Direct drive vs belt vs rim vs idler arm

Dover,

Final Audio High inertia TT has a resistance to stylus drag variation 4 times higher than the SP10mk3 & Kenwood L07D

Yet you already admitted that you have to reset the speed on your Final Audio TT to accommodate for stylus drag?

So my test procedure was :
1. Set the speed with the KAB with no record playing.
2. Use the Timeline to validate the speed at both inner at outer grooves.
3. Reset the speed again with the KAB with the record playing tracking at 2g
4. Use the Timeline to validate the speed at both inner at outer grooves.

Now I'm reasonably happy about the need for belt-drive decks without monitored speed correction.....to be set up for 'stylus down' accuracy.
But I have yet to see (via video)......a belt-drive (even with massive inertia) pass the Timeline test with and without stylus in the groove?
I think you agree with that:-

I think your test methodology would prove that only turntables with error speed correction built in will pass. We know that stylus drag exists and should always set speed with the stylus playing.

So I'm not quite sure where you're going with this 'High Inertia' argument unless you can demonstrate differences in the effect of 'stylus drag'?

Regards

Dover, Perhaps SP10-mkIII has a foot in both camps for good reason...

^ Brady, Chris (2008-10-06). "Teres MicroPrecise Speed Technology PDF". Retrieved 2009-01-15. "Dealing with stylus drag is another important aspect of a quality turntable drive system. It would seem that the tiny forces exerted by the stylus would fade into insignificance. However, given our extraordinary sensitivity to micro speed variations, the uneven force from stylus drag is audible and degrades sound reproduction. With a microscopic view, loud passages slightly slow the platters rotation. Contrary to popular beliefs platter mass changes how stylus drag affects speed but does not counteract the effects of stylus drag. A massive platter will reduce the magnitude of the variation but extends it over a longer period of time. A light platter will conversely allow a larger speed variation but it enables more rapid recovery. Heavy vs. light platters exhibit quite different sounding degradations but they are still degradations. We find the longer shallower variations that result from a heavy platter to be more benign. However, there are others that prefer the degradations from a light platter. The point is that stylus drag causes degradations that are changed but not eliminated by platter mass. The only effective mechanism for truly reducing stylus drag effects is application of torque from the motor. Increasing the available motor torque makes stylus drag proportionately smaller and therefore will result in a net reduction in the effects of stylus drag. However, increasing torque usually will at the same time increase cogging. Once again we are back to the need of finding a balance between two competing objectives. To further complicate the situation a compliant coupling between the motor and platter reduces the motors ability to control platter speed. Any compliance between the motor and platter causes a delay in the delivery of torque. When a rubber belt is used additional torque from the motor will cause the belt to stretch. This energy will eventually be delivered to the platter but only after a time delay making it impossible for the motor to compensate for short term effects of stylus drag."

From this, as an analogy, a bit like a steam engine...applying the brakes did not slow it down sharply, only a little, but the lower speed stayed for longer...

1) The Final has been shown, through your own testing, to slow down due to stylus drag.....end of story
2) You are quite right, the Final has much higher intrinsic resistance to stylus drag than the other TT's mentioned...if you assume that the others have their servos disengaged
3) Cogging, if present, at 11hz for the DD example you gave would be easily mitigated by a correctly operating servo. The corresponding frequency for the thread drive you mentioned would be around 120hz, with no servo present to corect. I leave it up to the listener to decide which frequency, would be the most benign. If you are talking about what I call "jitter" a much higher frequency artefact common on DD's, you will have to wait for my upcoming web site to see how it is addressed.
4) You need to revisit your laws on motion to see what happens to ANY drive system that does not reduce torque to stasis levels at design speed.
5) Regarding the 1000 tonearms, phase switching, full cycle detection FG, double servos,SPZ, high kinetic energy of rotation, sine cosine, et el. you shouldnt believe everything you read in sales brochures. They are, afterall, trying to seperate you from your money.
5) Hopefully, for the last time. There are many paths to enlightement. You like the Final, thats great. Enjoy the music it plays. This hobby of ours in not a competition.

