Hi Dover,
I stand corrected, I think. This is where I got tripped up on your post with the word "and" being key. "I said it is an assumption and that if the belt doesn't stretch then there is no creep."
More from Mark Kelly:
"Some form of tensioner (always on the "non-drive" side) will eliminate slip, but it won't touch creep.
Creep is necessary for a belt drive to work. The mechanism of creep is how the belt transmits force from the pulley to the platter, so no creep = no rotation."
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Mosin - no worries. The silk thread I use only seems to slip fractionally on start up, but the 20kg platter can be up to speed in less than 1 rotation, depending on how I tension it, which I think is pretty good considering the pulley is only about 10mm versus the 20kg platter. This suggests the silk has very good grip. With the high mass platter it does drive the motor pulley as well. If I turn the motor off, the platter/thread will drive the motor for a while. The designers original intent was that the silk should be "chalked", I presume for a controlled slip, but I prefer direct. The silk lasts a long time as in can go for a year or two. The only breakage I've had in 20yrs is when I've moved the deck and once when I went on holiday for 6 weeks and left the TT running ( I think high humidity weakened the silk fibre ).
Timeline speed checked on playing records inside/out etc and it's rock solid. These things all come down to the quality of the implementation, whatever direction is chosen. |
"These things all come down to the quality of the implementation, whatever direction is chosen."
Exactly. :) |
First, belt drive tt's in general have high mass platters. Tony, some belt drive decks have high mass platters, but MOST? Some certainly do, but I would venture to say that most belt drive decks on the market, both new and used, do not have or were not designed with platters that I would characterize as high mass platter. But I guess it depends on what you consider to be "high mass". |
I'd say that high mass would be something like 100 times greater than the mass of the record. That would be about 15 kg.
This discussion got me in the mood to check my platter speed again. After playing several records the tt was warmed up and I know from measurements before that warmup is critical. I had a small bit of drift (about 0.5Hz out of 3150 Hz) after setting the speed several months ago. I dialed speed back in and had some good results: -0.01%/+0.02% Wow&Flutter and the speed plot over time shows a sine wave with a 5 second period. I believe the +/- speed variation over 5 seconds is the control system holding speed about the setpoint (At any rate I feel these values are well below audible detection and are an order of magnitude better than the records themselves.) This app is a very good objective measurement tool, I think, for dialing in speed and checking to see if your tt is operating within the manufacturer's specifications. No more, no less. |
Here's an interesting test for those of you who have belt drives, especially those with rubber belts like the VPI's. Place your finger lightly on the belt where it leaves the motor capstan and is being pushed to the platter. Feel that vibrational energy that's being transmitted to the platter? You don;t feel it as much on the other side of the belt, where it is being pulled off the platter to the capstan.
A simple solution is to place something fairly heavy and smooth up against the belt between the capstan and the platter to help dampen and absorb that vibration.
I don;t feel any of that with my silk thread, and I would bet there is little to feel also with mylar tape. |
Here's an interesting test for those of you who
have belt drives, especially those with rubber belts like the VPI's.
Right, but this is based on VPI's ultra low quality. But you find that very often with the stuff from other Manufacturers, too. Ever checked a Raven belt? The word "Precision" you find mainly in their advertising ads. Try that with a Basis belt :-) Or try a Timeline, it is a disaster for the majority of Manufacturers, they aren't able to offer a proper motor, even when you can buy 3 of them. Based on that inferior Design solutions I agree that a direct Drive can give better results. But this is not based on its Design, it is based on the low quality from the others even when they are very expensive. The majority of owners believe that the offered product (whatever it is, Tonearm, Cartridge, Speaker...) is simply perfect form the Design, the Manufacturers and his cohorts are directly sent from God to bring joy to everyone and it can be made better, maybe only with more money, but they don't even think about the correctness of the Design itself. Or what they really get for the money. Most learn by spending money, but even that does not educate generally. |
Ptm, I tried your "interesting test" on my SME 30/12 belt drive. Not easy as the motor pulley is under and very close to the large platter. The rubber belt has only 1" of exposed length between the driven pulley and the platter. I felt none of "the vibrational energy being transmitted to the platter" that you mention. Perhaps the massive SME is built to a different standard than the VPI. I do notice though that the SME has a much shorter "free" belt length than most other belt drive tables - even Syntax's beloved Basis table. I've often wondered about the effect of belt length on these designs.
