Speed Stability

The SDS will make your motor run a bit smoother and more quietly. It will also permit you to set the speed very precisely and stably. I found with a similar product, the Walker Audio Precision Motor Controller, that these effects also resulted in a remarkable "opening up" of the midrange, where I could much more easily separate instrumental and vocal lines. I think either device or an analogous one made by the tt manufacturer specifically for his motor is indispensible if you are running a belt-drive turntable. But as the others have said, the symptom you describe is most likely due to an off-center spindle hole. If it happened on every LP, and if you could actually SEE a speed variation using the KAB strobe or similar, I would suggest you have a defective motor or you need to replace your tt belt or tighten it.

Macd,

I have spent the last couple of weeks dialing in and tweaking my new VPI TNT6/SDS/ET2 setup. I have owned VPI's (HW19's) for many years, and speed stability has always been an issuue to some degree. I am not prepared, yet, to blame VPI's for this, as I suspect that most turntables are guilty of some degree of speed instability. We are all sensitive to particular aspects of reproduced sound. I am particularly sensitive to speed stability. It was, in fact, my unhappiness with the speed instability of my first turntable many years ago, that started me on the road of audiophilia. Here are some things that come to mind:

-No, the speed stability of turntables (even the best), does not equal that of digital sources playing digital recordings. That is what my ears have always, reluctantly, told me. That is the one area, where, for me, digital has it all over analog. It may be acceptable, or even very good, but depending on how sensitive you are to this parameter, it is there to hear.

-Be careful with belt tension on VPI's. Don't assume that more tension is better. May be better for start-up speed, but not necessarily for speed stabiltiy. In fact, I have found that on my TNT, less is better. There is a "sweet spot", where the belt has enough tension to maintain good speed, but not so much tension that the belt wants to creep up or down the platter, and add to the problem.

-Make sure your table is ABSOLUTELY level. If possible check the pulley on the motor (or flywheel) and make sure that it is level. And make sure that it is CLEAN.

-The SDS helped a great deal. Best upgrade, that I have made to a VPI, ever.

I look forward to other experiences from VPI owners.

The rim drive may have speed problems if not set up correctly...there are fixes for all of it. Check the screw tension on the motor pulley(s). Talc or replace the belt(s)

Hi had the same problem, but on my NAD 533 TT. I initially though it was the belt. It however turned out that the motor spindle/pulley, on which the belt rests, had got spoilt (the brushes inside the spindle became defective). The belt was therefore slipping, causing a variation in speed and therefore the pitch.

I don't know if the VPI has a similar system (of a belt being driven by a spindle which in turn drives the platter) as the NAD

Frogman, You wrote, "No, the speed stability of turntables (even the best), does not equal that of digital sources playing digital recordings." What turntables have you actually auditioned for this property that you would characterize as "the best"? I don't mean to be provocative, but all of us occasionally make hyperbolic statements. Also, when you speak here of "speed stability" are you referring to accuracy (i.e., fidelity to the 33.33 rpm standard) or to constancy (i.e., ability to maintain the exact same speed over short time intervals while listening to music as judged by pitch constancy)? I think you would find that the best direct-drive and idler-drive turntables do very well on both counts, so well that you would no longer even think of the digital analogy. I think the finest belt-drive tables aided by a good motor controller would also cause you to re-think your statement, but I myself have not heard any of those for any length of time in my own system.