One of the downsides of having a turntable that uses an oscillator preamplifier and power amplifier to drive the motor means I have to run 2 MIT power cables/MIT Magnum MA interconnect/custom MIT speaker cable just to run the turntable. It was worse when I drove the TT with monoblocks.
|
I noticed that my LPs sounded cleaner after I upgraded the power cord to my Loricraft PRC 4. Just kidding. It's a mad world.
All of this serious writing about turntable speed and measuring devices had me wanting to contribute some levity to the discussion. Sorry.
Back to the topic and hand and thanks to those of you who are really thinking about this and sharing your results. |
Richard, Do you have any theories other than eccentricity as to why the results with the Feickert are inconsistent? That's my main one....although I suspect that fluctuation of mains power could affect the sensitivity of the sine-wave generation frequency? It appears that results are better late at night.....and without air conditioning on?.....at least chez moi :-) Regards |
You can fix the off centre hole by checking the run out and carefully open up the hole with a needle file to centre it. Then you simply mark with a pencil on the label which part of the elongated hole butts up to the spindle for next time.
Option 2 is to drill/mill the hole oversize. Then centre the record to minimise runout. You can make it easy by making up a washer with a spindle hole, and once you are happy that you have found the true centre, then push the washer over the spindle and glue it to the record. Now you have a record with a true centre.
PS As Tony has pointed out, dont assume the record is round, it isn't. You must play the record and work out how far it's out by measuring the lateral movement of the stylus.
PS2 : As this advice is free, there is no responsibility on my part if you screw up.
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Dover, Then centre the record to minimise runout. Can you please explain what you mean by this? Thanks. |
Halcro - exactly that. If the hole isn't in the centre, then drill a big one. Position the record so that the arm is not moving in and out from the centre.
Definition of run-out - oxford dictionary - noun
slight error in a rotating tool, machine component, etc. such as being off-centre or not exactly round:
Have you been watching too much cricket ? |
Have you been watching too much cricket ? With the current bunch of Aussie batsmen? Are you serious? But Andy Murray to beat Jokovic in the Australian Open tonight? |
Anyone remember a product offered in the 1980s called centre a disk?
Dover you notice a positive difference correcting your off centre records right? However doing this by eye is near impossible.
You can make a geometry jig, two intersecting diameters of a circle where the two diameter lines cross.
What it is are perpendicular "frame" called chords to form legs of a right triangle. A third side of the triangle is the diameter. A diameter is a line that passes throgh the centre of the circle and two diameters must cross at the centre.
Visualize a rectangular box shape with cross hairs,I used two pound fishing line as the diameters or cross hairs, practice on worthless vinyl.
It works very well however I would like to see something better. Halcro this could be a good project for you. |
Yeah should be a cracker of a match. Murray has definitely stepped up a cog - not so many kangaroos in the top paddock now.
Is that your Porsche ? Very very nice. |
Is that your Porsche ? Very very nice. Thanks........50 years old in June this year. Gets me in a lot of trouble when I say it looks better than most 50 year old women? Guess I should leave out the noun...."women"? |
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! |
Lespier,
I agree! the long delay after moderators have finally agreed that our contributions will not lead to revolution on Audigon makes it very difficult following the discussion. It takes away some of the fun we had in earlier times. Living in a fast world with the experience that on other Forums comments or responses are possible within minutes I may ask if this is the best/benchmark approach guiding an Audio Forum? |
Richard is dead on with his post, in my opinion. Our ears are critical for good reason, so let's go back and take a look at the thread as its originator intended. It is about the three different drive categories, assuming the string isn't in one all its own.
Direct drive:
How well it works depends upon how its speed is controlled and how it is coupled to the platter. Of course, there are many other variables, but these are most critical for this drive method. I believe a great direct drive is the most difficult to achieve because of audible artifacts introduced by most implementations, but some have accomplished the task beautifully. The Mitchell Cotter turntable comes to mind instantly, but others, like Brinkman have done an admirable job. Still, my ears hear a lack of dynamics and a "jitter" with 90% of the direct drives out there. One thing I have noticed about them is that the plinth isn't quite as important as it is in other designs. That's probably due to how the spindle is coupled with the rest of the system. It is a system that can be stellar, but it is difficult to do.
