Yep......
Vintage DD turntables. Are we living dangerously?
I have just acquired a 32 year old JVC/Victor TT-101 DD turntable after having its lesser brother, the TT-81 for the last year.
TT-101
This is one of the great DD designs made at a time when the giant Japanese electronics companies like Technics, Denon, JVC/Victor and Pioneer could pour millions of dollars into 'flagship' models to 'enhance' their lower range models which often sold in the millions.
Because of their complexity however.......if they malfunction.....parts are 'unobtanium'....and they often cannot be repaired.
TT-101
This is one of the great DD designs made at a time when the giant Japanese electronics companies like Technics, Denon, JVC/Victor and Pioneer could pour millions of dollars into 'flagship' models to 'enhance' their lower range models which often sold in the millions.
Because of their complexity however.......if they malfunction.....parts are 'unobtanium'....and they often cannot be repaired.
1,793 responses Add your response
Lewm - With the various mats the L07D stainless & Micro 180g Copper were very close on the SP10. It is possible the differences may be more to do with mass & the actual surface profile than anything else, since they are both high impedance type materials. People forget that platter mats are mechanical devices that not only provide an interface and base for the stylus/record, but also have significant impact on altering the resonant behaviour of the platter itself. In particular with aluminium platters, a metal mat such as copper/bronze/stainless will dampen the platter much more effectively than say acrylic or rubber. The reason is that if you combine two materials that are close in propagation speed then reflected resonances ( which end up back in the record and stylus) are minimised. Reflected resonances - whenever a resonance or energy passes through a material junction, most passes through but a percentage will be reflected back. The closer the materials in propagation speed, the less the reflected energy. This is why Goldmnd and others went the methacrylate way with platters to get the impedance much closer to vinyl and minimise reflections. In summary the mats on an aluminium platter are trying to bridge the vast difference in the impedance of vinyl versus aluminium. None of them will be perfect. |
Dover, I totally agree that it is wise to use a mat that approximates the weight of the OEM mat on a DD turntable with servo control. I have preached that gospel for years, but lots of folks ignore the principle and claim to be getting away with it. This is one reason why I stick to the OEM platter sheet on my L07D. That and the fact that the L07D sounds so terrific. I do suppose that there is a copper mat out there that would approximate the weight of the platter sheet (5 lbs, I think). Why do you suppose that copper might sound significantly different from, not to say better than, stainless steel? It's also the case that the L07D servo was deliberately designed to exert a much looser control on the speed than does the Technics servo, for one example. I think it only activates when there is +/-3% speed error. |
Lewm, You might like to try a copper mat on your SP10 if you haven't already. In a direct comparison of the L07D stainless mat, Boston, and a few others - the copper mat came out as the most complete in my experiments. A word of caution - for DD turntables mats should ideally weigh the same as original as the speed servos are optimised for the mass of the standard platter. For example in the L07D the manual carries a warning that if you run the platter without the mat the servos will not work properly. |
Thanks for changing the subject from vituperation and the definition of an I-beam to mats, a subject we can all sink our teeth into, or not. Mats are crucial in determining the sonic character of a turntable, all other things being equal. Thus inevitably one's choice will be to some degree a matter of taste. After mucking about with several different types, I have settled contentedly on the Boston Audio Mats 1 and 2. They are as good as or better than everything else I tried, but I do not kid myself that there could be nothing better out there that I have not tried. On the L07D, I stick with their stainless steel platter sheet, although I am otherwise convinced that the BA Mat 2 sounds a bit better than an SAEC SS300 (another metal mat), on my SP10 Mk3. |
Aigenga, "On the subject of platter mats I just want to re-iterate that I am using a lead mat glued to an Achromat. I thought that Fleib or someone else was about to try the same thing and wonder how that worked for them?" I'm experimenting with this now, and I'm wondering about the details of your mats. I bought a 3mm Achromat thinking 5mm might be too thick with an additional 2mm underneath. BTW, the 3mm version seems to have deficiencies when used alone. As it turns out, once flattened, roofing lead is more like 1mm thick and weighs about 510g. It seems to greatly improve the Achromat, but I suspect it would be better with the 5mm version. The question is, would the 5mm mat with 1mm of lead, outperform the 3mm with 2mm of lead. The Achromat is somewhat of a surprise looking like "fine" cardboard. It's more like 2.5mm and unless you glue it down the edges tend to lift if you only clamp the LP on the spindle. I find myself listening to the last 50mm of a side, for evaluation. Like most of you I have a collection of mats. Mine includes a 3mm hard acrylic, and one of expanded foam - also about 3mm. So far best results seem to come from the lead in the middle with either the foam or acrylic on the bottom and the Funk on top. The foam combination is a little warmer. The acrylic seems faster/cleaner, but either combo sounds pretty good. I'm thinking of die casting lead mats of different thickness/weight. A lead undermat seems to have great potential. Perhaps thicker sheet lead is less trouble. Regards, |
