Belt drive is much better. When you connect the motor directly to the platter it introduces vibration. There are other things that effect sound quality, as well, but don't think too may people would disagree on the advantages of belt drive.
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Ahhh, three posts and three opinions. Let me be the fourth post and fourth opinion. All systems at their ultimate execution, direct drive is best. Between idler and belt they are almost perfectly split with dynamics and punch in favor of the idler and signal to noise and simplicity in favor of the belt drive. Yes, I've owned all three, and multiple versions of each design type. |
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I agree with Viridian and (mostly) w/ Albert - execution is everything. I own (and have owned) all three types of decks, and I have had enjoyed some and others less so regardless of their drive type. I would not necessarily agree with Albert that DD is the best, although I have had some DD decks that I think stack up well with the best BD and ID decks I have heard. I will say that, IMO, the biggest downside to Idler Drive is that you will spend a lot of money and time (or more money for someone else'e time) to get a deck to sound as good as a top notch DD or BD deck. They are just more complicated machines. |
Zd542, You are of course entitled to your opinion, as is anyone else, but it would be well to keep your facts straight. Like it or not, in a DD turntable, the motor is not "attached" to the platter in the way you seem to think. Rather, the platter is part of the motor. Typically, the platter is attached to a permanent magnet that revolves around, but makes no contact with, the motor's coils. Thus, nothing at all is in contact with the platter except the bearing, not even a belt. Any well designed DD turntable can compare equally or favorably to any BD turntable, in terms of noise. (In a BD turntable, there really IS an external motor connected to the platter by its noisiest part, its drive shaft, via the belt.) You may still not like DD turntables, but find another reason. Perhaps it sounds better if you use the term "magnetic drive", which seems to be all the rage among hi-end BD turntable makers these days. They are one and the same thing. |
Just my 2 cents, but I have to agree with Albert, that all three are capable of excellent sound but when executed correctly i'd have to vote for DD. My current setup is a Technics SP 10 in a slate plinth and what you hear is a substantial increase in pace and drive probably secondary to the DD's ability to transfer the motor's torque to the platter and maintain it without issues of stylus drag etc. My prior turntable was a VPI TNT. The BD manufacture's have, in their way, acknowledged the issue by their efforts to upgrade the BD systems all of which are designed to increase torque transfer and decrease belt compliance. The VPI platform is an interesting microcosm of the issue. Prior to the introduction of the rim drive option they upgraded the belt material making it stiffer and less compliant which improved pace and drive. A few hearty souls even took it a step further modifying the table to allow for the use of Mylar tape in place of the belt, which improved things even further. The rim drive, when properly executed, takes it further still. Their rim drive though is kind of a hybrid DD, as the motor is connected to the rim drive via a belt. Happy listening |
Of all the DD turntables I have owned, I would say that three stand out as "best" in my mind: The Luxman PD-441, PD-444 and the Teac TN-400. The two Luxman decks share the same drive system, but the latter with a larger plinth to accommodate two tonearms. The TN-400 is probably the most quiet drive system I have ever seen (heard?), but they didn't make many and so are fairly rare. |
Rugyboogie, Thank you. You actually read my post and answered my question. When you list the big, well known names, (Sony, Denon, Pioneer etc) are you talking about vintage gear or current production? Also, would you say that a Technics 1200 would be in the same league as the ones you mention? The reason I mention the 1200 is that I can try one. My family has 2 nightclubs and that's what they use. There's 2, brand new, unopened ones in a storage room they keep for emergencies. Honestly, its not the kind of TT that I would have considered for myself, but since so many people seem to like them, I have nothing to lose from trying one. |
I think of "rim drive" as a variation on the idler-drive theme, nothing to do with DD. Only, unlike the classic idlers, there is no discrete idler wheel in the energy pathway, which in my view makes rim drive more likely to transmit noise into the platter. Zd542, IMO, the SL1200 is a "nice" turntable, for the money. And by all means, give one a try. But I think you need to go farther up the ladder (or farther back in time; either one) to get a good idea of what the best of DD turntables can do. |
As stated by various posters above, implementation and execution is key. Idler drives, in my experience, unquestionably require the most work to get right, but if properly rendered are simply brilliant. Rim drives, unfortunately, face certain unavoidable hindrances and I have yet to listen to one which compels me to believe otherwise. After having the pleasure of owning several SP10Mk3's, Mk2's, Garrard 301, Lenco and Micro Seiki, and spending extensive time evaluating each, it becomes rather obvious to conclude all respective drive types have their own merits and strengths. Subjectivity, rather, individual preference comes down to the listener. |
