Turntable speed accuracy


There is another thread (about the NVS table) which has a subordinate discussion about turntable speed accuracy and different methods of checking. Some suggest using the Timeline laser, others use a strobe disk.

I assume everyone agrees that speed accuracy is of utmost importance. What is the best way to verify results? What is the most speed-accurate drive method? And is speed accuracy really the most important consideration for proper turntable design or are there some compromises with certain drive types that make others still viable?
peterayer
Okay, I'm sure that I'm missing something hear as it relates to the Timeline. . .

Sutherland states that if your turntable is spinning at 33 1/3 RPM it will take 1.8 seconds to complete a revolution. His Timeline flashes at this 1.8 second interval, and if the revolutions are precise, the laser image will hit the same spot on the wall with every revolution. Makes complete sense.

However. . .33 1/3 RPM means that in one second (33 1/3 divided by 60 seconds/minute) your table will complete .5555 revolutions, or one revolution every 1.111 seconds, not 1.8 seconds.

What am I missing?
Dear Henry, What about listening? When you set the table up using the KAB vs using the Timeline, were there any audible differences? If the KAB was that far off, on the slow side, you ought to have heard it in the form of pitch distortion and/or rhythm distortion. One would have to think that one of your two devices might indeed be defective. Either that or neither is quite accurate.

I had an interesting experience just a few days ago. When I originally set up my Lenco, I had it running at 33 rpm per the KAB strobe, with AC direct from one of my dedicated house lines. (You can adjust speed on a Lenco by moving the idler wheel up or down a tapered shaft driven by the motor.) Then I inserted my Walker Audio motor controller and had the Lenco set at exactly 33 with the Walker. Then some months later, I removed the Walker and was running direct from the wall socket again, but I had not re-checked the speed when I went back to house AC. The other day, I had an audiophile friend here listening with me to the Lenco, and he remarked that it sounded "slow"; he perceived a pitch problem. So we took out the KAB strobe again, and indeed, with the stylus in the groove, the Lenco was slow. I was embarrassed that I had not picked up on this problem. However, after he left, I realized that I had been bothered by the musical timing with the Lenco. Tempo seemed consistently "slow", but I heard no real problem with pitch. I had even wondered why Ella Fitzgerald had chosen a slow tempo for a Harold Arlen tune that I considered to be a good swing. The point is that what he perceived as a pitch problem was perceived by me as a timing problem. Obviously, tt speed affects both. I subsequently re-inserted the Walker and now all is well. The brain is a funny organ. He cannot sing to save his life, and I am a long time amateur jazz singer. You would think that I would have at least as good a sense of pitch as he does.
Hi Dev,
I am using only two motors instead of the three. I found that with the standard Raven belt......the speed consistency was better than with the three.
I assume that the extra belt contact on the platter has something to do with it?
The same principle should apply to the thread and yes.....Daniel did warn me about possible marking and wear on the side of the platter with the thread because of the soft Delcrin material.....but I'm prepared to accept this for the increased performance.

Hi Lew,
The Timeline is dead-on accurate as I have proved using the TT-101.
The KAB Strobe must be wrong/faulty?
I haven't listened to the Raven set up according to the strobe since I received the Timeline. All I can tell you is that the TT-101 initially blew the Raven away (sound-wise) when the Raven was set up using the KAB.
With the Raven running the thread drive on two motors and set up according to the Timeline.......the differences to the Victor are not that great.
In other words.....I can happily listen to both decks.

Dear Solong,
Thanks for the hints.
Unfortunately......my cantilevered wall shelf slopes alarmingly to the front due to the weight of the Raven....and the motors require the utmost levelling of the feet to maintain their horizontality. Feet of some sort....are a prerequisite?

Hi Dover,
The Raven motor pulleys do not seem to allow the thread to move visually up and down.
I also have some French silk thread which I can try as well. Some sexy colours also :-)
Dover,

is your platter the same POD material as the TW product?

Looking closer at my platter I can actually run the thread either on the POD material or COPPER.

