Gentlepeople. Isn't this an interesting thread.
Ct 0517, that was a great video. Thank you for sharing it with us. Good to see what a well engineered closed loop speed control can achieve. It was also interesting how fast the high inertia platter slowed in the translator clip.
Tonywinsc has put very clearly the concept of inertia. In several of my posts I used the terms "radius of gyration" and "moment of inertia". I
apologyse for not making clear what I meant by this.
Radius of gyration is the distance where the mass of a rotating body appears to be concentrated out from axis of rotation. In the. 2001 space example this is almost out at the circumference on the station. Most DD TTs engineer the radius of gyration to be at some mid point out from the axis. In Dover's Final TT and most other belt drives or their derivatives, it is engineered to be further out. By calculating the radius of gyration and them knowing the weight of the platter we can calculate its moment of inertia which Tonywinsc clearly describes.
I have the moment of inertia figure for the SP10 MK3. This is 1,100 kg/ cm.
In other words in a rotational sense, the platter behaves as if it weighed 1,100kg with all of this weight at a radius of 1 cm. this is quite high for a DD. Good BD TT's as implied above will have higher moments of inertia than this. This is I think what Dover meant when he referred to "effective mass" .
The key here is that for a closed loop drive, the motor torque capability, servo response and platter moment of inertia all need to be in harmony. The video the Ct0517 posted clearly shows the positive effect of this.
Dev, you have asked for a list of TT's that approach the 3 rules. We could all build such a list. It is quite simple if you examine the TT under scrutiny.
Remember this is a list of rules that would apply to TT that is impossible to build.
Rule 2) is a catch all as it requires absolute dimensional stability between platter and arm board. It actually covers almost all of the requirements of a plinth design. This eliminates all TT,s that have, say, soft thrust pads in their bearings ( a trick employed to improve rumble figures )...allow any flex or bending of the plinth, have a soft Matt, excessive bearing clearance etc. The examples of breaking rule. 2 are many.
Rule 1) has been covered in this thread quite well
Rule 3) opens another can of worms. To suspend or ground. A tricky one as it depends upon where the TT is sighted.
We also need to look outside out hobby field for examples of engineering where similar design criteria are required.
High powered microscopes. Large telescopes. Aeroplane propeller balancing tables, are all areas where rules 2 an 3 come into play.
My fear is that today, basic engineering is being ingored in favor of fashion. If we look back at the.. 70s and 80s we see fantastic examples from companies . Micro Seiki, Final, Technics, Sony, Luxman, Onkyo,Victor, et el, producing flagship models that tried to address at least some of these requirements.
It is mouth watering to think of what the engineers involved in these designs could come up with today if they were given the R&D dollars.
We live in ( naive) hope. |
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. |
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. |
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. |
Ct0517
You are quite right, I should have said "Motor/Controller"
Many thanks |
Gentlepeople
A simple dynamic load test you might want to try if you havent already done so, is to hold your finger against the rotating platter while playing music.
No strobes, timelines needed just your ears. Can you hear a speed change?
How much drag do you need to apply before a chance is apparent?
Now the validity of this test is matter of opinion. But if we can hear an obvious change, one would think that there would likely be tiny changes
due to stylus drag and that this would be at least subliminally important and deleterious.
Again the method of drive/ control comes into play here and we each need to decide which does the least harm. |
Dover
No inconsistency at all. I have repeatedly said that there are many paths...,
Obviously within each family of drive there is bad and good engineering design.
Further I have tried to be as generic as possible in my posts. I mentioned the Goldmund only because it gave me a first hand view of the effect of stylus drag (which was astonishing in its magnitude).No other reason. I mentioned the SP10 mk3 only because I had the moment of inertia figure for its platter and I made no comment on its goodness or otherwise. It was simply to illustrate what moment of inertia meant and to quantify it.
I am quite familiar with the LO7 D, it is indeed a well built machine.
The discussion on arms carts etc is spurious as it is outside the realm of this thread. I agree they have an effect on perceived speed stability and that they place different demands on the TT and its drive, but what we need is a platform that is speed stable in the first instance.