Ct0517 Thank you, the ET2 I Beam is an excellent example of an I beam - no plywood, no lead or glue, just a piece of plastic with flanges top and bottom to give axial and structural rigidity - the whole piece being an extrusion to form the I. Richardkrebs may have forgotten what the ET2 I Beam looks like as he has removed the decoupled I Beam from his ET2 and replaced it with a much heaver M10 bolt, thus removing one of the key patented benefits of the ET2 design, the decoupled counterweight which was designed to keep the high horizontal mass of the ET2 as low as possible and minimise bass peak resonances. The ET2 is an excellent example of using I Beams and large thin walled tubes to deliver a light but rigid structure. |
Henry, sorry to digress further from your vintage DD thread; but I was having my coffee this morning, came across this thread, and I am a bit surprised at both Dover and Richard. All this "Debating" of I beams and not one mention of the best example of an I Beam, used for audio "on Audiogon", that I can think of anyway. This I-Beam Eminent Technology (ET) 2.5. tonearm. I am also using a ET 2.0 on a vintage DD. |
5-14-15: RichardkrebsRichardkrebs you described your plinth as a "form of I Beam". 05-13-15: RichardkrebsAn I Beam consists of a Web with a flange top and bottom. Your plinth that you describe has only a Web and no flanges. An I Beam without flanges is structurally weak, has no axial strength and will flex. Here is a link to help you understand how I Beams work.. http://en.wikipedia.org/wiki/I-beam There is no debate. The plinth that you built is laminated sheets of acrylic and lead and is not an I Beam, nor is it even a form of I Beam as you have claimed. |
05-14-15: Richardkrebs Richardkrebs, that is not correct. if you used sheets of plywood stacked vertically to make an I beam your house would sag and probably fall down. The essence of an I beam as I explained in my post is that the vertical component has high vertical and longitudinal strength, but can be flexible in the lateral direction. It has nothing to do with the layers of timber in the wooden I Beam. In actual fact plywood as you understand it is not used in the manufacture of I beams. I Beams use a special construct of layers of timber running in the same direction to give the structural longitudinal strength. Plywood has the layers arranged with the grain crossing at 90 degrees with each layer. It might help if you look at a metal I beam to understand the concept - there are no laminations in a metal I beam, but if you removed the top and bottom of the I then the beam will flex like a sheet of metal. |
Dover. The essence of an I beam and ply is the separation of the two outer layers (sheets). Any bending causes compression of one sheet and tension in the other. This increases the stiffness of the structure. As I said earlier. It is a 25 year old design. Were I to design one today, it would use different materials and architecture. (Dover "To be clear what was being measured in my post on the Timeline thread – the 2mm lag was generated by setting the TT speed with no stylus playing and then measuring the lag when playing. A 2mm lag at a radius of 400mm is a speed error of 0.08%") and ("In summary, your maths is wrong because your calculations are based on a misinterpretation of my Timeline test results.. When the 26kg platter speed was set with the stylus playing, there was in fact no measurable retardation.") My post calculates the retardation torque required to cause the slowing, from stylus raised to stylus lowered and then applies this to the pod. What happens AFTER you adjust the speed with the stylus lowered makes no difference to the calculated pod movement. Re the CofG of the crescent shaped pod. I didn't make this note clear. It appears that the feet have been moved back towards the rear of the pod, moving the CofG closer to the front feet. The photos are a little ambiguous. If this is not the case then yes the CofG will move away from the front pod feet reducing the tilt. The platter is heavier than I thought. If its radius of gyration is as I assumed, this extra weight will increase the torque required to slow it and by definition increase the pod tilt. |
Richard - to change the subject slightly, can you elaborate on the nature of the "Krebs" mod that you are offering for Technics DD tables? Not asking you to give away all of your secrets but since you have been so forthcoming on such matters, I would be interested in a better understanding of what I would be getting for my investment. I have a SP-25 in the rosewood Technics plinth and have already upgraded the bearing (Jim Howard). Does your mod do anything to the bearing? |
