Nude Turntable Project

Lawrence,
It was magnetism......not RFI/EMI that surprised me on the Cu-180 turntable mat?
The Micro Cu-180 is indeed non-magnetic.
My ignorance levels on electro-magnetism run deep.......but I'm guessing that there are materials which can act as 'conductors' whilst others are 'insulators'?
That's why the stainless steel of the 'cradle' I designed became 'magnetised' by the strong magnetic field and why the non-magnetic aluminium platter of the Victor becomes 'magnetised'.....or at least allows the magnetic field to pass through?
The same effect must be in operation with the Micro copper platter even though it is 3mm thick?
I can understand the rubber platter mat being an 'insulator'.......but a 1mm piece of pigskin being a sufficient insulator bowls me over.....
And why a 2mm thick piece of vinyl is NOT an insulator.....I don't know?
I'm sure someone will educate me?
Where's Al when you really need him?? :-)

You're right Thuchan,
There appears to be 10 times more Cu-180 platter mats available for sale.....even NOS ones.....than Micro ever made in their day?

Similar story with the Orsonic headshells....:-)
Aren't the Chinese great?

I tried that droid application for magnetism.
curiosity got the better of me. Some "fun" observations.
I set the magnetism scale to the highest level so the bar would not peak.
Holding my phone in my left hand I took hold of a fridge magnet with my right hand.
I have a boatload of these now leftover from my ET2 magnetic damping experiments.
Sure enough as I brought the magnet closer it would register on the proximity graph.
Sort of like in the movies where they show crew in submarines with radar. As I came in closer the levels would go up.
So it does work - but how accurate is it ?

The sp10mkII first.
While holding it about an inch above the platter away from the cartridge it showed numbers in the 40's.
Turning the power supply on caused the number to jump to the 80's. Now the interesting part.
Pushing start reduced the number to the 40's again.

Lenco. unfortunately this test was ???? as the big magnet laden Dynavector tonearm sits on this table.
It started in the 40's and as I brought my phone toward the mid section of the Dynavector the scale would want to shoot way off.
Which leads me to ask myself. Dynavector is a well respected company. if they thought there was a problem with magnetism would they have built their tonearm to be joined with their cartridges ?

Verdier - the most surprising since it uses two very large magnets (shielded) for levitation. With my phone just above the big platter. The lowest levels observed in the teens and 20's.

Cheers

Halcro, To reiterate, copper does not shield against magnetism, electro- or other, largely because, as you noted yourself, copper is non-magnetic. Also, electrical insulators that you list are not good insulators against magnetism. Stainless steel can be magnetized because it has a (low) iron content. Alu will be as good as rubber, i.e., not good. Distance from the source and ferrous materials are two ways to reduce the magnetic field.

Chris, I think you answered your own question re the Dynavector, if I understand you correctly. It seems there was no detectable contribution from the magnet at the rear of the DV pivot when your detector was at the headshell. Thus, I would think, there is nothing to worry about (based on the fact that you read the same value of 40-ish when the tonearm is not in the picture). Moreover, the DV magnet is actually two magnets held in place in apposition over the stabilizer blade that is fixed to the moving part of the tonearm. Most of the magnetic lines of force would stay localized to that area because of the interaction between the two apposed stationary magnets and the moving blade that is already deliberately created. Yes, I think DV knew what they were doing, as they have stuck with this basic design for nearly 30 years.

Same goes for the Verdier: it uses two huge magnets of opposite polarity to elevate the platter. The magnetic lines of force are therefore concentrated in that space between the two giant magnets. Stick your detector down there, and see what that does. Also, the thick platter gives distance from any possible problem up on the platter surface.

To be fair to Dertonarm Lew.....he was referring to belt-drive turntables with his 35 lbs platter comment.
His logic.....and that of many other belt-drive designers.....is that greater mass creates sufficient inertia in the revolving platter to overcome stylus drag?
He also advocates non-elastic string or thread drive instead of rubber which means that the platter is not insulated from the cogging of the drive motor.
This of course requires a superb motor design.
For a direct drive turntable with a quartz-locked servo motor.....particularly a positive and negative servo control like the TT-101......the lightest possible platter will make speed changes less perceptible than a heavy one.
A common mistake that critics seem to make when discussing quartz-locked servo control....is that the servo is always 'hunting' for the correct speed?
They disregard the notion that the speed is quartz-LOCKED. The speed is generally spot on and not 'hunting' at all. The only time speed correction may be applied is under localised untoward stylus drag when....as you correctly remark.....good torque and bi-lateral speed control come into their own.