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

Hiho

The creep is proportional to the strain in the belt divided by the parallel sum of the wrap lengths of the pulley and platter.

The compliance of the mylar belt is quite low, so there's not much strain present. The wrap length of your "pulley" is about 500mm rather than the 10 - 50 mm of conventional drives.

Your system will give about the lowest creep available (this side of direct drive of course).

Mark Kelly

Lewm, I did not mean to imply DD to be better, but equal in sound Performance characteristics w/ CMB, the latter having less-er friction. To tell you the truth I have both mechanical and CMB version and prefer the original mechanical bearing the best. It is not, i think, the magnetic bearing feature (which is horizontal BTW, the ceramic being the main spindle) but the ceramic spindle that hurts the overall performance. They have not optimized the stiffness spindle, me thinks and hence less stiff than the mechanical bearing metal ( steel)spindle.

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