My personal experience with Direct Drive versus Belt Drive

Lewm: "IMO, the rim drive is the worst of both worlds, not the best of both.  Mechanical vibrational energy from the motor is transmitted right into the platter with no belt to isolate one from the other.  At the same time, the typical rubbery contact point between the drive wheel and the platter is constantly trying to rotate the motor in the opposite direction (per Newton's 3rd Law of Motion), and flaws in the O-ring result in mechanical noise and speed issues."

I agree that it's the worst of both worlds. My main issue with it is that it takes away idler drive's advantage keeping the metal (motor pulley) to metal (platter) relationship with rubber (idler wheel) interface in between. In an idler drive the rubber wheel's size does not affect the speed (at least not much) because it's only an interface in preserving the relationship of two true round rigid metal circles of the pulley and platter. Idler wheel is compliant and will have pressed spots touching metal and yet the speed does not change. But a rim drive must have true round rubber wheel to have speed accuracy because that is also the pulley.  Just imagine a non-true round pulley in belt-drive and idler drive. Disaster. Rim drive's rubber too hard will not grip the platter and too soft will deform the round shape and affect speed. One might say rim drive has the advantage of transferring the effective torque (including motor noise) more directly to the platter, and it can be the reason people like the sound. It demands a very quiet motor too.  For me, I rather stick with idler drive between the two systems. 

Just for the record, I believe all three systems (belt, idler, direct drives) can sound good. It's the execution that matters. 

harold-not-the-barrel: "hiho, with all due respect I just get the impression that you are living in a world of theories and your illusions. My direct rim drive does the trick for me."

As long as it does the trick for you, that's all that matters.

I never said it doesn't work. It's just more demanding on the execution. Looking at pictures of your turntable, it uses a solid pulley and the platter rim is a softer material. That's a good solution to the issue I mentioned. The designer knows his theory and addressed it. No illusions there. 

Lewm: "if I was still interested in belt drive for my own use, would be two motors positioned at opposite sides of the platter, 180 degrees apart, so as to equalize the forces involved in rotating the platter through a belt connection."

I would simply placed another pulley next to the platter on the opposite side of the motor: one motor, one platter, and two pulleys. I think that would do the trick without the extra motor noise. VPI  did something similar in their early TNT model but with THREE pulleys!

Lew & Chris, I mentioned the VPI TNT 3 pulley design only as an extreme example of the multiple pulley genre. I agree it's gimmicky and pulleys make noise too. Three pulleys create too much empty spaces and not enough contact area for platter grip and might cause slippage. You only need one extra pulley at equidistant from the motor pulley to offset the tug on motor side, if that's the approach a designer would take to combat bearing imbalance. 

In belt drive genre, I am fan of non-compliant material such as tape, string, dental floss, etc... Without compliance, you still have decoupling but you do lose motor isolation. So a quiet motor becomes paramount. I used to use a direct drive table to tape drive a passive platter and it worked out really well. My preferred interface was VHS tape. Having two turntables side by side tape driving each other took up a lot of table space so I gave it up. But, yeah, non-compliant material works well and I am not surprised by the positive finding by others. Happy listening!

Harold, 
 
I'm not a scientist so whatever theory you heard from me is probably half-baked so you don't have to take me too seriously. I know I don't! :)  I'm just an experimenter whenever I have too much time on my hands. Of course you can try anything. Just don't forget to have fun! 

Few requirements necessary for dual-platter experiment: First, your active platter (DD table) must have speed adjustment or pitch control and the platter outside rim must be straight vertically, no sloped platters, in order for the tape or thread to ride on. Grooved platter is okay for thread or floss drive. If you have a sloped platter, like Technics, then you have to add a layer of platter or round disk thick enough for the tape to ride on and clamp it down. VHS is half inch tape so might be too tall so you can use you quarter inch tape from cassette or reel2reeel. If you do not have a DD table with speed adjustment, then your passive platter's diameter must match the active platter or vice versa so it's one to one ratio. 

I tried different DD turntables as driver. They include Technics SL1200Mk2 (because of sloped platter must add flat platter on top). Suspened tables with suspensions defeated SL-1300Mk2, SL-1400Mk2, SL-1500M2 and the unsuspended SL-150Mk2, SP-15, SP25. I regret not able to try SP10Mk2 even though I had two at the time. Technics without extra platter on top: SL-M2, SL-M3 and they are excellent. Also JVC QL-F6, Pioneer PL-570, PL-550. All of them have speed or pitch control. Obviously the intrinsic sound quality of the DD table will transfer into the passive platter. Compare to the DD table itself, the tape drive always sounds slightly smoother. I guess the decoupling adds a layer of filtering or damping to the rotation. Also make sure the tables are not on soft footers. Make sure the active table is seated solidly so there's no movement to affect speed stability. NO suspended tables. My favorites are JVC QL-F6 with coreless motor, super smooth and the Technics SL-M2, essentially an SL1200Mk2 with heavier platter, muscular sound. If you can find or machine a flat platter (preferably same diameter as your passive platter) to add on top for the SP-15 with a narrow plinth, it is the most versatile as it can also play 78rpm and have pitch control and doesn't take up much space. Of course I'm sure there are many other models out that I haven't tried. I know the Luxman PD-277 allows for speed adjustment but I never owned one. 

I also used two identical platters and motors gutted from two Pioneer PL-L1000 tables tape driving each other and also tried using idler wheel in between which made it an idler drive system. I should have tried wrapping one platter with a rubber band to rim drive each other! This experiment is the greatest revelation to me in terms of understanding drive system in influencing the sound. My own finding is that if all things are equal, the stylus does NOT care what is moving the platter, it can only "feel" the Torque, Compliance of the interface (belt, idler wheel, magnetism), and Motor behavior (cogging, smoothness, etc..). If those three elements are similar in different drive systems, their sound will be similar. Most tables vary so differently from each other in those 3 things that no wonder they all sound so different, not to mention dozens other sound changing things. That's why I say all three drive systems capable of making good sound so the execution and implementation are what matters. 

I splice the VHS tape diagonally, much like magnetic tape splicing, to avoid bumps. I tape them down with scotch tape first on emulsion side just to hope them, and then use super glue to glue another piece of VHS or scotch tape on the shiny side. When done, peel off the tape on the emulsion side. And the scissor off the extra on the edges. Just have to experiment few times to get to optimum result. Remember to cut diagonally.  Emulsion side or magnetic side is to face the platter, shiny side for adhesive facing out of the platter. VHS tape is designed to wrapped around a round metal drum anyway, just like a turntable platter so they work well. Other mylar tape will work too I am sure, just look online on those early Teres projects. Tension on the tape is important too but you have to play around with it to get the best result.

Happy experimenting!