Skeletal vs Plinth style turntables
While waiting for Halcro to answer Lew's question in his post of 02-13-15, I thought it might to be interesting to look at the pod movement thing from another angle. To me it is obvious that it 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 distance 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 identical 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 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. 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 the platter motor assembly cannot move. It can and will, but much less than the pod becaue of its wide footprint. 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. 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 more energy into the system, so the tilt would be larger. 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. 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 for sure it moves. This compromises one of the three ideals I mentioned featured in the mythical perfect TT. This was my starting point in these discussions. |
Hi Lewm Just to give all parties an update. I have gone with a bit of a balanced mix of compromises so to speak in my grand plans. But just so as to whet a bit of your appetites I have ordered 6 pieces of aluminium thus far - they are to be chamferred then anodized. In addition to this I have sourced panzerholz as well. I have also ordered some pieces of Corian. I will add that I now have access to CNC machining facilities, and have been banging out dimensions on my graph paper (can't figure out Autocad) It must be said that sourcing parts can be a real pain in the neck - especially in small numbers. I am still umming and ahhing about the use of some Lexan in its construction. I can't say much more save to say that it is not all about mass or damping. I am not going skeletal either, because I cannot abide dust getting into anything. |
Ct, For what it's worth, I built two plinths of the type you describe. Both from slate slabs, and I was motivated not only by the principle that there should be a rigid association between tonearm pivot and bearing/platter but also by the simplicity of the design. Simplicity is a virtue when you work with slate, because it is so tricky to cut slate without having a disaster. On the other hand, my favorite Einstein quote is to the effect that the solution to a (physics) problem should be as simple as possible, but NOT simpler. As a result of my perhaps too simple plinth design, I am limited to tonearms that bolt to the top surface of the plinth and which do not require a pass-through for a vertical shaft. Thus I have a collection of such tonearms: Reed 2A, Triplanar, Dynavector DV505 (two of the latter, in fact), RS Labs RS-A1 (the funkiest but actually sounds great). Both my Denon DP80 and my Lenco L75 reside in such plinths. For my SP10 Mk3, I did revised the basic idea so as to accommodate removeable tonearm mount boards, made of slate or aluminum. Yet the Reed 2A is king of the Mk3. And the Mk3 plinth uses constrained layer damping; the bottom half is solid cherrywood. For the TT101, I took the base QL10 plinth and extensively re-vamped it with heavy alu supports below deck to stiffen it and with an alu arm board to replace the supplied particle board one. I further stiffened the tonearm mount by bolting the alu "board" through to a heavier piece of alu below deck such that the wood of the QL10 is squeezed by the alu arm board from above and the stiffening alu support below. We shall soon see whether the TT101 will continue to function reliably when I re-install it in nude form into this plinth. |
Henry- in your last post you mentioned your Armpod Clan again. The Op (PB) is interested in discussing plinths. Skeletal versus Full Plinths. Stay the course man. Start Copernican 2. I do however have some new anecdotal evidence for you however. For the others be warned what follows is not pretty. You see my almost 20 lb armpod was responsible for beheading my XV1 many years ago. Yes....that is how I remember it now. And I am sticking to my story. It makes me feel better. You see, Instead of removing the cartridge (proper) and doing required solder work on the wire lead at the turntable location. An isolated and quiet area.... I decided out of convenience (laziness) to "bring" the whole pod enchilada with tonearm, cartridge and wiring attached, to my busy work area. While moving the pod to adjust for a better sight angle, a slight tug was felt. The nightmare was in play. The well endowed XV1 was toast. The coldness that followed led to my first out of body experience. So I bolted the bastard down to not tempt me again. Alas I can't be trusted. Screw the obvious fact of flexibility in changing out things especially if you are tonearm bi(a)tch. But I am a one tonearm, one cartridge kind of guy, you know ? Screw as well the ability to continually refine your alignment for better sound with an armpod. You see what the ANAL Armpod users don't want to confess to; is that "The Armpod" actually teases you if you don't try this, every week.... month. And Henry has four of them. Hmmm.... You know, the ANALog pivot arm guys like to play this game where they keep trying new alignments, to try to move the two points on the record that their pivot arm arm can track best at. Well with the armpod, no movement of cartridge in its shell is necessary to accomplish this. You just need to become very good at Lewm's Armpod Drag "Dance". Sorry to digress PB. Alas still waiting for you to do your magic with this cold weather .... I see NY was at -15 celsius this morning. You know, once it hits -10 celsius it really doesn't matter how much lower it goes. To get back on track maybe a question out of curiosity. PB or anyone else. Does anyone out there still make a full plinth turntable; one with no removable and/or pivoting armboards ? A full plinth that requires one to drill a hole or tap holes for their tonearm into the beautiful plinth itself. Imagine the stress level in installing the tonearm ? Unless its a Dynavector DV505 which has enough weight - by design - to just sit on top of the plinth if you like. Hey ..maybe this makes it the first armp..... oh oh..there I go again. |