Which is the harder material? anyone know.
... your new experience with a thread driven Raven sounds good.
Next, you could try this:
- disassemble the three feet from both of your motor housings
- set up the housings flat on some kind of damping mat (a piece of anti-drone mat for washing machines would help)
- rearrange the strings

Now the motor housings are no longer able to wobble slightly on their feet (that's particularly the case when strong tension of the belt/tape/thread is applied). In my experience this has also positive effects on speed consistency and sound improvement.
The Raven is a LP12 "in heavy". No matter what you do, it will always change its "performance". Typical sub level Design attribute. Tweaking a dead cow to a horse is interesting, no doubt, but other Designers made better work.
Solong's observations regarding play in the Raven motors feet is spot on. I utilize PTFE plumbers tape on the threads of the feet to eliminate the play and the metal to metal interface. I have since applied the tape to other applications in my system including speaker spikes and triplanar screws with very positive results. Metal to metal interfaces and improperly tightened components are generally not good a thing.
It's actually 1.80018... I think it's a repeating number. Let's hope Mr. Sutherland set his timing thus. Otherwise, the instrument is off by .00018 sec per revolution. Apparently this much error would drive some of us crazy or to a new turntable.
It is actually 1.8 sec/rev. 33 and 1/3 rev/min divided by 60 sec/min yields 0.5556 rev/sec (0.555555555 repeating). Your tt makes 100 revolutions every 3 minutes or 100 revolutions every 180 seconds. So if you divide 180 seconds by 100 revolutions, you get 1.8 sec/rev.
Dear Halcro: As Dover I'm using thread drive for all the years I can remember either the MS I owned till today and my Acoustic Signature ones.

What is weird is that only " today " many people is discovering when the option always been there.

I don't know you but even with a thread the DD ones performs overall better.

Btw, what Lewm posted and that M.Lavigne refered on other related thread and my own post ( not so specific as Lewm one. ) about that the Timeline is not accurate/perfect as we all are thinking finally there is a " light " that tell us on that non accurate device that already brought some TT owners to a " suicide ".

This could tell us that we have to analize this type of TT subject more carefully that what we are doing till today.

Maybe Mr. Sutherland can comes here to explain the overall Timeline design and to confirm or not that 0.00018 discrepancy.

Regards and enjoy the music,
R.
Hi Ikitch,

what the heck I was going to re-package that and sell it for say $$$$ ha! ha! and it actually works.

Hi Syntax,

nothing like going for the jugular, the TW product isn't as bad as you make it out to be. You might not like it personally and find faults which is okay but show me one table that is perfect? You won't be able to.

Even your own MS table has issues in it's original state, you have had to mod it to enjoy. Some MS owners have even changed from the original motor because they felt there was better performance to be had.

There will always be differences and that's life, to me I'm open minded to learning but in the end it's all about listening to music.

It gets real boring and it's just frankly so old now seeing the same replies, I think we all know you don't care for TW product but others do.


Regardless of the accuracy of the Timeline as long as it is consistent then it still demonstrates there's inconsistency when the laser mark moves off target so there is a CHANGE due to stylus drag. It proves there is a change in rotation and it may or may not change the sound but the fact is that there is a change. What is so hard to get? If the Timeline cost only $50. Everyone would just get one and start questioning and addressing the speed issue of the turntable.

I love the KAB strobe and it's a useful device but it cannot show me stylus drag visually the way the Timeline does.

______
Dear Raul, I did not mean to imply that I KNOW that the Timeline is miscalibrated. I was just musing after Timeltel's correction of Catastrofe's calculation that in truth the time for one revolution, if the speed is 33.333.... would be slightly more than 1.8 sec. It might be 1.800180018.... I would assume that Mr. Sutherland knows that, too. All he had to do was to build a circuit that can divide 60 by 33.33333... and then trigger a laser according to the result, in seconds. And apparently he warned end users that they might not want to know what the Timeline can tell them. It's like going to the doctor for that pain in your .....wherever.

Dear Henry, I would agree that if the Timeline and the Victor TT101 are in perfect sync, it is likely that the Timeline is bang "on". But in general it is not valid to calibrate an instrument against the thing you are trying to measure with it.
Ahhh the vagaries of the Audiophile mentality?
Rather than question the accuracy of their calculators ( because they can't go to infinity 33.333333333333333333333....) or the accuracy of a Strobe which needs to flash at constant and repeatable frequency whilst aimed at a disc with lines printed by machines to an order of indeterminate accuracy......or question the actual speed of their turntables with sometimes primitive electro/mechanical interfaces......the majority seem to question the accuracy of a scientific instrument whose accuracy can be definitively proven?
And those appearing to do this are invariably those who do not have the Timeline nor have used it on their turntables?

There appears to be an element of fear and trepidation about these 'doubters' with 'denial' being the protection of choice?
I am going to borrow the Timeline tomorrow.

