Direct drive vs belt vs rim vs idler arm

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.

Dear Tony,
Thanks for all your feedback and interest.
Surprisingly.......Ketchup and Richardkrebs who requested the testing I provided due to their keen interest.......have gone silent?

Halcro
Thanks again for doing these tests they are most interesting.
I did reply almost as soon as you posted. But it seems that I have suffered from moderator silencing
I did note the dampening influence of the second tonearm on the DD but it is interesting this doesn't seem to be reflected in the filtered results which showed no change. Have I interpreted the data correctly?
Also have you made any significant changes to the platters inertia from original?

Many thanks

Dover.
To answer your questions.

The servo does not know if you are going to play Mahler or Beethoven before the fact, but it does know very quickly when you do. The feedback is very fast. In much the same way that we do not know where a tennis player is going to hit the ball, yet we can follow its path smoothly without over or undershoot. This is the essence of properly designed closed loop control.

The no measurable speed change comment due to stylus drag was for the SP10MK3 and was taken from their specs. The power supply current draw observation was for the Goldmund and was a clear indication that stylus drag is real and significant. It does not, I agree, quantify its magnitude but it must be big since its effect was present even at treble frequencies. It does however give us a realtime picture. ( exluding propegation delay of the servo electronics, if you want to be precise ) I have not said that there is no measurable speed change with the Goldmund.

Loop rigidity and plinth energy dissipation. Of course these things effect attack, deacy et el. So does room treatment.

You didnt use the time line for the tests. My mistake.

The Goldmund and the LO7D are two completely different machines in concept and execution. The LO7D being an all out assult on the art of DD, TT design. The Goldmund was built to a price point using a badge engineered motor. While this motor does what it was designed to do, these price constraints show. Wrapping feedback around a motor does not elevate it above its core performance.

Peace.

Halcro.
Thanks for the test results. I agree with Tonywinsc, your dedication is impressive.