We are talking about drive methods and their various features and failings. They all have failings, hence my comment re the type, that in the opinion of the listener is the most innocuous.
"The perfect TT has absolute speed stability under all load conditions".
I have also been consistent that in my view that a well designed closed loop speed control is required if we are to approach this goal. This regardless of the drive method employed, the platters moment of inertia, motor self correction characteristics or its torque curve.
While technical specs are limited, the TechDas TT ( a refreshing take on TT design) .with a platter approaching 30 kg and a high moment of inertia. With a synchronous AC motor and belt drive....Appears to have closed loop speed control.
If this is so, it seems that I am not alone in this view and that the the designer considers these small changes in speed to be musically important. |
Halcro
Do you have any theories other than eccentricity as to why the results with the Feickert are inconsistent?
Thanks |
1) The Final has been shown, through your own testing, to slow down due to stylus drag.....end of story
2) You are quite right, the Final has much higher intrinsic resistance to stylus drag than the other TT's mentioned...if you assume that the others have their servos disengaged
3) Cogging, if present, at 11hz for the DD example you gave would be easily mitigated by a correctly operating servo. The corresponding frequency for the thread drive you mentioned would be around 120hz, with no servo present to corect. I leave it up to the listener to decide which frequency, would be the most benign. If you are talking about what I call "jitter" a much higher frequency artefact common on DD's, you will have to wait for my upcoming web site to see how it is addressed.
4) You need to revisit your laws on motion to see what happens to ANY drive system that does not reduce torque to stasis levels at design speed.
5) Regarding the 1000 tonearms, phase switching, full cycle detection FG, double servos,SPZ, high kinetic energy of rotation, sine cosine, et el. you shouldnt believe everything you read in sales brochures. They are, afterall, trying to seperate you from your money.
5) Hopefully, for the last time. There are many paths to enlightement. You like the Final, thats great. Enjoy the music it plays. This hobby of ours in not a competition. |
Gentlepeople
The problem with posts like this, where a difference in opinion is being aired, is that there is a tendnacy for us to talk past eachother and place significance on things that are written outside of what the author meant. This is perfectly natural.
That said I will try to clarify what I meant with my six points.
1) and 2) The Final has higher intrinsic resistance to stylus drag due to its platter which has a higher moment of inertia than the other two TTs, ONLY if you turn off their servos.
With the servo in play The SP10MK3 will show NO measurable speed change with retardation torque levels up to 10KG/cm. In their literature they use the analogy of 1000 cartridges tracking simultaenously. So we can infer from this that 1001 cartridges tracking will cause a speed change. I note that the Final slows down with 1 cartridge tracking. Lets make this clear, speed change due to stylus drag on the SP10MK3, even with 1000 cartridges in play, is so small that it is undetectable. You can take it then that I did do not acknowledge that the initial drop of in speed would be higher with the DDs. While a speed change must be there, with the SP10, it is not measurable. This is where correct matching of motor torque capability, servo characteristics and platter moment of inertia are critical.
I do not have data on the LO7D, but I expect that it would also perform well on this front.
For me the problem with speed changes due to stylus drag is that they are a function of the music being played, unlike wow and flutter which are independant of the music. Much like tape hiss, we can listen past w&f to engage with the music. This is not possible with stylus drag speed problems, as it is inside the music itself. That said it is obvious that lower w&f would be better.
Record concentricity problems are a pain especialy when one has just put down good money for a new record. But this is not a platter speed accuracy issue, so in that sense it is spurious to any discussion on absolute platter speed accuracy, even if its effect dwarfs any platter speed errors.
3)Cogging. I don't want to put words in your mouth, but I don't think that what you are hearing is actually motor cogging as in the physical effect of the motors construction. The very low frequency at which actual cogging occurs is, I suspect, not what bothers you. I do agree that there is a problem with many DD's, but it is not physical motor cogging and it can be fixed. (Maybe the Goldmund should be outside this comment.)
