Turntable speed accuracy

My Dual turntable has a built in AC light bulb to check the strobe marks on the platter rim. It drifts over time while the KAB strobe light is stationary. So there is a discrepancy between using AC line frequency and quartz locked frequency. Jeez, I am such a KAB sucker.

From the Dual manual:
"It can happen that the stroboscope lines appear to move slightly although the exact speed setting with stroboscope lines stationary has not been altered. This apparent contradiction is explained by the fact that the electronic central drive motor operates fully independently of the line frequency whilst the only relatively accurate line freqency of the AC current supply is used for speed measurement with the light stroboscope."

I am happy that some people found their perfect turntable without worrying about these things. Us neurotics just have to suffer.

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Your 60Hz line freq, may no longer be sacred! This COULD POSSIBLY become an issue soon. A copy/paste, from a previous thread: Something that got me thinking more about speed accuracy lately, as both of my tables are equipped with AC synchronous motors: (http://wattsupwiththat.com/2011/06/25/it-hertz-when-you-do-that-power-grid-to-stop-regulating-60-hz-frequency/) (http://radiomagonline.com/infrastructure/power/60hz-stability-going-away-0627/) If you are using a strobe disc, that depends on your house lighting's 60Hz flicker, or your table has a motor, dependent on your AC's 60Hz for speed regulation; take note. This may soon become a concern. (Note: They were NOT simply referring to the nightime correction, in these articles)

when i compare various turntables to the same recording on my Studer A820 it's easy to hear which turntables get the closest to matching the soliditiy of the music on the Studer.

Nojima Plays Listz is a very good recording of Piano on Lp, and is a Tape Project tape too; in theory the solidity and speed accuracy of that tape is the reference for the Lp as we know it's the actual source. on that recording there is no place to hide any speed variations as well as inaccuracies. and there are plenty of peaks to hear also.

i do have the KAB strobe and use it. however, it's limitation is the accuracy of the printed strobe and the perfection of the center hole of the strobe.

i think the tape-Lp comparison has more value to me.

Palasr wrote: "While frequency accuracy (and adjustablity) is one issue, it doesn't begin to address waveform shape, harmonic distortion, phase amplitude and shift, and all the other interesting things that go into generating a waveform suitable for driving a synchronous AC motor."

I have a Mark Kelly AC-1 drive controller on my VPI TNT that features separate manipulation of several of these parameters, while deriving an AC waveform from a 12V battery independent of the power grid. Unlike a VPI SDS, the AC-1 is a true two-phase controller-- it eliminates the phasing capacitor from the motor tower. Varying the separate effects independent of frequency is easily audible, as are differences between belts of varying compliance-- yet the strobe disk doesn't move a whit.

No one seems to set the speed as I do. I adjust speed while playing same known track on CD as well as TT. I measure with stopwatch and play simultaneously going back and forth such that the song start and ends at exactly the same time on both CD and TT. I change source back and forth, each note sounding exactly same that you can hardly tell diff. It helps that my main CD source and TT are set pretty much to same tonal balance. It takes few iterations, but then I listen without worrying about speed. Makes sense?