Direct Drive vs. Idler Drive vs. Belt drive

@atmasphere 
Once the motor is prepped for operation it might not do that. I pulled the motor out of my Technics as I am taking it to a machinist so I can run a longer spindle. Its really quiet!

That had not occurred to me. Thank you! Good to hear, so to speak.

But I can't hear the sleeve bearings on my little Premotec either - not until it is connected to the platter by a belt, and then only through the playback amplification. So I think that sleeve bearings are a problem anywhere in the chain, and the closer to the platter the worse it is. What do you think?

@mijostyn , comparing my big Nottingham Analogue Mentor with improved plinth, motor, and motor controller (all to Dais standard), to my DIY air bearing, is indeed no contest. The air bearing is dramatically better. Same model tonearm (TransFi Terminator), same identical cartridge (Koetsu).

But I can't hear the sleeve bearings on my little Premotec either - not until it is connected to the platter by a belt, and then only through the playback amplification. So I think that sleeve bearings are a problem anywhere in the chain, and the closer to the platter the worse it is. What do you think?

When the belt is tensioning/loading the bearings from the side (as happens with a belt), they're going to make more noise. When the bearing and the motor are synonymous, then its the thrust bearing that is likely more important.

Thanks, Ralph.  That's a very key point about direct drive (the absence of a force in the horizontal plane that pulls the spindle shaft up against the bearing wall) that the belt-ers choose to ignore.

Good point, both.

Yes, this is an advantage of a DD drive that is often overlooked. There is no horizontal force induced by a belt, thread, tape or idler wheel.

There is a toppling force if the thrust point is at the bottom of the bearing but this should be easily absorbed by a properly designed bearing. 
Invert the bearing with the rotating mass centre of gravity at the pivot and this force goes away as well. 

There is then the obsession with micro polished shafts. It might look great but technically it is sub optimal in an oil lubricated bearing. We want to maintain a continuous thin oil film. This is best achieved by a microscopically dull shaft surface finish which captures the oil film. Built properly a bearing like this has only the thrust pad as a contact point. Since this point has an extremely low radial velocity due to the small contact area, it can be made to be very quiet. Any noise in the bearing shaft/sleeve area is the shearing of the oil itself.  

cheers.  

In belt drive, you need to have everything ideal, otherwise the speed is floating.
A freqsion of needle, and bearing decrease the speed,  the motor doesn't control the platter but tries to hold a speed constant and it makes a belt tension change and speed oscillation.
Every small change of belt tension, material, width change sound dramatically.
Bass has rubber, soft sound, PRAT is broken. For classical music, especially piano music or fine rhythm jazz belt drive completely kills rhythm details and changes music for unconnected set of sounds. 

I respect all drives and am adamant they all have there strength and weaknesses. All have the ability to play quietly and appeal to the INDIVIDUAL'S preferences of what THEY believe is right for them. All of you that are biased closed minded to ownership not only ignore strengths , popularity, but embellish all faults of each in a general broad attacks not serving the truth to the improvements specific brand and model have.
Many inverted quality bearings in design and applied with a weighted platter show zero horizontal pull much less rubbing the spindle. General statements of ignorance not fact are common with all biased ownership rants. There were and are are an awful lot of horrible DD tables made not just the very very few better ones. Something few of you immerse in the generalized opinions paraded as facts.
Same as many belted units are sub par but far from all and idlers do indeed have a need of massaging out self noise. 

The final sound followed by users visual appeal is all that's important. Not what one or two gregarious opiners of one drive think here. Like when specs are brought up and championed, yet the fudging of how those numbers were done in Japan, a well known fact is left out. (Weighted )

Vinyl is a great medium for those that appreciate it and what it can bring to music. Bashing users like Rega owners who like the prat and prefer simpler less fussy of plug and play is childish. It would seem to me, inclusiveness would be a better way to respect choices and to learn. Being that guy that can only praise what he owns and shade anything or anyone else that doesn't fit their narrow view and generalized ignorance is killing interest and the participation in these forums.

