Hi Chris, The DD is only at a correct 33.3 in transition between the time the motor kicks in to speed up and shuts off to slow down. At all other times it is not at 33.3. I don't believe this is a fair assessment of the DD motor technology? There is no difference I believe, to the maintenance of the speed via the motor of a belt-drive or direct drive. Each one has to monitor its speed via a pre-programmed sine-wave algorithm related to the power supply. The differences between the two drive types I believe, has to do more with the speed of any correction applied once a deviation is detected? In this.....a belt or thread drive is at a severe disadvantage. The DD motor....usually with a lot more torque than that of a belt/thread drive....and being directly connected to the platter.....can correct deviations in micro-seconds theoretically inaudible to the human ear. With some DD turntables like the Victor TT-101......there is instantaneous 'braking' correction as well as speed-up correction...thus not relying on the time lag slowing-down procedure after an increase is applied. To my ears......this is a more optimum audible solution than the slow speed deviations and corrections allowed by some belt/thread drive decks? One point not properly addressed so far.....is how idlers or rim-drives perform against the Timeline? Perhaps Lew will be able to enlighten us on this? |
I don't like to post without actual direct experience but here goes.
Based on my TT's and what I am "hearing" and also not owning this Timeline device.
A Belt/string or idler will do one of two things on a timeline over time.
If they are slow
<----------------
If they are fast
---------------->
A direct drive because of the nature of how the motor works goes back and forth.
The DD's can not be picked up by the timeline.
The stop - go, stop - go, stop - go, nature of the DD motor keeping speed.
The DD is only at a correct 33.3 in transition between the time the motor kicks in to speed up and shuts off to slow down. At all other times it is not at 33.3.
Am I wrong ?
And another thing. I am going to say a really dirty word here to some people CD
Has anyone bothered to listen to a decent CD of your favourite music compared to LP as far as "pitch" is concerned.
I think you will be surprised.
Anybody?
Finally a message to SKSOS1 - is it your intention to have another thread shutdown ?
What is Sounds of Silence that you are affiliated with. You seem to be anything but silent. Please take Lew's advice.
Cheers |
Hi Tony,
Yes....I think speed accuracy was indeed mastered over 30 years ago but as I mentioned elsewhere......with the dominance of belt-drive over DD turntables due in large part to the Linn propaganda and the reviewers who championed it.....'speed accuracy/consistency'.......never was mentioned as a critical factor in their design philosophy?
How do we get back to it?........I think discussions such as this is certainly one of the ways and thanks to the Timeline......I hope more designers and manufacturers will be able to judge their successes or failures and hopefully make some corrections?
'Awareness'.....is our best hope?
The .5mm speed drift I am seeing on the Raven AC-2 is almost negligible.
For instance.......the Victor TT-101 allows me to speed up or slow down, the actual speed of the platter in 6Hz increments.
33.33rpm apparently gives a pitch of 440Hz which is the de-facto standard
pitch for orchestras.
However many of the world's orchestras use a pitch either 6Hz or 12Hz up or down from this?
When I adjust the speed on the TT-101 to 6Hz lower (33.25rpm).....the drift from the wallmark is 5mm every revolution and when the speed is increased to 33.40rpm (6Hz higher).....again the drift is 5mm per revolution.
So the Raven.....running at 0.5mm per revolution could really be called...'spot-on'?
And Lew is right Tony......the Timeline is not so valuable in terms of 'cumulative' drift or speed error (as even a 6Hz pitch deviation will add or subtract 5mm drift to each and every revolution which will appear quite dire over the full side of a record).....rather it is the instantaneous speed drift due to stylus drag which is valuable for us to know about our turntable's performance?
Instead of 'fear' governing our apprehension of the Timeline and what it will reveal about our turntables.......we should really welcome this information.