Sorry Aigenga, I should have been more explicit. I was answering Chris' question about the Raven and its 'slight' retardation when viewed against the Timeline and then compared it to the Feikert figure for the same thing. What most people don't realise (including apparently Michael Fremer) is that the Feikert App is primarily designed to measure and indicate Wow and Flutter. It does this against a benchmark tonal frequency recorded on a test disc of 3150Hz. The closer the measured frequency is reproduced to 3150Hz....the closer it indicates that the platter is spinning at precisely 33.33rpm. For all the other figures in the Feikert App.....the Raw and Filtered Deviations....they are simply measured against the 'actual' platter speed regardless of how close to 33.33rpm it might be...? For instance..if your platter were spinning at 31.06rpm but had little Wow and Flutter...the Feikert App figures would show -0.01%/+0.01% Max Deviation. It simply doesn't care much what your platter is spinning at...😢 Would you be happy with this...❓👀 In the case of the Raven speed...the Feikert shows 3149.4Hz (0.6Hz below the correct speed of 3150Hz) against the VPI Direct speed of 3154.5Hz (4.5Hz above the correct speed of 3150Hz). Here is Harry Weisfeld talking about the vintage DD turntables in relation to his VPI Direct and he makes a valid point about the weaknesses of the arms often bundled with the old classic decks. Until you've heard a TT-101 with a really great tonearm (as you know)...and separate armpods are a great way to hear this.....you haven't really heard how great a table this really is...😎 And despite having 35 years of technological supremacy over the TT-101...together with the Thingap revolutionary motor which claims to possess zero cogging....Harry still can't match the performance figures of the big Victor...👀❓ |
Hi Aigenga In all fairness I am not a fan of armpods as I think they are a bit clumsy and add-on in my view as opposed to those being part of the plinth. Likewise forming part of the whole plinth/turntable just strikes me as a heck of a lot tidier and means that it can't be knocked out of the way so to speak. Armpods of themselves don't render a plinth as skeletal - likewise, one can be skeletal like the Rega (Naid I think) and not have a pod. |
Not a believer in magic - not even david copperfield? paul daniels? PB actually that's the kind of magic I assumed you meant. Let me qualify a little. I know this kind of 'magic" is all tricks deep down. Oh, oh.....sorry to disappoint anyone reading here that believes in it. (memories of telling my younger brother that Santa Claus was not real just went through me) Well, you did not hear it here..... ok ? I guess this kind of magic just doesn't register as anything memorable and lasting to me. I can't explain it. Maybe my career line of work has conditioned me in a certain way here. How about the Audio Foolery that happens in my/our rooms? I enjoy it greatly and can't live without it as an audiophile. but it is not magic. It can be recreated in other rooms by many others. But the music itself, which even when heard in your car and causes a reaction ...that is a bit of magic to me as a music lover. Now think about this one... how about a comedian? Someone that can go to a foreign country where they speak a different language, have a different culture and values. And then do a show that discusses the same, and makes them laugh in their own house. That..... IS a little bit of Magic to me. Two honorable mentions 4 lb small mouth bass on 2 lb fishing line. When the wife pulls my keys out of her bosom, and allows me to drive my summer car; Even though she makes me take her to go buy ice cream. PB If you can make this cold weather go away. hmmm.... Make it happen first, then I will let you know. |
Hi Parrotbee (PB) regarding those internet links I believe I found them interesting at the time for the material resonance values. that was it. that lenco is the only plinth(less) deck - A plinthless Lenco ? - well even I find that one a little funny. Very different beast than a DD or Belt drive TT. One way to do up a Lenco Jean Nantais believes more mass will only improve the sonics of an idler. His designs focus on high solid mass which leave space around the critical turntable parts. So when you see a JN lenco do not think it is solid all the way through, even though the thing still weighs 100 lbs. "a massive non-resonant structure with voids" in his own words Armpod void Motor void As you can see there are Voids "open space" all the way down and the bottom is open. Hope you and others find the pics useful ? PB - All said and done it's gonna be a mixture of theory and magic... Well I don't have a lot of patience for theory. At least for those that dwell on it with no follow up. I also do not believe in magic. Cheers |
As much as I enjoy reading purely hypothetical arguments about how arm-pods of substantial weight and with high co-efficients of friction will move due to stylus drag. I believe that there are so many possible movements in: the tone-arm and armboard, the turntable chassis on it's supports, the platter mat, the lp, and as we know changes in speed of the platter - that will all absorb that force to varying degree. Making the movement of the arm-pod theoretically negligible. And certainly negligible in reality (based on years of direct observation). What is imho the more important aspect of plinth vs skeletal - the absorption and propagation of vibrations deserves most of the discussion. I never understood the argument that the shelf becomes the plinth. The shelf is a constant, plinth or no. And, that shelf being anything from the flimsiest free-standing crud to ultra-sophisticated designs anchored to brick walls it is impossible to imagine a single statement of its' theoretical contribution. I just want to say that having run both plinthed and skeletal set-ups for many years my ears are on the skeletal design. My eyes, on the other hand, like a nice plinth as much as the next guy. But music being what it is I will run plinthless for as long as I have a turntable to do it. Halcro, I read your Feikert results just the opposite of your statement. The Direct Drive has superior numbers. Have you mixed them up, or am I missing it? |