4) 5) Stasis torque levels. The platter will speed up if the torque output from the motor exceeds that requied to overcome bearing friction, stylus drag and windage. Not enough torque and the platter will slow down. Drive systems revert to stasis (low maintenance ) torque levels once design speed is reached. This is taught in engineering classes. Putting this another way. Motor torque output is a function of the load.
6) You are totally correct when stating that the DDs need a lot of work to bring them up to their potetnial. This, however, does not detract from the fundamental performance of the drive method.
Lewm said "If you prefer your thread drive to any and all direct-drives you have ever heard, that is all well and good. I am sure it is superb. But I don't think you can prove from first principles that it is inherently superior to all direct drive."
Totally correct. The opposite is also true, so let's call it a day and both enjoy this thrilling hobby of ours.
|
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.
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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 |
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. |
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. |
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. |
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. |
Gentlepeople
I have been pondering our obvious passion about speed stability with respect to different drive systems. If we put aside the potential for all of us to view this topic thru somewhat colored glasses, due to our purchase choices, we can tunnel down to what we can perceive.
So here is my thought experiment.
We can tell the direction of a sound source by the arrival time difference between our ears.
For the following calculations I made these assumptions
Preceptable threshold of angular displacement of sound source from straight ahead...,15 degrees ( I have no idea if this is accurate but it seemed to be a reasonable assumption )
Distance of sound source from listener ..,4 meters ( common speaker distance)
Distance between ears drums ....120 mm( I'm wide open to reposts on that one )
Speed of sound 343 m/ s
This makes an approx distance difference to the L&R ears of 1.8 mm from the sound source.
At 343 m/s this equates to a time difference of 0.0000053 seconds (5.3 u seconds.)
Obviously some big assumptions here and hopefully I have the math roughly correct but....
No wonder we are sensitive to this stuff! |
Ketchup
I will take your figure as correct. I did the calcs long hand while waiting in a Cafe for a Flat White ( that's a coffee to those from the Northern Hemisphere)
Yes the number is small and if you extend the distance out further, which we are all quite capable of decerning, the L/R delta gets smaller. Quite amazing.
Dover The jitter artefact, as Mosin quite correctly points out, is not limited to the Technics line, he hears it in DDs in general. Actually my testing and listening has shown it to be present in any motor that uses feedback be it local feedback ( self correction) as in free running motors like those in most BDs / idler drives or global feedback as in DDs. That is it occurs in all motors. Since all TTs have motors ......
I hasten to add that this is definitely not cogging, it occurs at frequencies above that which the physical motor build would precipitate cogging.
It occurs at a higher frequency still in DDs, where global feedback is employed and is more obvious in higher torque motors, but it is there in all drive iterations. |
Ct0517.
In my view both types of feedback have a distinct sound in their "as built" states. Firstly I need to state two things.
1) I have a commercial interest in this topic, so you may want to take that into consideration.
2) How a machine is designed and how it is built are often completely different things. The designer makes a number of assumptions on the motor and feedback performance. Commercial reality can get in the way of these assumptions being realised.
This is what I hear.
Global feedback when carefully designed, but not properly put together, creates a tension in the music, a greyness. The music does not flow and does not properly connect with the listener. It is not servo overshoot, hunting or cogging. This sound is what the BD people talk about. This problem, in my opinion, can be largely removed.
Local feedback is softer and slower to respond to demand, it creates a slurring effect. The music is slightly blurred like a soft focus lens. Drive and dynamics are diminished.
My research into motors has shown that this can be reduced only slightly. The method of coupling the motor to the platter is immaterial, as this effect is built into the motor itself. This is why I have pushed my view that global feedback is neccessary, regardless of the drive method employed. It is the reduced "drive" that the DD people talk about.
Of the two, if I had to choose, I would take local. That was before I found a way to mitigate the problems of global feedback.
I hope that this helps.
|
Ct0517
Re the Bear that tries too hard.
He doesn't have to been so stressed.
I can help him relax. |
Dover.
We have covered servo control in depth in this thread.
I do not understand why some people are so down on this approach. It is just feedback. Sure it has to take into account inertia, complaince and torque. These very same elements are present in purely electronic feedback in the form of inductance, capacitence and gain, respectively. Yet the same people who have no problem with their amps employing feedback, criticize its use in speed control. It is the same stuff.
