Tables That Feature Bearing Friction

Dertonarm,

the only table? Really? Perhaps you should try to listen to more 'tables. ;-)

This is an interesting discussion, thanks to all. It seems to be the case that some other manufacturers take a quite different approach. Nottingham, for example utilizes an extremely low torque motor, so any kind of breaking is out of the question.

I have no idea myself what are the merits of any particular design choice. All I can say is that I have, and like, my Basis Debut table and I have, and liked some of the others mentioned.

On a related point, one thing I've been wondering is why not integrate a flywheel with the motor pulley. For AC motors in particular this would have the advantage of smoothing out cog noise at the motor source, rather than pass it on to the platter(or an outboard flywheel) through the drive system. I know some of the older heavy-duty high-speed motors have some built in flywheel effect; it's surprising that this approach is not taken with some of the smaller motors in current vogue.

A flywheel can very well create problems if not done the right way.
It is only suitable to motors featuring a solid axis shaft and a very good and rigid bearing. The flywheel - if done the right way - add considerable amont of inertia to the motor shaft and to the whole moving system. Therefor it requires solid construction. Especially if the flywheel is directly attached to the pulley or part of it (which is the only way to use the inertia moment of the flywheel to smooth out most imperfections of the motor itself). The smaller motors envogue right now do not fare very well with flywheels.
The small motors common today have 3 big advantages. Even if all turntable-manufacturers using them do list some other advantages, it all comes down to these 3 only....:
1. they are inexpensive.
2. they are inexpensive.
3. they are inexpensive............

Dgarretson,

I addition to the practical difficulties that Dertonarm pointed out there are some good theoretical reasons against using a flywheel at the motor. In all motors motion is produced by magnetic attraction. When there is no drag the
magnetic fields in the stator and rotor will be perfectly aligned. When drag is applied the magnetic fields pull apart and the attraction creates torque. This is a very desirable characteristic in that torque is almost instantly created in response to a load perturbation. I say almost instantly because the rotational inertia in a motor delays the delivery of torque. Any delay in torque delivery adversely affects the motors ability maintain constant speed because the corrective torque is being applied after the fact. The longer the delay the worse the problem becomes.

Belts, particularly stretchy ones, have the same effect. They filter cogging, but also delay delivery of torque. Filtering cogging is a good thing, but it comes at a price. In many cases the fix is worse than the problem. Much better to just start out with a motor that has low cogging.

In addition to the theoretical arguments there is plenty of empirical data that indicates that low inertia motors tend to sound better. That has been my experience.

BTW: Certus turntables use an eddy current brake. The braking force is much greater than what a belt drive mechanism can keep up with.

Chris