Direct drive/rim drive/idler drive vs. belt drive?

Lewm,
that 'Clear Audio' magnet repulsion is comprised of two ring-magnets ~ 2 1/2" outer diameter and ~ 1/4" in of magnet width. They then replaced the centre bearing pin with a ceramic pin (as you noted, I think). All it now does is not sit on a tungsten ball down the bearing well, but ALMOST float - presto.

This system is pretty much the same thing also use with the 'Pro-Ject 10' and some others like Transrotor that sells it as an upgrade purchase for e.g. the Fat Bob and Z3 etc.

This is in COMPETE contradiction to the 'Platine Verdier' tt which on purpose applies a constant bearing friction-load to stabilise their high-mass platter.

From experience I can tell, that the SME motor/controller is loop-locked much quicker when a small degree of friction is present. In fact if the controller is still trying to lock (can see on the controller's light indicator) and you only put the stylus in the start groove - voila, it's locked!
The looser the bearing the longer it takes the controller to lock (SME main-bearings are conical and can be adjusted for more or less friction)

Go figure...
Axel

Axel, This is like the eddy current brake on a Garrard. Mark Kelly has written much on this subject. I now get what you and Nilthepill are talking about; the repelling magnets not only provide a force in the vertical plane but also they resist rotation in the horizontal plane due to the eddy current effect. Cool. I neglected that factor in my earlier post.

"This is in COMPETE contradiction to the 'Platine Verdier' tt which on purpose applies a constant bearing friction-load to stabilise their high-mass platter."

By my way of thinking, the Verdier approach is far more elegant. The bearing friction load, if that is what to call it, combined with compulsive obsessive tight tolerances can act in a way similar to a grease bearing by also creating a dynamic brake of sorts. The beauty here is that it doesn't have obstacles, like misaligned magnets to deal with, or any influences that might be caused by them. It's a case of less is more in that less complexity is involved to achieve a result that may in fact be superior. It also indicates to me that the manufacturer has taken more care in a traditional approach, if his result is an extremely good one.

A manufacturer can use tricks like magnets as a workaround for the unwillingness to spend extra for precision machining or better materials. I'm not saying that any particular company is doing that, but I do see the possibility.

Summary: I don't buy into magnetic levitation for platters.

Win
Saskia Turntables

Lewm

There is effectively no damping effect available from the two opposed magnets. Eddy currents are proportional to field strength times relative velocity divided by electrical resistivity. The configuration used results in low relative velocity. The electrical conductivity of available magnetic materials is quite high - NdFeB magnets have about 100 times the resistivity of copper.

For all: A distinction needs to be made between velocity dependent drag, which will tend to stabilise the system against speed variation and classical friction (velocity independent) which will not. Hydrodynamic drag and eddy current effects are in the former camp, standard bearing friction and stylus drag are in the latter.

Mark Kelly

Lewm
what Quiddity is relating, as I seem to understand it, is that eddy current 'friction' is very much on the minimal side with the magnetic repulsion, almost levitation, ring magnet concepts. Also recall those magnets are only about 1/4" wide rings. To support this, it is told, that if these platter are (disconnected from the drive) pushed by hand seem to run 'forever' and thereby VERY MUCH differently behaving the 'Platine Verdier' mentioned by example.

Now go figure yet some more ... :-)
Axel
PS: a difference in VFT of .75g, now I'm running at 0.75g with an Empire S1000ZE/X (0.25g! - 1.25g spec) as compared to 1.5g spec. for a 'M20FL super' give the my controller a lot more 'pain in the a...' - it take just longer to settle. This is for me a clear indication about what friction (needle and/or bearing) does in terms of motor/controller loop-feedback/response...