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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 ack

ack's avatar
ack
115 posts
 
The KAB strobe disc is an approximation - a good one, though - and that can be easily proven... I place it on top of a test record, lower the cartridge (to include stylus drag) then set the speed with it.

Then, using a very accurate voltage and frequency meter like a Fluke, I put on a 1kHz tone on the CD player and measure the frequency - dead on 1kHz; this measures the instrument's accuracy. Switch back to the test LP with a 1kHz tone at 33.33rpm and the meter shows (naturally) some variations of about 1/1000, but clearly the center frequency isn't 1000 Hz. I usually have to lower the speed (in this case a VPI SDS).

Then I switch the speed to 45rpm and the meter should now read 1350Hz - yeap it does. The KAB shows I am going slow, but I know my speed is accurate.

I think the Timeline would be just as accurate, but why spend $900 when I can just measure a test frequency.
ack's avatar
ack
115 posts
 
Sorry about the price quote on the Timeline - I got it from http://www.positive-feedback.com/Issue43/sutherland_timeline.htm

No one talked about anything being the gold standard. It's my approach, and the one I am comfortable with - and confirmed by ear, by switching between a test CD and a test LP using the same test tone at the same reference output level (after the latter having been set by measuring output voltage and adjusting the DAC's output - a Berkeley Alpha in this case). In the end, if it measures the same and sounds the same, it's highly likely the approach is sound.

But others can doubt it and the accuracy of the test tone all they want.
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