Knowledge is power....and ultimately the more we know about our system's objective performance.....the more equipped we are to effect improvements? |
Dear Tony,
You wrote, "the laser mark should drift slowly in one direction over the 30 minutes. That is the cumulative error" Yes and no. Yes, the drift of the Timeline laser over time is the cumulative error, but no (IMO), the laser may not drift only in one direction, as I wrote above. It could conceivably drift in either or both directions over a 30-min time frame. Therefore using the cumulative error over time as a standard might be misleading. You've got to sit there and watch that laser every single revolution.... (You are getting sleepy.... Your eyelids are growing heavy... You are in my power... You will do whatever I say...) |
Hi Halcro, That is excellent news. So is speed accuracy something that was once mastered and now lost on more recent tt's? How do we get it back? Do you feel you lose something with the thread drive since it drifts a bit? I would think not, but your opinion/experience here would mean something. |
Hi Tony,
I have left the Timeline running for an entire album side with zero drift.
If you go to YouTube and look up the Timeline video (not mine).....you will notice on the demonstration that his turntable.........demonstrates a significant drift when the tonearm is lowered.
The Timeline is the scientific device that conclusively proved that 'stylus drag' is a reality rather than a theory.
I cannot believe that my Victor TT-101 is the only turntable which can maintain this kind of speed accuracy?
There must be many other brands.......perhaps mostly of the quartz-controlled direct drive type......which are similarly capable?
If this is the case.......then we should have the right to expect this kind of accuracy from our turntables.
Even with my Raven AC-2 with thread drive.........the drift with a stylus in play is only 0.5mm per revolution from the wall mark. If I adjust the speed on the motor controller one step UP.....it then runs fast by 1mm per revolution. But these are both constant deviations which indicate that the turntable is maintaining consistent speed.......just not exactly 33.33rpm. If the motor controller had a finer adjustment......I could get it spot-on.
The Timeline is a wonderful instrument IMHO and it is not correct to believe that turntables cannot match its accuracy?
I await the day when you actually try one on your turntable.......it can only help you :^) |
Let me clarify my one statement a little better. Cueing up the tonearm is a one time event that may or may not cause the laser mark to move. It is not part of the cumulative error. So over the long term it has little or no impact on the results. Unless something funny is going on with the motor controller, the laser mark should drift slowly in one direction over the 30 minutes. That is the cumulative error. |
Hi Halcro, I saw your video. It is impressive how well your tt holds speed, but that was a relatively short period of time. Can you let it run for 30 minutes to see the results over the long term? I am very curious to see those results. If the laser mark has no drift after 30 minutes that would mean your tt has speed accuracy on the order of 0.00002%. That would be far beyond expectations in my mind. Some suggest that the speed accuracy fluctuates, but I believe that speed error is cumulative when using a device such as the timeline. That means tha the longer you run your tt with the timeline the more error, or drift you should see. I don't think that cueing and dropping the tonearm will make the line move the other way due to the motor controller. It reacts to the torque changes. |
Should have read Tony's post before writing the above post. I think the amount of error and the type of error Tony describes should be perfectly acceptable. It is a linear error; in other words it would be the result of the platter spinning a teeny bit too fast at some constant rate. That kind of error should be adjustable back to dead on accurate, and if it's not, it nevertheless would be inconsequential. I thought we all agreed that the concern is for transient or instantaneous errors related to variations in stylus drag. Such errors would in theory go either way, too fast or too slow. So the Timeline light might move back and forth in either direction from neutral. |
Sksos1. In a word, no. I do not own a TT Weights turntable. I own a tweaked Lenco in a slate plinth, a Denon DP80 in a slate plinth, a Technics SP10 Mk3 in a slate and wood plinth, and a Kenwood L07D. I should sell two of them, but I cannot pick which ones. They each seem irreplaceable. About 4 years ago, I went from a very good belt-drive tt ($5000 class) to the Lenco and then to direct-drive, and I have no second thoughts. But I do confess that vintage tt's appeal to the collector instinct in me.
