VPI 300 RPM vs 600 RPM Better?

I strongly suspect that the amount of motor vibration varies quite a bit based on the position of the magnets in the motor which I understand is not very precise.

Small changes in the phase of the motor drive makes quite a bit of difference in how smoothly the motor runs.

You can probably do this by tweaking the phase shifting cap value but the easiest way for me is to use a computer to generate the drive signal using an inexpensive frequency generating software.

I went back to the 600 RPM

Be careful about putting the motor pod on a compliant material such as sorbothane. As with most things in audio there is always a compromise involved; pluses/minuses. For best sound, the motor should be as mechanically grounded as possible; IOW, not be able to move. Sorbothane allows it to move as the belt tension and it's own internal vibrations affect it's stability. You have to weigh the very real advantage of a lower noise floor against the advantages of absolutely stable mounting. Movement of the motor in relation of the platter has a significant effect on speed stability, dynamics, and introduces it's own kind of "noise" (image blurring). Choose your poison. I found that a thin cork sheet under the motor pod was the best compromise for me.

I've got my motor pod sitting on top of this EAR product:

http://www.allsealsinc.com/1b.html

It has dampening foam seated in between 2 aluminum plates. Very hard and stable and still has some dampening and isolation properties.

Ah, an old thread I found valuable!

Figured I'd add my experiences here. I recently bought an Aries 1, all original stuff, in great working order. I absolutely loved it - sold my Clearaudio right away. 

A friend has an Aries 3, and he loaned me his 300 rpm motor. Darned if it didn't sound better than my 600 rpm. Crazy stuff. I even have an ADS. I felt that the noise floor was lower - maybe the 600 rpm emits electrical noise? And the details were crisper. Maybe because the RF noise was lower, or maybe because the 300 rpm has better speed control, even when handed a clean signal from the ADS.

I know the mantra with VPI is "older is better" but in the case of motors, I think the Aries 3 - era 300 rpm is better than the Aries 1 - era 600 rpm. 

Just my $0.02 from a half hour or so of A/B on a couple of tracks I know very well.