But not all my turntables are in service, so it will take a while to arrive at a full report.
Dev - the Final Audio platter material is aluminium with very heavy copper mat. The thread runs on the aluminium part. I would have thought the copper is harder than aluminium and should be safe but not absolutely sure.
Syntax: "Tweaking a dead cow to a horse is interesting, no doubt, but other Designers made better work."
That reminds me of an old Chinese saying, "ride a cow before you find a horse." For some people their turntable of choice is the cow... for the time being. :-) Or they think they're riding a horse? Or they are just "cowhide lanterns." :-D

______
Lewm ~ you don't happen to own a TTWeights table? I've now checked 2 TTWeights tables and both show inaccuracies via the Timeline, would like to have confirmed a third and then can surely say its a design fault!
Looking forward to your findings.
I'll ask this question again since the other post was deleted. What does everyone expect from their turntables when using the Timline device? Absolute zero drift of the laser mark? Here is another way to look at it. Leave the Timeline device on for 30 minutes. If you are comfortable cueing up the same record side twice, do that. So in 30 minutes the platter will rotate 1000 times. Since most tt's are spec'd to have a speed accuracy of around 0.02%, then you can expect to see the laser drift about 72 degrees in 30 minutes. That is 0.2 rotations out of 1000. Is that good or bad? That would seem very good to me. btw- the Timeline maker advertises an accuracy of 2ppm. I take that to mean the Timeline device is about 2 orders of magnitude better than a typical tt.
I hear you Tony but it seems nobody else is or wants to pay attention to you. They are believing that if the timeline isn't right nor is the turntble but yet there have only been just a couple of tables mentioned that the timeline is true on.

Brad
Tony ~ I'd be happy with what you propose BUT what I see currently with the TTWeights table is that the line moves EVERY rotation which to me is just unacceptable.
What does everyone expect from their turntables when using the Timline device? Absolute zero drift of the laser mark?
It's not an impossible expectation?
Have you not seen my video of the Victor TT-101 with the Timeline and three arms being lowered and raised with "absolute zero drift"?
Sksos1. In a word, no. I do not own a TT Weights turntable. I own a tweaked Lenco in a slate plinth, a Denon DP80 in a slate plinth, a Technics SP10 Mk3 in a slate and wood plinth, and a Kenwood L07D. I should sell two of them, but I cannot pick which ones. They each seem irreplaceable. About 4 years ago, I went from a very good belt-drive tt ($5000 class) to the Lenco and then to direct-drive, and I have no second thoughts. But I do confess that vintage tt's appeal to the collector instinct in me.

Since others here have also indicated that their turntables of many various types have "failed" the Timeline test, perhaps it is unwise or unfair to keep harping on the one brand that you found to be faulty by that sole criterion.
Should have read Tony's post before writing the above post. I think the amount of error and the type of error Tony describes should be perfectly acceptable. It is a linear error; in other words it would be the result of the platter spinning a teeny bit too fast at some constant rate. That kind of error should be adjustable back to dead on accurate, and if it's not, it nevertheless would be inconsequential. I thought we all agreed that the concern is for transient or instantaneous errors related to variations in stylus drag. Such errors would in theory go either way, too fast or too slow. So the Timeline light might move back and forth in either direction from neutral.
Hi Halcro, I saw your video. It is impressive how well your tt holds speed, but that was a relatively short period of time. Can you let it run for 30 minutes to see the results over the long term? I am very curious to see those results. If the laser mark has no drift after 30 minutes that would mean your tt has speed accuracy on the order of 0.00002%. That would be far beyond expectations in my mind. Some suggest that the speed accuracy fluctuates, but I believe that speed error is cumulative when using a device such as the timeline. That means tha the longer you run your tt with the timeline the more error, or drift you should see. I don't think that cueing and dropping the tonearm will make the line move the other way due to the motor controller. It reacts to the torque changes.
Let me clarify my one statement a little better. Cueing up the tonearm is a one time event that may or may not cause the laser mark to move. It is not part of the cumulative error. So over the long term it has little or no impact on the results. Unless something funny is going on with the motor controller, the laser mark should drift slowly in one direction over the 30 minutes. That is the cumulative error.
Hi Tony,
I have left the Timeline running for an entire album side with zero drift.
If you go to YouTube and look up the Timeline video (not mine).....you will notice on the demonstration that his turntable.........demonstrates a significant drift when the tonearm is lowered.
The Timeline is the scientific device that conclusively proved that 'stylus drag' is a reality rather than a theory.
I cannot believe that my Victor TT-101 is the only turntable which can maintain this kind of speed accuracy?
There must be many other brands.......perhaps mostly of the quartz-controlled direct drive type......which are similarly capable?
If this is the case.......then we should have the right to expect this kind of accuracy from our turntables.
Even with my Raven AC-2 with thread drive.........the drift with a stylus in play is only 0.5mm per revolution from the wall mark. If I adjust the speed on the motor controller one step UP.....it then runs fast by 1mm per revolution. But these are both constant deviations which indicate that the turntable is maintaining consistent speed.......just not exactly 33.33rpm. If the motor controller had a finer adjustment......I could get it spot-on.