I don't know of anyone who has tried thread or tape drive on an SME table.
As far as the quality of the belt itself is concerned, I have not directly compared the SME belt to the Basis belt which is purported to be one of the finest in the industry. I agree with those who have written that each design has its strengths and weaknesses so implementation of a proper design is critical to the end result.
Very interesting thread. |
I have never had a chance to try the Timeline device. Some have reported very impressive results with the Timeline. They have seen zero drift of the red line playing the entire side of a record. That is approx. 833 revolutions. I figure if my tt looses one revolution out of 10,000, I would be ok with that. That is 0.01% accuracy. Does that seem reasonable? Well, if so then that would translate to a 30 degree drift of the red line from the Timeline after playing one side of a record. I would still call that good. |
Syntax,
I may be even more cynical than you! I believe the overwhelming bulk of merchandise made is created mainly for profit, with the case being the part which receives the most attention. For example, one very famous turntable maker that almost everyone has heard of uses a $56 AC motor, and that's assuming you buy one, not a quantity. Well, we bought six of them, and they all cog an unbelievable amount. Even worse, spindle diameter wasn't at all consistent. The bottom line here is that some manufacturers build only for price points and marketing spin, yet audiophiles continue to eat it up.
However, I also know of manufacturers who live audio, and for them expanding the art trumps anything else, so hope springs eternal because they manage to find like minded customers.
We'll survive! :) |
I have learned allot first hand over the past ownership of numerous tables including the different designs mentioned and the ones I have tried I have been absolutely shocked with their lack of speed accuracy which at the end of the day all of these table designs all have in common and should have.
I could hear such in my own set-up prior to using this TimeLine tool to check such but was being brain washed by others including the manufacture suggesting this and that, suggesting it wasn't important.
I know there is allot more going on than just operating at an accurate speed but if you can't get the speed accurate from the get go then the rhythm and pace is effected "off" so the rest afterwards really doesn't matter, to me anyways and once you have heard it well ....
It's simple, your table using the TimeLine is either accurate or not.
I have found it seems that many are in denial, some don't even want to try this TimeLine in fear suggesting this or that works for them but in the end this is the real deal and so simple to use to truely view what's actually going on with the speed of your table so why fool your self in believing different.
Buy or find someone with one and check it out and maybe the manufactures in the end will work just a little harder ensuring theirs will be accurate.
Would love to see a REAL list made up of actual tables that can actually show they are holding an accurate speed for the entire side of a record both playing and not with an actual video with a time stamp on it.
The distance behind the tables all being the same just using a pce of tape with a BOLD line on it so one can see the laser location easily.
I won't mention the members name because that really doesn't matter, this person ownes the same table as I once did some time ago and was adamant his was running accurate when I suggested mine didn't and wouldn't, when I went over and checked the table in question with the TimeLine in hand which was really simple we found his was also off and in the end we couldn't get it to run accurate on both speeds either.
If your table doesn't have the capability of adjusting the speed like a SP10 MK2 I had on hand won't be an easy correction, if such in the end can even be done.
Lets not debate or get pissed off, instead lets work on that list of tables as per above with proof.
I would personally love to view such and there are allot of owners with different tables just reading and posting on this specific thread.
Happy New Year! to all :) |
The main problem of idler drive is people have opinions on it after hearing turntable from the 60'. I have built my lenco after reading Salvatore review of the J Nantais reference Lenco.
I have tried different material and finished with a non wood plinth, a reference bearing ,and some tweaks ,an OL conqueror mk II and a zyx airy 3 . The sound is impressive, nothing to hear here with the traditional sound of idler drive.
Then i have heard a Lenco made by a hifi fanatic, and very sympathic person. He built a 200 kgs Lenco with its own table (as the goldmund reference),the finish is impressive, there are many many tweaks but it's idler drive and the sound on his high end system is incredible, in the treble it betters all the belt drive turntables I have listened to. |
So let's start a thread with which tables have and which do not have accuracy using the Timeline device? |
Sksos1,
I think we all know which one you will put at the top of that list!
Seriously, such a list would be surprising to a lot of people, and it would undoubtedly generate angst among many manufacturers, not to mention all the explanations from end users claiming the results are from someone with an axe to grind, or it was just some unlucky random sample. Whatever, the thread would probably become Flame City right away.
