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Old 18th June 2013, 09:58 PM   #11
diyAudio Member
 
Join Date: Feb 2007
Location: HICKSVILLE TN
lead!!! thankfully working near nuclear reactor we have an abundant supply of lead sheets

or copper al tape.. or both

byt the one who said he never need to shield 4000 gain instruments never had a Grado MM cartridge on an AR turntable either!!!
you either sheld it or it hums..period!!!
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Old 21st June 2013, 04:12 PM   #12
dmills is online now dmills  United Kingdom
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Join Date: Aug 2008
Location: High Wycombe
Lead is fairly horrible for EM screening, being a poor conductor compared to copper.
It is obviously useful against charged particle and EM once the photon energy gets up where you can reasonably talk of photons as opposed to EM waves.
Its one desirable feature is that it is dense making it good at stopping alpha and beta particles and reasonably effective against X ray and gamma, it does little against fast neutrons.

However for a gram amp we are probably not too concerned with stopping the gamma photons, as if there is much of that floating aroud the correct answer is to put down the records and leave the area rapidly.

Copper is what you want for electrostatic screening, with steel (Ideally a high carbon type) being useful for screening stray magnetic fields (Which are almost always the bigger problem to deal with).

73 Dan.
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Old 23rd June 2013, 03:42 PM   #13
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Join Date: Aug 2004
Location: Italy
HI alls,
and thanks for precious suggestiuons from you , very expert technician.
But I remember to have seen a phono MC by KRELL, wich had the internal of all walls with a thin lajer of mu-metal.
And Mr. D'Agostino have said that the effect was little but audible .
So I have decided to try for myself in my DIY phono MC Hiraga preamplifer.....
Hope the cost will not be phroibitive for me.

So, skepticallysm apart, that i can understand, I search one kind person who show to me a good place where I can buy some thin lajers and long band ( as like scotch, I intend) to make my personal tests.

thanks for the helps, very appreciated,

Paolo,
Venezia - italy
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Old 17th February 2014, 11:47 AM   #14
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Join Date: Dec 2011
I realise that this thread is a little old now but it is very relevant to a problem I am currently trying to solve. I am working on a valve power amplifier design using toroidal mains and output transformers. Because of space limitations in the chassis, the two transformers are positioned very close together. Although flux leakage from the transformers is very low, it is enough for a hum current to be induced in the output transformer. Adjusting the relative rotational position of the two transformers enables me to reduce the audible hum considerably, but not to eliminate it entirely.

I started by wrapping a band of silicon steel core material around the outside of the mains transformer to see if this would have any effect, but the reduction in induced hum current was minimal. I am now wondering about winding a magnetic shield over the top of the audio transformer windings using some form of insulated mu-metal tape, in the same way that insulated copper tape is used for inter-winding electrostatic shields. Contrary to the comments above, there are plently of suppliers of mu-metal tape (LessEMF in the US and Magnetic Shields in the UK, for example), but I can't find anyone who does an insulated version.

Has anybody tried anything similar before or come across an insulated mu-metal tape?
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Old 17th February 2014, 05:17 PM   #15
DF96 is offline DF96  England
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Join Date: May 2007
Google 'transformer belly band'. This is a closed loop of good conductor (not high mu magnetic material).
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