After chiding someone on VA over miunderstanding servo loops I should correct an error in my description of the Denon.
Where I said "it also employs a PLL controlled servo loop to slave the coil drive to a motion dependent signal...." I should have said "it also employs a servo loop which adjusts the coil drive, using a motion dependent signal...."
The master is the quartz reference.
Mark Kelly
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My experience with coreless motor is not limited to just the Pioneer as I have several turntables here that exhibit this silky smooth quality. The Pioneer is better to illustrate the distinctive quality of coreless motors even in an inexpensive model. I believe the later Pioneer models, the "L2" series of turntable, such as PL-50L and PL-70L all converted L2 to use coreless motor with the same specs, all employing their trademark feature "Stable Hanging Rotor" SHR, basically a fancy way of saying an inverted bearing. Anyway, I realize many top or almost top of the line models from various brands used coreless motors such as Kenwood L-07D, Sony PS-X9, JVC TT101, Yamaha GT-2000, PX-1, Pioneer PL-70LII, Sansui XP-99, et al. I owned neither so obviously I am drooling here. I am not saying only coreless motors are good. It's just that whenever I detect this kind of smooth sound, invariably it's a turntable with a coreless motor. JVC have some core motor tables approach the smoothness I crave for - I haven't listened to my SP10 for a while now. That's why I reserve the core motored tables for tape-driving purpose as the tape smooths out the tiny bit of cogging or whatever you call it for the passive platter.
Raul, I admire your forward thinking. Keep up the good fight. Yes, sometimes audiophiles got what they deserve, un-innovative products. |
Dear Lewm: +++++ " reveal the nature of these especially good tt mats. " +++++
that mat/pad with our build blend material is only the tip of the iceberg in relation with build materials and its importance in TT- tonearms - cartridges and maybe some other items. The mat is only one kind of use in the audio world.
No, the material that Ralph describe is different from the one we own, between other things ours has a lower weight due to the blend material used.
IMHO I think that the real importance of that build material subject is that we are starting to talk about when one or two years ago we did not heard nothing on this build factor.
Sooner or latter the TT and tonearm designers/manufacturer ( mainly ) must take " the bull by its horns " if they want to offer better quality performance products to we the customers.
I posted several times that we deserve the very poor non-evolution audio products we have because we the customers never ask for more: sometimes because a very poor know-how, sometimes because we don't care about and sometimes because we are thinking like 30 years ago ( with no evolution attitude. ). Of course there are some exceptions on both sides: builders and customers.
Here in this thread we have a precise example of that " old thinking " way: where Quiddity try to expose and sustain with numbers a few subjects/factors the next post to it say something like this: " if we go for the numbers a Yamaha will be better than a Lamm unit ".
Well I say that almost any audio " stage/performance " can be numbers related ( here and now ) if we know what to measure, where and how to measure, when to measure and with which tools/instruments we must to measure.
Lew, we are talking in this thread ( like in many other ones. ) of products designed 30-40 years ago that are competitive with today designs: turntables, tonearms and cartridges, with almost no evolution in the audio industry, why is that? I ask, who has the culprit? manufacturers or customers, I think both but mainly the customers that are manipulated by the " professional " ( some corrupted with intention and some " corrupted " by non know-how. ) magazine reviewers and that are ( the customers ) the ones that buy those very poor audio design items, yes we deserve what we have!
I think there are a lot of talent out there for design and build a lot better audio products in any single link of the audio chain but unfortunately we customers don't give to them any " sign " that motivate them to be better than what they are showing today, we are proud with what we have.
Anyway, continue with the thread subject.
Regards and enjoy the music,
Raul. |
Thanks, Mark. That's a lot more information than I can glean from the Denon literature from that era. And the schematic is beyond my comprehension. Others, including Technics as you note, have spoken of the Technics SP10 motor as being of the DC type. Now I see that this is a distinction without a major difference. |
Lew
The DP80 uses an iron core stator.
The distinction between Denon's "3 phase AC outer rotor motor" and Technics "Brushless DC with integral magnet platter" is largely semantic.
The Technics motor is a 3 phase outer rotor motor which includes a circuit in the motor which generates 3 AC waveforms due to the motion of the rotor. These waveforms are necessarily synchronous with the rotor. The waveforms are then amplified to a level determined by the PLL controlled servo loop and fed back to the motor drive coils. The PLL is fed by Technics famous frequency generator circuit.
Without access to the Denons circuit details I cannot say exactly how the Denon generates the frequency required to run its motor but I can say that it also employs a PLL controlled servo loop to slave the coil drive to a motion dependent signal, this time generated by a magnetic signal recorded on the platter (a primitive version of a rotary encoder). The loop presumably also controls the voltage of the drive amplifiers - if it did not the level of cogging would render the motor useless.
From a practical point of view the only difference would be in the fidelity of the drive waveform. The forward drive voltage in the Techics motors I've seen is fairly ugly, the engineers relied on the high speed of the FG servo to smooth the rotation. Denon's encoder is a lot slower so they would have to have a cleaner waveform to start with. They are both neat solutions to the central problem, neither appears to me to be inherently inferior to the other.