Whatever the table, it should have a robust drive. If you look at the vintage machines that have really garnered a following, you will see that they all have that in common: the SP-10, the Garrard 301, the Empire 208, the Lenco... Wimpy drives seem to lack soundstage focus. My theory is that they are constantly off-speed, always correcting. This causes the arm to sway back and forth slightly due to skating forces. This is one of the reasons analog tape has such a following. But 'tables can have the consistency needed; you just have to have that robust drive. If the ones mentioned so far the Technics SP-10 is by far the best in the drive department, but it also has one of the worst plinths. That is why you will see anyone serious about the table using some sort of hopped up custom plinth for it. |
Oxford University entrance exam question: 1. If this is the question, then what is the answer? 2. How many angels can dance on the head of a pin? Or if you are torturing poor Dustin Hoffman: 'Is it safe?' The Rockport Sirius 3 was direct drive, and is often considered the 'final destination' of turntables - I have heard one and that was all too brief. Against this is the belt drive Continuum. I have said, in recent posts, that as my hearing changes, it has shifted from being obsessed with imaging and soundstage, towards timing to which I am more sensitive at the moment. I am convinced that each drive has a 'sound'. Direct Drive may be the most neutral - or what we think is neutral. Belt Drive the quietest and best imagers,idlers (from what I have heard so far' really do time brilliantly and have superb bass). I personally think that neutrality is quite possibly audiophiles most ludicrous and intangible concept. Most musicians I have spoken to say that all they want is for listeners to feel connected to and to enjoy the music, and if the medium of delivery achieves that, then that medium has done its' task. To that end we ultimately want a system that keeps us in our seat listening to music until far too late in the evening. |
Dear Rockyboy: +++++ " Is one TT type inherently better than another? " +++++ my experiences on all TT drive systems but the rim one tell me that no one is better than the other. Syntax posted: ++++ " The worst - by far - is idler drive, followed from DD and best is Thread Drive (when done right). " +++++ but he did not say why?????. He said: " best is thread drive ( when done right ) ". What about a DD " when done right "? Albertporter posted: +++++ " All systems at their ultimate execution, direct drive is best. " +++++ neither here he said it why?????? So, seems to me that all about is about: " personal preferences " on what we have/are playing in our audio system. The kind of TT drive system is only one factor/characteristic on a whole TT design and perhaps not the more important one or at least not the one that could define which kind of TT is better. A TT as a tonearm IMHO must be analysed against which kind of audio item is using it which kind of audio item " depends " and how of the TT or the tonearm. These two analog items are " slaves " of the phono cartridge that IMHO is the analog item that has the hardest task on analog that's: TO READ THE LP GROOVES INFORMATION WITH CERO DEGRADATION. ADDING AND LOSTING NOTHING OF THE PRECIOUS RECORDED SIGNAL. IMHO THE FIRST TWO " FOCUS " THAT GOES AGAINST THAT STATEMENT ARE THE TT AND THE TONEARM. ( obviously the tonearm internal wire and connectors. ). The TT, independent of what kind of drive system has, is a " tremendous " focus of cartridge signal degradation even if always runs at 33.1/3 rpm and mantain 100% of speed stability in the very short time: no speed variations not even tiny variations. In its best design any TT drive system can fulfil the whole speed subject and even to have the same posibilities to share in between same specs about: ruble, signal to noise ratio, wow and flutter or speed stability numbers. Main differences IMHO comes how a TT design handle internal vibrations/resonances at different levels as: bearing, motor, plinth, belt, platter, etc, etc.. In the very first second that a TT start to run in that very first moment are generated vibrations/resonances ( that we can name it: distortions, that will be pick-up by the phono cartridge. Distortions that are not on the LP grooves. ) due that a TT is a dynamic " circuit ": the platter mass in movement generate a dynamic tiny vibrations where different platter mass/weight generate different vibrations/resonances and these kind of distortions depends too on which TT build materials were choosen by the TT designer. Now, the TT plater generated distortions has to be added to the TT bearing distortions, to the TT motor distortions, to the TT arm board distortions, to the TT plinth distortions and obviously to all kind of vibrations/resonances generated out side the TT that affect the cartridge signal. I posted several times that till today ( and I'm not heard all the TT out there but almost all. ) no TT design per se fulfil the cartridge needs and the main reason is not because the