It's not a simplistic obvious fact which is better. Its a choice in preference of appeal to tone and timbre, degree of difficulty and ability and willingness to achieve it ......and like it or not estetics are a key to most for appeal as part of the draw. I find it amazing what some have done and produced in all drives to better the playback and reduce drawbacks. The negative biased drivel of anything other than what one narrow mind owns here. ...not so much. Enjoy the music, respect the individual and his choice....after all. ..its opinion in the end..

Miyostin,
you are right comparing air bearing and magnetic designs.
nevertheless what counts are bearing hardness, batch braking moment and energy transmission by the bearing.

E.

has2be

I was merely (re)stating an inherent advantage of a DD design with respect to its bearing, after all the OP has asked this.....
"I'd like to know your thoughts on the strengths and weaknesses of each drive system"
I did not say that overall DD is superior. 

An inverted bearing is inherently more stable, on that I hope we agree?
My comment about the shaft finish is simply engineering 101. In the outside world it is common to not polish a sleeved oil lubricated bearing. This for the reason I raised. I know of one, possibly 2 TTs that use the non polished technique, both have well designed and engineered bearings. . These are the Final Audio Research and the big idler EMT. These TTs have very quiet bearings thru good engineering not bias 

Sure you can remove horizontal pull on a BD  bearing by having 180 degree opposed motors or an idler. That said, one would need to be very careful not to introduce noise into the platter from the second (or third) rotating element.

All TT drives have strengths and weaknesses, there is more than one path to enlightenment. On that we agree. I prefer DD, that is my opinion, others do not. I'm fine with that. 

 My experience is that it is by far the hardest to achieve good performance from a DD design. This because there is no filter between the drive and the platter. Any aberrations in the drive are exposed warts and all. This is particularly difficult if the designer chooses a high motor torque to platter inertia ratio. Difficult but not impossible. 


Cheers 
 

@richardkrebs 

Actually, Richard. Your mistaken in that I was even referencing you or your comments . The only thing I would reply to a polished shaft as a fault would be if rifling was encorperated to draw the oil upwards such as michell does would negate your view of it.
My point was and always is there are more ways to get results than the narrow view of biased ownership. 
Clearly, you don't fall in the blind bias and I know you did not state DD was superior nor did I suggest you did or do. Please reread and you will see whom ALWAYS does as in this thread.
Your last statement on why DD is more difficult to do and although not impossible is fewer than those that don't  was refreshingly pleasing to read.
None of us hear the same either complicating our opinions wrapped in facts that have as many variables changed with design and implementation from one to the next.
Believe me, I certainly wasn't referencing anyone who ever articulated what you last posted. Cheers

has2be

Peace

cheers 

IMHO belt drive have a huge drawback that idler drive and DD don’t have.
Belt drive doesn’t hold speed stabile and as result ruins the PRAT.
And it is much more important drawback than bearing noise.
No PRAT - no music!

Here is Anatoly Markovich Liknitsky article where he compares idler and belt drive.
Sorry for a bad translation from Russian language.

