Direct Drive turntables

They are not as common because they are more expensive to do well these days as someone indicated early on.

I'm skeptical of any inherent benefits of DD to the average home record listener over other drive approaches. It ain't rocket science to get a table to spin at constant speed and there are lots of ways to do it cost effectively. ISolation from motor or other external vibrations is trickier.

For good sound, better to focus on matching a good cart to good arm and phono pre-amp optimally.

Well Raul, sure I am talking in my posts - otherwise they wouldn't exist - but certainly not to the length you are going to. What I have mentioned in my last post are issues and matters which should - due to their simplicity and plain objectivity of facts and their interrelations - be so obvious that they do not need discussion nor controlled tests the way you put it.
None of us has to re-invent the wheel. None has to proof again that our planet encircles the sun. In this audio world there is no such thing clear nor proven enough not to be questioned by some.
That you do not use any kind of clamp anymore - and many others do likely - is certainly not my problem nor does it proof or disapprove anything. Its just a personal preference based on your taste, preferences and the special individual matrix of your hearing.
Just like with everybody else's.
It all comes down to personal preferences and opinions which you have mentioned too again and again.
Hearing and the experience of "sound" in human brain (which is the place where it actually takes place...) is a most individual and not to be quantified nor qualified sensation.
My remarks about trying to come as close as possible to a point where platter and record do form one single mass was purely technical-wise.
The physical benefits in the playback process are so obvious that - sorry - this is far beyond any serious discussion from my point of view.
But of course, you will - and are most welcome to do so - as always have a different opinion. Fine with me.
Enjoy the long journey,
D.

Dear Dertonarm: +++++ " That you do not use any kind of clamp anymore.... " +++++

I don't posted to say any one is wrong or something, just like a " datum " but forget about it is not important as is the post subject.

++++ " be so obvious that they do not need discussion nor controlled tests the way you put it. " +++++

useless to follow: is so obvious!!!?????.

Regards and enjoy the music,
Raul.

Mapman, Spinning a platter at an average speed of 33.3333 is very easy. In fact it is fairly easy to get the accuracy to 4 or even 5 decimal points (not that it matters much). The problem is making it constant at a microscopic level, or at least to a level below audibility. This part is very difficult and in some ways at least as difficult than rocket science.

Isolation from the motor is all about constant speed. Motors vibrate primarily because the torque they deliver is not constant. The uneven torque translates into speed instability and speed instability (even tiny amounts) translates into degraded sound.

My experience with turntable drive systems has convinced me that speed stability is one of the most important, and challenging parts of turntable design. I have to admit that this finding was surprising to me so I understand your skepticism.

All,
I currently use a highly modified Rockport Sirius I TT with a 50# stainless steel platter and constrained layer damping driven by an external motor, oversized power supply, aramid fiber belt. The motor uses a flywheel, the platter a vaccuum draw down. I have experimented extensively with the vaccuum on and off and with an ancillary Lurne record clamp used in conjunction with the vaccuum hold down. In my system, I have concluded that the vaccuum hold down always results in better sound, even with flat records; however I doubt that the reason has anything to do with record slip/stylus drag. I say that because the sound even with the vaccuum engaged further benefits from the use of the Lurne clamp. I would note that Andy Payor bonds a proprietary material to the top surface of the stainless steel platter which he feels better interfaces the record with the platter and that the vaccuum is necessary to maximize the coupling. Prior to the Rockport, I owned both a Goldmund Reference (belt) and a Goldmund Studio (DD). I will note that the tables sounded very different with the same arm (T3F) and cartridge; however, I will not try to ascribe these differences to the differring drives mechanisms. Too many other design choices were different. I will note that the reference was not superior in all ways to the Studio and that both benefitted significantly from the use of the Lurne clamp in place of the Goldmund Reference clamp. I will say that my empirical conclusions based on many years of listening tend in many areas to align with those of Dertonarm, but that I also have great respect for Raul who has visited my home and listened to my system in its current configuration.