drive system but mainly because the build materials choosed on the TT design and more specific the build materials choosed for the platter/mat TT. According with my experiences the " major " differences in the music we perceived trough the cartridge and all the way to the speakers is: the build material choosed for the platter/mat that is in direct touch with the LP and the LP with the phono cartridge and not because the TT drive system. I'm not saying that the drive system is not important ( everything in a TT design is important. ), certainly it is but what is in direct touch with the LP is more critic/important and gives the TT " signature ". I did not heard yet and analog rig ( in any audio system. ) where I can say: " this TT really works " dissapearing " ( by dampening or some other way. ) internal and external vibrations/resonances that permits the cartridge can fulfil its needs. Some of the last DD designs are taking care about and I hope that in a near future we can have TTs that can fulfil the cartridge needs. The name of the game: TT design build materials chosen!!!!!!, DD or BD is almost unimportant. Of course that first rate design execution is a must to have. Regards and enjoy the music, R. |
From my many, many years of experience it really is all about the execution. From my 1st AR table to my current direct drive they all had something I liked. The belt driven Simon Yorke had incredible PACE (and looks IMHO) but lacked ultimate bass depth. The only table I can say for sure that didn't meet my liking was a TTWeights table which couldn't hold it's speed. I've now gone to DD and my journey is now over and I'm enjoying the music and forgetting about the gear......finally! (Dealer disclaimer) |
Dear Lohanimal, I realize your generalizations regarding the virtues of each type of drive system are thoughtfully arrived at, but even they are open to question. I agree with the others, who agreed with me (no surprise), that execution is paramount. I WOULD say a word in support of the unpretentious Lenco L75; it's absolutely amazing what you can get out of that turntable after bearing and chassis upgrades, a well-designed plinth, and a TOTL tonearm are added to the mix. Even though those extras may add up to a few thousand dollars in expense, the Lenco is definitely my choice for "bang for the buck". |
I was making generalizations, and i have to say that the DPS 2 has superb timing for instance, plus excellent imaging. The SME 10 and 20 (not heard the 30) are 'neutral' so to speak. Of course certain decks of course cross boundaries. I am currently awaiting a Jeremy Marine bearing for a Lenco L75, and am gonna either: get a second hand Townshend Avalon so I can steal the trough, or alternatively I might get such a trough machined for me. I personally think the Townshend trough is just revelatory. |
Been out of town visiting elderly mom and came back to enjoy the input. Appreciate your thoughts. I own a VPI Classic 1, but was toying with the idea of getting a vintage table from Artisan Fidelity (which drove my original question). But upon my return, I've decided to trade in my VPI Classic 1 for a Classic 3. Figured I can't go wrong. The 3 should be sitting on my shelf the first week of January. |
All these drive systems are competent, and all are poor choices, depending on implementation. You would be hard pressed to dismiss the sound quality of a Brinkmann Oasis or a Dobbins Beat for being direct drive. You would be hard pressed to dismiss the sound quality of a Shindo or VPI Rim Drive for having idlers that transmit energy from their motors to platters. And you'd be hard pressed to dismiss the sound quality of a Rega P9, a VPI Classic 3 for being belt drive turntables. And what about an EAR magnetic drive? Or a 47 Labs Koma loop drive? Let's start by saying that if the main bearing is excellent, and the mounting/anchoring scheme for the main bearing and tonearm is sound, drive choice is a matter of voicing, with convergence between them increasingly possible. That is to say, I agree that robust drive matters, so torque and speed precision can be delivered by all of these and yet they tend to sound somewhat different. The early years of my hifi interest coincided with an emerging orthodoxy about turntables and the elevation of the turntable itself as an influence on sound. The orthodoxy favoring belt drive was led by Linn in the form of the Sondek by the early 1970s but there were other players in the consensue, including Empire and Sony (before their move to direct drive). In a few short years back then, once-revered idlers became toxic, belt-drive became audiophile religion and direct drive achieved mass market ubiquity. As speakers and amplifiers got better, the reputation of idler drive turntables was done in by too-frequent use in poorly-conceived and built plinths and old noisy bearings. Belt drive was elevated by its simplicity and layabout sound. Direct drive was undermined by shiploads of plastic wax rotators that couldn't sound great with *any* drive system. My first discrete turntables were belt drive: Pioneer PL12D, Lenco L85, Transcriptor Saturn and Glass Skeleton, Linn Sondek. And then one day in 1976 I heard Luxman's then-new PD-441 and PD-444 direct drive turntables. At a time when a Linn Sondek cost $350, the Luxman PD-444 cost $800 and had two tonearm mounts. The smaller