Pod Stability 05-11-15: RichardkrebsA perusal of your numbers shows they have failed the sound check, and here is why - 05-10-15: Richardkrebs This turntable was indeed my Final Audio VTT1 - which has a 26kg platter system - Platter 15kg, Subplatter 5kg, Copper mat 4.5kg, Clamp 1.8kg all designed to be used together to provide optimum clamping and energy dissipation to ground from the record. An AC motor, driven from a sine & cosine wave generator and Onix OA60 power amplifier drives the platter via a silk thread. To be clear what was being measured in my post on the Timeline thread – the 2mm lag was generated by setting the TT speed with no stylus playing and then measuring the lag when playing. A 2mm lag at a radius of 400mm is a speed error of 0.08% If I set the speed with a record playing, which is my normal procedure, then there is no speed error at all as measured on the Timeline, and therefore the variation in stylus drag due to music playing is an immeasurable % age of the total drag. If we assumed that the variation in stylus drag is plus or minus 20% of the total drag (remember it is not registering at all on the timeline), then the string drive Final Audio VTT1 has at worst about half the wow and flutter of an SP10mk2, and about the same as an SP10mk3, without the induced negative effects of the servos. Another small matter to correct re your post on the movement of Halcro’s POD – 05-10-15: RichardkrebsThis is wrong. If a chunk of mass is removed that is in front of the feet (closer to the platter than the centre of the pod ) then the centre of gravity of the pod shifts back AWAY from the platter. This INCREASES the resistance to tilt. In summary, your maths is wrong because your calculations are based on a misinterpretation of my Timeline test results.. When the 26kg platter speed was set with the stylus playing, there was in fact no measurable retardation. |
05-13-15: RichardkrebsBy no stretch of the imagination could you refer to your plinth structure as analogous to an I Beam. I have never seen a lead sandwich described as an I Beam in the time I studied Engineering at University or in the 5 years I spent working for NZ's largest timber company. The middle of an I Beam has high structural integrity in the vertical direction so that the beams do not sag. The top and bottom of the "I" provide the lateral stability. Your lead spacer has no structural stability, it is not possible for this structure to work like an I Beam. Plywood in of itself is not structural, it flexes a lot. Flex in plywood plinths is reduced by running multiple layers and a lot of glue, but they still flex. If you want stiffness from plywood you would cut the plywood into strips and glue them with the board vertical ( as is done in I beams ), like Albert Porters layer of panzerholz in his plinth. The panzerholz is not used in sheet form, it is cut into strips and glued sideways. |
Dover. The figure I used for Aluminium is a generic number we use for calcs here. If we want to be more precise we take into account the method of forming the material and of course the specific alloy. I did say "around 0.04mm" The point I was making, was that the dimensional change is a tiny fraction of the several millimetres per degree c that Halcro sighted. When I made the decision to build my TT plinth out of acrylic the problem of stiffness was considered. My TT uses 2 x 30mm thick Acrylic sheets, separated and fused to a lead spacer. By separating the two structural plates a form of 'I' beam is produced since shear between the two plates is strongly resisted. This is a similar idea to that used in the light weight wooden 'I' beam floor joists. Individually the three parts of the beam are quite flexible. Gluing them together in this form however makes a very stiff structure. The same principle is at play in plywood construction, which my TT copies. The triangular shape with the motor centrally mounted puts the bulk of the material around the motor, concentrating the strength in that region. It then tapers towards the edges progressively reducing in strength as it approaches the feet. A square plinth, however, will be more sensitive to the problem you sight. If in fact it is actually a problem. My room is air conditioned 24/7. Temperature is tightly held It is a 25 year old design and I am still happy with it. That said, if I was to build a ground up TT today, just for fun, I would likely use different materials and architecture. |
05-10-15: RichardkrebsThis is wrong. When examining dimensional stability one needs to take into account materials engineering. If aluminium is produced by a rolling or extrusion process, then the dimensional stability is directional - much lower along the roll and higher across the roll. Furthermore if a metal is produced by a casting process then it is usually substantially more dimensionally stable than that manufactured through a rolling/extrusion process. The L07D is a cast foot. I think you will find the engineers went to great cost to produce a cast for this very reason. Richardkrebs - one thing puzzles me. You made your turntable from acrylic sheet, which has a Youngs modulus 60 times lower than steel ( which means it is 60 times less rigid ) and has a temperature coefficient of expansion 6 times higher than