Mark Kelly
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Mark, Just out of curiosity, do you know anything about the build of the motor in a Denon DP80, iron core or coreless? I do know that it is a 3-phase synchronous AC motor the speed of which is controlled via the servo by varying the frequency of the AC. This is different from the SP10, but I had not thought about whether the DP80 motor had an iron core or not. Indeed, I did not appreciate the significance of that fact until Hiho and you had the exchange above. I ask because the DP80 gives me the very same "smooth" feeling that Hiho experiences with his Pioneer. In a heavy slate plinth, the Denon is rather addictive.
Raul and Ralph, I hope some time it will be possible for you to reveal the nature of these especially good tt mats. It would be fascinating to find out whether both mats were made of similar materials. |
Dear Hiho: It is obvious that a TT build material ( any ) can't fix a mediocre motor that ca run on " speed ", but I think that is not the subject on what Ralph want to share with all of you.
I can tell you that through my TT experiences through the years ( dozens of TTs ) almost all main factors on TT performance are already addresses but the TT right build materials.
You can find several threads like this one speaking one and again the same TT topics with no single real advance out there.
I know that everyone has a lot of fun reading and making some TT changes on its systems but that main factor ( TT build material ) remain almost untouchable: I wonder why?. The " sad " issue is that almost all analog people does not care about just like you.
It is obvious that maybe does not care about because don't understand the critical importance on the TT build materials that like I posted the differences in quality performance is: night and day !!
I understand too that because almost no one already experienced what Ralph and I " live " there is not to much of what to talk/share from almost all of you.
IMHO and like Fm_loging posted: we have to evolution if we want to grow up and if we want to improve what we have.
I'm on evolution and that's why I share with all of you my findings. Stay steady where you are is up to you and fine with me.
Regards and enjoy the music,
Raul. |
HiHo
Here are a few things which I can prove to be true:
1. Newton's Third Law of motion holds for turntable motors so the reaction torque reflected into the chassis will be the mirror of the forward torque applied to the platter.
2. The variation in reluctance of a "coreless" motor is much smaller than that in a motor using an iron cored stator.
3. As an iron cored DD motor rotates, the servo loop compensates for the variation in reluctance by decreasing torque as the rotor pulls towards the lowest reluctance position and increaes torque as the rotor pulls away from that position. This happens many times per revolution, depending on the slot and pole numbers of the stator and rotor respectively. The exact quantum is the least common multiple of the slot and pole numbers.
4. It follows from 1 that the torque variation reflected into and propagated through the chassis is much smaller with an ironless stator than with an iron cored.
It is my conjecture that this phenomenon explains what you are hearing. Naturally I cannot prove this so I won't say that it is *definitely* the case.
Some support for this idea comes from some engineering work done at Sansui towards the end of the analogue era where they designed a DD with two counter-rotating platters to obviate the problem (called X-99 I believe).
Mark Kelly
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Can we get back on track talking about the genres of turntable drive system?
It's not that I don't believe the improvement of a turntable mat - of course they do - but we were talking about the TYPE of improvement, in what area the mat will improve the most and some of us simply question it will improve the "slam", "drive", or rhythmic quality, not tonal quality, that, we believe, has more to do with the drive system and, in my experience, particularly, the motor. I will be happy to be proven wrong that a turntable mat will improve across the board in every sonic area to the point where it even matches or surfaces replacing a mediocre motor with a better one. If there's cogging or speed irregularities or speed drift, wouldn't it make sense to address the motor, which is the singular active component in the entire system? For some reason, the thread ended up talking about turntable mats. Many stock Empire 208 turntables are a little fast, please illuminate me on how a turntable mat can make the speed spot on.
Back to motors or drive systems, shall we?
Question for Mr. Kelly. Is there a technical explanation on why, at least to me, most coreless motors in a direct-drive system sounds smoother to my ears? I know they've been advertised as having less cogging or coggin free and I have to admit they do sound silky smooth. They tend to have less torque and, again to my ears, less dynamic but I am willing to trade for smoother sound than just dynamics. Even on a cheap Pioneer DD table with coreless motor that I acquired recently I heard the purest smoothest violin sound from a turntable. Sonically, I am sold on this type of motor. Typically I choose a high torque core motor DD table to tape-drive my passive platter to equal the smooth sound of a DD table with coreless motore.
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Wow, what a great discussion. As a Galibier owner, I can't wait for RMAF to audition the new motor/controller.
I tend to agree with the opinion that while each design has its particular set of strengths and weakness (resulting in a signature sound), excellence in implementation is critical. The Saskia is a very different from my Galibier and each have their own sonic signature, however, I would be happy with either. With a well-designed system, it's not 'better or worse', it's a matter of taste.
One additional variable that hasn't been addressed is production variability. Since many of the high end tables have limited production runs, I would guess that there is variability between each table produced by a given manufacturer.
