Direct Drive turntables

Stiltskin, I believe that a high mass (whatever high mass may mean in the individual case...) platter can be fitted only to a direct drive if the heart of the drive - motor and axis - is designed with the respective resulting inertia and pure vertical mass in mind. As the direct control is in most cases an essential design parameter of a direct drive.
I for one wouldn't dare putting a 30 lbs (but I would favor 30 kgs anyway Lewm....) platter on a Denon drive coming originally with a 6 lbs platter. At least not for very long.
A direct drive working with a high mass (and resulting very high inertia) platter has to feature other design parameters in some key components than the average dd from the 1970/80ies.
Aside from that - not the material of the plinth is the core issue, but the internal damping (not bad with Panzerholz, but even better in composite materials) and most important the resonance frequency of the suspension.
I can not stress that point hard enough. Please remember that it was AR with its very first suspended TT which single-handed put in motion record playback high-end (a decade and more later adapted by Linn with their LP-12).

A happy new years eve and a healthy, peaceful and prosperous 2010 to all analog A'goners!
Cheers,
D.

Dertonearm knows I do not necessarily concur with his gross generalization regarding platter mass, as it may apply to anything other than a belt drive turntable. But we have beaten the subject to death on another thread. However he is quite right; it would be folly to add a high mass platter to any direct-drive system that was designed for a relatively low mass platter, based on my reading of posts by other more knowledgeable persons (specifically "Steerpike" and Mark Kelly, over on DIYAudio, who were discussing the design of a modern controller for an SP10 MK2 or Mk3).

The Kenwood L07D is interesting in this regard. It has a "relatively" high mass platter, much of which mass is concentrated at the periphery of the platter, and the servo system is designed to cut in and out once the platter is up to speed, so in part it depends upon platter inertia to maintain stable speed, like a weak belt drive with a massive platter. In addition, the magnet assembly that forms part of the motor is actually affixed to the underside of the platter, as in the SP10 Mk3. Thus the platter is in effect part of the motor and in theory the only "noise" injected into the playback could be that from the bearing itself, much like any belt-drive. I hope to have my L07D up and running by the end of January.

As many have pointed out, there are many variables to contend with (vibration control, tonearms, cartridges, etc) when trying to compare a BD to DD. Unless everything is equal, it is diffcult to say which is better.

From a theoretical standpoint, it may be easier to say which has better speed stability. If one then picks the better spped stable device and then focuses on correcting the shortcomings of that particular design then one is onto something. I think Johnnyb3 and detonarm were onto something in their threads.

It would appear that a good DD has better speed stability than BD but the particular features of tt's which use this DD drive system may detract from its speed stability (e.g., vibration control, etc). While a BD may not have as good of speed stability, TT's using BD could be better at other aspects, making the overall sound better.

Key would be to marry the speed stability of DD's without all of the shortcomings of tables whcih use this system.

Happy new year.

Hi all, thanks for your threads.
I recently cleaned my TT,and inadvertently had the belt twisted w/o knowing it. Something immediately didnt sound right so i checked VTF and platter speed. They were the same as before cleaning. Then i realized the belt was twisted, and correcting that at once normalized the sound. The belt on my TW acustic TT goes round three motor pulleys. Even with a twisted belt, the speed was dead on with a strobe disc. Didnt even waver. I assume a twisted belt is bad for speed stability and in this case caused the problem at hand. So perhaps the strobe disc is not sensitive enough to pick up the speed "jitter" or it was something else caused by the twisted belt that degraded the sound.
Happy New Year.

One of the posts above mentioned a wobble in the VPI rim drive. That is a common problem of poor setup. My rim drive is absolutely stable and sounds fabulous.