Direct drive vs belt vs rim vs idler arm

Richardkrebs :

Let's assume we are tracking at 2.0g.
Now let's break down the stylus drag components into 2 parts - one being stylus drag due to the tracking force ( A ) and the other being the variation in stylus drag due to the variations in the music ( B ).

I measured A, not B.

A - Stylus Drag Due to Tracking Force ( assume constant ).

When you drop the stylus into the groove the high inertia TT drops 0.008%.
( By the way - this was a very conservative estimate to avoid debate, it's actually less )
Now I believe the Technics will drop by 4 times this if the servos are not on due to the lower inertia.
The Technics maintains speed because the servo kicks in.
This is no different to me adjusting the speed via the controller to account for the constant drag...except for the following -
When I bring the speed up to adjust for the 2.0g tracking force I bring it up manually until it the speed is stable.
The Technics servo will react by increasing the speed. The catch here is that the servos only react to errors or changes in load and they dont know the magnitude of whats coming, so they ramp up the response until such time as they detect the speed is too fast - they overshoot. Then they have to correct for the overshoot. This becomes a constant cycle of overshoot and undershoot. You might not be able to measure it, but it is there.

B - Stylus Drag due to Variations in Music

I cannot measure any stylus drag with the high inertia TT. I checked for variations on both inner and outer grooves.
I assume if it exists it is too small to measure.
Same argument exists as in A above, if there is any variation then your DD servo will kick in according to some preprogrammed parameters, and once the servo kicks in, again you end up with micro overshoot and undershoot - too slow, servo, too fast, servo, too slow etc

Now we can argue until the cows come home a to which is better or worse, and which cow comes home first will vary depending on the design and quality of the individual design.

Wow and flutter versus Stylus Drag
I would give equal weight to these. If I am listening to a piano concerto, I want to hear the attack, intensity and decay of each note as well as the ebb and flow of the performance.
I would also suggest that to reproduce the attack, intensity and decay of the note, then the record/platter interface and platter/bearing/plinth design and how it deals with excess energy and maintaing a rigid loop will have a major bearing as well as stylus drag. Certainly the designers of the Final believe there is significantly more energy generated than that required to move the stylus which needs to be dealt with effectively, whilst maintaining a rigid loop between cartridge and record to measure the groove accurately. Removal of this excess energy in my experience is analogous to lowering the noise floor - increased resolution, less smearing of notes.

Re the cogging : I cannot be sure that the instability I heard is cogging. I have described what I heard a the response to Lewm which was posted prior to your last response. It may be the servos, lack of inertia or other issues, but I would add to your comments that cogging can be induced by poor power supply design if the current waveform driving the motor is not maintained accurately as well as the motor itself. I have seen a number of TT's where the power supply regulation is poorly designed and literally turns on and off whilst playing.

Cheers.

I was wondering if someone with two tonearms can do a simple test with the Feikert Android/iphone app. Play the test tone with the first tonearm and begin recording. After some data has been collected, drop the second stylus onto the record and see what happens to the tone. If the app is sensitive enough, this might show how much the platter slows due to the additional stylus pressure, how quickly it recovers, and how much it overshoots. It would be really interesting to do the exact same test on a number of different TTs.

Dover. I tried to get out of this thread by offering an olive branch since I sense that we are going nowhere.... oh well.
The argument that servos cause overshoot followed by a period of slowing and then repeat does not hold up to analysis. This pitch was likely put out into the market by BD manufacturers and it has taken root in the collective thoughts of the audio community.
We use servo control here almost daily on small and large machines. If they behaved as you describe the machine performance would be totally unacceptable in some cases destructive and dangerous. Servos are not fully on, fully off devices. They have response curves, gain, ramp rising and falling, dead band and frequency responce adjustments. These parameters are talored to the task. We tune then for this. Properly implemented they do not overshoot and as we apply then here they achieve a staggering level of accuracy. The same applies to DD and ironically this is proven by the scope tests I did on the Goldmund. You will recall I could see the music being played at the time on the scope, even treble information. If the servo was correcting, over shooting, correcting undershooting..etc, what I would have seen would be a series of square wave like pulses with little relation to the music as the platter acceleration/ decelleration time constant would smother the individual current draw/music waveform. (I have said before. A correct match of motor capability, platter inertia and controller) Say what you will about the Goldmund, but one feature it has is a very mechanically stable speed measuring system. This along with the servo iteslf was doing its job correctly. ( lets keep physical motor cogging out of this)

I hesitate to use the "spurious" word again, but while loop rigity, energy dissipation etc are topics dear to my heart, as you well know, they are spurious to the discussion on platter speed stability.