The Timeline is a wonderful instrument IMHO and it is not correct to believe that turntables cannot match its accuracy?
I await the day when you actually try one on your turntable.......it can only help you :^)
Hi Halcro, That is excellent news. So is speed accuracy something that was once mastered and now lost on more recent tt's? How do we get it back? Do you feel you lose something with the thread drive since it drifts a bit? I would think not, but your opinion/experience here would mean something.
Dear Tony,
You wrote, "the laser mark should drift slowly in one direction over the 30 minutes. That is the cumulative error" Yes and no. Yes, the drift of the Timeline laser over time is the cumulative error, but no (IMO), the laser may not drift only in one direction, as I wrote above. It could conceivably drift in either or both directions over a 30-min time frame. Therefore using the cumulative error over time as a standard might be misleading. You've got to sit there and watch that laser every single revolution.... (You are getting sleepy.... Your eyelids are growing heavy... You are in my power... You will do whatever I say...)
Hi Tony,
Yes....I think speed accuracy was indeed mastered over 30 years ago but as I mentioned elsewhere......with the dominance of belt-drive over DD turntables due in large part to the Linn propaganda and the reviewers who championed it.....'speed accuracy/consistency'.......never was mentioned as a critical factor in their design philosophy?
How do we get back to it?........I think discussions such as this is certainly one of the ways and thanks to the Timeline......I hope more designers and manufacturers will be able to judge their successes or failures and hopefully make some corrections?
'Awareness'.....is our best hope?
The .5mm speed drift I am seeing on the Raven AC-2 is almost negligible.
For instance.......the Victor TT-101 allows me to speed up or slow down, the actual speed of the platter in 6Hz increments.
33.33rpm apparently gives a pitch of 440Hz which is the de-facto standard
pitch for orchestras.
However many of the world's orchestras use a pitch either 6Hz or 12Hz up or down from this?
When I adjust the speed on the TT-101 to 6Hz lower (33.25rpm).....the drift from the wallmark is 5mm every revolution and when the speed is increased to 33.40rpm (6Hz higher).....again the drift is 5mm per revolution.
So the Raven.....running at 0.5mm per revolution could really be called...'spot-on'?

And Lew is right Tony......the Timeline is not so valuable in terms of 'cumulative' drift or speed error (as even a 6Hz pitch deviation will add or subtract 5mm drift to each and every revolution which will appear quite dire over the full side of a record).....rather it is the instantaneous speed drift due to stylus drag which is valuable for us to know about our turntable's performance?
Instead of 'fear' governing our apprehension of the Timeline and what it will reveal about our turntables.......we should really welcome this information.
Knowledge is power....and ultimately the more we know about our system's objective performance.....the more equipped we are to effect improvements?
I don't like to post without actual direct experience but here goes.

Based on my TT's and what I am "hearing" and also not owning this Timeline device.

A Belt/string or idler will do one of two things on a timeline over time.

If they are slow

<----------------

If they are fast

---------------->

A direct drive because of the nature of how the motor works goes back and forth.

The DD's can not be picked up by the timeline.

The stop - go, stop - go, stop - go, nature of the DD motor keeping speed.

The DD is only at a correct 33.3 “in transition” between the time the motor kicks in to speed up and shuts off to slow down. At all other times it is not at 33.3.

Am I wrong ?

And another thing. I am going to say a really dirty word here to some people – CD

Has anyone bothered to listen to a decent CD of your favourite music compared to LP as far as "pitch" is concerned.

I think you will be surprised.

Anybody?

Finally a message to SKSOS1 - is it your intention to have another thread shutdown ?

What is Sounds of Silence that you are affiliated with. You seem to be anything but silent. Please take Lew's advice.

