Direct Drive turntables

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.

I have had an opportunity to listen to DD, Rim drive and belt drive on essentially the same turntable and there advantages and disadvantages to each.

Belt drive is by far the easiest and least expensive to get good results. The isolation afforded by the belt hides motor flaws and cogging. But it does so at a price.

Direct drive is brutally revealing of even the most subtle problems with the motor. A typical single phase AC motor would be unlistenable on a DD turntable. But a good DD implementation provides some goodness that in my experience you just can't get with belt drive. The goodness includes the much talked about rhythm and pace but also a bunch of other positive attributes like clarity, low level detail, air, etc. It is really difficult and expensive to do DD right. So with a small to modest budget I would choose a belt or rim drive.

I see rim or idler drive as between belt and DD. Rim drive offers some isolation but far less than belt drive. Rim drive offers the same positives of DD but a smaller dose. Rim drive is somewhat forgiving of motor flaws (cogging) but less than with belt drive. Rim drive is a little more complicated than belt and done right will often be more expensive because of the higher demands on motor quality. I think that rim drive is where the best value hits. Rim drive is relatively easy to get right and in my opinion offers significantly better performance.

This is how I believe that the drive topologies stack up. But it actually says little about how turntables using these topologies will compare. With any turntable you are hearing the whole package and the drive topology is just one of many pieces. The well respected SL-1200 gives people a taste of the goodness of DD but at the same time you get the sound of a lightweight resonant base a flimsy platter and an inadequate power supply. Not that I don't like the SL-1200. At it's price point it is very good, but it is not representative of what a really good DD table is capable of.