Belt drive:
As we all know, these run from horrid to fantastic. It seems that most are copies of another one, in that they typically use essentially the same motors and same belt treatment, more or less. Others, however, employ ingenious workarounds to avoid any pitfalls introduced by belt creep. The SG Spiral Groove comes to mind with how the motor is oriented to the platter. There is very little spare belt hanging out there in air with that turntable. That differentiates it from the pack, and the results show it. That's only one example, but I gave it to illustrate that there are designers who build belt drives who think outside the box in extremely practical and creative ways. There are others, but most go down the path of the status quo. Anyway, I believe we will see a lot more done with belt drives because there are a lot of ideas that haven't been tried, yet. There are also ideas that have been tried, but forgotten for some reason. Possibly the finest belt drive I have ever heard is the Fairchild Studio 750. This old beast went against convention by using an incredibly high torque motor. Maybe someone will repeat that with a modern incarnation. Even if they don't, great belt drives exist in fairly large numbers.
Idler drive:
I realize that idlers are foreign in many circles, and that biases exist which are based upon vintage units that display what appear to be inherent weaknesses. Most of those weaknesses, however, are due to resonating linkage, clunky top plates, noisy idler wheels, etc. One thing to bear in mind is that the idler wheel tracks with greater inherent accuracy than a belt. The trick is to make it track quietly, which can be done. If one eliminates the noise of the vintage units by totally rethinking how the technology should be applied, an idler can be a wonderful turntable.
So...
Any of the three can be at the top of the food chain. It all depends upon how the design is approached and how practical ideas are implemented that improve on what was done before. We will never settle the discussion of which is best, as long as people fail to realize that drive methods are nothing more than points of departure, and that the devil is in the details, regardless of the method chosen.
I submit to you all that turntables exist, or can be made, of all three methods that are high performers, and that those turntables can satisfy anyone's personal preferences when the problems facing each drive discipline are addressed properly.
. |
Mosin,
an excellent summary you made which I will fully underwrite. Especially on idler drives many among us seem to have made not the best experiences and this is definitely due to the equipment they were working with. If you put a lot of efforts in carefully designing and implementing designs on belt drives (best with two excellent motors and a perfect steering) as well as idlers you reach wonderful results. It is more the concept and its implementation rather than the difference between the various drive technologies which makes the difference! |
Quote:I believe a great direct drive is the most difficult to achieve because of audible artifacts introduced by most implementations
I would have to say this is the total opposite IMO Idler would be the most difficult because of all the mechanical things it possess..... motor. idler wheel..idlerwheel arm etc. etc...I personally played with a few Idler TT but mostly the lenco...problem is these tables will not play the bottom end like a good direct drive period! most people that use idler tables use horn systems with limited bandwidth so they do not understand what i mean...the idler (lenco) can give you a false impression of bottom end because its shelved up in response in the 40 cycle range but homogenizes the last octave....please do not kid yourself they are very nice sounding but not IMO in the same league that the upper best DD are
win we talked about this remember...I think you may have taken offense and if so I am sorry... I hear what i hear and i know what i know
Lawrence
Fidelity Forward |
In_shore - The centre disc method you outlined is flawed. It assumes the record is round, which often is not true. Therefore the diameters are not consistant. The groove is what is round, not the edge of the record. The file method I suggested in the speed accuracy thread was trialled by Tonywinsc. 11-26-11: Tonywinsc
I filed the hole in my stereo test record. I improved the runout a bit. According to the iPhone app, I now have the raw Wow down to +/-0.16%. The filtered didn't change, -0.01%/+0.02%. The total spread within the published specs for my tt. With a little more filing of the center hole and more work/patient effort to center the record on the platter, I could improve the raw values even more. |
Richardkrebs Re Your post on the 24/1 I have alluded to another problem with speed stability in DD TTs that is unrelated to stylus drag or cogging...
It occurs at much higher frequencies...
Taking it away however is dramatic.
