Tables That Feature Bearing Friction

From a physics perspective, using the bearing drag to introduce a well defined load for the motor is certainly “sound” as nicely explained by Dougdeacon and others above.

The DPS differs from some of the other tables mentioned above: the bearing friction is significantly higher than on the other implementations since the DPS uses a light platter and doesn't have the benefit of the inertia of some of the above heavy mass tables. The reason behind the high friction is that, in comparison, any friction introduced by the needle (needle drag) is neglible. From my own experience, the DPS is one of the few tables with a light platter that does have any of the associated speed variations and in many ways sounds like a high mass design (of course the base is fairly high-mass anyway as it contains two layers of lead).

I have not noticed any detrimental effects for the DPS, especially not added noise. Several friends have commented that the DPS is in fact easily one of the quietest tables in our group with the blackest background (comparing to TW Raven AC, Platine Verdier, VPI Scoutmaster, Michell Gyro, etc.).

The DPS is IMO one of the most well designed and thought out tables out there. Everything is extremely carefully matched and optimized; e.g. Willi tried several different platter thickness and weight to optimally match the “loading” of the motor. If you are looking for a table with a slightly more compact form factor the DPS should be on your list. On the downside the design is not for someone who likes tweaking - the top base has to be replaced for a tonearm and it already comes with all the isolation and platforms you may ever need.

I don't know of any direct-drive tables that deliberately use this strategy, except possibly in their electronics. Can anyone think of any?

Lew,

Yes, there are direct drives that do it, although it may be a happy accident for some. By centering mass in the platter, some direct drives avoid excessive noise from their motors. As a result, they also introduce a better way to handle inertia. By my way of thinking, using inertia properly is key to the conversation, so in that sense, a lot of direct drives succeed.

Come to think of it, Win, I see your point. I observed the herky jerky movement of my SP10 motor without the platter. It almost threw itself off the benchtop where it was sitting. So clearly, the mass of the platter smoothes out the operation. Further, the mass of the platter is constrained to within certain limits, if a servo dd table is to operate well. Of course, that is quite different from an eddy current brake, but the principle is perhaps similar. I just had not thought of it that way.

Lew,
Chris Brady's Certus DD designs are said to implement this principle very thoroughly, as does his Verus rim drive, both due to the the motor design.

His belt drives used bearing design and choice of lubrication to achieve a similar effect (as do the similar designs from Galibier and Redpoint). Bearing noise on any of these is nonexistent in any system I've heard, including mine. Motor noise transmitted through the belt, while very low, is more audible than that.