Wow and Flutter, stylus drag speed change. Yes I knew the moment I pressed submitt that this would draw a response. I will concede that they are both troublesome. That said as per my earlier post, stylus drag induced speed changes are below the threshold of measurement with the SP10 MK3 and most likely many other DD tt's. On the other hand the time line is ineffective in measuring your type B stylus drag because, by its very nature, its effect is transient and the time line is measuring an average.

Agree, quality power supplies are critical to the correct operation of....just about everything in our hobby.

Ketchup. I like your idea of using two tomearms. I think that the test disc is 10 inch diameter, havent seen one. So could it be placed on top of a LP? Use one arm to measure frequency and use the second arm to play music on the outer track of the LP. That would be intersting.

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.

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.

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

Halcro, I am interested in your response re "platter inertia", which is to say, are you using an aftermarket platter mat that adds significant mass?

Would be interesting to look at the audio output waveform, to see whether those notches in the peaks are also present there. One could just put a 'scope on the output of the phono stage. 1000Hz is a good frequency to look at.

Now that we are adding a touch of real data to the discussion, things become more interesting and cordial. Thanks, Henry et al.

Halcro,

Thanks a lot! I was actually waiting to respond until I had some time to really study your results so I wouldn't ask any stupid questions, but all I have done so far was to take a quick look. So, a stupid question.

Is the app capable of outputting frequency versus time data instead of a graph? It might be interesting to see changes over very small units of time. When I requested the test, I thought it might be useful in seeing micro speed changes, but I'm not sure if that will be possible. What do you think?

the DD table seems to like a little more load perhaps

Does your DD table have an oil filled bearing well? If it actually does like a little more load on it, it might be possible to improve its speed stability by using a higher viscosity oil. This is getting interesting!

Have any of you thought it ironic that the speed checking disc and software you are using to evaluate stylus drag and its impact on speed stability is supplied by a company that sells rubber belt drive turntables. Creepy eh.

Richard/Lew,
I have added no mass to either the Victor or the Raven turntables.
In fact....I am playing the TT-101 WITHOUT the standard rubber mat. A 1mm thick sheet of pigskin being the only separation between vinyl and aluminium platter.
With the Raven...I am playing the records sitting directly on the copper platter top-plate.

Ketchup,

it might be possible to improve its speed stability by using a higher viscosity oil.

Have you seen my video of the TT-101 with the three tonearms going up and down monitored with the Timeline?
I have seen no visual evidence of any other turntable equalling this degree of accuracy and speed stability?
Did you note the 3150 Hz frequency on the Feickert sine-wave test with 2 tonearms on the platter?
How much improvement do you visualise?

Halcro

The reason for my question was that it is popular to add significant inertia via metal aftermarket mats. The thought is that this can screw with the servo, which if excessive, it should. I was curious, given the tight control, spot on frequency, if any significant change to the platters inertia had been made.
Great result.

Richard and Henry, Well actually Henry has made a change to platter inertia, in the downward direction, by removing the platter mat. I am guessing, based on my DP80, that the Victor OEM platter mat is a rubber one. If it's like the DP80 platter mat, it weighs a bit more than half a pound. The pigskin mat probably weighs far less. Now that Henry has this measurement system up and running, it would be very informative indeed if he/you could repeat your experiment with the OEM rubber mat in place, so see what happens to those notches. Then also you could do experiments with some of those very heavy aftermarket mats, e.g., the ones made by TT Weights if you have one lying around, to see just how much and at what point extra weight affects the servo. (Or just stack a bunch of LPs on the platter.) We've been talking about the possible effects of hi-mass platter mats here for years, with no actual data.

