Turntable speed accuracy

Servo design in a DD 'table certainly includes the expected mass of the platter. If that changes significantly it sill alter the response of the servo; likely to the underdamped side of things. Many cheaper DD tables have a platter that can be removed and the motor can be operated without it- in this case the cogging effects are often quite visible. This an extreme example of course, but illustrates an under-damped condition.

So you probably can decrease the electrical damping by increasing the mass, but you should also not be surprised if overall speed stability is also compromised. Servos often have to operate within some fairly tight parameters.

Hiho, Lets keep in mind that what you quote from the Brinkmann website is a commercial, full of blather with a sprinkling of fact. Like many politicians, they set up a "straw man" controversy in order to show how their product "solves" the problem that may or may not be a problem in reality.

What I especially found questionable was the part about 32-pole motors causing increased cogging. More poles should mean less cogging, if done right. Anyway, I am sure the Bardo is a nice product in spite of their blarney. The design brief resembles that of the L07D in many ways, including the copying of the Dual coreless motor with the odd raster. What's a "raster"?

Lewm, I meant DC motors. As far as I know the following DD's use DC motors - EMT948, Technics SP10mk2&3, Sony PSX9, Kenwood Lo7D, Exclusive P3. The Denon DP100 uses an AC motor.
DC motors react to variable loads quite differently to AC motors. Seems to me there is potentially as big a difference generated by DC/AC motor choice and implementation as there is by drive type.
Actually, I believe I'm right with regard to DC motors - DC motors do not self correct when speed fluctuates, hence the need for servos or speed sensors at the very least. Question is as Brinkmann suggests there is a trade off on sound "quality" between fast recovery and soft recovery type servos. Too fast and you get overshoot and more correction.
Platter mass also factors into the equation as well in that it can dampen the servo action in a DD TT.
There was no argument or generality suggested, but a question posed if you reread the post.

Dover, I think my response to you was too harsh. I apologize. Denon DP80 uses a 3-phase AC synchronous motor and also uses a quartz-referenced servo. Speed is monitored via a tapehead that "reads" the inner rim of the platter as it rotates. Knowing this, I was a bit confused when I read about The Beat turntable, which also uses a 3-phase AC synchronous motor that is claimed to self-correct by virtue of being so. (I think with The Beat there is a small amount of constant drag on the bearing, and the motor works against that.) Suffice to say that we need a motor expert here to straighten this out. I do think that the motor technology has not changed at all since the late 70s and that the designers of the tables you list used motors that they felt were best suited to the task. There are many high-dollar belt-drive turntables that use DC motors and no servo, as you know.

Lewm, no worries. I think there is a lack of real info as DD manufacturers and vendors placed more focus in their advertising on the fact that it is DD. I know the SP10mk3 and Lo7D well and agree with your descriptions of the difference in sonic signature. The Denon DP100 looks very interesting.