"Why is an idler drive better than a belt drive? If you focus only on reducing rumble, the Belt really has an undeniable advantage. After all, he has more flexibility than a movie. True, this is true only as long as the passage of vibrations along the second path is not taken into account. If we compare these drives with a predisposition to detonation, then all the advantages are on the side of the idler drive. It remains only to answer the question, what bothers us more: rumble or detonation? I personally am of the opinion that rumble is an unfortunate hindrance to the perception of music, while detonation of sound, especially low-frequency (with modulation frequencies below 10 Hz), even inaudible, destroys the integrity of music to the ground. It is because of this integrity that an idler drive should be preferred. I’ll try to explain why the idler drive has advantages in terms of detonation. In a belt drive, the moment of inertia of the disk and the moment of flexibility of the belt (rotational flexibility) form a low-pass filter [6] of the second order, which frees the rotation of this disk from irregularities. The source of irregularities can be a drive motor, as well as mechanical transmission elements of this rotation (idlers, belts, gears, etc.). It would seem that cleaning rotation from irregularities is very useful if you do not take into account that due to the absence of losses in the belt, a pronounced resonance is formed with a Q factor of 20-30 at the cut off frequency of this filter. This resonance, as it turned out, does not weaken, but rather enhances the irregularity of rotation. Due to insignificant mechanical disturbances in the drive, caused, for example, by slightly uneven friction in the axis of the rotary disk or by slightly varying thickness of the belt, a rotational “swing” of the disk occurs at the frequency of this resonance. We call this phenomenon, similar to the rotational oscillations of a pendulum in a mechanical watch, rotational resonance. Swinging of the disk in a belt drive is usually observed at frequencies of the order of tenths of a hertz and therefore causes low-frequency destructive music detonation of sound. For similar reasons, the actual, that is, not weighted, low-frequency detonation of sound in the B1-01 Electronics player reaches 0.5%. It can only be reduced by damping rotational resonance. However, in a belt drive, this damping is practically not feasible. Nobody has yet succeeded in making a flexible belt with the necessary internal attenuation, and adding viscous mechanical resistance to the axial bearing of the rotary disk, although partially correcting the situation, will increase the load on the drive motor to unacceptable limits. Trying to solve this problem, some companies tried to apply a belt, inflexible in the longitudinal direction, for example, waxed cotton thread, and immediately faced a new problem: how to hold such a belt in tension? After all, without tension, he will not be able to rotate the rotary disk and in the end it will simply fall down. The way out of this predicament is to pull the thread with a passive idler held by a spring or elastically suspended by a drive motor. By the way, in a similar way, that is, with the help of a thread stretched by a spring, the unit of variable capacitors was rotated in the radios of the 30s. But what have we come to? A thread drawn by a spring is a thread with flexibility introduced into it, and without mechanical losses! So, it turns out that we are back to where we started. The “inflexible belt” turned out to be a beautiful myth, which allowed for one audio season to hide the problem of the belt drive under the carpet. There is also rotational resonance in the idler drive, however, it is well damped and therefore does not enhance the detonation of sound. Good, that is, critical resonance damping is achieved in this drive in a natural way, due to the successful combination of flexibility and mechanical resistance of the rubber ring nozzle on the idler. No wonder the drive of this type was originally called friction."

alexberger, you are living in a dream world. After a point you are incapable of hearing speed variations. Any decent turntable of any type operates well below that point. What you do hear is noise particularly rumble which affects everything above it. Idler drives are a total loss when it come to rumble. Every last one that I have had in my system and heard elsewhere has failed miserably. With a properly equalized subwoofer system it is virtually impossible to use one. 
My arguments against direct drive are less fundamental, more ambiguous. Back when I was in a situation where I could compare turntables (I worked with Sound Components in Miami, FL back in the late 70's early 80's) we listened to several direct drive tables and in the end all of them sounded ....muddy in comparison to the best Belt drive tables. We hypothesized that it had something to do with an oscillating magnetic devise directly under the cartridge. They all had incredible specs. Nobody was using idler drives at the time. They had all been relegated to the trash bin of history.
You will notice that 90% of the best and most expensive turntables made are belt driven. You think that Techdas or Clearaudio couldn't build a direct or idler wheel drive if they wanted too? The reason they don't is because there are problems with those designs that can not be overcome and the only benefit is a level of speed accuracy you can not hear.
If you like vintage stuff that is fine but don't tell me it outperforms modern gear. That is just wishful thinking.  

Mijostyn,
Do not agree on your vintage design comparison. EMT R80 and Denon M100 outperforms most of the other modern gear. You need to keep them in a very stable and well serviced condition. 

E.