It also shows that we can perceive timing problems well below the threshold of measuring instruments. Thanks for your illuminating post. The jitter you are referring to is one of the fundamental shortcomings of the Technics SP10 that other manufacturers have taken pains to design out. It is all too obvious for those of us with a quality turntable that the Technics possesses jitter that would make its purchase unacceptable. I am all too aware of the Technics jitter because my Final simply does not have it. Your attempts to remove the jitter from the Technics is laudable. |
Thespier and Thuchan, I agree: posts should not be reviewed for censorship. Let the members have a free conversation. |
Richard,
Great post about the arrival time difference between our ears of a sound 15 degrees away from straight ahead. It really made me think about how sensitive our ears and brains are. I'm kind of surprised that I never thought about this. I wonder if this has something to do with components that soundstage and image very well. It could just be that the component processes or amplifies (whatever the component is doing whether it be an DAC or an amplifier) all frequencies and gets them to the output terminals in exactly the same amount of time. The component would also have to have the same exact, non-wavering processing time for the right and left channels.
I checked the math (twice) and got a time difference of 0.00008 seconds between the left and right ears, though, not 0.0000053 seconds as you calculated. I may have made the same error twice or maybe not. It still doesn't change the fact that the time difference is extremely small for a sound that is 15 degrees away from straight ahead.
For those who didn't do the math, at a distance of 4 meters, 15 degrees is equal to the sound source being about 1 meter away from straight ahead. 1 meter is a reasonable distance to use for this calculation. I think anyone could tell if something is straight ahead or 1 meter to the right with their eyes closed. We are probably capable of hearing even smaller changes in distance. |
We can tell the direction of a sound source by the arrival time difference between our ears. A sound source 15 degrees to the right of straight ahead at a distance of 4 meters will reach the right ear slightly sooner, but this is not all that clues us into where the sound is coming from. The sound will also be louder in the right ear because there is a more direct path into the right ear. It's more than likely both things that help us determine where sounds are coming from- time differences and volume differences. |
Dear Win, I place you way above me in experience and knowledge, when it comes to turntables. However, this is the first time I find myself disagreeing with you AND thinking that I have some personal hands-on experience to back up my quibble. Specifically, I would take serious issue with your contention that the plinth is not so important for direct-drive turntables. In my home system, I have had a lot of experience listening to different DDs in different plinths, meaning, the same motor mounted in different plinths and/or different motors mounted in the same (type of) plinth. The plinth is so "in the picture" and can do so much harm to DD sound that I have some empathy for Halcro, et al, who espouse the no-plinth approach to DD use, because a "bad" plinth does much more harm than no-plinth. (However, I maintain my position that, even with all the sonic problems a plinth can introduce, one is still necessary; it just has to be really carefully designed and built, and there is no substitute for trial and a willingness to admit error.) I would posit that what you do not like so much about DD's you have auditioned is largely due to plinths or to subtle suboptimal function of the drive system.
Hey, I love idlers too, as you know. |
Lew,
You you may be right. I spoke out of school because I lack the extensive firsthand experience that you have.
Thuchan,
You are right.
Lawrence,
I took no offense, but you haven't heard them all, and I'm here to say that an idler can be made that can do anything the others can do. I am sure of it.
Now, if I can only convince Syntax. Then, the fight will be won! That will certainly take some convincing, won't it? At least he and I agree about string drive! ;)
. |
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. |
Lawrence,
even if this is the case as you described very well with the Lenco users this is not an argument against idler drives per se. Not all horn systems have a limited bandwith. I am a running a perfectly adjusted EMT R 80 idler with my modern 5way horn system (TAD berrylium drivers) with two active subs and I am pretty sure there is no limitation at all. I am able to compare all three drive technologies in one system. As said before in the Top League it is more a matter of implementation than what kind of drive you are going for. |
Dover recently I had a demonstration of a Nakamichi 1000 table and was impressed, I just got caught up in the hoopla about it thats all,I should read this site more and I'll shut up .I know a reference position is needed of course to use a centre correcting jig and much more work can be done on my attempts.
