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

Hiho

When I said "about the lowest creep of any system outside DD" I was thinking that the drive I designed for Thom Mackris was probably slightly lower. I was wrong.

I've run the numbers, assuming you are running a 1/2" x 3mil Mylar belt around two 300mm platters placed 400mm apart, and you win. We have slightly lower compliance (0.063 mm/N vs 0.117 mm/N) but you have a longer effective pulley length (236 mm vs 68 mm) so your creep is lower: 0.003 vs our 0.005, referred to a radius of 150mm.

As a reference, a typical belt drive system might have a creep number around 5 - 10 and a good idler system (like Win's) will have a number around 0.05, over 100 times better than the belt drive.

Mark Kelly

Nilthepill, I guess I don't understand the concept of the CMB. I made certain assumptions that must be off base. I've actually never seen any Clearaudio turntable, except perhaps their low end ones, in the flesh. But then, I lead a sheltered life here in the Washington DC area, where the hi-end audio emporium is as rare as a dinosaur.

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