Turntable speed accuracy

Hi Peter,
Excellent. First, that is a really long tonearm. I'm not envious, just impressed. I noticed just a slight amount of drift over the 5.2 minutes of the song. It appears the speed is just a little fast by about 1.6%. I estimated that the line drifted about 1 inch over the 5.2 minutes and I also estimated the radius from the timeline center to the album cover to be 10 inches. So, if I did the math right, the angle changed 5.7 degrees over 5.2 minutes. If you have exact numbers then the calculations would be more meaningful. That means the number of record rotations was off just 2.8 rotations out of 173.33 rotations. Are you able to adjust the speed a bit? At the end it seemed like the line did not shift when you lifted the tonearm. Is that what you saw? Is your speed controller closed loop? When you dropped the tonearm onto the record did you see any shift in the line?

Hello Tony, You are correct in observing the slight drift to the left over the length of the video. I just measured the relevant distances and they are: drift from right edge of "Philips" label to center of label is 1/2" (0.5"). The distance from the spindle to the laser slash line is 13.5". That should change your calculations slightly.

The SME motor controller has incremental settings of, I believe, 0.1%. I can't remember where I read that though. The line does move slightly when lifting the stylus out of the groove. Halcros Victor TT video is very impressive in this regard. The SME belt drive table should be set for correct speed while playing an LP to account for stylus drag.

You are most observant to catch the slight drift to the left, which means the table is very slightly too slow. I can not hear this. A close examination of Halcro's DD Victor video also reveals a slight drift to the left of about the same 1/2". Note the laser dash is centered on the blue tack and by the end of the 4 minute video, it is just barely touching the blue tack as it has drifted to the left. This video has been held up as the gold standard reference for DD turntable speed accuracy. I have found no others on the net except the Sutherland website videos in which none of the turntables hold correct speed.

In the interest of collecting data on different turntable performance, and learning in the process, I borrowed Albert Porter's TimeLine and decided to share the results.

I'd be very interested in seeing your calculations and translating them into the actual speed, ie. 33.4 or so RPM. Thanks.

Hi Peter,

I updated my calculations and also found an error. My previous calcs were off by 100 because I had calculated a % and then used that for an absolute. The correct numbers now with your measurements are speed is fast by 0.003%. The 5.2 minutes of playing time were off by 0.0059 rotations out of 173.33. (That 100 makes a big diff in the numbers). Drift to the left means slow? Ok, I see that now too.

Thank you Tony. So, if I understand you correctly, my table is slow by roughly 6/1000th of a rotation out of 173 rotations or 0.0000346 per rotation. Said another way, 0.003% slow is 0.00003 RPM slow. So my table in this video is running at 33.3333333-0.00003 = 33.333303 RPM. Is that correct?

The precision of the Sutherland TimeLine is such that is can clearly show this deviation. I'm sure that SME and most other designers do not use such fine measuring tools when testing the results of their designs. I've mentioned elsewhere that my turntable shows correct speed while using both the KAB strobe and the paper disk supplied with the turntable.

I am perfectly satisfied with setting the speed with the KAB. But this experiment with the TimeLine has been very informative. The motor controller increments are course enough to be detected by the TimeLine. I've tested the number of increments I can hear, and it is somewhere between 4-5, either too fast or too slow. I can not detect by listening a variation of 1-3 increments on the motor controller in either direction. Perhaps others with perfect pitch could hear this.

The new TechDas turntable has "passed the TimeLine test." It would be interesting to see that video and the video results of other tables which have different drive types using a similar methodology to my and Halcro's test.
I have heard of some tables showing even better results, but without video documentation.

Hi Peter,
Sorry for the confusion this morning. I was rushing because we were preparing to go to a wedding. I was excited to see your post and wanted to reply before we left and my wife was bugging me to get off the computer and get ready to go.

The drift is 0.4 degrees/minute or 0.001133 revs/min. So after 5.2 minutes, the total error was 0.00589 revolutions out of 173.33 total revolutions. That is a speed error of just 0.003%. It may not be 0 as some DD turntables claim to be; but it is pretty close.

Your turntable is absolutely perfect. Its speed control is on the order of any type of drive system, ie. direct drive, rim drive, etc. in terms of accuracy. The only other check would be with a scope to see the constancy of speed over a single revolution (Wow and Flutter); but I'm sure it is laboratory grade as well. I wonder why the Timeline device does not flash more often. If it did, it would give some indication of speed variation during one revolution.

Thanks for sharing.