Mosin I agree with Lewm on the issue of direct drives, Halcros nude thread on plinth-less dd is a shining example of the influence poor plinth design and material used can directly effect performance. On the other side of the coin is the plinth of the fantastic Kenwood L07D. |
Mosin
Now, if I can only convince Syntax. Then, the fight will be won! That will certainly take some convincing, won't it? At least he and I agree about string drive! ;) Hi Mosin - seems like an easy fix. Send him one of your tables to hear, and see if he returns it. No? |
01-28-13: Richardkrebs
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 ...... Hi Richard/Mosin Looking to learn and substantiate what I hear. Can you please describe the feedback you are hearing Differences in sound between local and global feedback ? Thanks |
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,
I probably hear the same things that Richard hears, or more appropriately, I miss the same things that Richard misses. Mainly, dynamics suffer. Some dynamic information is missing, and micro dynamics are smeared. Subtleties in the high registers and midrange seem clumped together a bit. It can be difficult to notice at times unless you are very familiar with the music, but it really apparent to me with well recorded piano pieces. Transients suffer, in particular. I will say that I could possibly live with some of the machines that are flawed because some are better than others. Still, it is there. We are getting somewhat nit picky, but that's what high-end is about, right?
Like Richard, I have a commercial interest, so bear that in mind. You may want to carefully make some comparisons for yourself, however. I believe you will hear it, especially if you have the opportunity to make some A-B comparisons. |
Dear Thuchan, Once you get all the way to a "5-way" horn system, I should hope there would be good response at the audio frequency extremes. Most horn lovers insist on making do with one or at most two drivers for the full range, as I am sure you know. |
Hi Richard/Mosin Thanks for your posts and more information on local and global feedback which is what I was really looking for. Sorry for not being a little clearer. I would like to delve further into the technical nature of local and global feedback, but maybe on another thread? Thanks again for the info. Mosin,
You may want to carefully make some comparisons for yourself, however. I believe you will hear it, especially if you have the opportunity to make some A-B comparisons. Mosin, I did these comparisons already a while back, and they are the reason I ended up where I am today. I documented my results and opinions as an end user. If interested seek out Goldilocks on my system page. Warning Sense of humor a prerequisite before venturing to her. :^) Cheers Chris |
Ct0517
Re the Bear that tries too hard.
He doesn't have to been so stressed.
I can help him relax. |
Richardkrebs 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 ...... This statement is an oversimplification and a little disingenuous. You are conflating apples and oranges. There are 2 areas of instability 1. Any slip in the motor. 2. Any instability induced by speed correction and servo action. You are grouping 2 issues together, which have quite different outcomes in terms of how they impact a turntables speed stability and sound. Jitter is associated more with instability due to speed correction and servo action. Motor slip and its self-correction is much softer and more benign than jitter induced by speed correction and servo action. 1. Motor Slip 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. I would agree with this statement, but it should be qualified in that the amount of slip and its impact on the sound will depend on the quality and type of motor, its power supply and the inertia of the platter. One of the fundamental differences between AC synchronous motors and Brushless DC motors as used in the Technics SP10 is how they lock into speed. AC synchronous motors are dependent on the frequency of the drive current. In the Final Audio TT sine and cosine waves are generated from a motor controller and are not dependent on the stability of the mains supply. In Brushless DC motors, the stator windings are energized in a sequence. The sequence and timing is determined by the rotor position. Therefore accurate measurement of the rotor position is required for speed accuracy. In a perfect world these would sound the same, but the world is not perfect and they dont. My research into motors has shown that this can be reduced only slightly. . This is a generalization - how the motor self corrects will vary considerably depending on the motor design and how it is used. For example AC Synchronous motors and DC Brushless motors can behave quite differently. AC synchronous motors tend to be sinusoidal; DC motors tend to be trapezoidal. Trapezoidal motors give a back EMF in trapezoidal fashion and the sinusoidal motor‟s back EMF is sinusoidal. In addition to the back EMF, the phase current also has trapezoidal and sinusoidal variations in the respective types of motor. This makes the torque output by a sinusoidal motor smoother than that of a trapezoidal motor. Similarly the self-correction in a sinusoidal motor will be smoother than a trapezoidal motor. The method of coupling the motor to the platter is immaterial, as this effect is built into the motor itself. You are wrong. If a platter is direct coupled to a motor then the platter will act as a flywheel, with inertia. This will increase the resistance to drag induced motor slip and the behavior of the self-correction by the motor to recover will also be variable, for example higher inertia slower recovery. Factors that will influence the motor slip will be the design and implementation quality of the motor design, power supply, inertia of the system etc. You have not provided any comment on the magnitude of any instability due to motor slip you measured. How many motors did you measure? What types of motor did you measure? What parameters did you measure? How did you measure them? Did you use your thumb and pencil method you recommended in earlier posts? 2. Any instability due to speed correction and servo action. This is what I hear.
