Is Direct Drive Really Better?

If I may be permitted to point out something that seems to have been missed here, there is more to a turntable than speed stability, although speed stability is a very important requirement.

Another factor which comes into play is the effect of vibrations or other potential movements in the main bearing assembly(and thus the platter).

If stylus drag can affect the speed stability of a heavy platter or even a motor's torque, then it can also generate lateral movements of similar proportions, due to the angular nature of it's movements as it traces the groove. Externally generated vibrations can affect this also. Since any lateral movement allowed by the bearing/platter can materially affect the amplitude of the groove modulation being traced at the time of that movement, it can cause information loss or modification, based on that unwanted movement of the platter relative to the stylus. But wait, you say, the arm could be moved more easily because it has less mass, and I say that if the arm deflects, then you get similar information distortion as well.

Now, how does this affect our discussion?
Quite simply because direct drive motors generally(and I use that word advisedly) use their drive shaft as the main bearing, which typically does not have the precision tolerances of a belt-drive system's main bearing in a good turntable. In addition, making the platter part of a motor which has inherent vibrations as a natural characteristic is not conducive to ideal conditions for the stylus/groove relationship.
So, even if a direct drive does exhibit a slightly better measured speed stability, there are other factors involved besides that.

Also, wow and flutter are very different speed variations, and to lump them together as "wow and flutter" is deceiving at best. Wow is much less easily perceived by the ear than flutter, and 2 tables with the same "wow and flutter" specification can sound quite different, especially if one has mostly flutter, and the other has mostly wow component in that spec.

To sum up, all methods of analog drive systems have their pros and cons, and none is perfect, and implementation may be more important than basic concept.

To focus in on speed stability alone, with no discussion of other meaningful design aspects is incomplete and useless. I've heard very good sounding turntables of varying drive system designs, and also some terrible ones too.

Tunnel vision is not the most productive way to analyze componentry.

David12, if I read your post correctly, you seem to be saying that the Garrards are direct-drive (DD) turntables. They're idler drives.

TWL -- Glad you could make it. Upon looking at the design of my Technics DD, I see that there is no main bearing per se but rather a broad based rotor/stator interface. The notion of that being rocked or deviated from its center seems remote given its diameter, mass and magnetic hold. After all it isn't a pencil point on a hard disk balancing a 12 inch diameter spinning disk. With the Technics table the motor is about 4 inches in diameter and in the case of the SP-10 it is screwed to the motor assembly. Very stable.
I also wonder to what extent the gyroscope effect might assist in stability in both designs. Does the platter spin too slowly for that to be meaningful. I have observed that a spinning top is rather stable at high speeds but loses that stability as its rotation slows. Does diameter of the top add to its stability to overcome slowing? Is 33 1/3 fast enough to have this influence?
Time for Seandtaylor and the physicists to come back to the discussion. I'm just tossing out questions that I can't answer.

Hold up, I think both both TWL and Macrojack have a couple things wrong here (not that I don't agree with most of the gist of what Tom has said -- I think I said some of the same stuff myself above :-)

"...direct drive motors generally (and I use that word advisedly) use their drive shaft as the main bearing, which typically does not have the precision tolerances of a belt-drive system's main bearing..."

I believe this is a common misconception, which I talked about in my first post to this thread. I may not always know about "generally", but specifically, a DD like my SL-1200 >>does not have a drive shaft<<. The main bearing is similar to the main bearing in any conventional BD, passive meaning unpowered. The motive force to rotate the platter is applied purely by touchless electro-magnetic impulse -- no shafts, wheels or of course belts involved. (Please also see my first post.)

"...Upon looking at the design of my Technics DD, I see that there is no main bearing per se but rather a broad based rotor/stator interface. The notion of that being rocked or deviated from its center seems remote given its diameter, mass and magnetic hold. After all it isn't a pencil point on a hard disk balancing a 12 inch diameter spinning disk. With the Technics table the motor is about 4 inches in diameter and in the case of the SP-10 it is screwed to the motor assembly..."

I think maybe you're being fooled by the appearance of the TT with the platter off. If the SP-10 is anything like an SL-1200, the platter fits over the conically-tapered brass sleeve which forms the base of the spindle, which is integral to the main bearing. When you remove the platter, the spindle is therefore left behind -- you can rotate it by hand. That is the main bearing. What you're describing as 4" in diameter is the stator assembly, which is not "screwed to the motor assembly" as you put it (not sure if you meant to write it that way, since it does't make much semantic sense), but bolted to the cast aluminum chassis, the bearing housing of which you can see centrally located within the stator ring at the base of the spindle/bearing. (Again, if it's anything like the SL-1200 -- please let me know if I am wrong in anyway in translating this arrangement to the SL-10.)

I would recommend anyone fuzzy about the details who really wants to get a feel for how this works to take a trip down to your local pro-sound shop that sells DJ gear and ask to see their display SL-1200 with its platter removed. (With the power turned off, place thumbs or fingers in the opposing holes provided for this purpose, alternate gently lifting one side and then the other to unseat and then carefully lift straight up). Everything I'm talking about should become very clear.

Zaikesman,
My SP-10 MK II has a motor assembly with a top plate and the platter is fastened to that top plate by 3 flat head screws. On my SL 1100A, the arrangement is similar but the platter simply rests on the top plate without any fasteners. I also have an SL 150 MK II and that is similar to what you describe in the 1200 where the platter is an integral part of the motor.
The question remains however whether these DD models remain perfectly concentric in response to stylus drag or are spun off kilter by their looser bearings structures. I think that was what TWL was saying.
I questioned him about this because it appears that my DD tables are not vulnerable in the way he described. Maybe they are.
I also have a Luxman PD 441 and it has a magnetic mechanism which reduces the platter weight on the bearing by 80%. Is this better or worse in relation to Tom's premise?