but same design PD-441 cost $500. Both before figuring in the cost of a tonearm. In the latter '70s this was real money. I had no real complaints with my Linn and Transcriptors until I heard the vivid but even tone of the Luxman. I bought one, and later another as I began running two systems. In parallel I had Linns, Pink Triangle, VPI and Thorens in and out of my systems but the Luxman PD-444 always won out. I still have two of these turntables today. And to give you s perspective of the relative role of drive system in sound quality, in the last several years I achieved a greater improvement in the Luxmans by changing out the entire footing scheme than the Luxmans themselves offered over other good turntables with different drives. I repeat: The replacing the original demi-suspension feet on my Luxman PD-444 with a multi-layer mechanical grounding scheme yielded more difference than drive system differences. And how would I know this? Because the Luxman PD-444 and the PD-555 had the same physical plinth and footing but the 555 was belt drive and the 444 was direct drive, and I have had the chance to hear them side-by-side with same tonearm and cartridges. It's probable that if Luxman or anyone duplicated the 1970s PD-444 today, it would cost something on the order of a Brinkmann Oasis and yet I can't say it is the only way to go. I recently heard in my own system a Technics SL-1200 that was aggressively treated for resonance control by Sean Casey at Zu, and which I further modified by changing out the stock feet for 1 lb. solid brass cones. It also had Sean's custom-machined arm mount for Rega-gemoetry tonearms and in this case was fitted with an Audiomods arm optimized for the Zu103 cartridge. The platter was epoxy damped and balanced. The plinth was aggressively treated with a variety of internal damping materials. And of course the tonearm and mount is a massive upgrade over the stock Technics. The results were astonishing, especially coming from the prosaic Technics, much maligned and debated in audiophile circles (including here). That turntable was easily competitive sonically with anything on the current market selling for $3000 - $5000, once the stock mushy rubber and plastic feet were tossed aside. Want to make it better: there's a $695 super bearing available online, user installable. And yet a $1295 belt-drive VPI Traveler is sonically convincing, as is a Rega RP6 and they can be had for under $1500 with an entry cartridge. Meanwhile, I have a virtually NOS Garrard 401 idler drive turtable mounted in a Loricraft-style plinth crafted from solid teak blocks. Whereas my Luxman 444s are appliance-like in their consistency and reliability, the Garrard requires some attention and tweaking to keep it quiet. But it's worth it when I lower the stylus. With a Thomas Schick arm and either a Zu103 or Ortofon SPU cartridge, sound explodes from the speakers with energy and projection no belt drive equals and that most direct drive can only muster with perception of more distance between you and the performance. Same arm and cartridge, same surface, same vinyl, different drives/plinths -- big differences. Which one is right? Well, that's why I have both. What I don't have, presently? A belt-drive turntable. I won't say I'll never have one again. The 47 Labs Koma uses an elastic cord to drive both its playing and counter-roatating platters. That and the DD Brinkmann Oasis are the two most interesting successors when my 35 year old Luxmans die, or maybe one of them finds its way here sooner. Phil |
Ok I have to add that all these drive systems are "a little bit off all the time." just with different characteristics of deviance. The thread drive proponents usually depend on high platter mass to mitigate slippage and motor-derived speed instability, and this can produce a very quiet result and a certain relaxedness at the expense of vivid presence available from other drives. The Acoustic Solid thread-drive turntables are very good and sound beautiful, for example. Artemis achieved an admirable balance of characteristics with tape drive, including a reel-to-reel deck's tensioner. Tape drive applied to a wider range of choices in materials for platter, plinth, arm mount, and footer schemes could prove capable of reconciling drive differences better than most. Drive transmission elasticity, servos, pulley eccentricities, LP eccentricities, warp wow, idler eccentricities, power anomalies, stylus drag, bearing friction, platter or sub-platter eccentricities all contribute to all drive systems being "a little bit off all the time." Meanwhile, the drive system is just one influencer. How your turntable is deployed -- what it sits on, its footing scheme, its plinth and platter composition, whether it's coupled to or isolated from its resting surface -- can exceed the sonic differences between some of these drive schemes. Listen to several if you can, and decide which drive's and implementation's imperfections least distract you from what's good about them in service of convincing musicality. Phil |