Richard
1) The 0.0008% speed impact from stylus drag I measured on the Final is insignificant in the context of the other issues raised such as eccentric records etc - the ones you believe are spurious. The measured speed change is less than the wow and flutter quoted for both the SP10 and L07D with their speed correction engaged.
2) I recall you said it was a myth that the servos are operating frequently, and I assume they only occur after the drop off in speed, which will initially be higher as you acknowledge.
3) Cant comment on cogging as I dont have enough knowledge other than I can hear it on most DD's. You have acknowledged that whilst they may occur at different frequencies the magnitude is lower with the higher speed motor.
4) Pass
5) I dont believe much of what I read. Having studied engineering at the University of Auckland it is easy to identify the contradictions within the brochures. For example, as you have alluded to, there is no way the Technics would support the load of 1000 tonearms without the speed correction being employed.
6) No doubt there are many paths to enlightenment, but you haven't convinced me that speed correction is required on all turntables, which was your original assertion, based on your observations of the performance of a Goldmund Studio which I believe is a very poorly designed turntable.

Yes, thank you, I have enjoyed the Final for over 20 years.
It has not required a new plinth, redesigned power supply, additional mats & clamps , or any further expenditure to address inherent design issues.
It continues to be state of the art some 40 years after production commenced.

Gentlepeople
The problem with posts like this, where a difference in opinion is being aired, is that there is a tendnacy for us to talk past eachother and place significance on things that are written outside of what the author meant. This is perfectly natural.
That said I will try to clarify what I meant with my six points.
1) and 2) The Final has higher intrinsic resistance to stylus drag due to its platter which has a higher moment of inertia than the other two TTs, ONLY if you turn off their servos.
With the servo in play The SP10MK3 will show NO measurable speed change with retardation torque levels up to 10KG/cm. In their literature they use the analogy of 1000 cartridges tracking simultaenously. So we can infer from this that 1001 cartridges tracking will cause a speed change. I note that the Final slows down with 1 cartridge tracking. Lets make this clear, speed change due to stylus drag on the SP10MK3, even with 1000 cartridges in play, is so small that it is undetectable. You can take it then that I did do not acknowledge that the initial drop of in speed would be higher with the DDs. While a speed change must be there, with the SP10, it is not measurable. This is where correct matching of motor torque capability, servo characteristics and platter moment of inertia are critical.
I do not have data on the LO7D, but I expect that it would also perform well on this front.
For me the problem with speed changes due to stylus drag is that they are a function of the music being played, unlike wow and flutter which are independant of the music. Much like tape hiss, we can listen past w&f to engage with the music. This is not possible with stylus drag speed problems, as it is inside the music itself. That said it is obvious that lower w&f would be better.
Record concentricity problems are a pain especialy when one has just put down good money for a new record. But this is not a platter speed accuracy issue, so in that sense it is spurious to any discussion on absolute platter speed accuracy, even if its effect dwarfs any platter speed errors.
3)Cogging. I don't want to put words in your mouth, but I don't think that what you are hearing is actually motor cogging as in the physical effect of the motors construction. The very low frequency at which actual cogging occurs is, I suspect, not what bothers you. I do agree that there is a problem with many DD's, but it is not physical motor cogging and it can be fixed. (Maybe the Goldmund should be outside this comment.)
4) 5) Stasis torque levels. The platter will speed up if the torque output from the motor exceeds that requied to overcome bearing friction, stylus drag and windage. Not enough torque and the platter will slow down. Drive systems revert to stasis (low maintenance ) torque levels once design speed is reached. This is taught in engineering classes. Putting this another way. Motor torque output is a function of the load.
6) You are totally correct when stating that the DDs need a lot of work to bring them up to their potetnial. This, however, does not detract from the fundamental performance of the drive method.
Lewm said "If you prefer your thread drive to any and all direct-drives you have ever heard, that is all well and good. I am sure it is superb. But I don't think you can prove from first principles that it is inherently superior to all direct drive."
Totally correct. The opposite is also true, so let's call it a day and both enjoy this thrilling hobby of ours.