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Wouldn't it be interesting if the only tables to pass the 'Timeline' test were all 30 years old? |
Halcro,
Yep, but that won't happen. A lot of new ones pass, but the surprise is which ones.
Some old ones don't pass, however. I built a DIY turntable around eight years ago that started life as a Lenco. It runs a little less than 1/4 RPM too fast no matter what I do, so after a frustrating hour wasted I quit tinkering with it. I could never get the wheel placed accurately enough to correct the issue, as minor as it may be. It's dead on according to the KAB Speedstrobe, so I suppose it is close enough. Maybe I'll revisit it someday.
The real problem is with those turntables out there that do not keep a consistent speed. It is one thing to have an ever so slight speed issue that is evenly paced, but quite another when it varies, especially if it varies abruptly.
. |
Mosin, A lot of new ones pass, but the surprise is which ones. This sounds like you could already produce a list for us? :-) |
I have checked a few, but mostly I have checked motors that are commonly used. I was surprised. |
Mosin,
please list ones that actually pass, this will be a starting point |
Well, I'm going to put my vote in for the Trans Fi Audio Salvation direct rim drive tt (with Terminator T3Pro linear tracking tonearm).
I'd been running a belt drive Michell Orbe/SME V for 10 years, and investigation of uber pricey belt drives like the SME 20/30, TW Acustic AC3, Brinkmann La Grange /Balance etc showed an incremental improvement, but not enough to go with the upgrade. And, this in tts costing $20000-$40000.
But I then came across the Salvation, and wow!
I'm NEVER likely to go back to belt. I'm getting a unique combination of the best of analogue ie bloom and tonality, with an almost digital-like accuracy and neutrality.
It's unlike anything else I've heard when playing vinyl.
Getting away from belt related speed drift really produces a fantastic unwavering solidity to music, most noticeable on rock solid piano notes, even as they decay away in the soundstage, and no audible wow and flutter as lp side end approaches. Previously I would always be aware of fluctuations as piano played, especially individual notes, but not anymore, and often I'll be suprised that I haven't picked up on side end groove modulation as the stylus plays the last few seconds of the end of sides.
I've run a thread on the tt/arm giving a more in depth appraisal of my experience. |
Spirit, Have you tested the Salvation TT speed stability with Timeline?
I agree with SYSKOS, that Timeline results of members' various TTs would be a very useful grade scale (pass or fail). |
For a Timeline test to be truly useful, some standard should be applied. For example, I saw a DD table tested with the Timeline. The owner held a piece of paper behind the turntable and demonstrated that the red dot did not drift during the 20 second test. I asked him what would happen if he let the dot fall on the wall about 4-5 feet away and waited five minutes. He admitted that a further distance would show a drifting over time. A video with a set distance of the laser dot to a wall, say 5 feet away during a period of ten minutes, or with the stylus at the beginning, middle and end of an LP would be good, but I don't want to have to watch a 20 minute video showing the entire length of the LP. Perhaps a fast forward feature with a time stamp and mark on the wall for some kind of consistency would work. Also the test should start with the stylus not contacting the LP and then during the test, it should be lowered onto the LP.
I agree that the results would be interesting, though I really wonder if the speed variation of a successful KAB strobe result versus an unsuccessful Timeline result would be audible. My table shows a steady result with the KAB and I have not had the opportunity to borrow a Timeline.
I would think that any manufacturer who has a design which passes a Timeline test would want to show such a video for marketing purposes. This issue came up in another thread about speed accuracy and someone asked about the accuracy of the Timeline device itself. If the strobe is slightly off, but the table is accurate, the red dot would also drift slightly. Measurements are only as accurate as the measuring devices themselves. |
Gentlepeople
I have not used the timeline but understand that if a TT was to say AVERAGE 33 1/3 rpm over a LP side, it would pass the timeline test. Am I correct in my assumption?
If so we can easily discount any TTs that are not averaging the correct speed. But this test does not take into account dynamic speed changes.
With most DD TT's using a DC motor, a controller produces a rotating field at the desired speed. The magnetic poles are pulled around at this speed. Contrary to some opinions expressed in these forums, the servo does not intervene unless an external load causes a speed change. ( this assumes that the TT has been put together as the designer intended). If the load does change, the magnetic poles will move back in phase slightly until output torque matches the new higher load. The magnetic poles will still be following the rotating field so it will be again rotating at the correct speed. But while this is happening the motor tends to self correct as its torque increases with the phase shift between the rotating field and the magnetic poles. AC motors exhibit the same self correcting characteristic. For a DD TT to fail this average test it would have to be incorrectly designed.