Hi @mijostyn ,

I had Nottingham Analogue Spacedeck and Lenco L78.
I used a heavy 20kg plywood plinth with Lenco and vintage SME 3009 mk2 tonearm.
With the same cartridge Lenco had:
Better bass, better separation better PRAT.
In term of dynamic and tone (on vocal, strings) both turntables sounded similar.
On piano and organ Lenco sounded much better.
The classical piano interpretations had logic and content on Lenco,
in contrast on Nottingham classical piano interpretations sound like unconnected set on notes.

My friends and I moved to DD EMT (950, 948) turntables and they don’t sound muddy at all.
The one important thing - don’t use EMT (950, 948) internal phonostage.

Regards,
Alex.

Mijostyn, have you had direct communication with techdas and clearaudio? I was wondering how you would know the basis for their marketing decisions. I don’t know about techdas but in my opinion clearaudio is a company that does not really make anything much. It seems they collaborate with other anonymous companies who make the products that are then marketed under the clearaudio name, in at least many cases.Before anyone attacks me, this is not to say that some of their products are not very good. I know that they have a large following. And in the current atmosphere, there are not too many companies outfitted to make direct drive turntables. Whereas as I have said before it is quite a simple matter to make a belt drive turntable and then market it under several different guises with increasingly elaborate bling  that can be priced at different levels from low to high.

Axelberger,
you need to have a look at real good belt designs, not a platter transported by just one small motor as the most are. You need to have two big motors to the left and right steered by a control unit where you may change the pitch slightly. If you have the chance listening to one or the other table comprising these features (also tape) you will open up your eyes ☺️
E.

Hi @thuchan ,

Yes, 3 motor belt drive solutions like Audio Note or Clear Audio have to be technically excellent in term of Wow and flutter.
I didn’t listen these turntables at my home. They are out of my budget.
I listened 3 motor Clear Audio in other system. It is really good. But I can’t compare it to my stuff, because the system was different (including the cartridge).

What is really matter for me,
I spent $500 for Lenco + SME 3009 + plinth.
Which belt drive turntable in this price range (including second hand) can compete to Lenco? Nothing came even close!!!
I bought EMT 948 with EMT 929 tonearm for 2500 Euro. Which belt drive turntable in this price range (including second hand) can compete to EMT 948?

Regards,
Alex.

Problems with two or three motors are: (1) They have to be perfectly in synch with one another, and (2) you now have two (or three) potential sources of noise that could be transmitted via the belt to the platter.  No free lunch.  I also think that we anal audiophiles worry perhaps too much about issues that are in reality way below background, if the product is well made and engineered.  So 2 or 3 or 4 motors (how about that?) might be fine.

Hi @lewm ,

People think that belt drive is a black magic, technically perfect solution.
You just need a heavy platter on a good bearing and you have very low, inaudible level of Wow and flutter. But it doesn’t work this way. At least, mid-price belt drive turntable have a very perceptible level of Wow and flutter, and it is much worse than rumble that good designed, affordable idler drive like Lenco has.

Regards,
Alex.

In a synchronous motor the rotor lags behind the rotating field. This angle changes with changes in load There are subtle differences between motors, even with apparently the exact same build. This results in slight differences in this lag angle for a given load between (identical) motors
In a multi motor design, this means that one motor will be the master and the other(s) will slave this. 
The master providing the bulk of the drive torque. 

Consider the implications of this characteristic when 2 or more motors are used to drive a platter    

Thucan, more wishful thinking. If you can't afford new stuff that is fine. Buying used gear that is within your budget can be a smart way to increase the performance of your system.  But trying to compare a D103 in any form to a Lyra Atlas or an Ortofon Windfeld Ti is ludicrous and delusional. However most do not have speakers capable of resolving the difference so spending the extra money would also be sort of silly.

Alex are you kidding? I would wager $1000 that you can't hear the difference between a cheap belt drive and an SP10 in regards to wow and flutter. Not only can you hear rumble but it also distorts everything else you woofers are doing. And, since when have you made that comparison in a scientific fashion. Let me answer for you. Never.