This is all about speed stability, servos, and the like. I have no doubt that the TT101 probably sounds better with the pigskin mat than it does with its OEM mat. Same holds for the DP80, on which I use a Boston Audio mat.

01-24-13: Richardkrebs
Halcro
The reason for my question was that it is popular to add significant inertia via metal aftermarket mats. The thought is that this can screw with the servo, which if excessive, it should.

Krebs Upgrade

Hi RichardKrebs
As part of coming up with the Krebs upgrade were you able to determine what the weight threshold is for an SP10MKII platter before it starts to ^%*% with the servo. Very much interested in your opinion as I have a couple mats. Thanks.

Ct0517
The Krebs upgrade causes no material change to the platters inertia and I have not done any tests on the effect, if any, of extra mass via heavy matts or clamps. This was part of my line of questions to Halcro on any changes to the 101's platter's inertia.

So the quick answer is that I don't know where the threshold is, but would very much like to find out.

Just a little plug here. Customers of both MK2 and MK3 upgrades have universally noted a marked improvement in percieved speed stability. Some of these customers are using heavy aftermarket metal mats and clamps/weights, which appear to have no negative effect on the servo.
Ken McCarty's review of the MK3 upgrade on Albert Porter's system thread covers the speed topic nicely.

What a great thread! I tune out for a couple of weeks and almost miss the best thread in ages.
Halcro: Here are the results from my DIY dd turntable. I used the motor and electronics from a Revox B790 which is based on the dual eds but with more sophisticated electronics with a platter from a feickert tt. https://picasaweb.google.com/114629926159017275364/MyPictures?authkey=Gv1sRgCLqX-P6Iw6SUdA#
Hope the link works.
Your results for the tt101 are interesting but more telling (as you have multiple arms) would be to place the smaller feickert test disc on top of a (heavily modulated?) 12" lp and play the lp with one arm and the test disc with another. This will give us a picture of what's going on in real time under dynamic conditions.
I proposed this a while ago on the tt speed accuracy thread.

Thanks for the response Richard. Was curious.
My copper mat does not cause a problem to the servo from what I can tell but longer term I haven’t a clue. My “gut” says don’t use it based on the difference in weight with the original mat. A clean SP10MKII is worth $$$$ in working condition. One with a %#@* up servo is worth a quarter of the amount to me personally.
Cheers Chris

Has anyone on this thread used an SP10MKII with a copper mat for 5 years or longer - any issues ?

Richard,
I did try a Micro Seiki Cu180 copper platter mat as a replacement to the original rubber mat on the Victor TT-101 DD deck.....and heard a definite improvement.
The trouble was not audibly discernible with the servo correction mechanism....as you and Chris allude to.....but the 'brake' mechanism of the TT-101 was not able to handle the added mass of the platter when the 'stop' button was pressed.
This certainly worried me as, like Chris......I did not wish to stuff my perfectly working TT-101 for a slight improvement in performance?
After much experimentation......I found that the Victor pigskin mat laid directly on the aluminium platter......sounded as close as damn-it to the 1.8Kg copper mat without affecting the 'brake' mechanism one iota?

Go figure......?

One thing all this testing has shown IMHO......is that the performance of belt-drive turntables in general.....and the Raven AC in particular.....can be surprisingly good?
Just study all the test data in comparison to the TT-101 (which is demonstratively as good as it gets from an 'objective' point of view)....and those who bemoan the inability of their Ravens to 'hold' correct speed, should re-assess their set-ups?

I suspect that the big Micros and Dover's Final belt drives can be even better than the Raven in this aspect....which would push them even closer to the speed-accuracy performance the best DD turntables?

Richardkrebs,

Just a little plug here. Customers of both MK2 and MK3 upgrades have universally noted a marked improvement in percieved speed stability.

How is this possible ? For the last 5 days you have argued that the SP10mk3 is impervious to stylus drag and to substantiate this you quoted the manufacturers specifications.
Do you think the specifications are erroneous ?
Are there other speed stability issues, not related to stylus drag that you are aware of ?

