SSM w/Rim Drive - Cloud 11 Vibration issues?

I don't doubt that the speed stability of VPI's rim drive improves upon standard belt drive.

Aiming for the correct amount of compliance in a drive system is probably an elusive design goal. With the 300RPM motor on a TNT, I heard significant improvement using a carpet thread-- which has much less compliance than VPI's soft rubber belt. But performance audibly degraded when I tried virtually inelastic Stren braided fish line. The complete lack of elasticity requires that the fish line be tensioned very tightly to grip. It pings like a piano wire and transmits all AC motor vibration to the platter.

From what I can gather, part of the problem is vibration inherent in any AC motor. There needs to be at least some minimal compliance (or "lossiness" as stated by HW) in the drive train to absorb it. In rim drive, noise at the contact point between the driving pulley and the platter introduces additional noise. I believe HW mentioned on AA that the surface contact noise of his rim drive was reduced by using a large-diameter driving wheel. If this is true, then his approach would seem to be preferable to the small-diameter O-ring/motor pulley used by Teres. HW's email suggests that they're looking for softer materials to improve in this area, and also perhaps to improve grip at reduced pressure from the driving wheel.

On the other hand, the quieter DC motor used by Teres would seem to be a better choice for rim-drive. It introduces fewer problems to solve, requiring less compliance(slop) in the drive train than an AC motor. Less compliance = tighter coupling = >speed stability.

It remains TBD which system sounds better. However, VPI's retaining soft belts between the motors and flywheel looks like a kluge approach. While fooling around with thread, I found that even the short rubber belt between VPI motor and flywheel sounded slurry relative to low-compliance thread.

Another way to tackle the AC motor noise issue is through the speed controller that governs the 2-phase AC motor. In this regard I think Mark Kelly's AC-1 controller is something of a break-through: it allows voltage (and other paraments) to be separately varied for each phase of the AC motor. With some tweaking, you can virtually eliminate detectable vibration from the 300RPM motor. In constrast, an SDS(or Walker) cannot do this. With the VPI two-motor cassette, the situation is further complicated by the random phasing activity of two unsynchronized motors.

Of course it's about implementation, not just theory.

Thank you for your responses. I tried some felt substance pads under the feet. I then removed the Cloud and put the table on a granite base. The problem is non existant and the table sounds great! I guess I'll have to make a decision whether to go back to the Cloud or be happy with the granite.

Zenieth,

My phono stage finally came in and I was able to play my system with the rim drive after having stabalized speed for about a week without music. The table sounds great with no indication that the rim drive is causing any problems or noise. Break in and attention to set up make all the difference with this drive. My guess is you should leave it on the granite. Mine's working great on maple while I wait for the Critical Mass platform to be completed.
I hope nobody has been discouraged from trying the rim drive by the dicussion of these "bugs". I can tell you they are minor and easily compensated for. If VPI does come up with a tweak upgrade or next generation I'll likely get in line for one. Until then it's really quite enjoyable as is.

My replacement feet showed up from VPI. They are a much softer material. They are much taller than the original stock feet. I haven't went back to the Cloud since the granite is working well. I do believe that the new feet would raise the motor drive considerably. This will create a problem since the Rim Drive needs to run in the middle of the platter. This wouldn't work unless you raise the table so that the rim can drive where it is suppose to. Then there is the issue " how do you raise the table on the Cloud 11? The table's own adjustable feet wouldn't be able to raise it high enough. I guess, I'll stick with the granite base.

My replacement feet arrived also and I would agree that they raise the motor higher than I would like. I tried them anyway and raised the table accordingly.(This may be easier for me since I have the mini feet) They do work well when set up this way but probably no better than with felt pads under the original feet. In fact, there may be a slight loss in livliness. It's a simple matter to switch back and forth if you're so inclined but if you're happy the with the way you have it, you may just want to leave it. I'm looking forward to trying the softer drive belt as this may obviate the need for softer feet.