Since others here have also indicated that their turntables of many various types have "failed" the Timeline test, perhaps it is unwise or unfair to keep harping on the one brand that you found to be faulty by that sole criterion. |
What does everyone expect from their turntables when using the Timline device? Absolute zero drift of the laser mark? It's not an impossible expectation? Have you not seen my video of the Victor TT-101 with the Timeline and three arms being lowered and raised with "absolute zero drift"? |
Tony ~ I'd be happy with what you propose BUT what I see currently with the TTWeights table is that the line moves EVERY rotation which to me is just unacceptable. |
I hear you Tony but it seems nobody else is or wants to pay attention to you. They are believing that if the timeline isn't right nor is the turntble but yet there have only been just a couple of tables mentioned that the timeline is true on.
Brad |
I'll ask this question again since the other post was deleted. What does everyone expect from their turntables when using the Timline device? Absolute zero drift of the laser mark? Here is another way to look at it. Leave the Timeline device on for 30 minutes. If you are comfortable cueing up the same record side twice, do that. So in 30 minutes the platter will rotate 1000 times. Since most tt's are spec'd to have a speed accuracy of around 0.02%, then you can expect to see the laser drift about 72 degrees in 30 minutes. That is 0.2 rotations out of 1000. Is that good or bad? That would seem very good to me. btw- the Timeline maker advertises an accuracy of 2ppm. I take that to mean the Timeline device is about 2 orders of magnitude better than a typical tt. |
Lewm ~ you don't happen to own a TTWeights table? I've now checked 2 TTWeights tables and both show inaccuracies via the Timeline, would like to have confirmed a third and then can surely say its a design fault!
Looking forward to your findings. |
Syntax: "Tweaking a dead cow to a horse is interesting, no doubt, but other Designers made better work." That reminds me of an old Chinese saying, "ride a cow before you find a horse." For some people their turntable of choice is the cow... for the time being. :-) Or they think they're riding a horse? Or they are just "cowhide lanterns." :-D ______ |
Dev - the Final Audio platter material is aluminium with very heavy copper mat. The thread runs on the aluminium part. I would have thought the copper is harder than aluminium and should be safe but not absolutely sure. |
I am going to borrow the Timeline tomorrow.
But not all my turntables are in service, so it will take a while to arrive at a full report. |
Ahhh the vagaries of the Audiophile mentality?
Rather than question the accuracy of their calculators ( because they can't go to infinity 33.333333333333333333333....) or the accuracy of a Strobe which needs to flash at constant and repeatable frequency whilst aimed at a disc with lines printed by machines to an order of indeterminate accuracy......or question the actual speed of their turntables with sometimes primitive electro/mechanical interfaces......the majority seem to question the accuracy of a scientific instrument whose accuracy can be definitively proven?
And those appearing to do this are invariably those who do not have the Timeline nor have used it on their turntables?
There appears to be an element of fear and trepidation about these 'doubters' with 'denial' being the protection of choice? |
Dear Raul, I did not mean to imply that I KNOW that the Timeline is miscalibrated. I was just musing after Timeltel's correction of Catastrofe's calculation that in truth the time for one revolution, if the speed is 33.333.... would be slightly more than 1.8 sec. It might be 1.800180018.... I would assume that Mr. Sutherland knows that, too. All he had to do was to build a circuit that can divide 60 by 33.33333... and then trigger a laser according to the result, in seconds. And apparently he warned end users that they might not want to know what the Timeline can tell them. It's like going to the doctor for that pain in your .....wherever.
Dear Henry, I would agree that if the Timeline and the Victor TT101 are in perfect sync, it is likely that the Timeline is bang "on". But in general it is not valid to calibrate an instrument against the thing you are trying to measure with it. |
Regardless of the accuracy of the Timeline as long as it is consistent then it still demonstrates there's inconsistency when the laser mark moves off target so there is a CHANGE due to stylus drag. It proves there is a change in rotation and it may or may not change the sound but the fact is that there is a change. What is so hard to get? If the Timeline cost only $50. Everyone would just get one and start questioning and addressing the speed issue of the turntable.
I love the KAB strobe and it's a useful device but it cannot show me stylus drag visually the way the Timeline does.
______
|
Hi Ikitch,
what the heck I was going to re-package that and sell it for say $$$$ ha! ha! and it actually works.
