turntable speed control

The best belt would be a endless rubberized steel cable style belt like the old micro seikis. Quiet and they can't stretch. Micro did things right

To me a a constant stable speed is always better than a changing one.

Agreed.  But constant motor speed does not equal constant platter speed, it's basic physics.  Belt creep does exist and it is measurable.  With an elastic drive belt, it cannot be cured, but the effects can be mitigated by holding the platter speed constant as we do.

By your own assertion, a constantly changing speed could affect the audio.  A table driven by the SDS will have constantly changing platter speed for the first 30-45 minutes;  it will either be off-speed (slow) initially then correct after 40 mins, or correct speed when cold, then off-speed (fast) after that. 

With  the Eagle PSU and  tachometer feed back, the platter speed will always be constant, therefore, it will sound correct both when started and after the table warms up.

Thanks for helping make my point.

phoenixengr   "Agreed. But constant motor speed does not equal constant platter speed, it's basic physics. Belt creep does exist and it is measurable. "

That really depends on the turntable.

" A table driven by the SDS will have constantly changing platter speed for the first 30-45 minutes; it will either be off-speed (slow) initially then correct after 40 mins, or correct speed when cold, then off-speed (fast) after that."

Again, that depends on the turntable. It certainly is not an issue with my VPI and, yes, I've measured it.

It certainly is not an issue with my VPI and, yes, I’ve measured it.

May I ask what you used to measured it? My VPI table changes speed considerably from cold to warm and so does every belt drive table I’ve measured. If you have the first belt drive table that doesn’t change speed over time, then congratulations.

If a particular turntable platter truly doesn’t change speed over time, then the argument is moot: The Eagle would not apply correction so there would be no perceived issue either from "constant correction" or constant drift. End of problem.

As far as the rest of the tables that do drift over time, would you agree that constant platter speed is better than a slow drift upwards in speed?

phoenixengr " May I ask what you used to measured it? My VPI table changes speed considerably from cold to warm and so does every belt drive table I’ve measured. If you have the first belt drive table that doesn’t change speed over time, then congratulations"

I use a DIGIstrobo to measure turntable speed. It's very precise, although I find you can't use it hand-held if you want a really exact measurement.

This notion of off-speed turntables until after warmup is rather odd. Not only doesn't my VPI have this issue, but neither did my previous turntable, which was an Oracle Delphi Mk. III. (To be clear, I didn't have the DIGIstrobo when I owned the Oracle. Back then, I relied on a strobe disc to ascertain speed.)

You've claimed that " belt creep does exist and it is measurable." That's another rather odd claim. How have you measured this phenomenon? How can you be certain that whatever speed issue you may have detected is attributable to "belt creep?"