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Turntable speed accuracy

There is another thread (about the NVS table) which has a subordinate discussion about turntable speed accuracy and different methods of checking. Some suggest using the Timeline laser, others use a strobe disk.

I assume everyone agrees that speed accuracy is of utmost importance. What is the best way to verify results? What is the most speed-accurate drive method? And is speed accuracy really the most important consideration for proper turntable design or are there some compromises with certain drive types that make others still viable?
peterayer

Showing 2 responses by dgarretson

dgarretson
2,588 posts
 
Don_c55, try comparing a carefully tensioned cotton poly thread to the stock elastic band on your TNT. This will demonstrate the clearly audible difference between absolute and transient speed stability.
dgarretson
2,588 posts
 
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.
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