Hi Syntax,
nothing like going for the jugular, the TW product isn't as bad as you make it out to be. You might not like it personally and find faults which is okay but show me one table that is perfect? You won't be able to.
Even your own MS table has issues in it's original state, you have had to mod it to enjoy. Some MS owners have even changed from the original motor because they felt there was better performance to be had.
There will always be differences and that's life, to me I'm open minded to learning but in the end it's all about listening to music.
It gets real boring and it's just frankly so old now seeing the same replies, I think we all know you don't care for TW product but others do.
|
Dear Halcro: As Dover I'm using thread drive for all the years I can remember either the MS I owned till today and my Acoustic Signature ones.
What is weird is that only " today " many people is discovering when the option always been there.
I don't know you but even with a thread the DD ones performs overall better.
Btw, what Lewm posted and that M.Lavigne refered on other related thread and my own post ( not so specific as Lewm one. ) about that the Timeline is not accurate/perfect as we all are thinking finally there is a " light " that tell us on that non accurate device that already brought some TT owners to a " suicide ".
This could tell us that we have to analize this type of TT subject more carefully that what we are doing till today.
Maybe Mr. Sutherland can comes here to explain the overall Timeline design and to confirm or not that 0.00018 discrepancy.
Regards and enjoy the music,
R. |
It is actually 1.8 sec/rev. 33 and 1/3 rev/min divided by 60 sec/min yields 0.5556 rev/sec (0.555555555 repeating). Your tt makes 100 revolutions every 3 minutes or 100 revolutions every 180 seconds. So if you divide 180 seconds by 100 revolutions, you get 1.8 sec/rev. |
It's actually 1.80018... I think it's a repeating number. Let's hope Mr. Sutherland set his timing thus. Otherwise, the instrument is off by .00018 sec per revolution. Apparently this much error would drive some of us crazy or to a new turntable. |
Solong's observations regarding play in the Raven motors feet is spot on. I utilize PTFE plumbers tape on the threads of the feet to eliminate the play and the metal to metal interface. I have since applied the tape to other applications in my system including speaker spikes and triplanar screws with very positive results. Metal to metal interfaces and improperly tightened components are generally not good a thing. |
... your new experience with a thread driven Raven sounds good.
Next, you could try this:
- disassemble the three feet from both of your motor housings
- set up the housings flat on some kind of damping mat (a piece of anti-drone mat for washing machines would help)
- rearrange the strings
Now the motor housings are no longer able to wobble slightly on their feet (that's particularly the case when strong tension of the belt/tape/thread is applied). In my experience this has also positive effects on speed consistency and sound improvement. The Raven is a LP12 "in heavy". No matter what you do, it will always change its "performance". Typical sub level Design attribute. Tweaking a dead cow to a horse is interesting, no doubt, but other Designers made better work. |
Dover,
is your platter the same POD material as the TW product?
Looking closer at my platter I can actually run the thread either on the POD material or COPPER.
Which is the harder material? anyone know. |
Hi Dev,
I am using only two motors instead of the three. I found that with the standard Raven belt......the speed consistency was better than with the three.
I assume that the extra belt contact on the platter has something to do with it?
The same principle should apply to the thread and yes.....Daniel did warn me about possible marking and wear on the side of the platter with the thread because of the soft Delcrin material.....but I'm prepared to accept this for the increased performance.
Hi Lew,
The Timeline is dead-on accurate as I have proved using the TT-101.
The KAB Strobe must be wrong/faulty?
I haven't listened to the Raven set up according to the strobe since I received the Timeline. All I can tell you is that the TT-101 initially blew the Raven away (sound-wise) when the Raven was set up using the KAB.
With the Raven running the thread drive on two motors and set up according to the Timeline.......the differences to the Victor are not that great.
In other words.....I can happily listen to both decks.
Dear Solong,
Thanks for the hints.
Unfortunately......my cantilevered wall shelf slopes alarmingly to the front due to the weight of the Raven....and the motors require the utmost levelling of the feet to maintain their horizontality. Feet of some sort....are a prerequisite?