steel. Given that your TT is a triangulated structure and the SP10 motor is mounted in the centre of the acrylic sheet, it would appear that you have mounted your SP10 motor on a trampoline. This seems at odds with your stated design goals of absolute dimensional stability. Furthermore, on the plinth you made, the arm is mounted closer to one of the three structural legs. So not only is your TT plinth expanding and contracting at a higher rate than say a cast chassis like the Melcos & Microseikis of this world, or even the L07D, your VTA is constantly changing due to the large differential in vertical structural rigidity between the centres of gravity of the SP10 motor and the arm. In layman's terms in your plinth the SP10/platter will move up and down at a greater rate than the tonearm when excited. |
A plinth or chassis is a logical design for a commercial table,And I think that just answered Lew's question why most turntable manufacturers produce the 'attached' package. It's easy, convenient and generally 'plug'n'play'. But this discussion really belongs on the Copernican Thread which, despite its absence from recent activity, has had nearly 1,000,000 hits so hopefully some readers are inspired to try it out...❓😎 As I repeated many times...I'm not trying to convince the sceptics here. I'm merely relaying my findings after creating the model and comparing it to all the commercial turntables I have heard and owned myself. The only answer I could find to explain the improvements I was hearing...was the presumption that a massive level armpod was perhaps the important ingredient❓👀 I never imagined the hostility this simple mission would unleash....and all from those who have never tried it themselves...😱 Please forgive me...🙏🏽 |
Lewm, Okay, take away the movement in unison aspect of a suspension, and exactly what are these extraneous sources of energy? Why is it better if they are joined by a plinth or whatever, than planted on the base? Don't tell me they will act in unison to some undefined energy and cancel affects, because they won't. I'm saying it's more likely negative affects will be increased. A plinth or chassis is a logical design for a commercial table, but it is also good at transmitting extraneous energy between platter and arm. I can't understand why you think this is desirable. Heavy pods coupled to a heavy base is more likely to resist this negative energy, depending on design. Regards, |
"Whatever" means normal disturbances that occur in the typical playback setting, not f**king seismic events or dog accidents or children running into the tt or etc. This has NOTHING to do with suspended turntables. Nothing nothing nothing. I don't like suspended turntables, as a rule. What you are thinking of is that in a suspended turntable the tonearm and bearing/platter MUST respond in unison, else you have all sorts of problems. But I am not in any way, shape, or form talking about suspended tt's per se. Are we clear? It's hard enough to make the point without these exaggerations. |
Lew, I suspect a massive pod on spikes threaded into the bottom of the pod might be better than bolted to a base/shelf. I understand what you're saying, I don't think it's necessarily true. **Whatever happens to the tonearm, from whatever source of spurious energy of any kind at all, should also "happen" to the platter/bearing at the same point in time.** "Whatever" covers a lot of ground. Are you tracking through a seismic event, perhaps your dog bumped your TT stand? I chose sound pressure waves because it's the logical choice for a non-suspended table. In that case I think it might be better if the pod and platter were not joined at the hip. Spurious energy would more likely to be transmitted and propagated from one to the other by their common joining. This is a bad thing, not good. Once again, having the platter, arm and motor moving in unison is the law of suspended tables. Even those with a fixed motor seem to get half decent results sometimes. Throw out the suspension and what specifically are you talking about with spurious energy? Why is it better having them joined? Methinks it's worse, with greater potential for degradation. Regards, We're not |
Fkeib. I agree, 100% torque conversion is not possible. That is why I listed this assumption..."TDs motor only provides enough torque to maintain original speed before stylus is lowered, after it is lowered." I have assumed that the motor plays no part in dealing with stylus drag. It is only delivering enough torque to overcome windage and bearing friction. Any additional friction in the form of stylus drag is resisted by the stored energy in the rotating platter. That is why I needed to calculate its moment of inertia. This makes my calcs conservative, since there will be some restorative torque from the motor. Since we don't know how much, it was considered best to ignore this parameter. The info I did find online relating to calculating stylus drag used a free wheeling platter, running at rated speed. Timed to stop without and then with the stylus lowered. My calcs are a derivative of that method. I don't think that Maynard and I would agree on very much at all! |