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What is quite interesting is that there is a clear shift in the direction of higher torque designs. Do bear in mind that Nottingham Analogue go for a high mass low torque design that transmits as little vibration as possible. Likewise the Linn LP12 is not exactly a high torque motor, nor is the one on the townshend rock I recently acquired. That said all three of these decks sound excellent in their own way. A truly circular (hope you don't mind the pun) discussion. As I have said earlier my hearing has changed (or the grass is greener on the other side) and i am beginning to favour the high torque drive and boogie woogie of an idler. |
Quite a difference between Nottingham and Linn tt's. The former use massive platters with a low-torque motor. The latter use a light weight platter with a low torque motor. The Nottingham philosophy has merit, IMO. Quite a few very expensive turntables are of the high mass/low torque type, including Walker Proscenium, etc. There are even a few direct-drives that ascribe to the low-torque/high mass approach, e.g., the Kenwood L07D. This can work very well if well engineered. I am not a "Linnie", obviously. |
I am always fascinated from technical solutions and an idler drive is THE best (by far) way to transform any vibration and smearing from motor to the bearing and platter. These distortions are called Rhythm (well, the" Subway below Kingsway Hall" in every record), the loss of High frequency information is a result in better Bass (like a compressed MP3 file to the midrange). Most record stations replaced those units as fast as possible. Personally I think, the audiophile world waited for them. Here is a version with an updated motor. PRAT counts |
I'll take belt drive over the over versions and here is why. First, belt drive tt's in general have high mass platters. That provides not just speed stability but also dampening; dampening not just external vibrations but also motor cogging. The mass of the platter provides inertia to help keep the speed constant. For example, my tt has a 14lbs (6.36kg) platter. A 1 gram change in stylus drag (assuming a drastic change in the record groove) generates 0.00155Nm of torque at the outer rim of the record. Assuming all else is constant except for this torque change, the platter is going to lose 0.29% of its speed in 1 second. Of course the motor is going to increase torque to compensate, but for this analysis you can see the impact of stylus drag on the platter. The deceleration is proportional to platter mass, so if your platter weighs 28lbs, then the speed loss would be half or 0.145%. Conversely, the stylus drag will have a proportionally larger impact on lighter flywheels. Motor speed control and belt compliance play a larger roll in speed stability than inertia, but I wanted to point out the value of higher mass platters. Now imagine a low mass platter directly coupled to a motor. Not saying it is impossible, but it is definitely an engineering challenge to smooth out the torque ripples from the motor and isolate the record from external vibrations. |
I would posit that one cannot argue from principles alone that one way to drive the platter is superior to another. I say this, altho I do agree with Syntax that idler drive turntables must deal with the issue he cites. Other drive systems have other issues. Tony, what you claim as a merit of belt drive is also a demerit. If the belt is elastic, then you have speed instability due to that. The big fat platter does provide inertia to minimize that problem. If you have an inelastic belt, then vibration (and cogging?) from the motor have a pathway to the platter, and "belt creep" occurs nevertheless. Any deviation from perfect roundness (or flatness) of the belt also can introduce speed instability. I say all this only to support my opening statement; they are all flawed in one way or another. |
I never said that the Linn and Nottingham are the same - I was saying they have the similarity of being low torque designs and sounding excellent 'IN THEIR OWN WAY'. I have to say I was never a Linnie myself, however, I heard one with all the Funk Mods and thought it sounded wonderful - I never thought I would ever say that. |
Lewm - he didn't say elastic belt drive, he said belt drive. My silk thread "belt" does not stretch, the ac motor doesn't cog, and I dont get belt creep whatever that is. According to both the Timeline and KAB the speed on my deck is rock steady. I have dispensed with both a 301/401 so I know what those idlers sound like - musical but far far away from state of the art in resolution & transparency. I agree with you they are all flawed, but which has the least flaws. |
Truly, as Rhett Butler said, I don't give a damn. I respect all of our opinions, and really being happy with one's turntable is all that counts. For me, in practice, there is such a thing as "good enough". The theoretical discussions are a separate bit of play. For a definition of "belt creep", which is a factor for any conventional belt-drive turntable where the belt travels around a pulley that is some distance from the edge of the platter, go to Vinyl Asylum and search on the phrase. There you will find Mark Kelly's explanation. To a large degree, the phenomenon can be mitigated by having the motor pulley as close to the platter as possible, a la Nottingham, or better yet by having the belt completely encircle the platter, or nearly so. I believe the DPS or Artemis table (one or the other) nearly achieves that by employing a separate capstan. Also, the 47 Labs tt takes a shot at it. |