My wife and I experienced a similar phenomenon when we purchased our piano. After months of auditioning, we decided we perferred the Steinway sound. We spent many hours over two counsecutive days, auditioning 18 Steinway L models. Each piano had the Steinway sound, but every one sounded and played a little differently. On the 2nd day of our auditions, Van Cliburn was visiting the dealer's showroom and he played each of our finalists. That really brought out the individual personality of each piano. (Analogous to the difference between having your analog system set up well versus set up perfectly). |
Dear friends: Atmasphere is spot-on in the subject. The fact that almost no one of you already have that kind of experience does not means he is wrong and you are right, please let me explain on it:
in the deep research that we make ( and still doing. ) in our self tonearm design one of the main factors for achieve our main tonearm target ( a Universal tonearm where any cartridge shows its best like in no any other tonearm. ) is the build tonearm materials especially at the headshell/arm wand.
Testing different available build materials we can't find the one that help totally to achieve our main target so we have to start a whole build material research that bring us to " build " by ourself the main tonearm build material: this is a propietary blend.
Well this propietary blend material help us to achive our tonearm main target.
Through all that research that take us several months we learn the critical importance that have the build material where the cartridge is attached ( tonearm ).
The cartridge is like a very sensitive micro that detect tiny very tiny ( microscopic ) resonances/vibrations/distortions that you and me are not aware even exist and that affect the quality cartridge performance in almost the same way between the TT plater and the cartridge.
Today I can say that that tonearm build material makes a paramount difference in the cartridge performance.
Well, I ask my fellow Guillermo why not try that same tonearm build material in a TT mat/pad and VOILA!! the differences ( in six different TT's. ) in dynamic, tonal balance, transparency, soundstage, focus, top to bottom coherence, in any single performance parameter improve ( not only different but better. ) like night and day!! lowering ( almost disappearing. ) distortions/colorations level to almost CERO!!!!
I can say that this is a unique experience and that's why I understand in a precise way what Ralph posted about that almost no one of you can't understand till you have/hear that experience.
For months and in different threads ( mostly on tonearm/TT's related subjects. ) I posted ( anyone can read it. ) the critical/crucial importance of the tonearm/TT build materials that makes a difference for the better, till today no one ( but Ralph ) gives the right importance to this main factor and you can see in this thread: everyone speaking ( one way or the other ) about motors, belts, bearing, drive system, etc, etc. I'm not saying that all those factors are not important certainly are but till today no one ( tonearm/TT designer/manufacturer address seriously ( I mean in the right way. ) the item build materials.
I know ( Lewm. ) that exist several commercial mat/pad options but no one is near of what Ralph or I already experienced and know about.
I know too that is a little frustrating for almost all of you don't have an opportunity to hear that unique " audio experience " but if in anyway serve for anyone of you my audio system is OPEN for you anytime you want it.
In the midtime we are almost finishing our tonearm design and starting our TT design ( with that propietary blend material. ) along a cartridge.
Regards and enjoy the music,
Raul. |
Lew, I myself think that is a good idea. I agree there are a lot of platter pads out there, as Axel says, its just that most of them are a joke. If you are going to make a decent pad, it should use materials science and physics- like understanding how vibration travels through materials.
Keep in mind that the stylus exerts tons of pressure on the LP. Yeah, its only a 1 1/2 -2 grams but the stylus is tiny. The result is that the LP depresses, just like ice on a frozen lake does when a car drives over it (of course, we probably see more of that up here in the frozen wastelands).
So the mat cannot allow the LP to sag- it has to stand up to it. And it has to do that while controlling resonance. That is why this is such a tricky issue- and why so many platter pads are really not even close.
I'm sorry that this pad that I and a few others have is not in production (IMO/IME it was the biggest advance in LP reproduction when it appeared). That it contains lead dust likely has a lot to do with it :)
Warren says he can't get some of the materials anymore. He also said it was very labor intensive- the materials had to be combined in the right order and with correct timing. He used a special oven to cure it. I have seen a few examples come up for sale- the last one I saw went for $1200.00. Based on that I would guess that there is a budget for someone who wanted to get serious about this.
Obviously not every table could manage this thing- it weighs about 5 pounds.
Since there are only a very small number of these made before SOTA got the rights to it, there are only a few people who have heard what it does and how profoundly it affects things. However my point here is not that I have this thing, but what it taught me: that **only** when the platter pad and platter issues are reduced to a common denominator can you have an intelligent conversation about drives. This assumes that the 'table is otherwise on speed and working right, with no 'measurable' speed issues. IOW I suspect that many here are describing other differences and ascribing them to the drive when there are more fundamental issues involved.