Hi Dover,
The Raven motor pulleys do not seem to allow the thread to move visually up and down.
I also have some French silk thread which I can try as well. Some sexy colours also :-) |
Regards, Catastrofe. Reverse your order of operation: 60/33.3 = 1.8.
Peace, |
Catastrophe u missing .68 of a revolution - try 60 / 33.333333 |
Dear Henry, What about listening? When you set the table up using the KAB vs using the Timeline, were there any audible differences? If the KAB was that far off, on the slow side, you ought to have heard it in the form of pitch distortion and/or rhythm distortion. One would have to think that one of your two devices might indeed be defective. Either that or neither is quite accurate.
I had an interesting experience just a few days ago. When I originally set up my Lenco, I had it running at 33 rpm per the KAB strobe, with AC direct from one of my dedicated house lines. (You can adjust speed on a Lenco by moving the idler wheel up or down a tapered shaft driven by the motor.) Then I inserted my Walker Audio motor controller and had the Lenco set at exactly 33 with the Walker. Then some months later, I removed the Walker and was running direct from the wall socket again, but I had not re-checked the speed when I went back to house AC. The other day, I had an audiophile friend here listening with me to the Lenco, and he remarked that it sounded "slow"; he perceived a pitch problem. So we took out the KAB strobe again, and indeed, with the stylus in the groove, the Lenco was slow. I was embarrassed that I had not picked up on this problem. However, after he left, I realized that I had been bothered by the musical timing with the Lenco. Tempo seemed consistently "slow", but I heard no real problem with pitch. I had even wondered why Ella Fitzgerald had chosen a slow tempo for a Harold Arlen tune that I considered to be a good swing. The point is that what he perceived as a pitch problem was perceived by me as a timing problem. Obviously, tt speed affects both. I subsequently re-inserted the Walker and now all is well. The brain is a funny organ. He cannot sing to save his life, and I am a long time amateur jazz singer. You would think that I would have at least as good a sense of pitch as he does. |
Okay, I'm sure that I'm missing something hear as it relates to the Timeline. . .
Sutherland states that if your turntable is spinning at 33 1/3 RPM it will take 1.8 seconds to complete a revolution. His Timeline flashes at this 1.8 second interval, and if the revolutions are precise, the laser image will hit the same spot on the wall with every revolution. Makes complete sense.
However. . .33 1/3 RPM means that in one second (33 1/3 divided by 60 seconds/minute) your table will complete .5555 revolutions, or one revolution every 1.111 seconds, not 1.8 seconds.
What am I missing? |
Halcro great to see you trying the thread drive. The pulley shape should be concave for thread drive so it self centres and does not ride up and down.
Dev I have been using my thread drive final audio Parthenon for over 20 yrs with silk thread , surgical silk, quite high tension and there is only a very faint mark on the platter, no wear. |
Dear Halcro,
your new experience with a thread driven Raven sounds good.
Next, you could try this:
- disassemble the three feet from both of your motor housings
- set up the housings flat on some kind of damping mat (a piece of anti-drone mat for washing machines would help)
- rearrange the strings
Now the motor housings are no longer able to wobble slightly on their feet (that's particularly the case when strong tension of the belt/tape/thread is applied). In my experience this has also positive effects on speed consistency and sound improvement. |
Halcro, interesting and thanks for sharing. What's very interesting is if you already had it set-up for accurate speed with the belt which I assume you did and by just installing the thread the variance.
Is the thread now longer then the belt size was? Not the same tention possibly?
Another tweak to try would be with your table is to use only two motors, have one motor on each side with separate threads but only one operational motor.
Are you not concerned with the thread maring the platter POD material? D mentioned someone else whom did this and it did such so this person has since moved onto using a 1/4 mylar belt and actually has the two motors set-up as mentioned above. Table being isolated separate from the motors.
I also have the thread on hand and my table being the TW BK with an almost all copper platter being mostly different than yours I'm concerned and have yet to do it, last thing I want to do is damage the looks of the platter.
