetic coupling

twisting, star quad, coax all reduce magnetic field coupling - both radiation and pickup - so applying these to both power/motor wiring "threats" and to sensitive signals works fine in most cases - in the extreme wiring can be ran in steel conduit - not too handy for phonograph wiring


I have used welded corner steel boxes with EMI gasketing to house the amplifier circuitry, tinned steel internal shielding boxes around uC, DSP within inches of those Av 4000 strain gage amp circuits

but I never needed mu metal - never seen it used except in extreme low level signal transformers or RF tunning inductor housings

Last edited by jcx; 18th June 2013 at 05:39 PM.
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Old 18th June 2013, 06:24 PM   #4
dmills is offline dmills  United Kingdom
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Seconded, mu metal is a pain to deal with, and must be annealed after any bending, you will not find it as a tape!

At audio frequencies, tight twisting is actually far more important then screening as far as magnetic coupling is concerned, and I would put the gram amp inside the plinth of the record deck and export low Z line level rather then worrying about exotic pain in the **** materials.

Regards, Dan.
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Old 18th June 2013, 07:37 PM   #5
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On Ebay its easy to find mumetal ( german for sure)

Maybe you can use also amorphous tapes. Although very thin and less shielding effect then mumetal it needs no anealling after bending.

Last edited by esltransformer; 18th June 2013 at 07:39 PM.
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Old 18th June 2013, 08:09 PM   #6
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Percy sells something called TI shield which is supposed to have magnetic and EMI shielding
http://www.percyaudio.com/Catalog.pdf

BTW, an easy way to perform a relative magnetic field measurement is to use a compass, and see how much deflection of the compass there is. The stronger the magnetic fields, the more the compass will deflect from north.
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Old 18th June 2013, 08:28 PM   #7
qusp is offline qusp  Australia
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you could make a nice mu-metal foil hat!, might be more appropriate? sorry just joking around, but as jcx said, its simply not needed in any audio design and chances are if you have enough interference problems that you are considering it, the mu wont fix it anyway.
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Old 18th June 2013, 08:53 PM   #8
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I have used mu metal to wrap toroid transformers, not sure if it helped but I seem to recall I slept better that night. I noticed on some plastic cases with digital equipment inside they spray a copper paint on the inside of the case and tie it to ground, I wonder if that paint can be purchased? Also is it worth the trouble for a Dac?

Bill
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Old 18th June 2013, 09:16 PM   #9
dmills is offline dmills  United Kingdom
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The conductive paint is actually mostly an RFI measure usually aimed more at radiated emissions control then anything and is a cheap fix late in the design process when you realise you will not meet the emissions limits for FCC/CE approval in a plastic box.

Nickel is somewhat more common then copper as a metal to load a conductive paint, but really, neither is particularly relevant to audio outside of very specific circumstances (Like say guitar control cavities).

Note that at low frequency (and all audio is nearly DC for this purpose), a thin copper screen is only effective against electric fields, it does little or nothing for magnetic induction, for that only reducing the loop areas, or going for a rather large and heavy hi mu material, helps.
The loop areas are easy to reduce, so that is always the first thing to try, and it almost always solves the problem.

Regards, Dan.
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Old 18th June 2013, 09:23 PM   #10
jcx is offline jcx  United States
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mu metal saturates at very low H - up close to a power transformer it is useless

if you really must shield against magnetic field you should 1st use cheap Iron - low carbon steel - lower initial perm but is so cheap you can use mm thickness to handle much more flux

wrapping with tape would be wrong too - spacing mag shielding from the source is good - air is poor magnetic field conductor and even a little spacing add lots of reluctance to the magnetic circuit == reduced flux in the shield compared to little or no air gap with conforming tape

old school OEM power supplies used mm thick perforated steel boxes to allow air flow for transformer cooling and contain the EI transformer's leakage, rectifier/C charging current loop flux

any conductive material, surface coating << 1 Ohm/sq will be an effective electrostatic shield and reflect RF, EMI wavelengths shorter than the skin depth
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