For a long time I agreed that the tonearm and the platter should resonate in unison to avoid added distortion. But after reading about good results from the separte armpod approach, I started to question my original thinking. I realized the tightly coupled arm to platter approach would work only if the stylus is also tightly coupled to the arm, that is, extremely low or no compliance at all. But most cantilevers are attached to a piece of compliant rubber and that automatically decouples the stylus from the rest of the arm so the separate armpod becomes really inconsequential and therefore it's not surprising that it can sound good reported by those users. That's just my current thinking and I'm open to other possibilities. . |
I don't know where the subject of a sub chassis came up in this discussion. Whatever you want to put under your tt should affect the tonearm and bearing/platter equally and simultaneously, is all I say. Yes, if you bolt the outboard pod to a shelf, and you also fix the tt base to the same shelf, you do get a semblance of the same effect I favor. Henry was not about to do that at the outset of this thread. I am not sure he espouses that approach even now. You also wrote, "Cancelled? This is the mantra of the suspended. What external forces, sound pressure? You're just as likely to increase consequences, as cancel. Extraneous vibrations should be dissipated, not perpetuated." OK. Whatever happens to the tonearm, from whatever source of spurious energy of any kind at all, should also "happen" to the platter/bearing at the same point in time. You can choose whatever base you want, whatever source of spurious energy you want. I don't like suspended tables for other reasons. I think we're talking past each other. But I see you disagree, and that's fine. Thuchan asked for opinions, and I am certainly not alone in mine. |
Lewm, I see your point, but what you fail to see is, it's completely dependent on design. Any pod rigidly coupled to the base is connected to the platter, assuming the platter is rigidly coupled. Suppose you have one of those pneumatic vibration isolation stands or a lead balloon under your table. What difference would it make? Complicate matters with a subchassis and you're just as likely to insure spurious resonance as avoid them. **Whereas, if the tonearm and platter are well coupled and must move together, then such external sources of energy are cancelled, in effect.** Cancelled? This is the mantra of the suspended. What external forces, sound pressure? You're just as likely to increase consequences, as cancel. Extraneous vibrations should be dissipated, not perpetuated. Regards, |
Henry, Just for the record, I stated long ago that while I would agree with the hypothetical aspects of Richard's analysis, I do not and did not think your pods were in fact being moved by stylus drag, but like you say, it is a question open to experimentation. I performed the analysis of thermal expansion using F degrees and inches. (By the way, I left out a minus sign on the exponent; the coefficient is 1.3 X 10^-6.) By this analysis, an alu bar that is 9 inches long at 68 degrees F (roughly the pivot to spindle distance of an L07D) would expand to 9.000468 inches at 72 degrees F. The expansion of .000468 inches is equal to .0119 mm. This is less than insignificant, even if the construction of the L07D were to be of pure alu, which is not the case (see above). So let's put that to rest, just as I am willing to put to rest the idea that your pod moves strictly due to stylus drag. Fleib, Try to see the point that if the tonearm and platter move at different times due to differences in resonance or susceptibility to spurious energy sources, then those movements are added to distortions produced by spurious movement of the stylus. Whereas, if the tonearm and platter are well coupled and must move together, then such external sources of energy are cancelled, in effect. For this reason also, we are told to wear seatbelts. I once saw a short movie in which a porcelain cup was put into a small barrel. Then the barrel was thrown down a set of stairs. Of course, the cup inside the barrel was shattered. Then the experimenter strapped the cup firmly to the side of the barrel and repeated the experiment. This time, the cup emerged intact. Keeping the tonearm and platter in consonance has the same beneficial effect. You may disagree, but that is the basis for my thinking, not to mention the thinking of 9 out of 10 designers of commercial turntables. |
Richardkrebs, A powerful motor doesn't validate your conclusion. It does bring the platter back to speed quickly. You assume a 100% torque conversion between motor and platter. All that happened was the transmission (string) slipped for a moment. Once again, stylus drag is a bit of friction not some powerful force. That is, unless you're talking about Super Drag which can bend steel and leap tall buildings in a single bound. BTW are you related to Maynard G ? Regards, |
You accept without question that a stylus can slow a 22kg platter.Untrue.....I never accepted this fact until proven to me by the Timeline. And I still find it hard to believe...... Your calculations are frankly nonsense IMHO. Simply provide the evidence.... Even the Greeks 2500 years ago could easily set up an experiment using tensioned string to prove your theory. Stop waffling and simply prove what you say using the dozens of methods available to real scientists today. If you can't or won't, it would seem reasonable to keep your imagined beliefs a well protected secret...🙈 |