A good string drive with zero slip and idler drive would I imagine also pass this average speed test.The only way for these to fail would be for the motor to be under such high load that it jumps a pole. No normal retardation torque would be sufficient to cause this.
But here is the tough one, the motor does slip back in phase due to stylus drag without jumping a pole.Even at treble frequencies with one DD TT I have tested. This can be seen by scoping its power supply. And watching the current draw. It was actually possible to recognize the music being played at the time on the scope. The speed sensor was measuring these tiny errors and correcting. This could be observed by watching the motor draw current in sync with the music. An amazing observation.
The conclusion is that some form of speed correction is required if we are to seek good dynamic speed stability. High moment of inertia platters will of course help but only for momentary load changes. Sustained increases in load will cause the same phase shift. If no speed correction is employed, we are relying on the motor self correction characteristic. This may be enough but note the motor needs to move back in phase, I.e momentarily slow down before the automatic increase in torque output comes into play. As with all things engineered, compromises are a sad fact. We each need to decide what compromise best meets our biases.
Some of you may have been asked the thought experiment at college where a tennis ball was thrown directly at the front of an oncoming train.
The train in theory slows down. |
The timeline has a quartz clock. It is accurate, according to Ron Sutherland, of two parts per million. That's very good, and I have no reason to doubt him.
I don't know the limits for other drive types, but it is theoretically possible for an idler to be accurate to around one part per million, so my controller was designed for that. You could go further with a GPS referenced OCXO clock in the controller, but could anyone hear it, and could the device keep up with the clock?
At some point we have to question the merit of it all because there are mechanical limits. And, just because a turntable has a great clock doesn't mean the turntable spins accurately, and just because it spins perfectly in the lab doesn't mean it will do it under every condition, in every environment. Still, I believe it is the responsibility of a manufacturer to get as close to perfect as he can given the price point of the machine he is selling. If you pay small money, you aren't going to get super accuracy, but you may get a very musical turntable that is consistent. To me, that's worth a great deal, although I personally try to push the limit to its threshold. Essentially, you should get what you paid for.
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I made an error in my last post. The Timeline is accurate to one part in two million. |
Peterayer,
A distance for sure is important, I have been doing this very easily for a while now and if the table isn't close to a wall I just use 2 light rulers and tape them to the back of the table stand along with a pce of paper between the two with a pce of painters and a dark line on such so it's very easy to view between so it's under 2 ft
All the tables I have tested, no worry about waiting for 20 minutes either. Most failed within a few rotations even after using the TimeLine to actually try and set the speed accuratly. I found most tables were not capable to be set for accurate speed.
Using the strob, numerous tables that were used and then rechecked with the TimeLine proved the TimeLine is a more accurate devise and all these tables failed within 10 or so rotations either too slow or too fast and that was with no stylus even on the record.
This has really left me scratching my head. |
Richard, That was a great post. Very informative. Answers a question I have been privately asking myself: Several of the latter day DD turntables, and I believe one or two of the new rim drives, tout the lack of a servo mechanism as a selling point. You can guess the rest...
However, those of us who have been around here for a while have in fact addressed the question of instantaneous speed variation that could go undetected by any measure of "average" speed. Whether the Timeline is any better than the KAB strobe (the best of all strobes, IMO) at detecting such short term errors, I do not know.
Mosin is too smart to post any lists here, and who could blame him for not doing so? |
Interesting how the general question regarding drive implementation has quickly narrowed to a focus on speed stability per single revolution. I suspect that this is because this is one of the most easily measured paramters. It is human nature that people respond to what is being measured and audio is no different. However, this can have untoward consequences. I am old enough to remember when THD was touted as the ultimate measure of amplifier quality but improvements were acheived with increasing negative feedback; ultimately with deleterious effects on the end product.
Single revolution speed stability is clearly important, but, perhaps, this is not the only (or even most) important consideration. As others have alluded, the Timeline only measures accuracy per revolution, not speed changes within a revolution. Theorectically, if the first half of the revolution was 16 2/3 rpm and the second half of the revolution was 50 rpm, the Timeline would be spot on at 33 /13 rpm. I doubt that anyone would consider this a quality turntable.