The belt creep that Mark Kelly expounds assumes the belt stretches and thins slightly, ergo if the belt doesn't stretch then there is no belt creep. Japan. Big and round. There are lots of ways to reducing or eradicating cogging, varying the ratio of slots to poles, angled slots or stators, variable drive applied to the motor windings, running the motor at high speed etc In the Final Audio it uses an AC synchronous motor with precisely controlled regenerated sine/cosine waves for the motor and variable voltage regulation to optimise the torque applied to the moving high mass/high inertia platter. I can actually dial in cogging via the torque controller if someone likes to listen to that. |
Motor speed control circuits have to be designed for the various types of drives. For belt drive tt's the circuits must likely be tuned specifically for the belt compliance/platter mass being used. DD tt's must have altogether different speed control circuits as compared to idler or belt drive. Back to belt drive; I think changing belt types on a tt affects the sound because the spring rate of the belt has changed thereby affecting the dynamic response of the system. The speed control circuits are designed around a specific set of parameters including the belt type. Changing belt types alters the spring rate side of the equation and may make the table sound better or possibly worse. It might be hit or miss. The same goes for adding mass to the platter. You have to try the Dr. Feickert Analogue iPhone/iPad app. I think it is a killer app. You need a test record with a 3150Hz test tone. You can order one through the maker of this app or in my case, I have a test record with a 3150Hz test tone. This app does three things; it lets you dial in platter speed while the cartridge is tracking in the groove, it analyzes and computes your table's Wow&Flutter (it automatically filters out the record's runout which can accentuate Wow&Flutter) and it charts your platter's speed over time. My particular tt has Wow&Flutter measuring +0.02%/-0.03%. That is within specifications. The speed plot over time shows a small, smooth sinusoidal wave. That might be motor cogging smoothed out by the platter mass, but I think it might be the motor speed controller cycling about the setpoint. I measured the speed of an old Oracle tt and it did a little better than my tt. It had a Wow&Flutter measurement of +0.01%/-0.01%. It also had a smooth, low frequency sine wave for speed vs. time. The Oracle was harder to adjust and dial-in an exact speed of 33 1/3. I would really like to hear from others how their idler drive and direct drive tt's compare with the speed vs time plotted by this app. It might give us some insight into why the different drive systems sound different. |
I respect all of our opinions, and really being happy with one's turntable is all that counts. For me, in practice, there is such a thing as "good enough". The theoretical discussions are a separate bit of play. Well said, Lewm, and a welcomed reality check in a discussion verging at times toward angel-counting on a pinhead. |
As to Dover's post, belt creep is not caused from stretching the belt. Find Mark's writing on the subject because he explains it far better than I ever could, and he backs it all up with the proper math. It is a physical limitation of a belt drive system that generates an inherent tracking error. As far as I know, Mark doesn't address tape drives or string drives, however. I don't look at a string drive the same way as a belt drive, but tape may be a viable way to avoid the problem. String drives have a limited slip that has always intrigued me. Syntax discounts the idler drive out of hand, but I assure you that all the problems that he mentions have been addressed. It has a lower tracking error than a belt at around one part per million, and it has fewer maintenance worries than a string. Not only that, but with a proper controller it is more speed accurate. However, that's not to discount the string because I believe similar outcomes can be reached with a string when the system is designed correctly and built well. It can be fiddly, though. . |
Mosin - please re-read my post. I did not say that elasticity causes the belt creep. I said it is an assumption and that if the belt doesn't stretch then there is no creep. Mark Kelly's calculation of belt creep is : Creep = T/r x A/E If the belt has no elasticity, then the Elastic Modulus (E in the above calculation ) is ∞ ( infinity ), and Belt Creep will be effectovely 0 ( zero ) exactly as I said. To give some examples of tensile strength : Rubber 15mpa Human Hair 380mpa Silk 1000mpa Aramid fiber 2557mpa These are single fibres only. Here are the calculations using Mark's example, and assuming the cross sectional area is arbitrarily 1/10th the size of the rubber belt. T R A E Creep 1 5 10 50 0.04000 1 5 1 380 0.00053 1 5 1 1000 0.00020 1 5 1 2257 0.00009 On the subject of thread drive TT's, they do have to be designed properly, as in the Final Audio. The Final Audio uses an AC synchronous motor with precisely controlled regenerated sine/cosine waves for the motor and variable voltage regulation to optimise the torque applied to the moving high mass/high inertia platter. In addition to this the pulley profile must be designed for a thread rather than a belt. If I recall correctly the pulley should present a concave hemisphere to the thread. |