On tables like the MS appear to be no issues due to the different plater material, gun metal or stainless. |
I have just replaced the rubber belt on my Raven AC-2 with the Bavarian thread sent to me by Dertonarm ( thanks Daniel).
The speed consistency is slightly improved with this thread drive but the sound of the turntable has been somewhat transformed.
There appears to be a half octave of added bass together with an increased level of excitement and realism to each and every track and record.
Is there more to the drive method than pure speed accuracy?
When I changed to the thread drive, I needed to adjust the Raven motor controller to correct for the differing characteristics and I used the KAB Strobe to quickly get me to the 'ballpark'.
I then installed the Timeline and was shocked to find how inaccurately the platter was now running? I needed to press the 'UP' button about 7 times to reach the correct speed on both 33.33rpm and 45rpm.
When the speeds were corrected with the Timeline......the KAB Strobe indicated incorrect speeds!?
I know the Timeline is correct as it agrees exactly with the speeds on my Victor TT-101 which are quartz-locked.
Perhaps it is only my KAB Strobe which is faulty?.......but I urge caution for all those relying on strobes to set their speeds?
And for those who claim that speed accuracy does not matter.........how do you know if you haven't heard it? :^) |
I'm sure because TTWeights places many ads here on Agon they had a BIG say in why the thread was closed. My own search for a table that has spot on accuracy still continues...... |
I have just fitted a thread drive to replace the rubber belt on the Raven AC-2 (thank you Daniel for the Bavarian thread)........and apart from the increased accuracy in speed constancy over the original rubber.......the actual improvement in sound is astonishing?
The bass appears to have added a half octave in depth, the clarity and dynamics have improved and the sense of excitement and realism on every track is palpable.
Is there more to this than speed consistency?
Incidentally......I had to reset the speed on the Raven motor controller because of the differences in force transfer between the rubber and the thread and I used the KAB Strobe initially to find the 'ball-park' setting.
I then set the 'correct' speed using the Timeline and the adjustments to the controller were quite severe. I'm not talking fine adjustment here.........it required about 7 or 8 presses of the 'faster' button to reach 'correct' speed over that settled by the KAB.This is rather a serious indictment of the KAB which simply cannot be correct?
I don't know if it's just my strobe or whether this is endemic to the functioning of the KAB?
I know that the Timeline is exact as it agrees 100% with the speed indication on my Victor TT-101 DD turntable which is quartz locked.
So the question to those relying on the KAB or other versions of a strobe to set the speed of their turntables........you may wrongly believe your speed is correct.
And to those who state that it doesn't matter......how do you know when you haven't heard? |
Dover, that was funny. :-D The thread " TTWeights table and Timeline accuracy" is mysteriously closed but at least we still have this thread to talk about speed issue. I don't want to stir up the pot and point fingers at certain brands but I still enjoy discussing speed issues in turntable designs. We are still waiting for Lew to report back on his Timeline experience. :) _______ |
Raul try testing the timeline it goes like this - - - - - - - |
hi there-------------------------------testing only. |
Dear Peterayer,
Do understand. Sometimes threads are dissapearing without the community being informed for what reason this was done, if it happens accidentically or because someone asked for deletion. In my case I asked Audiogon. on one thread it was restored, on another thread I did not get any reply, maybe a dealer wasn't` happy - just wondering ...
Best @ Fun Only |
Dear Pryso, *now wasn't that non-engineer Harry Belafonte strollin' down the beach in sunny Jamaica with his father who tried to explain to him the thing with the birds and the bees .... ? |
Dear Decibell: Please email me.
Regards and enjoy the music,
R. |
My friend Raul. Thanks, got it!
Or as was once suggested, "it's as clear as mud but it covers the ground."*
* Observation by a non-engineer. |
Dear Rauliruegas,
This is very interesting! Does this document exist on the web to be downloaded? If not, can you email a copy with graphs etc.? I would be very interested.
