Hello,
Is there any norm about acceptable speed variation? When I look at the dots, it's moving back and forth in the same dot for about 1 1/2 minute while gradually moving to the next dot and then moving back and forth in this dot, gradually moving to the next one and goes on and on...
I don't ear specific pitch problems but it stress out my OCD a bit.
Is it normal speed variation?
Yes, there is a norm for acceptable speed variation. The DIN standard calls for a speed accuracy of +/- 0.2% for professional equipment, 2% for consumer equipment. According to your post, your SL-D2 is much more accurate than that - in fact, better than the mains so you can't really tell whether you are seeing the fluctuations of your turntable or of the mains - seriously! You are overthinking this
And you are unaware of several points that will make you sleep better (or worse, depending on your temper
) once you know them:
- The SL-D2 is not crystal-driven, it uses a resistor-capacitor circuit to set its speed, and both components have some temperature drift. As a result, it is perfectly normal for the speed to evolve over the first 15-30 minutes, and to fluctuate somewhat even after that.
- The stroboscope of the SL-D2 is not crystal-driven either. It is synchronised to the mains which is not perfectly stable: the regulations allow 0.1% drift on a regular basis, and even worst-case fluctuations of 1% for a limited time. It is not considered important as long as the long-term average frequency is accurate. So don't take that stroboscope too litteraly, it is not completely accurate either.
- At 33 1/3 RPM the stroboscope dots are accurate, but at 45 RPM they are off. This is because it is impossible to match the mains frequency with an integer number of dots. The difference is not taken into account when engraving the 45's, so if you adjust the speed with the stroboscope you are very slightly off - and don't even notice
- You will never get the stroboscope perfectly still, so stop staring at it and enjoy the music instead
- If you really really must know the speed accuracy of your turntable (and assume that your mains is perfectly accurate), you can measure it by the time it takes for a dot of the stroboscope to visually drift to the position where its neighbour was. The speed drift is given by the following formula:
dS = 1 / (F * t)
where:
- dS = relative speed drift (multiply this figure by 100 to have it in %)
- F = strobe frequency: for the SL-D2 it is 100 or 120 Hz depending on your country.
- t = virtual strobsocope drift, in seconds/dot.
Oh yeah, one last thing: since the speed tends to drift a little for the first minutes of playing, it is best to adjust it only after roughly half an hour of spinning. After that it will remain practically constant.