Calculating force to slow a 22kg platter is looking at it backwards. Stylus drag is nothing but friction. It's applying the brake to a rotor (platter) and the feeble motor slows. Instead of a heavy platter requiring more friction to slow it, it requires less to slow the under torqued motor. I doubt if this is enough friction to tilt a 25 lb. pod, even 8 microns which isn't a whole lot. Time to move on? |
Halcro. You accept without question that a stylus can slow a 22kg platter. This, while said platter is being driven by a substantial motor. Why can't you accept that a lighter structure can be rocked on its feet by the SAME applied force, which now has a mechanical advantage? I am not saying that the movement is a problem. What I'm saying is that it exits. It is clear that many people get brilliant results with this type of setup. I myself have auditioned rigs like this and liked the results. But that does not detract from the facts. The pod moves Check my math if you like, the numbers are sound. |
So what are we left with,the stylus moving a 4 or 5lb pod?Ooh no Totem... The stylus actually moves a 25lb pod...😝💩 And Lewm apparently agrees with this 'theory'.... But here's the really puzzling thing....we have many tools available to actually prove whether or not the pod is actually moving under stylus drag. Accelerometers, lasers, high-speed cameras etc which any competent scientist would utilise before making a fool of himself. I have video evidence of the Timeline in action with 3 pods and 3 styli in contact with zero movement displayed yet Richard Krebs prefers to proffer theoretical calculations masquerading as quasi scientific proof intended to add verisimilitude to an otherwise bald and unconvincing narrative. Give us one shred of practical evidence Mr Krebs.... Just one shred of verifiable evidence instead of your constant and unprovable speculation.... |
Totem. I first posted this on another thread. Here updated for relevance.... To me it is obvious that a pod will move due to Stylus drag. The question is how much. In order to calculate this I needed a figure for stylus drag. A search on the web proved inconclusive but then ironically the answer came from the original timeline thread. There, one TT is mentioned where specific data is given on the amount of laser pointer movement per revolution and its distance from the centre spindle. This TT is a beautifully engineered machine with, from memory a 22 kg platter driven by a fractional horse power motor via a thread. Hereafter I will call this TT. "TD" The specifics were 2 mm movement on a radius of 400 mm, per revolution. With this information it is possible to calculate the retardation torque and hence the drag. From this it is possible to calculate how much the pod moves. So assumptions...... A pod similar to Halcro's is used on TD Platter 22 kg of uniform section Pod plus tone arm 11.5 kg Height to record surface above mounting surface 150 mm Pod feet 100 mm spacing in a equilateral triangle Pod/ arm CofG, 75 mm above mounting surface Pod CofG Central inside the mounting feet Pod feet are not adhered to the mounting surface. ( no penetration of the cones into the shelf ) The same arm and cartridge used on TD is used on the pod. TDs motor only provides enough torque to maintain original speed before stylus is lowered, after it is lowered. Stylus is lowered at a radius of 140mm Platter has a diameter of 320mm The first answer is the force applied to the platter to cause this retardation torque. This works out at around 0.0031 newtons. Actually a large number under the circumstances but it is slowing a 22 kg platter! Using this force and applying it at a height of 150 mm to the pod we get a tilting of 8.2 microns towards the platter, more or less. Observations. With the stylus at a radius of 140 mm, the two front feet of the pod do not appear to be a right angles to the arm when viewed from above. This will reduce the tilt a little. It is unknown what happens to the magnitude of the stylus drag as the arm tracks towards the centre, so it is possible that the pod will tilt as calculated once the arm is at right angles to the feet, assuming that this happens before the end of the inner grooves. As an aside the tilting at a radius of 140 mm produces a yawing effect on the pod such that the arm rotates approximately along its axis. This effect is caused by the configuration of the feet. It is tiny and likely insignificant. The calculations assume that TDs motor does not sense the slow down and produce restorative torque. Since it is a synchronous motor it will act to try and maintain speed. This will put more energy into the system and increase the tilt. The pods appear to be slightly crescent shaped. If this is the case the CofG will be biased towards the two feet closest to the platter. This will increase the tilt. The CofG is probably higher than shown here due to the feet and the weight of the arm. If it is the tilt will be greater. The calculations assume that TDs platter has a uniform section. If its radius of gyration is larger or smaller than this suggests, the tilt will similarly be larger or smaller. If TDs arm and cartridge was fitted to a pod and used on Halcro's TT, things would be different again. This because the TT-101 does NOT slow down. It is putting even more energy into the system, so the tilt would be larger. The calcs assume that the motor assy cannot move. In Halcro's case it can and will. The 8.2 micron figure is an average. The pod will move more or less depending upon the groove modulation. Actual dimensions and weight of the pod will materially change these numbers. I do not know if the amount of movement is of any significance, but yeah baby, it moves with the grooves. This compromises one of the three ideals I mentioned featured in the mythical perfect TT. This was my starting point in these discussions. |
