Ketchup. I like your idea of using two tomearms. I think that the test disc is 10 inch diameter, havent seen one. So could it be placed on top of a LP? Use one arm to measure frequency and use the second arm to play music on the outer track of the LP. That would be intersting.TT-101 TT-101 TT-101 TT-101 RAVEN RAVEN RAVEN RAVEN |
Dear Halcro, what an excellent job you did testing your turntables. Your dedication to the hobby is impressive. It looks like the DD table actually increased speed just a bit with the 2nd tonearm while the belt drive dropped by about the same amount. The magnitude of change being just at or under 0.1%. If I were to guess, it looks like you dropped the 2nd tonearm at around the 10 second mark? And on the Raven at about the 11 second mark? Notice that the speed on the DD recovers after 2 rotations, but the belt drive speed remains about 0.1% lower. As for being able to hear that differnce in terms of pace/rhythm, I don't know. Keep in mind too that this is an extreme test beyond any music- dropping a 2nd tonearm onto a platter. |
Hi Tony, My 'dedication' is made somewhat easier by the free Feikert App and Test disc you recommended. The 'Test Procedure' is quite easy and quick to perform. A few questions you might help me with:- 1. The Mean Frequency on the TT-101 seems to be MORE accurate with the drop of the 2nd tonearm than without it? 2. Do you have any comments on the 'shape' of the 'raw' frequency sine-waves between the two tables? Regards |
Hi Halcro, the DD table seems to like a little more load perhaps. Notice that the filtered sine wave has a period of 1.8 seconds or one complete rotation of the platter. That could be the runout of the platter, the motor controller oscillating gently around that speed set point or the way that the app filters the raw signal. The plot of my tt shows the same 1.8 second period. Since the raw signal will show record runout every 1.8 seconds, it is an easy filter to make; but some small amount may be left in the final output. The belt drive Raven filtered sine wave is showing the slow, gentle speed correction being made by the motor/controller- at least that is my guess. Someone who has done design work and measurements of turntables would have a much more valued opinion than mine. On the Raven, I wonder if given more time, ie. beyond the 10 seconds after you dropped the 2nd tonearm, it had gently corrected the speed back to the original set point- even if it was just 0.1%. As for the raw waveforms, I'm thinking that one possibility might be the response of the phono cartridge. I see the similar waveform like your TT-101 on my plot- the little breaks at the tips of the sine wave. Or maybe the more likely answer is limitations of the iPhone or the app. The sampling frequency may be too low to round out the peaks. |