I supect that the amount of internally generated noise and vibration and ability to dissipate borth internally generated and external noise and vibration are also important to the overall quality of any turntable.
At a certain level of performance, are other parameters more important to vinyl playback performance, i.e. tonearm and cartridge quality?
For the record, I'm not a turntable designer and own a belt drive turntable but would be comfortable owning any number of idler wheel and direct drive tables. |
Just to clarify for those not familiar with the device, the Timeline flashes a dot on the wall once per revolution; it is not a continuously illuminated reference point and hence cannot show aberrations occurring in one revolution, but only deviation from a fixed reference point (on the wall for example) over some period greater than one revolution. Jazdoc's point is well taken. |
Palasr, I am fairly certain the Timeline flashes more than once per revolution. (I cannot recall the exact frequency; maybe Mosin knows.) Thus it may detect short term speed instability, in fact, altho with what accuracy I cannot know unless I know the frequency.
You would think that the KAB strobe could also hint at short term speed instability, as the "33" would waver or even flicker back and forth while under observation. But I don't know how sensitive it would be to such aberrations. |
Mosin/Richardkrebs – thank you for your excellent thoughts on this thread. Mosin – as just an amateur hobbyist myself, most of what you have said is in sync with what I have heard with my TT’s the last few years. I agree that string drive could be a little fiddly, when trying to convert a belt design TT to thread/string. But I have found that on a string designed TT – once the string technique is learned (there was a learning curve with mine), it was pretty much plug and play after that for me. RichardKrebs It was actually possible to recognize the music being played at the time on the scope. The speed sensor was measuring these tiny errors and correcting. This could be observed by watching the motor draw current in sync with the music. An amazing observation. I find this simply incredible. Are you able to tell us what turntables / tonearms /cartridges you used during this analysis/testing? |
I am now using laser tach to determine my platter speed and stability. IMO, it is the most accurate way to gauge the speed on the platter. Accurate to 1/1000 th of a rpm. Only $200.00. It should be placed on a tripod for the most accurate measurement. Monarch PLT 200.
http://www.omnicontrols.com/detail.aspx?ID=3720 |
An accuracy of 1/1000 rpm is 0.003%. This is only as good as most high end tt's. It needs to be an order of magnitude better than that. It will be good for dialing in speed, but not for examining Wow&Flutter. If it is off 0.003%, then the platter will gain/loose 1/3 of rotation per 10,000; assuming all else is constant. I'd call that good. Why doesn't anyone talk about the iPhone app? It at least plots speed over time for you. |
The original Timeline flashes once every 1.8 seconds (1 revolution). The latest version, which is at least about a year old, flashes eight times every 1.8 seconds.
Tonywinsc,
I don't know how much faith I have in the accuracy of an iphone microphone! |
I have an FFT analyzer app on my iPhone. I used a B&K calibrated 1000Hz test tone and the FFT plot was dead on. It is about the frequency counter tied to the internal clock. I don't know the accuracy, but I figure it must be within the range of the timeline- quartz crystal clocks inside their processors. |
Yes, and the closer the dot on the wall or paper is to the Timeline pointof origin, the harder it will be to for the eye to detect any drift. So if it looks fine at 18" it may be apparent at 10 feet over time that the speed is off.
I agree with Jazdoc's observation that as long as one is very close to accurate speed other issues are very important. IE, How the turntable deals with vibrational energy generated from the motor, the bearing, airborn, floorborn, the stylus/groove interface, the armboard etc. It is not clear to me that absolutely perfect speed accuracy and consistency is the most important characteristic of a turntable. |
My thoughts on my direct rim drive is that it's torque is of a magnitude greater than comparable belt drives which rely on platter mass and momentum to maintain speed.
The Salvation's high torque smooths out the speed inconsistency I became more and more aware of with my belt Orbe. This enables the Salvation to deal with groove modulation effects much better than my Orbe.
It's been a total revelation to hear piano notes solid as a rock when struck and as the note decays. My Orbe never quite managed this trick.
I'm convinced eliminating groove modulation timing variability eliminates a whole series of artificial warmth artifacts, and allows a real cognitive ease when listening to vinyl.
But Pete, I'm sure you're correct other factors eg isolation etc. contribute to the overall sound. However my paradigm shift moving from belt drive has convinced me that high torque average speed stability and instantaneous resistance to groove modulation is critical. |
Spirit of music
Where are the specifications that suggest the Transfi has high torque.
