Building high-end 'tables cheap at Home Despot II

Mike, as I imagine an electro-magnetic field to work, the waves are not absorbed but are deflected by mumetal. If I am right, then the waves would flow out and emerge around the edges of the motor - still interacting with the cartridge as it plays the record. When the shielding is done for the platter, this flow around the barrier would also happen, but shielding the platter would disperse the field to the outside of the record and the interference would occur outside the playing surface of the record.

I had also thought of shielding the bottom of the platter rather than the top - this way you won't have to be so particular at adhering it. But I'll have to wait until I see the material in the flesh. Mario, is there any reason for doing the top versus the bottom?

Of course, I may be full of hot air here and this is a guess based on my extensive ignorance of electro-magnetic fields.

Hi Mike,

“Who Dat?” Really Mike, you’ve been far too south for far too long. Red Green is the lead in a Canadian comedy troop carried on many of the PBS TV stations up here. The show always includes some outrageous Red Green DIY project where he invariably ignores the premise of “Why would anyone want to do something like that?” – as in the case of outfitting a hulking 70s Buick with Gull Wing doors after yanking the stock ones off their traditional hinges with his trusty van and chains. After massive amounts of duct tape and cumbersome home brew hydraulics, he gets it to work – after a fashion.

We know that the unseen spouses behind these and other all-male shenanigans often assert some clout over what they’ll tolerate. So that we have the commencement (at the end of the show) of their Possum Lodge meeting starting out with the head-lowering Credo: “I am a man, but I can change, if I have to … I guess.”

I’ll endeavor to tie in this wildly off-topic ramble by aligning myself with Red Green as a “practitioner” in the old sense of the word on my DIY MuMetal experiment and not a scientist with all that much knowledge of the behavior of EMF – especially as it applies to the direction it takes at the shield edges. It is, however, a scientific given that what comes off those edges is highly intensified EMF because of the unabsorbing nature of the MuMetal. This has the potential of worsening the situation that we are trying to correct with Lenco motor induced hum. From this premise, I decided that shielding areas of the motor and/or top plate was impractical and I never tried it.

The critical question of EMF’s directional behavior at the shield edge is one I cannot answer with certainty. My only gauss meter is a Grado cartridge mounted in its intended environment. Does MuMetal blocked EMF act like a fluid with a degree of “wrap around” at the edges? The more I think about, the more I’m inclined to think that it does. The literature accompanying my MuMetal, while not specifically addressing the edge intensification as a “wrap around”, nevertheless implies in its caution that it does. Otherwise, why a caution at all, if blocked EMF continued outward on its blocked plane?

But Mike, don’t let my guesswork discourage you, another practitioner over something that I have only the thinnest grasp of. I’ve got a 12” by 4” sample of MuMetal (Hi permeability - and more, if you need it) that I’ll be happy to send along to you for the furtherance of Red Green science.

- Mario

Oops! A simultaneous posting with Chuck's.

Hi Chuck,

The top application will be much easier. No flanged casting supports to contend with, nor that tricky area around the bearing hub interface. Also, there's the question of idler wheel getting proper purchase on the slick MuMetal.

The combined thickness of the two foils is .01" - no geometric threat to tracking, whatsoever.

Humm... now that you say it, I see the gauss field in my mind too - but what if one made a modified L shape to fit mostly over the coils without interfering with the spindle? Someone with a gauss meter could make quick work of this speculation...

I recall hearing once that galvanized steel as used in AC ducts in North America, is somewhat effective in the same EMF blocking applications as mu metal - any opinions?

Mike

Hi Mike,

Was trying to find information that related to secondary transmitters of EMF based on alloy ferrous content, but was unable to locate it again. Somewhere in researching this last year, I visited the whole question of whether unabsorbed redirected EMF off a MuShield would pose additional emitter difficulties as various metal alloys in the Lenco (platter, motor shaft, top plate) were permeated to the degree of iron in their respective mixes.

I do remember that it was of enough concern with the unknown (and unknowable?) alloy contents in various exposed Lenco parts to solidify a decision for going up top of the platter. Even then, I had concerns that the record spindle itself, might act as some RKO tower and omni emitter of interference. Thankfully, this is not the case, and one hears only a small amount of hum when the Gauss detecting Grado is directly over the spindle. Whether this is due to chrome plating of the spindle, or the brassy elements of the bearing sump, I haven’t a clue.

But I did come across a couple of notes today that should be highlighted as REVISIONS to the Lenco MuMetal recipe. (Grant & Chuck be advised)
1- It DOES matter which layer should be glued to the platter first. The thinner, low permeable foil should be closer to the EMF source and get pressed in first.
2- Hammering MuMetal reduces its effectiveness because it changes the crystalline structure of the alloy. Put your energies into cutting the MuMetal foils with a hard surface and many, many utility knife blades. Ridging of the cut edge is the bane of this project and must be avoided. It will not promote a smooth meld to the platter and its removal is problematic. Shearing often causes its own ridging.

In my application, I was able to get away with minimal shearing of edge burrs and some very light tapping with a hammer at the spindle hole.