Lewn, I do not own a Clearaudio Turntable because I do not care for their designs but they are very well made. Way better than say VPI. I do own one of their cartridges and it is well made and quite delightful.
I do not have to have direct communication with either. I only need to see what they are doing, knowing that both are trying to attack the state of the art in their own way. Anyone can make a direct drive table. The motors are readily available. Even VPI managed to come out with one. Belt drives are not that simple. There are complexities under the surface that take careful engineering. It is how ever and this is not IMHO, the most elegant way to make a high performance turntable and the vast majority of turntable manufacturers feel the same way. The vast majority of audiophiles with expensive systems also feel the same way. There are a few new DD turntables that I have yet to hear but the basic problem remains, an oscillating magnetic device directly under an exquisitely sensitive magnetic device who's job is to resolve magnetic oscillation.
Magnetic field strength drops off with the square of the distance. Every centimetre increase in distance between the motor and the cartridge decreases the motors influence over the cartridge by a factor of 10 increasing exponentially. I believe I would prefer an idler wheel drive table over a direct drive (haven't made that comparison) even though I would have to shelve my subwoofers. 
This is why Howard Johnson's made 28 flavors. Some people would rather look at a turntable than listen to it.      

mijostin  I would offer the counter view. It is far harder to build an acceptable DD than BD for the reasons I noted earlier in this thread

Further with respect to the distance from the source, as you say the inverse square law applies. Double the distance and the field strength falls to 1/4 of the original. The 10 times per cm factor you sight applies only if the reference field source is originally 3.16mm away from the cartridge, a physical impossibility. 

Also one would think that a ID would experience this interference issue since the motor is similarly close to the platter. 



I

Mijostyn.

Correction to my earlier calc, for those of you looking at my numbers.
The original distance would be 4.63mm, where plus 10mm gives a 10 fold reduction in field strength. Still a physical impossibility. Apologies, for my typo. 

Cheers. 

Once one hears a great idler or direct drive, it would be very heard to go back to belt drive.  I have not heard a belt drive under 10 grand that can deliver the punch and very organic sound of the idler drive or the very accurate sound of the direct drive.  They really make music sound like music.  Under 10 grand if you want a decent belt drive table and can live with MM cartridges, the older B & O tables actually are not bad and can outperform many other belt drives.

Hi @mijostyn ,

Good designed idle drive and DD don’t have high level of rumble.
But Steinway piano on a belt drive turntables sounds like cheap $100 electrical piano.
The sound of organ on a belt drive turntables is a total disaster.
If you listen pop music and sounds you don’t care, but for classical music a fine rhythm accuracy is everything. The fine rhythm makes a difference between a genius interpretation and mediocre interpretation. Also belt drive turntable sound has lack of energy, dynamics and life.
I think belt drive fashion it is the worst delusion in Hi-End audio.

Regards,
Alex.

@mijostyn

Not only can you hear rumble but it also distorts everything else you woofers are doing.

I have a Rek-o-kut and it has a little rumble. It’s old and the plinth is crap. I also have 2 rebuilt and updated Garrard 401s. There is no rumble or woofer flapping on my Spendors or REL S3 sub. And piano and organ sound right. 

Mijo always trots out the good old high rumble fluff whenever idler drive is brought up.
Mijo, I invite you to come over and listen to my 401 playing through Spatial Audio M3 TM and a pair of ML subs.
Pretty sure between all of the large cones there one would be able to see/hear them “flapping” very easily.
Hey but what do I know,maybe I am blind as well as deaf, that must be it.....

Dear Lewm, from your description it looks to me you have never experimented with two motors and a serious belt (tape). Forget three motors! Four motors is an option if you put it in a design like Burmester does. Having implemented a serious 2nd motor in a proper way (use a very good steering appliance) you may reduce additional sources of noise and you have counterfighted the source of drawing the power to only one side! Think about it and maybe do it!

E.