On the contrary, from their website -
"Note1: The 9kg platter has immense inertia & will take a few seconds to respond to the control knob. Only very slight tweaks are needed.
Note2: You will find speed drift may require frequent minor adjustments until the bearing, motor & electronics are burned in.
Typically, starting from cold the system will run slightly fast. As operating temperature is reached it will slow. A suggested method of operation is to let the system warm up then set the speed. Play several records & fine tune until the speed remains constant.....then leave the control alone.
When you switch the system off, the motor does not need to be disengaged from the traction belt. The next time you start the system from cold, it will run fast. If you try to adjust the speed at this stage it will slow as the system warms, so best to let it run fast until it settles to the correct speed.
IMPORTANT
The whole system of speed control is finely tuned, & any variation in consistency may require adjustment, from VTF of the cartridge to the weight of record clamp used. Sophisticated motor speed control methods have been ditched in the case of Salvation as these all proved detrimental to the sound using this direct rim drive method. In practice, speed drift on Salvation is not an issue providing you are not varying the way you play your records from record to record or are a stickler for speed accuracy! Please consider this before ordering."
If you have a temperature controlled room, the angle of your dangle is stable, and you are not a stickler for speed accuracy, then this is the turntable for you - this is their own words.
The Michell Gyrodeck is not a paragon of TT speed accuracy that should be used as a standard either - tiny motor, stretchy flimsy elastic belt, floppy suspension and all.
|
Dover, your post leaves me with a lot of questions, but I won't go there. However, there is a need to explore torque and inertia. They can be confusing terms. Explained in the very most simplistic way possible, torque is what you need to get the platter spinning, and inertia is what you need to keep it going smoothly.
So, it is possible to get very good results with a very low torque motor because you can still have good inertia. The downside is that the turntable will reach its speed much more slowly, assuming the platter is a heavy one.
You can have both high torque and high inertia, but there is usually a price to pay. That price is motor size and lots of heat generated by it. Ashland was noted for making such motors, and quiet ones at that. The one used in a Fairchild 750 studio machine is the size of a clothes dryer motor, and it runs very, very warm. So does the more common one found on some Rek-O-Kut turntables and the Canadian made McCurdy. I would be happy with either motor in the Saskia, but they are no longer available.
By comparison, we are stuck with lower torque motors, if we want great precision, but we can still have lots of inertia. This is where system design comes into play, and done right a design can greatly benefit speed accuracy.
I suppose the point here is that most turntables, if not all, are compromised to some degree, however small. The trick is in making certain that any of those compromises do not negatively affect the end result. Hopefully, reliability and looks aren't affected, either. It isn't as easy to accomplish as you might think. Such an undertaking requires a lot of thought.
. |
...unlike my clunky grammar which required zero thought. :D |
Tony,
The issue I see with test record frequency measurements is that on the test record, groove anomalies and the good possibility that the test record center hole is not exactly center can throw off the measurements. Prior to using the laser reader I used a 1000 hz test tone on a record and used a Fluke digital multi-meter to measure the output frequency. It would oscillate + or - 1 hz measuring the frequency at 1000 hz...With the laser, my table is stable at 33.00x rpm, where x fluctuates up to .008 every few rotations. I think that is quite good for a belt drive. I am going to try the platterspeed app for iPod to see how it compares and I am especially interested in the time plot. |
Richardkrebs - Interesting post. Could you please elaborate on a couple of points. Contrary to some opinions expressed in these forums, the servo does not intervene unless an external load causes a speed change. ( this assumes that the TT has been put together as the designer intended). the motor does slip back in phase due to stylus drag...This can be seen by scoping its power supply. And watching the current draw. It was actually possible to recognize the music being played at the time on the scope. The speed sensor was measuring these tiny errors and correcting. This could be observed by watching the motor draw current in sync with the music. An amazing observation. The conclusion is that some form of speed correction is required if we are to seek good dynamic speed stability. So as I read it Para 1 - The servo only cuts in when speed changes Para 2 - Motor slip is occurring as a result of varying stylus drag to a degree that you can follow the music by scoping the current draw Para 3 - Your conclusion is speed correction is required for dynamic speed stability