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SME speed adjustment

I have been reading with much interest the thread about speed accuracy and the Timeline device.

I have an SME Model 10 turntable which has no speed adjustment on the motor controller. I use the KAB strobe and my table is fine, but I fear that if I have the chance to check it with the Timeline, and the speed is off, I will not be able to adjust it, so the exercise would be futile anyway. Currently, when the speed changes over time, I replace the belt, as SME suggests and this usually works.

Could someone suggest a method to adjust the speed on a motor controller that does not have such an option? Is there an aftermarket device that can be used to alter the voltage to the motor controller or some other method?

Any advice would be much appreciated. Thank you.
peterayer
tonywinsc
583 posts
 
I calculate the speed error by using the distance difference between the two timeline marks over one revolution. Using a radius of 350mm, the circumference at that distance is 2199mm. That means a 1/2", or 12.7mm per revolution drift is a speed error of 12.7/2199*100, or 0.5775%. At 440 Hz, the frequency is off by 2.54 Hz. If the two laser marks were on top of each other after one revolution, then the drift is zero and the speed error is zero.
halcro's avatar
halcro
2,664 posts
 
Sorry Tony,
Whilst I measured the distance from the turntable spindle to the wall at 350mm at right angles.....the laser line was actually projected approx. 400mm from the spindle to the wall at approx. 30 degrees.
Everything I said was approximate not expecting anyone to actually do the maths?
This was just to give Peter some relativity to his concerns :-)
Incidentally.....+6Hz from 440Hz @33.33 is 33.41rpm
+12Hz from 440Hz @33.33 is 33.48rpm
-6Hz from 440Hz @33.33 is 33.25rpm
-12Hz from 440Hz @33.33 is 33.18rpm
tonywinsc
583 posts
 
Hi Halcro,
I do not quite understand how the platter speeds given correlate to the +12Hz, -12Hz and +6 Hz and -6 Hz shift from 440 Hz. 12 Hz out of 440 is a 2.73% variation. That means the platter speed must vary 2.73% as well. So I would expect platter speed to be 34.24 rpm to shift a 440 Hz tone by 12 Hz to 452 Hz. What am I missing?
halcro's avatar
halcro
2,664 posts
 
Hi Tony,
I'm not into the maths :-)
I'm simply quoting the read-outs on the digital display of the TT-101 as I change the pitch in 6Hz increments.
Perhaps someone can help with the correct calculations?
ketchup
699 posts
 
Perfect timing. I actually just made a calculator in Excel for the Sutherland Timeline. You enter the distance to the wall and the laser deviation per revolution and it gives you the circumference of the virtual circle that the laser travels, the speed error of your platter in percent, the RPM your platter is off by, and the actual RPM of your platter. It can also tell you how many Hz a given frequency is off by.

Let me know if you would like to try it out!
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