Dear Mijostin,
Clearaudio make some very good cartridges. Just take the Goldfinger II. They are famous for that, much more than their tables and arms. So I do agree with you on that. But not on your old/new comparison.  I do have new stuff, no problem about that. This is the reason why I am able to compare. If you go for an old and perfectly looked after vintage R 80 you end up at about 50 mios. I would not call it a bargain. Comparing a D103 against an Atlas is very easy, not forgetting that we have some very nice improvements on that cart. If you end up with subtle differences you really should change your amps and speakers. So we are talking about good systems and a serious approach to compare units in your own room.

E.

...not mios but thousands. Sorry.

E.

Just to clarify that I am not a hater of any drive format but just I know what I hear and what i am liking in said hearing.

Prior to the 401 I had numerous belt drives including a Nottingham Analog Spacedeck, not their best but a good table.
With exactly the same lomc cartridge running on the 401 there simply was no comparison, the 401 has dynamics, life, soul whatever you want to term it in spades over the Notts.
Now I have also owned two Victor DD, the TT-81 and the TT-71 both with respective Victor plinths and tonearms ( ua7082 and ua7045).
Again both just sounded flat and lifeless next to the 401.
Just the way it was in my system, I never wanted this result, it just is what it is.
All are gone now apart from the 401.

A wise friend said to me while were discussing this...." you cannot unhear what you hear" 

Thuchan, I was only joking when I mentioned using 3 or 4 motors. However I think there actually was or is at least one commercial product with 3 motors as an optional “upgrade”. In these discussions, it is my tendency to favor direct drive and idler drive over belt drive, but I certainly do recognize that there are very fine belt drive turntables that have sounded wonderful to my ears. As I noted earlier in this thread, I think, the Doehmann helix turntable is one of those latter. But you have to spend what is for most of us big bucks in order to get to that level of performance. And lesser levels of belt drive turntables just don’t cut it for me.

Richard, I was surprised to read your comment about the difficulty of designing and building a direct drive turntable. With respect to vibrations. Because to me a saving grace of direct drive is that there is no physical contact between the motor and the platter, the platter itself is the rotor of the motor. It is driven by the magnetic forces generated at the stator which never touches the rotor. So the only issues are accurate speed and speed stability despite stylus drag, bearing friction, etc.This is not to say that designing and building the world’s best direct drive is not a challenge, but I would have thought that one of the challenges is not motor noise of the mechanical type.

Dear Lewm,
got you! 😀 there are many products with three motors which is just a waste of energy, time & money. When I went to Burmester in Berlin I had the chance to look deeper into their new 4 motor concept. Brilliantly implemented!
E.

One could argue that if they have to add so many motors, the fundamental belt drive implementation might be flawed.

So, although I was joking about 4 motors and never dreamed there actually IS such a turntable, Burmeister have built it.  I'll probably never get to hear it, so I leave it to you to consider. But the more motors you have driving the platter, the less of the circumference of the platter can be contacted by the belt, which means a smaller "contact patch" and greater energy losses, more opportunity for belt slip, unless each motor or each pair of motors drives/drive the platter via separate belts.  I'd guess that is the case with the Burmeister.

Burmester, not "Burmeister".  I just looked at a photo.  One cannot see how the belts and motors are implemented but from the text, I am not sure.

Some more detail on the Burmester 175.

"The drive is not only equipped with its own tonearm and MC system, but also with a first-class phono equalizer, which is even supposed to keep the legendary stand-alone component Burmester 100 at bay in some areas. The barely compact turntable may still be worth its price of 31,800 euros, but its fighting weight of 60 kilos is not. This classy lathe is incredibly heavy!"

They are not joking as regards the pricing, I say! 🤭
Michélle 

Some more if you please... 😉 

The fact that the housing of the new Burmester 175 record player “builds so high” has, of course, also very practical reasons, after all, the developers packed in some key features. Above all, four motors, which, according to the manufacturer, are in the outer square around the sub-plate. One speaks here of the squaring of the circle, and relies on several belts, so that no uneven pull on the central bearing can arise. A total of four belts are used here, two for two motors each, which, according to the manufacturer, improves the synchronization, but also shortens the start-up.