based on your observations. These seem contradictory. Are you saying that most direct drives dont speed correct all the time, but that they should be correcting more frequently for variable stylus drag ? Isn't speed correction for stylus drag shutting the door after the horse has bolted ? If the current draw is up AND down with the music, when do you propose to correct the speed UP and DOWN before, during or after the event ? Doesn't this just suggest that for whatever drive system/platter/arm/cartridge you have it must have enough energy storage or overkill in terms of motor drive & inertia to ensure the variable stylus drag does not impact speed at a micro level. Are you not presenting a strong argument that all TT's should have a very high mass platter ? ( unless of course you can scan the grooves and preprogram the required changes to the motor controller to preserve micro dynamics ). The other question I have for you is torque ripple, or cogging. As I understand it the torque ripple or cogging torque will vary because a Direct Drive motor is running much slower than a small pulley/platter. For example DD - 33.33rpm x 20 poles = 20 poles per revolution of record. AC/belt - 1800rpm x 4 poles = 216 poles per revolution of record. Disclaimer here - I know you also have to factor in the number of slots, which could increase or reduce the differential in this example, but doesn't eliminate it. Cogging torque results in torque as well as speed ripple; however, at high speed the motor moment of inertia filters out the effect of cogging torque. Presumably a high mass platter, provided it is direct coupled to the pulley with an inelastic belt, can assist in smoothing out any torque ripple if it exists in both instances. Can you explain why I can hear such a big difference in speed stability between the Technics SP10mk2 and SP10mk3 ? Do you think it is the higher torque, superior motor controller, higher mass platter of the mk3 or all of the above ? Cheers, Dover |
Jazdoc
I agree totally with you. There are many other important parameters that must be addressed in a TT design
To state the obvious. A complete TT assembly including arm and cart is a machine that measures tiny movement with respect to time.
Over the years I have built maybe 10 TTs from the ground up, BD and DD. plus a few arms.
The conclusions drawn from this experience which parallels much written in the various forums here is this. If we are seeking the unatainable goal of perfection a TT must..,,
1) have absolute speed stability under all load conditions.
2) have absolute dimensional stability between platter and arm support.
3) be absolutely still, with total immunity from external movement.
Obviously there are other considerations, but these seem to be the core requirements
For example we would fail requirement 2) if there was any bearing noise, as this would cause dimensional instability since it would be moving the platter about.
Ct0517 the TT under test was a Goldmund studio with a Syrinx PU3 arm and I think a Monster 2000 MC cartridge.
I agree it was an astonishing finding which clearly demonstrated the effect of stylus drag. I hasten to add that I am in no way criticizing the Goldmund. It was simply correctly doing what it was designed to do. From memory it had a 2.5 kg platter with lead weights around its circumference. Thus for its weight, the platter had a relatively high moment of inertia.
The conclusion drawn from this test however would indicate that some form of real time speed monitoring and correction regardless of drive method, should be employed if we are to satisfy condition 1)
It is up to the listener to decide if this level of speed stability is necessary and can be engineered in such a way as to be benign.
For me the answer is yes and yes. |
Dover
Yes we are measuring an error and correcting it before it gets worse.
This is the old argument about feedback correcting an error that has already passed. The nature of this feedback and the torque/ platter moment are critical here. The motor must totally dominate the platters rotation. We are only asking the motor to correct a tiny change in speed. With sufficient torque and the correct feedback curve this is not an impossible ask.
I agree it has to go some way wrong for it to sense and thus correct. What we are preventing here is it getting any worse. Further, as I said the motor self corrects as well. This action being independent of the servo.
You said in one of your posts that you needed to correct for stylus drag when you tested with the timeline. Obviously the drag is not constant so we are ( in an open loop system) relying on inertia to save the day. The question is. Is this high inertia enough? (I wonder how quickly you observed the speed change after lowering the stylus)
Lets say in an extreme example we had a sustained high amplitude low frequency organ note lasting say 20 seconds followed by a flute playing very softly.
The platters inertia even a massive one would not be sufficient to maintain the correct speed during the organ note. Thus the motor would slip back in phase slightly to compensate for the higher torque demand. When the flute comes along the torque requirement would reduce. If the motor has high torque capability there is a risk of temporary over speed.