The linear temperature coefficient of expansion of Aluminium is 0.000023m/m degrees C and is indeed approx. double that of steel. Using this figure on a LO7D and assuming a 5 degree C delta, we get a change in distance to spindle of around 0.04mm. (approx 1.6 thou inches) Further the arm is lengthening and shortening relative to the ambient temp. This would somewhat mitigate the distance change. Of course if one goes the pod way, the shelf's thermal expansion, contraction becomes the decider of the dimensional change. The thermal expansion "problem" has been grossly overstated. |
Good one Halcro, this debate gets funnier by the minute. Assuming the Kenny was set-up and then played at room temp, there should be virtually no discrepancy in distance. 70°F = 21.1°C, and 79°F = 26.1°C (for those of us...). Is that enough to cause several mm change? Still, the point is made and it seems valid, at least to me. Why is it better to have arm and platter joined at the hip? Potential for extraneous interactions seems greater, not less. |
Henry, Come back to me with actual numbers to describe the possible change in mounting distance, given what you perceive to be the problem. My listening room varies in ambient temp by about 4 F degrees, from 68 to 72. According to my calculation, the fractional expansion of an alu bar (which this is not) would be .000052 (4 times 13*10^6, using the inches/F coefficient) over this 4 degree F span of temperatures. Further, the aluminum yoke embraces a stainless steel and brass pod (yes, a heavy and damped pod like yours, except it does not touch the shelf) that in turn embraces the vertical shaft of the tonearm in a clamping collet (not with a flimsy set screw). The alu is constrained from expanding and contracting by the bond between it and that pod plus the fact that it is also surrounded by the concrete-like material that constitutes the plinth itself. In other words, your critique of the L07D is off the mark, at best, and a sidebar to the central question. But let's stop here; I am OK with your belief structure; it has no effect on me whatever, and I am sure your music sounds just fine. This is all about splitting hairs anyway. Dear Thuchan, I may be wrong in my assessment of the top line MS tonearm mounts; I have only ever seen them in photos. Possibly they are more rigid than they appear to be. If so, my apologies. |
The L07D is a system, using several different metals (stainless steel, alu, brass) with different temperature coefficients of expansion,The basic frame of the L-07d shown in my attachment is cast aluminium which has twice the expansion co-efficient of steel. For every centigrade degree change of room temperature (and unless your room is fully air-conditioned 24/7 the variation can easily be 5 degrees C)...there is clearly change in the distance between the spindle and tonearm pivot of several millimetres which is disastrous in the scale of vinyl groove information extraction. Now please tell me Lew....what is the exact "drift of alignment" of my fully outboard armpods? |
Moonglum, No, I have not tried it, yet. Halcro et al, I only re-stated the case for a rigid connection between tonearm and bearing for the benefit of anyone who is reading this thread for the first time. Such an individual (Thuchan in this case) ought to hear both sides of the question before deciding which direction to choose. Like Henry, I am past trying to convince anyone else who has already made up his mind. But Henry, with all due affection and respect, your analysis of the L07D is ludicrous, certainly compared to the risk for drift of alignment of a fully outboard arm pod. The L07D is a system, using several different metals (stainless steel, alu, brass) with different temperature coefficients of expansion, closely coupled with substantial fasteners and massive. The temperature of a typical listening room varies by a couple of degrees during the course of time. Of course, if you leave your tt in the freezer on off days or cryo-treat the entire unit, you may want to do a re-alignment. |
Aigenga, I won't bore you with excuses. I have yet to make the mat. Since the lead I have is about 2mm thick I'm thinking of getting the 3mm Achromat. If anyone wants to experiment with sheet lead it's not hard to source online, but the shipping will usually be more than the product. I found some at a roofing supply. I think they call it flashing. This is a piece about 3 feet sq. and it cost something like $70. Don't think this is used much anymore. When I called, the guy said they had no sheet lead until he remembered flashing. Wear gloves. Regards, |