Cheers
Hi Chris,
The DD is only at a correct 33.3 “in transition” between the time the motor kicks in to speed up and shuts off to slow down. At all other times it is not at 33.3.
I don't believe this is a fair assessment of the DD motor technology?
There is no difference I believe, to the maintenance of the speed via the motor of a belt-drive or direct drive. Each one has to monitor its speed via a pre-programmed sine-wave algorithm related to the power supply.
The differences between the two drive types I believe, has to do more with the speed of any correction applied once a deviation is detected?
In this.....a belt or thread drive is at a severe disadvantage.
The DD motor....usually with a lot more torque than that of a belt/thread drive....and being directly connected to the platter.....can correct deviations in micro-seconds theoretically inaudible to the human ear.
With some DD turntables like the Victor TT-101......there is instantaneous 'braking' correction as well as speed-up correction...thus not relying on the time lag slowing-down procedure after an increase is applied.
To my ears......this is a more optimum audible solution than the slow speed deviations and corrections allowed by some belt/thread drive decks?

One point not properly addressed so far.....is how idlers or rim-drives perform against the Timeline?
Perhaps Lew will be able to enlighten us on this?
"One point not properly addressed so far.....is how idlers or rim-drives perform against the Timeline?
Perhaps Lew will be able to enlighten us on this?"

As a idler user I would appreciate Lews results on his Lenco. I would also appreciate how his DP80 performs, you would think it would be spot on as the TT101. Halcro have you tried the timeline with your TT81?
Henry - my post was not an assessment of the DD technology as you know.

It was strictly my theory based solely on what I have heard/read here about this timeline and how I think either of my Technics SP10 MKII's would do up against it.

Speed corrections are made very quickly with my SP10's - I do not think they would therefore register with the device. If someone in my area wants to lend me a timeline I will try it as well.

The SP10 MKII's are both "very" accurate as far as maintaining speed is concerned.

Cheers
I've got the Timeline in house.
On the Lenco, with AC supplied through the Walker Motor Controller, speed set by the KAB with an LP in play, and listening tests suggesting that rhythm and pitch are like real life, the Timeline says my Lenco is a touch fast. I will need another day to determine whether it is "regularly" fast (the error increases in a linear fashion with each revolution) or "irregularly" fast (the error is haphazard in magnitude per revolution). The first kind of error can be "fixed", if I care to do so. The second kind indicates that the Lenco is affected by stylus drag. Not so easy to fix. One red herring: the LP is sitting on a Boston Audio Mat1, which is kind of slippery; the LP itself could be sliding due to stylus drag. I hate when that happens. I hate record weights.
Halcro have you tried the timeline with your TT81?
Unfortunately I didn't have the Timeline when I had the TT-81 set-up.
Now it is too much of a hassle to remove the TT-101..... Install the TT-81....and then re-install the TT-81? Sorry :^)
One red herring: the LP is sitting on a Boston Audio Mat1, which is kind of slippery; the LP itself could be sliding due to stylus drag. I hate when that happens. I hate record weights.
Lew.......please remove the mat. Slippage can be a real problem?
Thanks Halcro, was just wondering by chance. Dang Lew that was fast, look forward to future comments you may have.

Have our monthly club meeting this week, have to ask the guys if anyone has a timeline. If not might have to break down just for kicks since I am love tools of the trad :).
I would love to know the results of using a Timeline on a massive platter, belt driven turntable like the Walker. Maybe it's a touch fast or a touch slow (which will show up as "cumulative error"), but I find it hard to believe that a 70 pound platter will be affected by even the greatest amount of stylus drag. Of course you would have to set the timeline on top or the Walker record clamp to compare apples to apples.

This makes me think. When testing your tables with the Timeline with the stylus in the groove, and you see what appears to be a slightly slow speed, how in the world do you know that it's not just the LP slipping on the platter? It seems like you would need to make sure that the record is mechanically clamped to the platter for the results to mean anything. And I'm not just talking about a little record weight. I'm talking about a several pound weight or a clamp that threads or clamps onto the platter spindle.

To put it another way... You test your TT with the Timeline on the platter with no LP and it maintains perfect speed. You then test your TT with an LP and the stylus in the groove and the Timeline says that your TT is slow, which makes you think it's due to stylus drag. That seemingly "slow" result could simply be because of the LP slipping on the platter, not the platter slowing down due to the stylus drag.
Ketchup: " That seemingly "slow" result could simply be because of the LP slipping on the platter, not the platter slowing down due to the stylus drag."
That's easy to figure out. Simply stick a piece of tape with, say, a pencil mark on the edge of the record line up with another mark on the platter and then check their alignment after the speed test to see for any drift or slippage. This was proposed by a smart forum member (Dertonarm) before.