Global feedback when carefully designed, but not properly put together, creates a tension in the music, a greyness. I agree with this, it is, I assume, what I have heard from most DDs I have heard, including the SP10. It is less apparent in the L07Ds that I have heard. 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. I agree with the hunting and cogging these issues have quite a different impact on the sound, musical timing and instability, particularly noticeable in the bass range, for example the Goldmund Studio. With regard to loop control feedback systems as used in most DDs you seem to be in denial of system overshoot. As far as I am aware most feedback system will have input parameters based on some sort of modeling. Usually algorithms are used requiring control inputs based on measuring past errors, the present error and a prediction of future error based on the current rate of change. Past errors (Integral) are included to accelerate the process and remove any steady state errors in the present error (or proportional if you want to get technical). Since the integral term responds to an accumulation of errors from the past, it can cause the present value to overshoot the set point value (where you want to get to). In terms of correcting the present error, if the gain is too high you get instability, too low and you get a less responsive controller that may not deal with fluctuations. The prediction of future errors (called the Derivative) is required to minimize overshoot. So, summarizing this then these inputs have to be balanced to maximize the correction and minimize instability and overshoot. There are always tradeoffs. For any given Speed Correction Feedback Loop you should be able to measure or calculate the following parameters: Rise Time Overshoot Settling Time Steady state error Stability Since the Technics was built there have been significant advances in technology. We now have computer simulation software to model motor behavior and generate more accurate algorithms, from which the input parameters are derived. There are now faster chips and amplifiers for driving the motor PWMs are switching at a trillionth of a second today. The problem is the Technics is full of obsolete chips and trying to optimize the feedback loop would be like trying to tune a car that has a very basic engine management system. You would probably be better to throw the boards away and start afresh. There have also been newer methodologies to apply global feedback, which are the subject of patents. I think from memory Fujitsu has some. For the DIY person because the whole feedback loop performance is based on accurately measuring the rotor, eliminating any flex or instability in the physical motor could in theory help to reduce the issues endemic in feedback loops. You have claimed that you have managed to reduce these issues related to speed correction/servos. It would be helpful to see some hard data measurements to quantify the level of improvement. I would also be interested to know if there are any turntables available commercially that do not have speed correction/servo induced issues. |
The myth of Direct Drives and Lathes
Direct Drive devotees often refer to cutting lathes and make claims about the suitability of DD's for replay based on their use in record cutting lathes.
I would like to point out the following :
The Technics SP02 is considered one of the best DD lathe motors. Yes it is Direct Drive, but in most cutting lathes the platter is 70lbs or so ( Neumann for example ) and designed to act as a flywheel - more weight on the outer. So in other words cutting lathes are usually using very high inertia platters to provide stability in conjunction with whatever drive system is chosen.
Most of the best classical music in my view was recorded before the mid sixties, when multi miking became popular and the engineers took over the asylum. Most music was recorded on shaft driven or belt driven ( some Scully lathes for example ) lathes with very high inertia flywheel/platters.
This to me this is a compelling argument for using high inertia, irrespective of the drive methodology chosen. |
I should have made it a bit clearer in the last post, most Technics SP02 cutting lathe motors I have seen are coupled to high mass flywheel/platters in the order of 70lbs/30kg. |
I have a pragmatic question. I did some maintenance on my tt last weekend. I checked screw torques and surprisingly, all of the armboard screws turned about a quarter turn. I got it all back together and dialed in speed perfect. All is looking good. I put on Fresh Aire III again. Nice bass, a little tighter than before, I think. So I put on the CD version and give a listen to track 1. On the CD I can hear the skin on the drums; on the record- almost, but just not quite there. My question is: is that the smearing of detail you all are talking about? Is that really due to speed control, or could it be tonearm, preamp, etc? |
Dear Dover, There you go again. Trying to "prove" that one drive system is "better" than another (or in this case, "worse") by arguing from first principles. First, I think there are a lot of holes in your arguments, and second, have we, or at least most of us, not agreed that execution is paramount? That each drive system has its failings?