I cannot tell you how many times I have seen people come into a room and upon hearing something they like, immediately ascribe it to the speakers, taking nothing else into account. I believe this to be the same phenomena, since I don't know of a decent production platter pad. If someone can point me to a pad that has the exact same hardness as vinyl but it otherwise completely dead, I'll immediately make an exception. Any takers? |
If the speed of a turntable is off by 1%, which can happen to some Rega tables, you think a fancy platter mat(I am sticking to the term "mat" instead of pad just for conventionality, why change now.) can improve that? Enough said. |
Dear Ralph, I would have to agree with Axel. Platter mats (pads) have received LOTS of attention during the vinyl renaissance, both in the aftermarket and from turntable manufacturers. Just do a search of any website that features products for vinyl reproduction, and you will find dozens of candidates. In fact, there are too many different choices for any one person to evaluate. Materials include felt, rubber (or some variant thereof), sorbothane, carbon fiber, graphite, copper, other metal types, dots (made of cork, felt, what have you), and combinations of any of the foregoing, plus no mat at all. I guess what you are saying is that only the one mat made in small numbers and sold only in Minneapolis area and on early SOTA tables is really proper. Can you reveal what it is made of? By the way, many would agree with you that the mat should take energy away from the LP and therefore should be made from a material that is similar to vinyl. So why not vinyl? |
Atmasphere,
hope I don't sound boring by now?
Ever bothered to look at that funny platter-pad material of the SMEs at all?
Re: >> I find it astonishing that platter pads have received little or no attention in the last 2 decades <<
Not so, I'd say.
Bonded copper-pad of TW, bonded vinyl-pad of TransRotor, bonded cork-pad by Acutus, bonded glass by Brinkmann, non-bonded felt by Linn :-), etc. those are all pads on the platter, even though they are bonded except Linn.
Does that make the difference with your definition?
Axel |
If a turntable company has succeeded in making several versions of a turntable, essentially with different drives, while at the same time keeping the platter pad and platter signatures exactly the same, I would agree that the differences one heard in them could be ascribed to the drive.
However- the drives themselves require that the platter design be different! Thus I severely doubt that *any* company has demonstrated this successfully.
In working with the Empire into its evolution into our model 208, we found that the platter pad affected the sound, but if you did nothing to control the resonance of the platter itself, you were missing a bet. IOW, although the pad I've been working with is head and shoulders better than anything else I have seen, it still did not control the platter; damping the platter was still a major improvement.
BTW, the platter pad in question was designed and built by Warren Gehl (currently at ARC) about 20 years ago. It was used by SOTA on the first 50 to 75 Cosmos tables, at which time the formula got modified. So an early Cosmos would have some of the same advantages, if you could fix the drive. I use this pad on my personal table only.
I find it astonishing that platter pads have received little or no attention in the last 2 decades, despite the extreme importance they play in controlling vinyl resonance caused by the needle tracking the groove. Resonance control otherwise has been one of the biggest strides in turntable technology over the years- but almost no work on the place where it counts the most.
And for the record, if the mat is too soft, like a rubber mat, dynamics will be suppressed. The interface has to be exact- the pad has to be the same hardness as the vinyl, so that no energy is reflected back to the LP, yet the mat has to immediately absorb the energy. Acrylic mats are too hard, rubber and felt way too soft. Honestly if these things are not sorted out first its almost impossible to tell anything else about the table! My advice is to try it first before you knock it. The only problem is- where do you get a proper mat and for that I have no answer- there isn't one anymore as far as I can tell. That is how bad this situation is- the platter pad is one of the most audible artifacts of a turntable excluding the arm and cartridge, and there are no definitive pads even available.
Warren saw to it that a good number of serious audiophiles in the Twin Cities area had his pad (FWIW he spent about 5 years perfecting it- I personally had about 5 or 6 earlier versions before he got it right). So we have had ample opportunity to compare it on the SP-10, SL1100, Conneseur, Rekokut (idler drive), Empire, SOTA, and the like. FWIW, a salesman at one of the local shops figured out how to install the pad on a vacuum SOTA, which resulted in his getting a job with SOTA. That person was Allen Perkins, and is why the early Cosmos tables featured that pad. |
Hiho,
you reflect my own listening experience and thank you for sharing your own findings on that.
Even with quite, or REALLY powerful motors like I've heard on an Transrotor Z3 or on a Thorens 2010 (motors where modified, with beefed-up controller power-supplies), due to the long thin belts they remained still more laid-back then e.g. my SME, even though one could notice some improvement in the dynamics department. Two motor yet did a little more but still just don't seem to get there.
Problem with a lot (more affordable?) DD's is the 'affordable' motor/controller as I understand it. It seems VERY difficult to get this completely right, because of the DD's 'unforgiving' 1:1 coupling.
Despite some of the ~ strange Linn 'behaviours' (some love it some don't), I think they got the motor to platter coupling just right I.E. sub-platter, short belt, powerful enough motor.
SME I think went a step further, smallish as the Papast-motor is, it pulls like a train, has a lot of torque --- BUT they had to spend some time and money on a very good motor-controller without it, it would NOT work.
The spec.: Reference oscillator is a 10Mhz quartz crystal, multiplied by 4 to obtain 40Mhz microprocessor clock speed. Driver stage has CMOS buffers/MosFet drivers with 1.2 Amp peak drive capability.