Ref my generic comments on local and global feedback. Of course there are variances within each family. It is all in the implementation. I am only reporting what I hear with every TT from the respective groups. With some designs its obvious, with others it is more subtle.
The Technics uses old technology. yep, That is one reason why I said on 01-05-13 that it would be great if the big companies, who originally built these models, looked at making updated gear.
As Lew said, the motors employed in say the Technics employ very similar circuits to AC synchronous motors. The rotating field voltage does not cross zero volts so it is not an AC motor but it performs in a similar way.
Further in AC and DC synchronous motors, the rotor turns at the same speed as the rotating field, only slightly behind it. Imagine a clock having two minute hands one 5 minutes behind the other. The trailing hand being the platter. They both rotate at one rev/hour. If load increases the gap will increase to say 7 minutes, but after that momentary drop off in speed the two hands will again rotate at one rev/hour. It is interesting that people have had to adjust the speed of their TTs after lowering the stylus. If there is no belt or thread slip, with synchronous motors, this speed adjustment should not be neccessary. Something else is going on.
Ct0517.
yeah I much prefer happy bears, no one wants to be in a room when they are angry.
I have a customer who has just had a MK2 upgraded after originally getting his MK3 done. It will be interesting to read his comments. |
'Ultrasonic' They are possibly referring to the speed measuring sample rate. It is a long time since I looked at the Goldmund speed sensor, but from memory, it was around 34,000 samples per revolution. This is not an unusually high number for a speed sensor. If you want to call this an audio signal, which it isn't, it would be almost ' ultrasonic' |
Have just pulled apart an old Goldmund motor I have lying around.
I am impressed all over again with its speed sensing design.
It has 164 slotts and 176 magnetic poles ( north plus south) in the speed sensor assembly, per revolution.
This gives 14,432 counts if they only consider, say, north pluses and 28,864 if they use both north and south. My memory was a little out. Apologies |
Halcro
Yes it is a JVC motor. After I sold my Goldmund, I had plans to build a TT based around this motor. It was an easy purchase from JVC in Japan, at the time. The project was shelved after further research on motors. |
Lewm. I am sure that the Monaco's controller is very advanced in the way it responds to the platter speed signal. What the JVC ( Goldmund Studio ) motor demonstrates however, is that its speed sample rate is not unusually high.
|
Dover.
Are we not getting off topic here? My reasons for dropping the Goldmund motor as a mule for my TT project will in no way advance this thread. It is an average motor with an above average speed measuring mechanism. Further you have described how it works. I only used it by way of example to back up my earlier assertion that high sample rates were used way back then. You are quite right, the sample rate and feedback loop bandwidth of two different things. It is probable that the samples are put thru several divider networks to bring the sample frequency down to a manageable level while simultaenously improving accuracy. (Other TT's of that era do this). I no longer have a circuit diagram so cannot confirm.
And yes, wavy lines on a PCB under a multi pole rotating magnet are one way of measuring speed. Their output count is exactly as I described. Still used today in our industry for their robustness and long term reliability. |
Lespier/ Mosin
Yes it must be very expensive to cover the R&D plus tooling for a complety new TT and motor.
Mosin, perhaps you can give us some insight on this, from within the industry, when developing your spectacular TTs? Not DD I know but it would be informative to hear any comments you are prepared to share with us.
Thanks |
Mosin.
Thanks for this. A great read.
It seems that there is a common theme driving all small audio manufacturers and that is "passion" |
Ct0517
Thank you for that. I gave up trying to build the website myself, so employed a professional.
The triangular TT is my own design and build using a SP10 MK3 motor. New platter added 12 years ago. I have used this TT to develop my upgrade. Arm started life as an ET2. As you can see it has undergone a little surgery. |
Ct0517 et el
Just to clarify things. Albert Porter has no financial interest in the Krebsupgrade. I used photos of his plinths because he kindly allowed me to and because I think that they are really cool. Bill Thalmann is my appointed agent in the America's. He does great work.
Thanks. |
