Direct drive vs belt vs rim vs idler arm

Richardkrebs
I seemed to have missed the olive branch. Was it before or after "end of story"and "for the last time".
I have continued the discussion as you have misconstrued some of my comments and not fully addressed some of my queries.
I cannot understand how the servo/speed correction system knows whether you are going to play Mahlers 2nd Symphony or a Beethoven Sonata.
You seem to be certain that there is no measurable stylus drag on the DD by measuring the power supply. This simply doesn't quantify the the stylus lag in real time that is occurring at the stylus tip.
The comments on loop rigidity and energy dissipation were put forward in the context of maintaining the attack, intensity and decay of each note. You have overlooked the fact that even if you had perfect speed stability, the attack, intensity and decay of each note can be distorted by an inadequate plinth that is not rigid and doesn't deal with the energy reflected into the platter.
It is of no consequence to me really, but you assumed I measured the variation in stylus lag using the Timeline. That assumption is not correct.
Finally, I am trying to understand how Direct Drives address these issues, but you have offered no explanation for the differences I heard and described between the Goldmund and the Kenwood L07D, particularly in speed, timing and coherency.

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.