Power output stage is six high power complimentary MosFets in a 3 Phase Bridge Driver configuration.
Close loop speed control is implemented using pseudo sine wave commutation sequence and a proportional-plus-integral (PI) algorithm.
So, there you go. This is not some wall-wart using the power-line cycle for speed control. With a long 'forgiving' belt it will work fine, but the closer you get to 1:1 drive-line coupling the more need to have a close to cog-free drive with torque to boot.
Greetings, |
One other thing I wanted to add was with respect to what can perceived as a cartridge alignment issue, which in reality is actually a micro-dynamic speed issue. I don't know what other term to use to refer to this, hopefully you guys can get a hint of what I'm on about. I would guess this is probably more prevalent with belt drives. |
While it has been several years I do remember hearing a demo of the prototype Teres Certus. I recall that there was/is a difference between the Certus platter and that used on the non-DD Teres tables. One of the differences was the use of a significant amount of brass. This was on my mind during that demo. How much of the presentation was due to the drive and how much was due to the difference in platter material? I suspect a bit of both, and I do believe that there were differences in arm/carts. To Ralph's point, the surfaces were the same as far as I know.
I don't know if the present Certus controller offers the torque adjust feature that was on the proto. That adjustment did make for an effective demonstration of the effect of torque on the sound. At one point the torque was turned up such that the sound changed immediately from analog to digital.
Since that time I've never stopped wondering if the transient sounds I'm hearing are real or not when I am experimenting with speed. I posted earlier about my experiments with really taught mylar and a more robust controller. At present I am drawn to the sound, but my mind still asks if it sounds real.
As interesting as this all is, I feel the need to remind myself that not everyone agrees with what I think LP playback should sound like. There are many people in this hobby that prefer what I would call sluggish and syrupy presentation. |
"But lack of 'slam' and 'drive' is more related to the drive then a platter-mat, in my current experience."
Totally agree.
I can't seem to understand how a platter mat can improve dynamics, slam, and "drive". No matter what mat I put on my Empire or other belt-drive systems, it aint sounding like my Technics SP10. I have smoother sounding DD tables than the Technics but none can surpass the bass dynamic and slam of the SP10 due its powerful motor. I also played with an idler table with an Ashland motor and it has huge dynamic. Again, the motor. From my experience is that small motor small dynamic and if it's a belt-drive even worse, the Nottingham is one example. I do believe changing mats can change the sound and the extra mass sometimes helps smoother rotation but the sonic benefit, if any, is more of a tonal one and signal to noise issue. Again, that's just my current experience. I would love to try some TTWeight mats.
I am, I guess, a "Technics guy" for 20 years. Briefly, I circumstantially became an Empire guy. I missed direct-drive so now I am back to be a Technics guy again, with a vengeance and end up with dozen other direct-drive tables. It's been fun.
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Albertporter
thanks for at least questioning, that dynamics are not quite the same a colouration.
I yet have to hear a system sounding more on-the-point/dynamic as is with a 'harder' connected drive, by simply using a different platter or platter-mat.
That's wishful thinking to me.
It can sound 'cleaner' and may leave this impression? But lack of 'slam' and 'drive' is more related to the drive then a platter-mat, in my current experience. |
Maybe some Teres or VPI guys who participated in this will chime in. I'm not a "Teres or VPI guy" but I play one on TV, and I already chimed in above on that very topic. Peter used to be a Teres guy and he heard that demo too. As you know, he's been replaced his Teres and has become one of those Technics Guys. Or is it, once a Teres guy, always a Teres guy? Or maybe once you've had Technics you can't ever go back? |
Ralphmasphere 08-03-09: Atmasphere
Axel, I regard differences in dynamics as a coloration, just like tonality and soundstage. All are **definitely** aspects of platter pad vinyl resonance control (or lack thereof). Do you not separate the drive system of a table from the damping or lack of damping of the platter? I definitely hear differences in drive systems. Several reputable companies have done experiments where identical systems and platters (a VPI) were driven with belt drive and then rim drive. I also read about auditions with a direct drive Teres versus belt drive Teres. Both have been discussed here at Audiogon. I remember the designers as well as listeners saying there were repeatable and conclusive results based only on drive system, even though table, platter and mat remained the same. Maybe some Teres or VPI guys who participated in this will chime in. |
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Jb0194, The fact that your turntable still runs at the correct average speed after you added all that mass, especially a heavy periphery ring, is not proof that there is no deleterious effect. But I don't think the Dual has a servo mechanism at all to worry about, and I believe it's an idler type in the first place, not a DD. You would of course know better than I about that. My remark was strictly with regard to servo-controlled DD tables. Moreover, if it sounds better to you with the added gadgets, that's the bottom line. |
Dan
It would be giving something away, but you are on the right track. It's the design of the filter that takes all the time and effort in the Spice model.
Matt:
Q 1 Asked and answered.
Q 2 No.
Q 3 No.
