Direct Drive vs. Idler Drive vs. Belt drive

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.

@noromance please check your system page

WRT to platter mats, the concept that materials cannot absorb/attenuate vibration is not correct.

@antinn I suspect you misread my post, as you and I are on the same page w.r.t this statement; it is the same point I was making (or at least was attempting...)

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.

@terry9 If the platter is unable to move up and down or in any other plane when subjected to vibration, such that whatever vibration might be present in the plinth is the same as that at the base of the arm and the surface of the platter, then the needed mechanical engineering principle is satisfied and the pickup will be immune to that vibration.

Agreed.