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.
I have an ADS on a classic with the outer ring clamp. Have never owned the SDS, but what I have noticed is that with either the ADS or the ring clamp alone, there is a significant improvement. With both, the improvement over either alone is very small, if at all.
You say you have a "very old SDS."  Some VERY old VPI speed controllers are not SDSs. So what do you have exactly?

Were it up to me I would prefer an old SDS to the more recent ADS units.

The best controller you can buy for the VPI is sold by SOTA and would include a new motor as well as the Roadrunner for continuous speed measurement.

Other things that you can do to help speed stability is add a heavy peripheral weight as was said, or get the VPI motor-flywheel combo.  

Everything will make a difference.
I had the very old PLC (Power Line Conditioner, the one with the thumb wheel dials) with my TNT-1.
I've upgraded that twice in the last 30 years - first to the PLC with the rotary dials and then to the SDS with the push button adjustment.
If you actually have an old PLC the SDS will be a very worthwhile improvement.
Still have my old TNT with various VPI upgrades. I sold off my Graham Phantom arm and put on a Grace G-1040 arm that I bought for about $150 in 1982. It actually sounds really good!
Other posts are correct, the SDS is better than the newer ADS.  The ADS is cheaply made and has been the subject of many complaints.

However, you seem to be aiming for high performance.  If you want the very best, SOTA sells a motor-controller-roadrunner combo.for VPI tables.  It has been discussed at length in the VPI forum.

Other ways of improving performance would be the motor-flywheel combo, if they still offer it, and the peripheral weight.
@ joeyfed55-    To be more concise:  Here's something to consider, regarding the VPI Prime's maintenance, if you haven't already:    https://www.youtube.com/watch?reload=9&v=AHmYWT3wKqs    Happy listening! 

That was a very  funny video.  Putting oil in the top of the pulley to lube the bearing.  Who is that moron?  He certainly doesn't know anything about turntables or motors.
Agree with the other posters.  Keep your SDS.

Oil will migrate, between the pulley and the shaft, down to the top motor bearing.      Letting the motor run overnight warms things up, and facilitates the process.       The option is to remove the pulley, as demonstrated.                    The, "moron" is Mat Weisfield (current President of VPI), who just might know a thing or two, regarding the maintenance and design of his company’s motors and TTs.                      Of course; that’s just my opinion, regarding Mat.     Thus far; I've been very happy, with VPI's designs/equipment.                                            
I would not use any VPI speed controller. Your best bet would be going with SOTA. It uses the technology developed from the old Roadrunner and Eagle PSU. No comparison!!!!
>I would not use any VPI speed controller. Your best bet would be>going with SOTA. It uses the technology developed from the old>Roadrunner and Eagle PSU. No comparison!!!!

See comparison and review of the motor here:
I'll trade you my square wave PLC for your sine wave SDS!

The PLC makes all my AC synchronous motor turntables hum, even though it also makes them keep perfect speed.