Building high-end 'tables cheap at Home Despot II

Hi All,

First, let me offer apologies for “My System” which resembles the untidiness of a flophouse. Instead of coherent exposition, there resides jumbled teasers. Someday soon, I must pursue some tutorial help in getting it order. Anyway, Chuck got hold of me and now has the MuMetal/Lenco application recipe and I believe he’s going to pursue the fix – a fix that will utterly banish motor generated EMF hum.

Work continues on my automated record-cleaning machine. Already there have been departures from Jimmy Neutron’s machine. The plastic gear drive interface between the ice cream maker motor and the cleaning platter had too much slop in my design which translated into wobble. This called for the introduction of a 12” “Lazy Susan” bearing assembly for the platter to ride on. With 80 balls this is quite the rumbler! A neoprene-lined chamber within “plinth” will house the 3 hp DustDevil vac motor and have a fabricated mini-furnace filter to keep cleaning fluid off the motor (fused – just in case).

Looking forward to visiting Ottawa in ten days or so to hook up with Grant for a CD release (mastered by our very own - gjwAudio1 – aka Grant) party featuring Terry Gillespie and The Granary Blues Band. Weather permitting, my wife and I hope to pay a visit to one of Jean’s old Archeo haunts, Bon Echo Park.

And maybe, just maybe… another Lenco.

Hey Mike,

You’ll have to split those royalties with Mr. Red Green.

- Mario

Who dat?

Mario, I was thinking, now that I am getting close to a two or three armed monster, you covered the platter with the mu-metal. Did you try to cover the motor first - i.e., attach shielding to the bottom of the Lenco's top plate over the motor's coils? Visualizing it, it doesnt seem impractical(?)

Mike - who has a cousin named Blue; fortunately, last name not Greene :0)

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.