The AC synchronous motors used here are driven by digital motor electronics, based on a high-precision oscillator and a perfect sine voltage. According to Burmster Home Audio GmbH, the electronics here are designed so that they are completely immune to fluctuations in the mains voltage frequency.

La di da, 4 motors, 4 belts - is this because they can not build a DD table? — Or is it they think 4 belts are better than none? 🤔 
M. 🇿🇦 

Lew.
The problem is not the motor it self making noise. 
This assuming the designer has used a good one. The problem is the interaction of the controller/ motor/ platter feed back loop.

IMO the designer should use what I call a very tight motor. I mentioned earlier the phase lag between the rotating filed and the rotor...... 
Imagine a clock with 2 second hands. One is driven by the motor the other is pulled along by the driven hand via a rubber band ( now where have we seen this before?) As load increases on the hand being pulled, it stretches the rubber band a little but still takes 60 seconds to complete a circle. Reduce the load and the gap between the two decreases, but again it still takes 60 seconds to complete a circle.

In a tight motor the rubber band is very stiff and it takes a lot of extra load to make it stretch further. In a loose motor the opposite is true, the hand can easily move about, increasing or decreasing the gap. 

If we now apply feed back around these  two types of motors we can see that we can be less precise with the loose motor as it will have a softer response to and input command. Whereas a tight motor will respond quickly feeding into the platter. This does not mean that the loose motor is a better choice, since,it will not control the platters speed as well. There is an unavoidable lag between command and response. What is does mean is we need to be very careful to finesse the feedback to a tight motor to give us good dynamic speed stability. If we don't we will induce noise into the platter as the motor rapidly responds to an excessively aggressive command.  

And no, a high inertia platter won't save you, it just extends the time constant, meaning that it takes longer still to correct. The motor needs to be able to dominate the platter. 
An iron fist in a velvet glove. 

cheers. 

An update to my last post. A point I didn't make clear. 
The change in angle between the  rotating field and the rotor due to dynamic changes in load is a momentary change in platter speed. It is measurable and audible. Over time the average speed does not change, so we would not see this effect with say the Timeline laser. This, because it only tells us if the average speed is correct. These multiple subtle speed changes go unnoticed when this type of  measurement is used. We need to use much higher levels of granularity to see them. 
Further we do not perceive them as actual speed changes. ("that piano decay is wavering") isn't a descriptor one would use for this effect. It is more along the lines of solidity. Can we imagine walking up to the sound and actually holding it. Does it have mass and texture. These features are negatively impacted by these micro speed deviations. 
An aside, the cartridge doesn't differentiate between a change in platter speed or a momentary change in platter/ arm position. Both actions will be interpreted as a speed changes. So we need to have brilliant bearings in the arm, we need to pay close attention to the paltter bearing, the mounting of the arm with respect to the platter and of course we need to carefully control any tendency for things to resonate. I think that the key imporvements we will see in future TT designs will be the holstic attention to this time domain parameter. 

cheers.    

 

why servo’s suck.....

In order to pick up sound accurately from the analog disc, the rotation of the platter must be rotated at a constant speed without any “fluctuation”. In general, accurate rotation is obtained by servo control by negative feedback, but at the micro level, if it rotates or becomes faster, it detects it and slows it, and repeats the operation to make it faster if it gets slower. Although this level and cycle are determined by the gain of the control system and the loop speed, the period of the speed control of the platter which is the mechanical system surely comes into the audio band. In general, accurate rotation is obtained by servo control by negative feedback, but at the micro level, if it rotates or becomes faster, it detects it and slows it, and repeats the operation to make it faster if it gets slower. If you try to measure a period with a small level, you can not measure the instantaneous state, so you measure the average value. Therefore, fine vibration generated by servo control can not be measured by the measuring instrument, it depends on the human ear.

yes.......the human ear.

when we consider belts, idlers, and direct drive........2 of those have the choice of no servo’s.

i’ve owned a number of top flight direct drive turntables; including the Rockport Sirius III, the SP-10 Mk2 and Mk3, and now the Wave Kinetics NVS for the last 9 years. taken singularly; none of those were obviously lacking in speed solidity and musical flow. but over these last 6-9 months, in direct side by side comparison to the Saskia model two idler, and the CS Port LFT1 Belt drive, neither of which have servo’s......this idea of the human ear hearing the musical cost of feedback is very real.

execution of an idler or belt to the degree to take full advantage of the lack of feedback is paramount, but when you do your ’ears’ will thank you.