_______
TIMELINE
Here is the video with the Timeline on the Transrotor Fat Bob which has a massive platter.
Watch how the Timeline immediately slows when the stylus is lowered?

The Timeline is also sold as a 'record weight'....although on the light side.
It is fairly easy to see if slippage is causing a problem by using the Timeline without a stylus playing firstly, then with a stylus playing on the mat and then without the mat or a different mat. It's not rocket science but this mentality of assuming the Timeline is somehow wrong and the turntable correct.......is the real problem here?
Regardless of what the speed inaccuracy is due to.......one must find it and correct it as it is distortion of the analogue sine wave...pure and simple.
The Timeline will show it....and you must correct it. Not look for excuses :^)
Hi Lew - regarding the Lenco l75. Can you please do the testing with and without the Walker motor controller. I realize setting the motor speed with the original slider is a bit of a pain. Am very interested in your impressions findings between the two.
Cheers
Hi Henry
I just re-read what you wrote. I am assuming when you say

“ In this.....a belt or thread drive is at a severe disadvantage”

that this is your opinion only.

Have you heard a string drive TT that was designed by its manufacturer for the use of string ?

Cheers Chris
Actually, since the Timeline is sitting on the spindle, and cannot fit completely over the spindle on a Lenco, which has a "fat"spindle, slippage of the LP would have no direct effect on the Timeline, in my particular report above. The Timeline is nowhere near to contacting the actual LP surface; it is kind of perched about 1 cm above it, which is as far down as it can go on the Lenco spindle.

Ct, Please say why you think there is anything of value to be learned by running without the Walker MC. I don't see the point, once I were to re-set the speed using the idler wheel adjustment. The Walker has no feedback mechanism; it only regenerates the AC used by the motor and controls motor speed by altering voltage. If anything, the WMC may reduce the torque of the single phase induction motor of the Lenco, because for this type of motor, voltage and torque are interdependent, within a limited range of adjustment.
Hi Lew - do u have a center weight with a flat top ? Bit of blue tac on the bottom of the Timeline and place it on top of it maybe? Yes that Lenco has a really fat spindle.

I am not familiar with the WMC - thanx for explanation. I have experimented with my SDS and my Lenco in the past - reason for my post. thx
Hi Chris,
My statement was directed at the 'speed' of any correction performed by the motor controller being felt by the platter?
I don't think there is any doubt that in a DD situation with the platter being attached to the motor......any speed correction will be effected faster than via a belt or thread connected to a motor/s at some distance from the platter?
If you re-read Peter Moncrief's excellent article that I posted several times........he provides a great deal of information regarding this very subject.

I'm not sure what the differences might be in a turntable designed for a string/thread drive over a belt?
Can you or someone provide some further thoughts on this subject?
Regards
Henry
Halcro, you have done a fantastic job bringing us up to speed on this and also leading the way on trying alternative ideas on your Raven. However I must pull you up on a couple of comments on DD
"The differences between the two drive types I believe, has to do more with the speed of any correction applied once a deviation is detected?
In this.....a belt or thread drive is at a severe disadvantage.
The DD motor....usually with a lot more torque than that of a belt/thread drive....and being directly connected to the platter.....can correct deviations in micro-seconds theoretically inaudible to the human ear."
Thread drives do not self correct as DD's do.
Didn't your mother tell you 2 wrongs don't make a right ? You could argue a DD is twice as bad as a thread drive. One assumes if there is a time slippage and it is a one off why stuff the next few seconds of music trying to catch up ?
Then there is the correction of the correction when the DD overshoots on correction.... as my learned engineer tells me, nothing wrong with DD's they are only a little bit out all of the time.
"The DD motor....usually with a lot more torque than that of a belt/thread drive"
This is a presumption, I'm not sure it is correct. I'm not sure how many DD's could spin my 20kg plus platter up to speed in less than one revolution as does the AC motor on my thread drive.
But to balance the argument I still lust after an SP10mkIII for a second deck.
I said it once before long ago- any tt motor that brings the platter up to speed in about a half of a revolution (less than one revolution) has plenty of torque to hold speed stable.
Also, I wanted to be the 300th poster on this thread. Yay!!