Dover

I do not think that the published specs for the SP10 are wrong.....There is no measurable speed change due to stylus drag.
I have alluded to another problem with speed stability in DD TTs that is unrelated to stylus drag or cogging. See my earlier posts. This problem can be fixed. It is related to the method in which the TT measures its own speed. Get this wrong and we have problems. It occurs at much higher frequencies and at a much lower level than the overt cogging and stylus drag phenomena.
Taking it away however is dramatic.
It also shows that we can perceive timing problems well below the threshold of measuring instruments.

Halcro -
I'm a bit like you - the Raven doesn't look that bad. When you study their website, the motor supposedly has some accuracy, and the belt is elastic, so presumably the steepness of the initial drop will be due to the elasticity.
I have listened to the Raven - but not played with it, I gather some have said that the speed issue is more around that the adjustment is stepped, and you cant get it spot on ??
Techdas on your shopping list for this year ? Retro EMT idler will go nicely with the classic Porsche. You do need more TT's for all those arms dont you.

Dover,
Techdas looks interesting........if not 'Classic' material?..although I was surprised to see no comments on its 'sound' from anyone at CES?
Can't wait for Fremer's review coming shortly and I can see Thuchan having one if it's positive?
I simply have no real-estate for another turntable?
Thuchan has been at me for ever to buy a big Micro like the SX-8000.....and I've never heard a good idler...but again....Thuchan does love his EMT?

If I could find a turntable that looks as fine as THIS...and sounds as well as THIS and performs as well as THIS......I might buy one?

Regards

How about this ... very retro....very rare Fidelity Research idler....as Syntax would say the quiet rumble of the London Underground on every record can be comforting...

http://www.hifido.co.jp/KW/G0301/E/450-10/C12-65456-39066-00/

Ha ha,
Never seen or heard of that idler before?
In fact......didn't know that Fidelity Research made ANY turntables?

Hi Lespier,
Very impressive results. Congratulations on your tt design. I am also amazed at the unfiltered results. Your test record is centered nearly perfect based on the extremely low Wow&Flutter results. Did you do anything special to your test record to center it? I think we all want to know how to do that.

Tonywinsc, thanks for your comments. As far as centering the record goes, I didn't do anything so I think I'm just lucky to have one with a reasonably well centered hole. When I did the test I was actually at first disappointed. as the pitch waver was still quite audible. Goes to show while we debate the minutiae of 0.008 % speed errors the record itself is much more to blame for wavering pitch than most good tt's regardless of drive system. Halcro, when I made my tt , the fact that I used a much much heavier platter than the Revox tt it came from caused some anguish but have had no real issues in practice , the tt comes up to speed quickly and seems to hold speed pretty well even if I use a record brush. I still need to somehow rig up a second arm and do the test I proposed in my previous post to see what happens when playing music just to make sure the servo isn't going crazy with the added mass. Finally , I apologize if my posts come up in the wrong spots in the thread as the powers that be took almost 24 hours to put up my previous post.

Dear Ct, The copper mat cannot really "damage" the servo permanently. It's just that the servo is operating suboptimally. Excessive platter mass can only damage the bearing in the long run.

Henry, If you tell me how to do it, since the photos are on my desktop, not on the internet, I will post a photo of my "new" 1959 Alfa Romeo Giulietta Spider Veloce.

As you may know, I have owned (in the past) just about every model of 356, up to a Carrera GT Speedster, and finally a 550RS Spyder. But I have been bereft of old cars for more than 10 years, until now.

Lespier,

Your results for the tt101 are interesting but more telling (as you have multiple arms) would be to place the smaller feickert test disc on top of a (heavily modulated?) 12" lp and play the lp with one arm and the test disc with another. This will give us a picture of what's going on in real time under dynamic conditions.

That's exactly what I have done on my latest Posting which shows 4 photos for each turntable.
The last two photos of each....show the effect of another arm dropped midway onto 'heavily modulated' disc whilst the test tone is being played by another arm
Please read the descriptions beneath each photo?