By now I get it; you don't like direct-drive. You do like your Final Audio TT. Live and let live.
On terminology: Motor "slip" is a term I have only read in connection with induction motors. They must slip in order to generate torque. This would apply only to idlers, as the older idlers are the only TT's I know of that used induction type motors. Induction motor combined with eddy current or other type of "braking" can make for excellent speed stability. Also, "jitter" has a specific meaning in terms of digital to analog conversion. Let's not confuse matters further by using it to describe a phenomenon related to what? Cogging or servo correction? These two phenomena are entirely separate and independent of one another, and yet they are being lumped.
FWIW, The top end Denon DD's used 3-phase AC synchronous motors. The top end Technics DD's use what you would call DC motors. But Bill Thalmann told me in conversation that if you look at the actual circuit of the Technics, the distinction between the two is not so great. DC motors are used in some of the most expensive BD turntables, as well, and the manufacturer's tout the fact. |
Hi Richard 02-02-13: Richardkrebs
Ct0517
Re the Bear that tries too hard.
He doesn't have to been so stressed.
I can help him relax. Big smile when I read that. Thanks. In the bear room when they are happy; I am happy. They are picky about the type of honey they like. :^) SP10MKII - Not being an electronics engineer I always attributed the phenomena to cogging, or the servo having to keep speed (always a little high or low) in order to stay at speed ? Your posts have shed new light on this. Dovers last posts :^) again raise a number of points. What is it about audiophiles from New Zealand? A competitive bunch. To improve the SP10MKII based solely on what I hear I always thought; A little less speed correction if possible - but enough to just keep it stable? As an owner of one I will be interested to hear/read about any direct comparisons between SP10MKIIs and MKIIIs, which have your mod. Does the gap get closed? The SP10 is still my PET project, self pride is involved and I continue to learn from her. Cheers Chris |
Not picking on you Dover but you talk about digitized sound from DD motors because of there electronics..but you dismiss the FACT that your Final vinyl TT uses some kind of sine wave generator so it does not rely on the line freq stability but hmmmm lets see what kinda electronics could or would they imply in practice?! Quartz oscillator? feed back?! etc. you get the point..lot more to understand before we/YOU can come to a "more better" conclusion
kind regards
Lawrence
Fidelity Forward |
I guess the propensity to assign cause and effect without data to connect the two is inherent in human nature. This is why we have... religion. Because one knows there is a servo in action, and because one hears a coloration - this is not enough information to say that the servo causes said coloration. I think I know what coloration it is you are talking about vis the SP10 Mk2; I heard it too. I found that it can be ameliorated or aggravated by the choice of plinth. So, how could the choice of plinth influence servo action? Maybe there is a way that could happen, but one has to test it before jumping to conclusions about cause and effect. Plus, we have the (correct) testimony of Richard that the servo does not operate like a full "on", full "off" switch, which might indeed lead to a kind of incoherency. The servo is more sophisticated than you (and certainly Dover) think. Yet despite what Richard wrote a few weeks ago, we have reverted to talking about servo mechanisms as if they are nothing more than on/off switches.
What about the latest megabuck DD turntables? I think the one from the Northwest (NVS) does not use servo correction. Is it free of the sort of coloration we are talking about? Rumor has it that it does not pass the Timeline test. The carbon fiber Grand Prix Audio Monaco uses a very advanced mega-fast modern state of the art speed correction system, yet it is not widely loved. Why is the SP10 Mk3 very much more natural sounding to my ears compared to the Mk2, if this is only about servo problems? (I don't imagine there are major differences in servo design between the two, but maybe.) |
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. |
lewm I became aware of some sort of vail with three examples of the Sp10mk2. For a lack of a better discription I found it similar to that of flutter that seam to be consistently fixed into the upper top frequency's. |
Lewm, Lawrence
Could I ask you respectfully to reread my post.
My post addresses some points made in earlier posts about "motor slip" and "speed correction systems/servos", both of which can be present in any type of turntable or motor.
AC motors have been used in Belt Drive,Direct Drive & Idler
DC motors have been used in Belt Drive,Direct Drive & Idler
Furthermore there are many variants of both AC & DC motors.