Mark Kelly
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Jb0194, I think they have advantages if your system will allow them, in controlling warp. Since the platter pad controls the LP's resonance signature, the ring won't do much to help- it will merely insure that the coloration is consistent across the entire surface. |
Axel, I regard differences in dynamics as a coloration, just like tonality and soundstage. All are **definitely** aspects of platter pad vinyl resonance control (or lack thereof). |
Ralph,
Have you tried "record periphery rings"? It would appear to benefit warped lps, of which I have a number.
Your feedback would help me in considering same. I've already tweaked the mat and use a spindle weight. My table is a Dual 721 with robust DD motor. FWIW, speed has been rock steady (by strobe) with the 4 or so extra pounds added by "steel/polymer/steel sandwich + carbon fiber donut" platter mat and TTweights heavyweight brass spindle weight. |
Hi,
all said sound fine, -- BUT there is clearly a difference between colouration and dynamics!
The platter material / mats / pads / and other damping are ALL colouration items (excluding some really heavy lead-loaded mats adding more mass)
The drive-line performance is an issue with dynamics / timing / rhythm etc. I don't think both should be just dumped into on pot so to speak.
Axel |
Good point, Ralph. Also, if you use this un-named but "very heavy" pad (I assume you mean "mat") on an SP10 or the like, it may have a negative effect on the performance of the drive system, since the servo mechanism was designed specifically for the mass of the stock SP10 platter + mat. Whereas the same mat might have a less deleterious effect on the performance of your Empire. |
I've been working with a modified form of the old Empire table for some years now. It has a very powerful motor that has a lot of torque, runs at high speed and has a lot of flywheel action. Years ago I ran an electronics service center- while there I service all sorts of tables including the Technics Sl-1100, the SL1200 and the SP-10.
It is my opinion that the drive does not matter as long as it is robust and executed well. Weak drives just don't seem to do it and I have seen very little in the way of servo-controlled belt drives with weak motors that work right.
However, to my ear the platter pad has a far more profound artifact than the drive! Years ago I was lucky enough to obtain a platter pad that was truly neutral- and use it on a variety of 'tables. With it, the SP-10 sounds identical to a stock Empire and any number of older Pioneer belt drives (the platter pad is heavy so 'table needs a robust bearing to support it).
Without maintaining the platter pad's contribution in audition of all these drive systems, a huge variable is introduced that IMO/IME makes it impossible to ascribe a difference properly. The platter pad should reduce resonance in the platter; IOW the resonant signature of the resultant platter cannot be ignored!
Now it might be that someone here has been this careful- has anyone in auditioning all these different tables (Lenco, Technics, Garrard, Micro Seki for example) been able to keep the resonant signature of the various platters constant, as well as the durometer of the platter pad surfaces? If yes- differences might be ascribed to drive. If no- differences are probably not the drive at all, but the platter's resonant signature as the vibrations in the groove are decoded.
What I am saying here is that the needle playing the LP makes a physical sound and vibration that the LP itself reacts to. If the platter does not control that, you have a coloration. IMO/IME, 95% of table differences are this effect. |
"Similarly if a manufacturer sends me several samples of a high cost three phase motor and says "do your best then bill me" the results can be pretty good."
I resemble that remark. Yuk. Yuk. ;)
I do have a habit of sending motors to Mark, and leaving the task open-ended. It can result in sticker shock, but the result can be stellar.
An external rotor three-phase eddy current motor that has has a 90W draw can be very inefficient, but the payback is in extreme smoothness, and also wonderful dynamics. So, I agree with others that a decent motor is key to high performance. In the case of Saskia, my turntable, the platter gains equivalent mass from this approach, too. The external rotor provides this to a point that when used with an idler it is the equal of a belt drive that has a platter that weighs several hundred pounds. The motor counts for a lot, but the platter can be further tuned to enhance inertia even more. Then, there is the spindle, bearing well and associated parts which also play important roles when it comes to ruble control, dynamic braking, evenness of play, etc. Again, if any aspect is neglected, performance suffers in one way or another.
Win |
Mark, I think you'll be surprised at what can be achieved with standard AC motors and belts even less compliant than your Mylar when the drive mechanics are understood. If it isn't giving anything away, how is the filtering by the belt done differently with less compliance in the AC approach? Or am I confused by my own assumptions? |
HI Matt,
I can't help with the technical questions. I will offer this. My wife and I decided to stop "working" on our relationship after the first three years. That's when my first son came along. After that we just "worked" on making it through the day. It will be 34 years this winter. :-) |
I have to jump in here, perhaps a little late, but I have definitely enjoyed the banter. Especially the literary references; and I thought I was the only one who kept an unabridged Websters first edition at my reach. And what does my wife mean when she walks in the room and says "if you spent a third of the time you spend on this stereo stuff on our rlationship things would be better". This reminds me of a line from a poem I like "If you can keep your head when all about you are losing thiers and blaming it on you"
Back to the topic:
Question #1- Is the torque(twisting force)acheived by the platter dependent solely(sp) on it's driving force, or does it at some point become a product of it's rotating mass?