Agree with Tony......very impressive results from your turntable. Congratulations.
Can you describe the motor and modifications you have made?

Halcro. Thanks ... will have another look at your results. I've read about the Dual eds motors and have long contemplated a DIY using one of these. I still have a couple of these so the next project will involve using one of these motors. I managed to pick up a cosmetically trashed Revox B790 with a broken arm so scavenged all the working bits. The motor looks to be based on the dual with an identical upper casting but the electronics are much more complex and use quartz locking. I replaced the thrust pad and changed all the capacitors on the boards and housed the power transformer in an outboard enclosure ... no other mods except for the platter. I picked up an acrylic Feickert platter with brass inserts on German eBay and decided to chance using it as it is MUCH heavier than the Revox one. Decided to use acrylic for the plinth as I had a Basis Vector and figured that tonearm had been voiced on acrylic. I have used it over 6 months now with no problems. I pulled it apart a couple of months ago and the bearing seems to be holding up so far. I'm very happy with how the tt sounds.

I am beginning to suspect the accuracy of the Feickert Platter Speed App and/or Adjust 7" Test Record?
As I mentioned previously......every time one does a test on the same turntable with the same arm and cartridge....slightly different results appear in the Data.
Additionally....as Tony has pointed out.....turning the disc 1/4 turn at a time will give differing results due to record eccentricity.
But the real problem as I see it....is that one can achieve far better results from a 10 sec-20 sec Test than with a 4 minute or 6 minute test?
Hmmm.......

Halcro
Do you have any theories other than eccentricity as to why the results with the Feickert are inconsistent?

Thanks

All measurement equipment has an accuracy and a repeatability factor. As engineers we have to measure our measurement equipment and it can get frustrating and confusing at times. Like the old saying: "A man with two watches is never sure what time it is." I still think the weak link is the test record. Eccentricity tolerances of the center hole is the first and foremost issue; but another problem is flatness. Any variation in the surface of the record is going to cause a speed change at the stylus- ie. the linear speed of the stylus in the groove. I see the same things. The longer I play the test tone the higher the values. The better that I center the record on the platter, the lower the values that I see. Overall, I have results that vary from 0.01% up to 0.04% with my turntable. I have my own 25 year old test record. Maybe the 7" disc is better with respect to flatness as compared to my test record. It would be nice to find a 180g test record.
As for the iPhone app, it occurred to me that I have a test CD with a 1kHz test tone. So I just did a test with the CD. The app reports a mean frequency of 1000.7Hz. The line is dead flat. The deviation is 0%. Short or long test had the same results; but here is an interesting observation. First, I held the iPhone in my hand and the result was 0%; but the raw result showed waviness in the line. Very small peaks and valleys. So I placed a small table in front of my speaker, placed the iPhone on that table and reran the test. This time the line was dead flat, but still had a small wiggle right at the beginning where I had to hit the start button on the screen. So as I suspected before and just saw, holding the iPhone in your hand while recording will cause additional variation. I suspected that before and always rested my iPhone on a table for the tt tests. This just proved my suspicions.

Also, it looks like to me that the app is reporting peak values, it is not averaging. I noticed that while looking at the handheld CD test results vs. resting the phone on a table. So like I was saying, one blip on the test record, like a high spot and the resulting values will increase.

As I do the tests with the 1350Hz Test Tone.....I can graphically see the frequency on the iPad App moving backwards and forwards equally about the 'mean' frequency.......so that the average mean frequency comes in very nicely on the Data......but the wow and flutter is high.
This is definitely caused by the off-centre hole on the 7"" test record.
I suspect Lespier does not use the Feikert 7" Test disc.....or if he does.......his is a 'good' one?
As you say Tony.......I think our turntables are testing the 'test' equipment?