I agree than servo feedback can cause some compression.
But if the motor-platter system has a smaller inertia the harm is leser.
Because that EMT 950 that has a very powerful motor and very light platter sound best and most dynamic compared to other DD turntables.

Yes, the belt drive have advantage of very low noise.
BUT, when you listen an orchestra,on one hand you can listen a 10th violin separately and other small details, but on the other hand the rhythm and flow of music is broken by belt drive momentary speed fluctuations. I think the rhythm accuracy and flow of music is much more important than small details.

I agree than  servo feedback can cause some compresion.
But if the motor-platter system has a smaller interia the harm is leser.
Because that EMT 950 that has a very powerful motor and very light platter sound best and most dynamic compared to other DD turntables.
Belt drive have advantage of very low noise. But OK, when you listen an orchestra,
on one hand you can listen a 10th violin and other small details, but on the other hand the rhythm and flow of music is broken by belt drive momentary speed  fluctuations. 
I think the rhythm accuracy and flow of music is much more important than small details.

atmasphere's (Ralph's) point about tension on the spindle with the belt pulling to one side was addressed by one table I'm aware of.  I owned an original Well Tempered TurnTable and the spindle well had five contact bearing points.  Two were inside the well (maybe 45 degrees apart?) near the top nearest the belt position, two more were nearer the bottom of the well and opposite position of the upper two, the fifth was at the bottom of the well in the normal position.  This way the tension applied by the belt held the spinal shaft against the upper two bearings while a vertical position was maintained by the two opposite bearings lower in the well.  The spindle shaft could wobble within the well until the belt was installed to bring it vertical with pressure on all five bearings.  I don't know if any other manufacturer adopted this simple but ingenious solution to retaining a vertical spindle shaft? 

i’ve owned a number of top flight direct drive turntables; including the Rockport Sirius III, the SP-10 Mk2 and Mk3, and now the Wave Kinetics NVS for the last 9 years. taken singularly; none of those were obviously lacking in speed solidity and musical flow. but over these last 6-9 months, in direct side by side comparison to the Saskia model two idler, and the CS Port LFT1 Belt drive, neither of which have servo’s......this idea of the human ear hearing the musical cost of feedback is very real.

execution of an idler or belt to the degree to take full advantage of the lack of feedback is paramount, but when you do your ’ears’ will thank you.

At 53K before tonearm I would hope the Saskia has what your previous DD’s did not. I would love to hear one to compare with my much less expensive set-ups. I have maybe 18K in my hot-rodded 301. 4K for a nearly NOS drive unit. Close to 2K for a solid brass platter, another 1K for a solid brass spindle/main bearing, close to 2K for a PSU to decrease motor noise, 3K for a custom plinth that weighs 50 lbs or so in layered cherry with cocobolo outer veneer, another 2K for things like an AS idler wheel and stillpointes, and 4K for my Reed 3P arm.
I trust yours sounds even better (since you are a regular on what’s best) and I happily surrender as to bragging rights and perhaps curb appeal. I can not convey how much pleasure my 301 gives me in every way. I have grown to love it more than my totally hot-rodded TD124 with nearly identical improvements and arm. By a smidge.
Both combine the durability of transcription table design with modern aspects and yet again with vintage aesthetics.
To me and perhaps me only, a turntable need not look like a piece of laboratory equipment. And I don’t think the Saskia looks like lab equipment, but stuff from TechDas et al.......