Direct Drive vs. Idler Drive vs. Belt drive

I'm really glad to see so much information and ideas being exchanged here.
The point of my post is to get a general understanding of what each drive type might sound like or what people thought it sounds like, so it's good to hear opinions from many different people. I won't be picking just one turntable as I do enjoy having many options. At some point, I will be adding a DD turntable, it should be fun to experience all three drive types in my own system.
I do agree that there are so many different variables in a vinyl setup that contributes to the final sound from the stand it sits on all the way up to the record weight, so deciphering what is contributing to what is almost impossible.

@atmasphere 

Thanks for your thoughts, Ralph. About air bearings, I think that a very heavy platter on an amorphous carbon thrust bushing is virtually immovable - at least, mine is. You need a lot of force to raise it - and more to lower it - 87N per micron, plus the inertia. Compare that to a fragile cantilever. For radial stiffness, see above. The New Way figure is 34N/u.

What you get is a noiseless bearing, and you really can hear bearing noise. I've compared a first class turntable oil bearing with New Way air in a test rig, and it really is no contest. I've demonstrated sleeve bearing noise from a Premotec 1.8W motor through a belt - subtle, but it's there.

Could you please define 'isomeric isolation/mounting'? Is this a journal bearing in an elastic mount? Thanks!

Nice Post Neil 😃
I have tried over a dozen different platter mats from copper, carbon composite, felt, suede, leather, glass, rubber etc and have found that the MICRO SEIKI Cu180 solid copper mat sounded subjectively 'best' on my VICTOR TT-81 and TT-101 turntables.
I was concerned however, at the increased weight on the relatively lightweight aluminium platters Victor employed.
More importantly....the method of Bi-Directional speed control Victor utilises might surely be compromised by tampering so drastically with the 'mass' of the platter...?
Strangely enough....of all the other mats and materials I tried, the VICTOR PIGSKIN 1mm original platter-mat sounded the closest to the Cu180 🤗
Those Victor Engineers knew their 'onions'.....😃
Jico came out with their own version a few years ago....but using deerskin.
Not as good....😕
My RAVEN AC-2 BD Turntable....because of its solid copper bonded top-plate.....sounds best without any mat.
Regards
Henry

cleeds, I took examples of 1kg vs 5kg out of thin air. Most OEM platter mats weigh less than 1kg (2.2 lbs). I picked 5kg as the upper extreme, just because it is 5 times what might be the weight of a heavy OEM mat. Furthermore, a lot of the vintage DDs have rather lightweight platters.  So the total platter mass (platter plus mat) might be under 5kg.  When you add a 5kg mat to such a platter, you are about doubling its mass.  Can that be wise? Now we know you can bring any platter to a dead stop with palm pressure, so we know there is SOME platter weight that is too much. Just because a platter continues to rotate and the music is not obviously off-pitch on the low side,to indicate gross slowing of the speed, does not mean that one has done no harm to the operation of the table with a very heavy mat. Not too many people have the objectivity to be able to hear that (listener bias), and fewer people still will be able to make the relevant measurements that would reveal a problem. I certainly do not know that ALL turntables will be functionally harmed by a 5kg mat; I just used that as an example. Even among DD turntables, I think it’s impossible to generalize, because there is quite a bit of variability in motor torque and the "tightness" of the feedback loop (how much error is tolerated before a correction is initiated) also varies quite a bit from one design to another. For example, Technics seems to have favored very tight control. Whereas the Kenwood L07D uses a looser feedback loop. So perhaps I added to the confusion by seizing on two particular exact numbers in my first statement. I hope this is more clear. Heavier is not always better.

When I got my Pioneer PL-70L II DD turntable a few years ago I was planning to use a CU-180 copper mat, which had worked wonders on my Micro belt drive tables. I inquired at HiFiDo where I bought the table and they forwarded the question to Pioneer, who had serviced the table prior to the sale (Pioneer still operates a service shop for their Exclusive range and a select few other units, including this table).

The reply was firm: please refrain from after market mats exceeding the weight of the standard mat (made of thick soft rubber) as this will interfere with the PLL feedback circuitry and could compromise speed stability. Just as lewm suggested. Apparently Pioneer also adopted a very tight control. I refrained from trying out the CU-180 (which took some discipline), but did try alternatives within the same weight range, like hard rubber, cork and leather (even a sandwich of the two). This was no improvement. Quite the opposite in fact, so I decided to stick to the standard mat.