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Old 17th February 2019, 10:28 AM   #1421
cubicincher is offline cubicincher  Germany
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Default answer to MEPER

Hello MEPER,


very interesting test of the M2! Was fun to read.


I am not sure if you can get the metalshield for the transformer in a perfect fit.
I've ordered a pair metalshields which are too big. And I did not install them yet. Have to make them smaller.
Greets Dirk
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Old 17th February 2019, 10:34 AM   #1422
cubicincher is offline cubicincher  Germany
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Default M2X experience

Shielding case for EDCOR.

Greets Dirk
Attached Images
File Type: jpg M2X EDCOR shielding case.jpg (100.5 KB, 400 views)
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Old 17th February 2019, 01:04 PM   #1423
MEPER is offline MEPER  Denmark
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So you build your own little metal box shield.

It seems Edcor shields some of their transformers using a thin copper shield like this:
EDCOR - MXLcs Series

It looks like tape. I wonder if it is "enough" just to apply the tape like on the picture and not cover the whole transformer. It would be easy to do. Mu-metal tape is a bit expensive but does not need much…..just a small sheet.

If the shield is for not picking up noise it is probably enough just to cover the windings.
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Old 17th February 2019, 01:06 PM   #1424
WKCox is offline WKCox  United States
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The diyAudio First Watt M2x
Quote:
Originally Posted by MEPER View Post
I just read the 6moons review of M2. He had the top off the amplifier:
6moons audio reviews: FirstWatt M2


Was the shields on the Edcor's "handmade" or something the factory makes? ….is it mu-metal or "just" steel?
Pass uses mu-metal. I believe Nelson posted earlier in this thread. I tried steel but that didn’t work well, so I purchased some mu-metal foil. Expensive but effective.
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Old 17th February 2019, 01:09 PM   #1425
qwertyl is offline qwertyl  United Kingdom
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Quote:
Originally Posted by WKCox View Post
I tried steel but that didn’t work well, so I purchased some mu-metal foil. Expensive but effective.
I had similar experience, steel boxes didn't make any difference, mu-metal foil works great.
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Old 17th February 2019, 01:23 PM   #1426
MEPER is offline MEPER  Denmark
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I will get a small sheet of mu-metal tape. It would be most easy just to cover the windings with tape. One piece of 17mm all the way round like they do at the Edcor factory (where they use copper...if must be for RF shielding not magnetic).
I know that the steel used for magnetic shielding has a special grain structure. They write a bit about it at Don-audio as they sell shielding for e.g. toroid transformers.
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Old 17th February 2019, 01:38 PM   #1427
MEPER is offline MEPER  Denmark
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The Lundahl's like this one is by default in a mu-metal case:
https://www.lundahltransformers.com/...heets/1674.pdf
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Old 17th February 2019, 03:29 PM   #1428
cubicincher is offline cubicincher  Germany
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Default EDCOR shielding

MU-metal, selfadhesive shield sounds very good to me (yes, expensive).
I did not want to cut those cases into 2 halves, make them smaller and soldering/welding back together. A lot of work.
And then the metal case was very close to the pins / contacts of the EDCOR.
Because of this I tried the rubber-welting.

Greets Dirk
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Old 17th February 2019, 04:11 PM   #1429
MEPER is offline MEPER  Denmark
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I ordered a couple of these sheets:
Ultraperm 80 Metal Shield; MuMetal Mu Metal Alloy Shielding Sheet Audio HiFi USA | eBay

Will see how it is to work with. Mu-metal should saturate easy so it is not for shielding strong magnetic fields…..but that should not be the case inside the M2X chassis. Some light stray fields from transformer and PSU wires.
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Old 17th February 2019, 04:54 PM   #1430
maty tinman is offline maty tinman  Spain
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Talking about Mu-metal, a book.

Audio Transformers by Bill Whitlock

[PDF] http://www.jensen-transformers.com/w...rs-Chapter.pdf

Page 9

Quote:
The effectiveness of magnetic shielding is generally rated in dB. The transformer is placed in an external magnetic field of known strength, generally at 60 Hz. Its output without and with the shield is then compared. For example, a housing of 1/8" thick cast-iron reduces pickup by about 12 dB and a Mumetal can by about 30 dB. Where low-level transformers operate near strong magnetic fields, several progressively smaller shield cans can be nested around the transformer. Two or three Mumetal cans can provide 60 dB and 90 dB of shielding respectively. In very strong fields, because high-permeability materials might saturate, an iron or steel outer can is sometimes used.

Toroidal power transformers can have a weaker radiated magnetic field than other types. Using them can be an advantage if audio transformers must be located near them. However, a toroidal transformer must be otherwise well designed to produce a low external field. For example, every winding must completely cover the full periphery of the core. The attachment points of the transformer lead wires are frequently a problem in this regard. To gain size and cost advantages, most commercial power transformers of any kind are designed to operate on the verge of magnetic saturation of the core. When saturation occurs in any transformer, magnetic field essentially squirts out of the core. Power transformers designed to operate at low flux density will prevent this. Often a standard commercial transformer, when operated at reduced primary voltage, will have a very low external
field.
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