Thanks |
Dear Lewm: Yes, they did indeed. These are exerpts from a Sony research in 1975:
++++++++++++++++++++++++++++++++++++++++++++++++++++
Ordinary Motor Servo System
The design object of a turntable motor servo-control system is to
have the least amount of change in rotational speed when the motor
is subjected to changes. Load conditions, such as application of
stylus pressure on the record and the change in fractional resistance
between stylus and record groove. Fig. I shows the static characteristics
of the servo system.
When the motor load torque is to and the supply voltage is Vo, the
angular velocity is Po. If the load increases to tl, the angular
frequency goes down to Pi provided that the supply voltage is kept
at Vo. In this case, th8 amount of change in angular velocity per
unit change of load is as shown below.
6P Po-P_ I
KT- a_- - ?,-7o - Do I-o.
Do=Fluid resistance
In order to bring the angular velocity back as close as possible to
Po, the supply voltage must be increased when the angular frequency
is lowered from Po to Pl' The amount of change in angular velocity
of the motor per unit of supply voltage, Ky, is shown as follows:
81_ KT
Kv=_,V - 0o I-b
KT = Cons'i'anf of 'torque .generefion
The amount of change in voltage per unit angular velocity, K, is expressed
as follows:
aV
K- FC
AW
_p in FiE. 2 is the amount of change in angular velocity after the
servo system has stabilized and is shown as follows:
Ap = I+K Kv
_7 = chanqein Icedtorque
i + KKv in the preceding equation Is called the loop gain. From the
equation 1-a and 1-b the following is obtained:
f
P Do
---- I-C
Ay I+KKV
Thls shows that curve S In Fig. I which indicates the amount of change
In angular velocity after the serve has stabilized, is improved when
multipled by the loop gain over the change in angular velocity before
the serve is stabilized. Above, we discussed the function of the serve
system with a change in load torque under DC conditions. In the case
of a change In load torque under AC conditions, the relation among various
parameters in shown in Fig. 3.
The dotted lines in Fig. 3 show the characteristics of disturbance suppression
by the moment of inertia of the motor rotor and turntable.
The solid line shows the characteristics after the serve is stabilized.
Fig. 3 is also expressed In the following equation:
Po I -.f
glo= (I+KKv) j
I.
z_P(Jl) Do
A7 (,.Pt,) - I,KKv t-9
when J_ ¢ d'_co
Therefore,
aPfJ_)
I-h
/',7'(_'t,) J-d"bo
This indicates that in order to obtain higher suppression of external
disturbance, it is necessary to make the moment of inertia of motor
rotor and turntable as well as the angular velocity response of serve
system larger. For example, under the following conditions:
,.,T=ZOO(§.cTn. seci), J_o --Z/-(X lO (red/acc)
Stylus point from spindle = 15(cra)
Stylus pressure = 3f§)
Coefficienf of frichon, xz =0.4
_Y = I_ x 3 ×O.Z..=I-18 (9 .cra)
The amount of change in angular velocity of the motor spindle dP is,
therefore, expressed as follows:
2
Ap = J_L_ ' AZ = ZOOx Z 7_x IO X 18 = I,z+33XIO -3 (md/sec)
· = O.OI37(rpm)
This change in the standard speed of 33 1/3 rpm in percentage,_, is:
/
aP O.OI37
?_ ---- _P_3__- X IOO --- lOC X IOO = O,Oql (%)
3
Phase-locked Motor Servo System With Quartz Generator
As discussed above, conventional servo system requires detection in change
of angular velocity for compensation in changes of speed. Therefore, unless
the moment of inertia in the mechanical system is infinite or the
angular velocity of servo response is infinite, it is impossible to avoid
changes in speed totally. Increase in the moment of inertia will result
in shorter life of the motor/turntable bearings and slower start-up time.
Increase in angular velocity of servo response has also its limitations.
