I've used both the VPI SDS and the Walker Precision Motor Controller on my Basis 2500 Signature. Each product improved the speed acurcey by degrees and you can hear the music improvement easily. The Walker was my final choice because it did more to lock in the speed. This translated to improvement across the musical spectrum, better image control, and just more natural music.
The caveat is that (I thnk) Jay Conti says his (Basis) AC motor needs three phase control and that single phase control is not as good as his Basis speed control product ($3900.00). This also requires new belt ($xxx), and requires modifications done to the Basis AC motor ($xxx). Jay Conti is most likely right. After all, he is the genius behind Basis excellent products.