So the question of always needing a high inertia platter is better answered that the motor torque, platter inertia need to be matched to optimize speed stability. A platter of say 20kg has 8 times the moment of a 2.5 kg platter as fitted to the Goldmund I tested, assuming they have the same radius of gyration. The correction current I observed would indicate that a 8 fold increase in moment would not be sufficient to push through the drag modulation. Note high frequency correction was evident
BTW I was not arguing the superiority of DD over other drives. I was stating that stylus drag is real and significant and to improve the resultant speed errors, closed loop speed control is indicated irrespective of the drive employed or for that matter the platters inertia. It just happened to be a DD where I observed stylus drag in action. It is everyone's personal choice coupled with their biases when choosing a drive method and if open or closed loop. As I said earlier there are many paths to enlightenment and this should be celebrated. My opinion is simply that. My opinion no more valid than anyone else.
Clogging of course this is present in all drives employed
It is up to the listener to decide which is less intrusive
Clogging at approximately 11 hertz with the DD example you gave or clogging at approximately 120 hertz with the BD example,while acknowledging the lower amplitude of the BD.
As to the perceived superiority of the MK3 over the MK2
I can only assume that the engineers learnt something in the intervening period between the two designs. So probably all of the above. Further the general engineering in the 3 is superior. This has to have some bearing on the performance. |
Dover, with my Salvation, correct speed is normally reached within 3 seconds, as opposed to the 10 seconds plus my belt drive did. And additionally, it takes a LOT of manual pressure to slow the platter down in the Salvation, a lot more than my belt Orbe. I'll take that as a high torque system. Certainly higher than any of the more expensive belt drives I auditioned. But I'm sure it's not quite in SP10 Mk2/3 territory. |
Richard mentions the issue of 'Stylus Drag' which many think is an exaggerated myth? On Timeline's own YouTube video.......using a Transrotor belt-drive turntable with a heavy platter (and high inertia).......notice at the end, how after the speed has been corrected according to the Timeline......when the tonearm drops on the record, the speed immediately slows HEREWith the Victor TT-101 DD turntable however.......notice the complete lack of 'stylus drag' even with two or three tonearms in operation HEREPlease forgive the amateurish video technique as I held my iPhone whilst talking and 'acting' :-( |
Richardkrebs,
very informative, thanks for taking the time to post.
I have learned first hand that specific tables I have either owned and/or have listened to don't meet even your number 1), not sure about the other two.
I do like what you wrote that tables need to;
1) have absolute speed stability under all load conditions.
2) have absolute dimensional stability between platter and arm support.
3) be absolutely still, with total immunity from external movement.
Can you or anyone else please provide a list of tables that actually meet and pass these requirements |
The iPhone app filters out the record runout. Easy to do since record runout has a 1.8 second period. And I go right back to the record runout issue. Record speed accuracy is at least an order of magnitude worse than any high end table made today. Sure, you might loose between zero to 1/3 of a rotation during one side of record play (approx 833 rotations total). So what? Don't tell me anyone can hear that. WoW&Flutter is more critical an issue and that gets back to the motor quality and it's speed control circuits. Maybe I am wrong, but I don't believe drive types matter that much regarding speed accuracy. I think drive types affect the sound character of the turntable as much as all of the other design features of a given turntable such as plinth, mass, and dissapation of vibrational energy. If Wow&Flutter is <0.05% then it is all about the record and how the table/tonearm extracts the information. I just can't get past the fact that the record center hole accuracy produces a Wow&Flutter in the 0.5% range. Without a self centering tt/platter design, that number cannot be bested. |
Dear Richardkrebs: I agree with Jazdoc too. There are several targets on a whole TT design and certainly what you posted:
+++++ " have absolute speed stability under all load conditions. " +++++
is a primary one but is only one link/part of the TT design and execution design. As you said: TT bearing is critical, platter weight and motor match, arm board design, platter build materials, plinth build materials, arm board build materials, mat ( if any ) build materials, drive system, motor choosed, TT footers, damping/drain vibrations/resonances, etc, etc.
Good to read your posts and other people ones that in many ways what we read it in this tread ( at least for me ) was/is a learning one.
Regards and enjoy the music,
R. |
Halcro,
I recall your video prior on another thread and that's exactly what I'm referring to, thanks for sharing that again.
You also answered my question in relation to how many turns should it be by lowering the three stylus onto the record, doesn't matter!
So we have one table that clearly demonstrats it holds accurate speed, any others? I'm very curious to see.
Can you show the results for your TW table, non of mine including the flagship BK would hold an accurate speed. |
