The SDS lets you set the speed by changing the frequency of the AC supplied to the turntable motor. For example, you can switch between 33 and 45 rpm with the push of a button. As Sidssp so aptly described in his earlier posting, the SDS also facilitates fine speed adjustment in case the table is running slightly fast or slow.
VPI SDS or Powerplant for speed control?
I have a VPI Aries table and use the PS Audio P600 Powerplant for turntable speed control and line conditioning. Recently at my VPI dealer and he states the SDS is superior in both areas to the powerplant. Spoke with PS Audio and their opinion is that they both work well and there is no real benefit using the SDS over the P600. Does anyone have have any experience and recommendation with these two products?