VPI Speed Controller

Hi, hope you are all well. I would like to hear from VPI owners about speed controllers. I have a very old SDS and wonder if the newer ADS is much better. I have the Prime Sig. with the Fatboy arm and Soundsmith The Voice cart, Pass XP25 phono, Luxman L509X, and ML ESL11As. Sounds great except for solo piano which does not sound good at all. I heard that speed stability could be the culprit and wonder if the old controller is the cause. Thanks for any input,Joe.