Back to the Timeline for me :-)

I know what you are saying. Our simple measuring equipment has limitations. If you stare at this data too long and try to interpret something that is just not there, then you will start to see fairies dancing on the screen. I think the app is perfect for dialing in platter speed and it gives us some assurance that our turntables are holding speed an order of magnitude better than the capability of the records themselves. And because of that limitation built into the records, the app is limited on accuracy probably to the 0.03%-0.05% range. Keep in mind too, like I said before; the Timeline needs to run for several hours on your tt in order to get a reasonable data set for evaluation. One side of a record play, 600 rotations, is not enough data points. You need thousands of rotations to conclude anything in the 0.01% range or else you will be seeing those fairies dancing around.

Keep in mind too, like I said before; the Timeline needs to run for several hours on your tt in order to get a reasonable data set for evaluation. You need thousands of rotations to conclude anything in the 0.01% range or else you will be seeing those fairies dancing around.

Tony,

I said this earlier in the thread:

If your Timeline was 31" from a wall, a speed error of .01% would appear as a 0.02" (0.5mm) laser deviation per revolution.

So, if you played a 20 minute record side, the platter would have made 666.66 revolutions. 666.66 * 0.02" = a total deviation during that one record side of 13.3". What if the total deviation was half that (6.65")? Your speed error is 0.005%. What if it was a quarter (3.25")? Your speed error is 0.0025%.

My posts are not in sync as moderators are really taking their time . My last posts took something like 20hrs to come up. Seems the A'gon forum is run with a degree of paranoia that is just unbelievable...... I don't how I can take part in a meaningful discussion with such a long delay. ...... so frustrating. Anyway now that I've had my rant I think Tonywinsc hit the nail on the head when he said that our turntables are holding speed an order of magnitude better than the capability of the records. As I said the pitch waver from my supposedly well centered test record was easily heard. Even my belt drive tt while not quite as good as the dd was quite good compared to error caused by disc eccentricity . Halcro & Richardkrebs wrt worse results from tests of longer duration, could it be the stylus heating up when playing for a longer period and perhaps increasing the amount of friction which in turn might be throwing the servo out ?? Just speculating, in reality I have no idea.

You guys are making me feel.... normal.

Hi Ketchup,
The fewer data points that you have, then the higher the standard deviation which let's say is increased uncertainty. Just the fact that you are going to make two 0.100" pencil marks 0.02" apart is going to add to the measurement error. A few hours of running time will make the marks far enough apart to at least minimize the pencil mark measurement error.
Ok, you have a measurement after 666 revolutions. Go ahead and let it run for a few hours and see if your results are the same. The results might look worse, or they might look better, but I doubt they will be exactly the same. (I've been known to eat my words before). :)

I used to think I was normal until I heard a difference in power cords. Why oh why did that have to happen to me.

Good read guy's, as some here are well aware off centre record holes including test recrds are problematic especially for us that are sensitive to variations of pitch and are acutely aware of it. With a off centre spindle hole,as the stylus traverse through the grooves changes in velocity occur which of coarse with change pitch , low in the beginning of the Lp to high as the stylus traverse toward the label, then add this to a table that can't keep speed when the needle is in the groove.

Tony,

I'm not totally sure what you're trying to say. There is no problem or error with the pencil marks. You make one mark on the wall at the beginning of the record and you make another mark on the wall at the end of the record and measure between them. If the two marks are 3.25" apart after 20 minutes and your turntable's spindle is 31" from the wall, your total speed error over those 20 minutes is 0.0025%.

I haven't even tried aftermarket power cords. We both use Thiels, solid state power amps, and ARC tube preamps. Can you recommend a "cheap" aftermarket power cord for one of my components that will make me think I'm even more abnormal? Sorry for the diversion. Back to speed stability...

Off the deep end will be when someone here says that a power cord made a difference in turntable speed accuracy. Which is both on- and off-topic.

Hi Ketchup,
I'm not sure how else to say it. If you have a timeline or someone who has a timeline could do that test- measure after 20 minutes and then do a 2 hour measurement. See if the per rotation error calculates out the same or not. That would dispel my notion about too few data points.
I have a MIT powercord on my CD player. It made a difference; but I would not call it a cheap powercord. btw- seems like I saw a thread somewhere once that claimed a better powercord on their VPI controller, maybe, made a difference?