Hi all,
A couple of quick comments ...
Firstly (to Dan-ed), yes, I've seen examples of various turntable architectures (high mass, low mass, suspended, unsuspended) that have PRaT and Dynamics. One of the most impressive and honest products in the low mass, suspended category was my dearly departed Merrill Heirloom. I'd like to think that my unsuspended high mass rig is up to this standard.
This is one more case of choosing your architecture and either getting it right, or screwing it up ... nothing to do with the choice of architecture.
When I say PRaT (or dynamics, or soundstage, etc.) I'm referring to a component that doesn't get in the way of what's on the recording. There are numerous components in any equipment category which hyperbolize or exaggerate a particular sonic attribute in order to fool the listener. I'd prefer to leave this sort of dishonest product out of the discussion.
To clear up the confusion about potential for slipping motor pods, I currently supply 'tables with small cones. They don't have to be used, and all components can sit flat on the shelf if the end-user prefers.
The small contact surface of the cones makes it very difficult to move the motor pod accidentally. As Dmailer noted however, even the flat surface of his motor pod resting on his relatively smooth Vibraplane is non-problematic. Yes, Dmailer can play with feet if he so chooses (threaded inserts).
A manufacturer needs to design for a worst-case scenario. For this reason, I went to the cones. Redpoint went to very thin, silicone rubber pads under their motor controller. Perhaps this is the source of the confusion.
To Nghiep, a 6" diameter pulley would mean that the motor rotates at roughly 66 rpm to spin the platter at 33 rpm - this, in the absence of any reduction mechanism. This would require an extremely high-torque motor - along the lines of a direct-drive rig. It certainly can be done. By the time you design this powerful a motor, the flywheel effect of the pulley is likely to be swamped by the motor's torque.
Cheers,
Thom @ Galibier