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

Nilthepill, To answer your question with my opinion, no. I don't see how a magnetic bearing, which acts in the vertical plane only, can possibly have such a dramatic effect on the drive system, which is mostly operating in the horizontal plane. But your question assumes that low mass/direct drive is inherently superior to belt drive/high mass, which probably is not categorically true. Success of either design philosophy will have a lot to do with execution. I am thinking that, while I personally have begun to favor the low mass platter/direct- or idler- drive turntables based on my listening, this approach is the most difficult and potentially expensive to perfect. Whereas I think it is easier to get "decent" results with a high mass platter/weak motor/low compliance belt. Maybe that explains the predominance of the latter type of turntable in the "high end". I'd love to hear a Grand Prix Monaco myself. I wonder whether the carbon fiber adds a coloration, for one thing.

Hiho

Consider the speed of three things: firstly the belt on the drive side of the motor pulley, this being the section which is pulling on the platter; secondly the belt on the non-drive side of the pulley, this being the section where the belt is feeding off the pulley onto the platter; and thirdly the surface speed of the pulley itself.

Belt slip is where the speed of both parts of the belt is slower than the surface speed of the pulley.

Belt creep is where the belt speed on the non-drive side of the pulley is slower than the drive side, so the belt creeps over the pulley to make up the speed difference. This is because the belt is stretched by the torque it is transmitting and that amount of stretch must relax over the pulley. If the belt were equally stretched on both sides there would be no tension difference and thus no torque transmitted.

Mark Kelly

"If the belt were equally stretched on both sides there would be no tension difference and thus no torque transmitted."

Thanks for the explanation. On my system, the active pulley is the same size as the passive platter so I would have to assume there would no or little belt creep, right? I use two identical turntables to drive each other via a VHS tape. So far this is the best sound I got from a belt-drive system and the only thing that can match it is a quality direct-drive turntable with a coreless motor. Since I am lazy, I like the convenience of direct-drive table with some automatic features. :-)

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.