SOTA Sapphire speed issue

VPI SDS, Walker Precision Motor Controller.  Neither is state of the art but both provide an audible improvement.  There are many new developments in this area; I am now using a Phoenix Engineering Eagle power supply with a RoadRunner tachometer.  The RR feeds back to the Eagle to hold speed around 33.3333 rpm. (Yes, according to the 4-decimal-place readout of the RR, the speed flirts with that level of accuracy.) This is on my Lenco L75.  But sadly, Phoenix is out of the business.  I just noticed that George Merrill sells a tt PS.  Check whether SOTA markets one for their tt's.  VPI also has a newer power supply that may be less expensive than the SDS.  Look also on Audiogon for used stuff.  There are kits under development, as well, if you have DIY skills.

Rebbi, For another step up in performance, I would consider an outboard motor controller.  Not only would a good one stabilize the speed of the SOTA but also the MC isolates turntable motor noise from your local AC supply.  Without this filtering effect, the motor contaminates the AC feeding your other equipment.  You may not hear any problem now, but when you insert the MC, you'll notice the effect by comparison.

For what it's worth, if the belt is riding low on the pulley, and if the pulley is narrowest at its mid-point, then the speed of the platter would tend to be a bit faster than correct, assuming the pulley is rotating at its intended velocity.

rebbi, From what you describe, it sounds as though the belt is a bit looser than intended.  Ergo, the belt may be slipping momentarily at start up. In your original post, you do not mention that SOTA replaced the belt when they performed the previous service.  I'd do that now and see what happens. My bet is that the problem will be ameliorated.