Speed correction systems have been used in both Belt Drive and Direct Drive.
Speed correction systems have been used in both AC & DC motor applications.
I use those particular TT's mentioned as examples because I know them and know what type of motor they use.
Ct0517 wanted to know more about speed controllers & servos.
My post tries to explain that most speed correction feedback loops would include the following parameters - Rise Time, Overshoot, Settling Time, Steady state error, Stability - and any solution has to be a compromise between these parameters.
The question is " Do the issues inherent in speed correction/servo loops outweigh the benefits ? "
The correct answer is "We dont know".
Why ?
Because nobody has quantified the error versus the errors generated in correcting the error.
|
Tonywinsc,
In answer to your question, it's my opinion that it could be any of those things you mention. If I heard it, I might be able to tell, but it's impossible to say from here. It is too bad you don't have the luxury of trying several tables, arms, etc. in your system. Then, you might be able to make a determination. It could be the record, you know? |
What about the latest megabuck DD turntables? I think the one from the Northwest (NVS) does not use servo correction. Is it free of the sort of coloration we are talking about? Rumor has it that it does not pass the Timeline test. From the Wave Kinetics website Speed Control Capable of both 33 1/3 and 45 RPM Utilizes a laboratory grade motor control system High inertia platter Speed accuracy to 1 part per 1000000 Direct drive system Tuning optimized using a 17 degree of freedom tuning model In linear regression the degrees of freedom is the number of estimated predictors. Degrees of freedom is often used to quantify the model complexity of a statistical modeling procedure. This tells me that they have sophisticated speed control programmed into their speed controller based on the prediction of errors ( see my post of 02-02-13 where I explained how the algorithms are derived ). 17 degrees of freedom does not mean 17 parameters either - I can send you the linear regression mathematics behind this statement if you like. It tends to suggest that their programs are using statistical analysis, and a continuous shrinkage technique to improve the prediction of error on the fly. In other words, the input parameters for the speed correction/servos are not set in concrete, as in the old days, they are calculated on the fly. As suggested in my earlier comments on the age of the Technics SP10 circuitry, these folk are using much greater computer power and new thinking on statistical prediction that is now available. Caveat : Just so everyone is clear - I make no comment on how this turntable might sound and I am ambivalent as to the drive mechanism used. |
Dover, This is what I fear as I grow older: "continuous shrinkage". If you can help me avoid that, please do send the relevant information. |
Oh yes, I meant to add that the gibberish you (Dover) quote from the NVS website does not really tell us for sure whether it uses a servo mechanism. Could be that they are talking about the ways in which they assure the synchronicity of an AC synchronous motor controller, to compensate for drag of any kind, stylus or otherwise. I had read from another source that they don't, in fact, use a servo.
The difference, in my mind at least, would be that a sophisticated controller for an AC synchronous motor (which may be what NVS does) would affect the motor's ability to sense that it had been slowed or pulled out of AC synch by some external force and correct for that. Whereas, a servo would require a speed sensor at the platter end that would tell the motor that the platter had deviated from the programmed speed. Then the motor fixes that by applying enough torque to overcome whatever new drag had been introduced. Both cases are a form of negative feedback. You might analogize this to the difference between local and global NFB, respectively.
(I don't much care for NFB in my power amplifier.) |
Lewm,
According to the Stereophile Review of the Wave Kinetics NVS it uses a DC motor with a laboratory grade servo controller with an active ultrasonic feedback loop
Reference - Stereophile vol 35 no 10. |
"Ultrasonic". I don't doubt you for one minute, but WTF does "ultrasonic" mean in this context? Stereophile reviewers are notorious (in my mind anyway) for uncritically re-stating just about any pile of BS given to them by the manufacturer of a product under review. Sometimes the verbiage in the review is taken right off the manufacturer's website or sales brochure. But in this case, none of that would matter, as the only issue is servo or no servo.
I could have sworn that one way in which NVS claimed superiority over the "old guard" DD turntables (e.g., Technics) was that they had eschewed the use of a servo mechanism. I thought that was mentioned in that thread on NVS that eventually got deleted from this website. I must be incorrect. |
'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' |