#2 If the bearing matches the mass of the platter, no matter how great (e.g. the fan blade on a jet engine), are the problems brought up about bearings solved?
#3 I believe the Feikert Twin TT uses a kevlar belt. Not much stretch there. If the belt is for all practical puposes stretchless, does it become a direct drive?
Thank you all for your responses, I appreciate the time you put in this, even if my wife doesn't.
Matt |
Axelwahl says, "One expert put two Micro-Seiki on top of each other --- and then waits 5 minutes for the darn thing to stabilize the speed."
I think the flagship Nottingham Deco took such approach, with a massive 64 pound that is as thick as a microwave and driven by an extremely low torque motor that you have to finger spin it to start. Definitely doesn't seem very user friendly to me. I had a Spacedeck in the house at one point, very quiet table but the sonic was so mellow that it put me to sleep.
I use direct-drive turntables. Sometimes I use them to (VHS)tape-drive a "passive platter". So the motor is any one of my dozen direct-drive turntables. I no longer see these DD tables as record players, they are motors with a 12" pulley, "active platter", along with a controller. The combination of two platters takes up a lot of table space for sure. But they sound good. The only time when I can't hear any improvement from this tape-drive approach is when I use a dd table with a coreless motor. The coreless motor DD table sound just as smooth as the tape-drive set up. I have yet to try it with my Technics SP10mk2 table. It will be fun. I don't have any Denon turntables right now but I would like to try them as they are the only company I know who use an AC motor for their DD turntables. |
Dan
For the kit designs I had two overriding criteria: they had to be as cheap as possible whilst still providing acceptable performance and they had to be almost universally applicable (hence your comment about platters / bearings). Unfortunately this means that they are a long way from optimised for any specific application.
For the bespoke designs I gather as much information as possible, to the extent of getting specific numbers for the rotational moments of inertia of the motors used from the motor manufacturers or in the case of one drive having to measure the numbers myself. I then build a model in a Spice program using some translational analogies and spend a lot of hours doing dynamic modelling.
Depending on the sophistication of the drive, the specific platter and bearing numbers can have some influence on dynamic performance but the most important parameters are the motor and its electrical control. When I am happy that I understand what's going on, we go to prototype.
The results? Well, I think you'll be surprised at what can be achieved with standard AC motors and belts even less compliant than your Mylar when the drive mechanics are understood. Similarly if a manufacturer sends me several samples of a high cost three phase motor and says "do your best then bill me" the results can be pretty good.
The downside is that the controllers end up being quite expensive. I don't know if there's a viable model for producing an aftermarket controller using any of these techniques.
Mark Kelly
|
I want to ask opinions on belt approach that Hiho has mentioned a few times. I was also of the opinion that any kind of compliant belt was not going to be the best solution. It seems in my brief experiences with speed controllers of late that with a DC approach the system does benefit from tight coupling, hence mylar can work very well.
The difference in DC controller operation can make or break this theory of mine. I would characterize one controller/drive system as being similar to the approach Dertonarm mentioned, that of counting on a certain amount of slippage. Another controller, (same motor, different controller) just happens to be one of Mark's old DC controllers, seems to improve with increased tension => no, or almost no, belt slippage. This does require a pretty hefty motor pod to help keep things taught. The presentation of this second DC approach is very much like what I hear with rim drives and maybe some lower end DDs. How much like rim drive I can't say as I don't have a good candidate for A/B.
So I thought I was all set with my drive choice. And then a friend brought over an AC motor and a Kelly AC controller. As you might expect, the cogging of the motor is very apparent with the mylar belt, even with less tension. The best setup was achieved with very little tension and a fair amount of slippage. Even more than what was used with the first DC controller. So it would seem that a more compliant belt would be called for with the AC approach. The amazing thing to me was that even with the huge amount of slippage the AC motor/controller was really kicking the DC arse in many ways.
After learning some these new things for myself I am no longer so convinced of what I thought before about belt compliance. Surely we would all love to have the perfect motor. But since that probably isn't going to happen, it seems to me that the controller becomes more important. At the same time, the selection of the motor and controller would seem to dictate what belt candidates should be considered.
Mark, I am still somewhat surprised that the particular platter/bearing does not seem to influence your designs. Or do you just make it look too damn easy? :-) |
Axelwahl,
On your first point: That one's easy. I take it as a truth universally acknowledged that if the motor were not running, frictional forces (of whatever source) would cause the system to slow down and in doing so it would lose kinetic energy.
It therefore must be the case that energy is being put into the system for it to remain at constant speed. The only possible source of such energy is the motor, therefore the motor must have the primary role in maintaining constant speed. All that platter inertia does is to reduce the slope of the decelerations (and equally the accelerations).
Your second point falls foul of a fundamental property of feedback loops, that the speed of the feedback loop must take account of the speed of the "forward" portion of the loop. If you interpose a low pass filter such as the belt and platter in the loop then you must slow the loop down to prevent oscillation. If you leave the belt and platter outside the loop then the loop cannot possibly compensate for losses in the belt / platter system such as torque dependent belt creep.
