SSM w/Rim Drive - Cloud 11 Vibration issues?


I was wondering if any other members have run into a vibration problem. I upgraded my SSM with the Rim Drive. I also use the the Cloud 11 vibration control system. The Rim Drive is creating vibration to the 11 platform. This creates a slight wobble to the tone arm. VPI was extremely helpful and they are sending new motor mount feet. They aren't sure that this will fix the problem. But they state that the new feet will give a little to the vibration control. Has anyone else experienced this problem? If so, what coarse of action did you take to compensate? Thank you in advance for your input!
zenieth
Wish they'd come out with the single motor/flywheel combo version of the rim drive.
Also wondering if I'll have to change my isolation (assuming they do produce the rim drive for mine). Now the motor sits on a platform raised slightly above the Gingko. Hoping the slight give of the Gingko will negate the need for softer feet on the motor. Really like the Gingko under there.
I think everybody needs to wait until Harry comes up with the 'third' generation version of the 'rim'. By then, all the bugs will be out, hopefully. Until then, the 'fly' will be the way to go. When the third generation comes out, it will have a custom motor platform and table feet will be matched to the platform for height and damping. Until then, the mod is just not cost effective for the sound it produces. Also, I will not be surprised if Harry comes out with a complete rim turntable, arm and motor. Say, $8K. When you engineer it as 'system' results are always better.
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.