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In Reply to: RE: TI Shield on my Rega P25 posted by Maprik on March 02, 2009 at 09:48:45
Just an FYI: Mu-metal loses its magnetic shielding properties if it is mechanically deformed. It has to be annealed to recover those properties. TI-Shield is a sandwich of copper and Alloy 49. The makers claim that Alloy 49 does not have the mechanical problem of Mu-metal, so it can be deformed without the need to anneal it.
I've found that Tarn-X (available at Home Despot and Ace Hardware) cleans the copper surface of TI-Shield instantly. It has to be rinsed off, but doing this is much easier than getting the residue of Brasso off. You want to clean the copper thoroughly where you intend to solder a wire to it, and use an iron with sufficient heat to get a good solder joint. I use a 40-watt iron.
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Karma Means Never Having To Say You're Sorry
Michael Percy Audio.
What are TI shield and mu-metal used for beyond the asylum of audioland?
TI Shield is a clad metal product of Engineered Materials Solutions. They were owned by Texas Instruments at the time the product was developed, hence the "TI" in the name. We think of TI as a semiconductor chip company, but they were originally an oil well instrumentation and defense electronics company. Thus, I think the original use of this stuff was probably for down-hole instruments and I'm sure a lot of it is used in military hardware.
See also
http://en.wikipedia.org/wiki/Texas_Instruments
Does a double layer of TI shield make audible difference?
What about thin refrigerator magnet material wrapped in alum foil?
What about the TI shield wire lead? Could it pick up interference and run it back into the shield? Does the shield attenuate any such signal. Does wire need to have a filter circuit applied?
Time for a little experimentation if the parallel filters make an audible difference in my system in the first place.
Bill
Sorry that I don't have definitive answers to most of them.
TI-Shield would be more effective in a double-layer, but that might be overkill. There could be harm in the interaction of the two layers.
I have no idea if refrigerator magnet material has the high permeability of the Alloy 49 used in TI-Shield. This alloy does not carry a permanent polarization.
The shield made of TI-Shield material may act as an RF resonator itself and add noise to the ground. It is also very important to insure that the TI-Shield material does not vibrate: it will act somewhat like an electric guitar pickup and induce an emf related to the vibration into nearby circuits.
TI-Shield has too much copper in the cladding to provide effective self-damping, so, yes, a low-pass filter in the ground wire may be useful.
With regards to the magnet among other magnet drawbacks the action of the TI Shield material may be dependent to some extent on the bonded nature of the boundary between the materials. What could be cooked up at home would not approach that interface....Thinkin' out loud, lol sometimes that can land one in an asylum, oh too late.
The copper layers on TI Shield are there to act as shields. It is good practice to make sure any electrical connection to the piece of TI Shield contacts both sides equally well. For some applications, it may improve performance to ensure electrical bonding of the copper layers around the edges, to keep the Alloy 49 interface electrical properties out of the situation.
If the copper layers were sufficiently thin, they would act to damp RF waves, whose magnetic components were picked up by the Alloy 49, by way of resistive loss in the induced circulating currents. As it is, the copper can support circulating currents without much loss. Here is a neat home project for the audiophile who happens to have a sputtering machine in his garage...
Mu-metal is commonly used for signal transformer shields. The fancy ones use multiple layers separated by fishpaper. I've used it for some of the internal metalwork in aircraft radios where isolation was a severe problem. It's been around a long time.
Regards, Rick
foil is okay to use as you are not making any real Sharp bends in wrapping a motor. I suspect if the bend radius is kept fairly large, mu metal sheet say up to 16 gauge would also be sufficient without ht need for annealing. That being said, since we are simply trying to contain the magnetic field, simple sheet iron would also work just fine. Pkuys sheet iron or steel is a lot cheaper.
Stu
Thanks Al,
I used ProGOld and some steel wool to polish the copper to a mirror like finish. Tarn-X is probably a LOT cheaper, thanks! I'll remember that for my next TI shield projects. I did not solder the ground wire though, I used a copper crimp-on eye ring that I painted with Quicksilver Gold and and bolted it onto the copper with a brass nut/bolt, then used a little super glue to lock the bolt tight.
Phil
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