No free lunch.
Mark Kelly
|
Interesting this inertia talk.
That raises the (old?) question who should control the STEADYNESS of speed - inertia of the platter, or the motor AND IT'S CONTROLLER.
If the motor sux, or the controller sux, you have to look back to the platter's inertia. If you manage to make it THAT heavy (never mind the resulting bearing problems) there must come a point where any conceivable variation in friction-changes of the needle to vinyl interface become SO SMALL as to approach zero.
I have a notion we have to look for some mighty heavy platter to get there. One expert put two Micro-Seiki on top of each other --- and then waits 5 minutes for the darn thing to stabilize the speed.
You see, we are now starting to move big-time out of the practical useful user-application --- which in turn also sux.
So it's back to the more practical idea as was mentioned above platter-weight not much more then ~ 4.5kg, still using a belt for a tiny bit more forgivingness, than a DD which translates its little faults too immediate into the speed stability.
Lastly a motor / controller package with the best available feedback speed / loop to mankind :-)
A thing to note: that bearing friction has to be present at a controlled level to "damp" the controller feed-back loop, preventing feed-back resonance, so to speak.
Now have a look who is doing something like this, and I guess you'd have a 'best of breed' and still user friendly tt.
Greetings, |
Platter is important but in my experience the motor is the most important and then combination of platter and bearing. After all the motor is the active component here, hence it's called TURN-table for a reason. It has the most demanding job and requires the most sophisticated engineering that involves electrical and mechanical skills. If you get a good motor, you are more than half way there. Of course, if you use a soft rubber belt to conceal the flaws of the motor then the platter is more important. I do agree that a record player should be seen as a whole system not just a collection of parts. |
And to take that theme and refer back to the OPs question, I might ask: how much of the total inertia of the system should the platter represent? What influence does splitting some or most of the inertia away from the platter have on the perceived "drive" of the system?
It seems to me that many of the designs which are known for having lots of what Albert calls "drive" have moderate mass / moderate inertia platters tightly coupled to a high inertia drive system. If I'm not mistaken Win had a similar concept in mind when he desgned his TT.
Mark Kelly
|
Back on track...
The discussion so far has been about torque, but in my opinion the most critical component of a turntable may be the platter. With all three types, belt driven, idler driven and direct drive, the platter can be the make-or-break piece because it is the final interface to the record, it is key to how inertia works and it is the interface to the rest of the mechanism. That said, I really believe that a turntable should be seen as an entity because, like the audio chain in your system, it is only as good as its weakest link. There is no single part, no matter how seemingly insignificant, that should be overlooked. Designing a decent one is easier said than done for certain.
Win |
While we are getting offtrack...
Mine comes in memory of Colonel Sergei Ivanovich Mosin. He had a fascination of mechanical things enough that the rifle bearing his name has survived from 1891 til this day in one form or another. I respect him because he fully appreciated and practiced the principle "form follows function" even before Louis Sullivan wrote about it.
Win |
Excellent story, mine is much simpler.
My Mother and Father picked out Albert Porter for me when I was born and it seemed like a good name for Audiogon as well :^). |
From the Websters dictionary 1905 edition: "A barbarous term used in school philosopy for essence" - gotta love a dictionary with that degree of vitriol.
My intended career was as an academic in philosophy. My chosen field was logic and the structure of consciousness, especially with reference to linguistics and mathematics.
One of my heroes is Willard van Orman Quine, who was a logician at Harvard.
http://en.wikipedia.org/wiki/Willard_Van_Orman_Quine
One of Quine's books is titled "Quiddities". I rather liked the term so when I established my consulting company I called it Quiddity Technical Services.
I don't like monikers but Audiogon insisted that I register as a business and that I take a moniker which referred to my business name, so there you have it.
Mark Kelly
|
Mark Kelly (Quiddity).
How did you come to choose your moniker? I looked it up:
1. The essence, nature, or distinctive peculiarity, of a
thing; that which answers the question, Quid est? or, What
is it? " The degree of nullity and quiddity." --Bacon.
[1913 Webster]
Anything to do with that? |
Johnny B
You don't seem to understand the function of a low pass filter. It is not possible for the belt drive flex per se to affect anything by more than a few parts per million for the reasons given.
A change in belt tension will however create belt creep and this effect will be around 1000 times larger. That was my point.
Mark Kelly
|
08-01-09: Quiddity
Johnny
... The maximal velocity variation for a given length change is the product of the radial displacement produced by the length change and the corner frequency of the filter system expressed in radians per second. The numbers come out in the parts per million range.
How long is the initial transient of a piano note, a string pluck, a drum or cymbal hit? I suspect the initial dynamic jump is well under 1 ms. How large, physically on average, is such a transient "bump" in a record groove that is 1400' long for a 20-minute side? If belt drive flex lengthened that transient by 10-20%, it seems to me we would be talking about parts per million from one standpoint, but possibly a quite audible 15% variation from another. |