The phase-locked servo system utilizes the prinipal that if a change in
angular velocity is converted to a change in phase, the conversion constant
becomes infinite at DC. The change in angular velocity P(t) is expressed
as follows:
Pit) =A PcosJ1t &p: arnountchangedin
angular velocity
The change in phase f8 (rD;n this case is-
_(:t)=fPtt)dt- AP sin Zlz / ./ _b
Therefore, the transfer function H (_) is =
Therefore,¢h¢¢rans_r fu_ffion H(_) is:
H(g) = -p-=(t) ..I... 2-_
Pit) jJ_
The preceding equation 2-a indicates that when a change in angular
velocity (_) is zero (or DC), the conversion gain becomes infinite
and the phase is always 90° behind regardless of angular velocity.
The transfer function, HT (_-) is the change between angular velocity,
and voltage is expressed as follows: .
Ka
Hr (Z1,)= K,_ H(_%)=
K_: Cons-Cainntconvertingchange
inphase intochange in voltage
Fig. 4 shows the block diagram of the serve system with HT _ in the
serve loop, and Fig. 5 shows its disturbanee suppression characteristics.
In Fig. 5 the dotted lines show the disturbance suppression
3
characteristics of the moment of inertia in the mechanical system.
The solid line shows suppression of characteristic after the velocity
detection servo is stabilized. The broken line shows the characteristics
of servo system including the phase comparator system. As shown,
compared to the system only with velocity detection, the phase comparator
system improves the disturbance suppression characteristics when
the torque disturbance angle frequency is belowS; and when there is
no disturbance _.=O), the change in turntable angular velocity_p becomes
zero, or in perfect equilibrium. If there is an error in the reference
itself, to which the angular velocity of the motor is compared,
this will of course result in an error in motor speed. In the case of
the Sony PS-8750, a quartz generator is used as the reference source.
Since the speed error of the motor in this case is equal to that of the
generator, it is kept to below 0.003%.
The effect of the stylus pressure and friction between the stylus and
record groove is shown in Figures 6-1 and 6-2. Fig. 6-1 shows that
with "velocity only" servo systems a two-gram stylus pressure on the
outer grooves results in approximately 0.02% slow down inturntable
speed in addition to the speed fluctuations of about 0.014% caused by
the audio signal modulation in the record grooves. Fig. 6-2 shows
speed stability of the phase-locked servo system. As it is shown,
there is little effect from stylus pressure and the change in friction
between the stylus and grooves on the turntable speed. The frequency
of the external disturbance stays mostly below 1Hz. Therefore, as shown
in Fig. 5 it is suppressed very effectively with the phase-locked servo
system, j_In the PS-8750Jcase, the phase-locked servo responds below 1.4
Hz (fc =_-_= 1.4 (Hz). At around 0.07Hz where most of the disturbance is
found the suppression is approximately 20 times greater than that of
the "velocity only" servo system. If the same effect is to be obtained
with the servo system without a phase comparator, 20 times more moment
of inertia is required in the mechanical system.
++++++++++++++++++++++++++++++++++++++++++++++++++++++
Denon use/used that PLL system as other manufacturers.
Regards and enjoy the music,
R. |
If you take a look at one of the old brochures for the Denon DP80 (I think), they present an actual plot of instantaneous speed v time. The DP80 is not perfect in this graph, but Denon claim it was superior to the un-named competition. This is really just to say that the old guys understood and were able to graph this phenomenon. |
Your timeline device is averaging speed. It is not giving you an instantaneous reading. The laser pulses every 1.8 seconds. As long as the turntable achieves one revolution in 1.8 seconds, the laser spot remains stationary. Your turntable could be speeding up 25% and slowing down 25% in one revolution and the timeline will happily show a stationary spot on the wall as long as the platter rotation averages 1.8 seconds per turn. The best way to determine how your turntable is behaving is to look at speed real time. One way is some type of encoder with the output to an X-Y plotter. Another way is to play a record with a fixed frequency such as 3150 Hz. The inherent errors are 1) accuracy of the recorded frequency and 2) record runout. Using an FFT analyzer you can see any speed drift realtime. A good substitute is the iPhone app. It seems very good to me. It will show you your turntable wow and flutter real time and filters out the 0.5556Hz frequency caused by any record offset to the platter.
I would like to know if anyone's turntable wow and flutter measures less than 0.01% regardless of drive type. |
