Stroboscopic disk sets wrong speed for turntable?


Hi all! I am new here.

I have just set up my Clearaudio concept turntable. Unfortunately, the speed of the turntable was wrong so I had to reset it. In order to do this I have used two methods: an iPhone app called RPM; the stroboscopic disk + the iPhone app StrobeLight.
The problem is that when everything is correct at 33 1/3 (both verified with the RPM app and the stroboscopic disk), the songs are playing one semitone lower than what they should. In order to make them play at the correct note, I have to set the speed at around 34 RMP as shown by the RPM app. Also the stroboscopic disk shows that now I am going faster than the 33 1/3, being consistent with the RMP app. How is this possible? Am I doing something wrong or even the stroboscopic disk is not accurate enough? Could it be the StrobeLight app not being an accurate enough light source for the stroboscopic disk? It is just peculiar that both the RMP app and the stroboscopic disk are consistent in saying that I am going too fast. 

Any help is much appreciated. Thanks!
agforte

Showing 2 responses by oldears

I presume you are counting on having perfect pitch to determine if the speed is correct. This is a wonderful gift!In any case, with  the strobe disc, be sure to use an incandescent lamp as mentioned before. As a cross check, use a test lp such as the The ultimate Analogue test LP from Analogue Productions and the hz function on your Fluke DVM. This is more precise than the strobe method and negates any presumption that stylus drag could cause a difference.
It is for the first 3 tunes where one of the tape machines ran slow. As the playback for mastering was on a different machine, these tunes are sharp on the early lps.
This was corrected later and is explained on the columbia legacy jazz cd that I have,