02-13-15: Parrotbee Way back when I found these links helpful... Plinthbuilding Plinths you've probably come across them already.. imo - You need to tackle everything at the 50,000 foot level first. this would imply alot of research which you are doing - good From Timeltel's post on this thread. It would seem the first choice is that of tonearm, the remainder is a matter of tweaking for best outcome. My experiences agree with the Professors's statement. @Halcro, Lewm ....... maybe Copernican 2.......are you game ? I am definitely showing signs of cabin fever ....... |
Henry, Life is short indeed, and you're too smug to learn anything new. Instead of the snide remarks, I beg you to think about what you're saying when you say that the Timeline can show you whether your arm pod is moving or not moving. That's the only question we're debating, and I've spent enough effort to show you why it cannot. It can only show you whether your tt is running at correct speed (within its own limits to do that), or not running at correct speed. It cannot show the cause, in either case. But if you disagree, and you're really sure I am wrong, perhaps you can launch a logical response in lieu of sarcasm. I invite you, in other words, to tell me WHY I am wrong. |
Wide awake now Chris....👀 Now Henry can confirm better, but if I recall he said that the timeline on the Raven turntable moved; but that it moved slowly and consistently. This implied that his turntable although not right at 33.3, maybe a little above (line going --->) this way or below line going (<-----) this way, the speed was still stable. So for purposes of enjoying records - just fine. Is that right Henry or am I blowing smoke out my ears ?No smoke blowing here Chris....you got it..👍 In fact the drift to the left (indicating slightly less than 33.33rpm), whilst registering on the Timeline...produced this on the Feikert Platter Speed App. Compare that to the VPI Direct and you can see that the Raven measures better than the VPI Direct on the Feikert App whilst the Timeline shows its slight inaccuracy. Not quite sure what you're asking me for....❓ Before Basephysic's succinct Post...I had contemplated filming the Timeline on the Raven whilst I slowly pivoted one of the tonearm boards to demonstrate the laws of physics...but as can still be seen.....there are those who will develop their own 'physics' to explain away any evidence which collides with their views of the physical world..😥 Life is just too short...😎 |
Parrotbee, That's a rather subjective decision. You'd have to make two plinths, one with Panzerholz and one with acrylic and then do your own listening tests. However, if you're talking about all-acrylic vs all Panzerholz (no mixing of disparate materials), I personally would choose Panzerholz or some other hard wood. Acrylic in layers with other materials can be used to effect constrained layer damping, nicely. Basephysics, Perhaps you have some deeper understanding of how the Timeline works. I am not an owner of one, but I have borrowed one and long ago returned it to its owner. As I understand it, the Timeline is an idiot. It just flashes its laser(s) at a regular pre-determined interval such that if the platter is rotating precisely at 33.333... rpm, the laser "spot" on a nearby flat surface will not appear to move. In other words, the laser does not "sense" movement per se, it just flashes at a regular interval. If I am incorrect, please educate me. Now, if my understanding of the Timeline is NOT incorrect, then will you or someone please tell me how the Timeline can show us anything but the fact that the platter is or is not rotating at correct speed? If it only senses correct speed, how would it also be telling us about arm pod "movement", if such were happening? Let's say you put your finger against the side of the spinning platter, adding drag, and let's say that the Timeline continues to tell you that the speed is exactly correct. Does that mean you are not touching the platter, despite what your eyes and your senses tell you? "Arm pod drag" is no different from that. I should add here that I do NOT think that the very large, well constructed, and well thought out arm pods used by most of the arm pod aficionados is actually moving. Henry, for one, made some beautiful constructions that are very massive, and his shelf is not a sheet of ice in fact. This has devolved into an argument about hypotheses. As to "basic physics", Basephysics, you must be familiar with Newton's Third Law of Motion: For every action, there is an equal and opposite reaction. We all seem to accept the notion of "stylus drag". This is due to friction between the stylus tip and the vinyl groove. Correct? If stylus drag is real, then it stands to reason that the groove is also exerting an opposite force on the stylus tip which is in effect pulling on the tonearm. If the tonearm is mounted on an outboard free-standing arm pod, then the arm pod is subject to the theoretical possibility that it could be dragged by this force. (Again, I emphasize that I do NOT think this is a real world issue for a well built arm pod, until proven otherwise.) But in theory the arm pod might move. If this additional drag on the platter were to be overcome by the motor and servo so as to maintain exact speed, in spite even of the fact that the arm pod may be moving, then the Timeline would be oblivious to the whole thing. That's my point. The Timeline tells us nothing, zero, zilch about whether the arm pod moves or does not move, due to arm pod drag. The Timeline might be affected or might not be. It depends as always upon the tt motor and servo mechanism or other elements of the drive system. That's my story, and I'm sticking to it. |
02-12-15: Basephysics Henry.... time to wake up now. We need your help. We need you to pull a volunteer from your Victor "Armpod" team, and have him join forces with your Raven "tonearm fixed to the turntable" team. If he resists, tell him its in the name of Copernican good and the switch will be only temporary - maybe. Well "maybe" leave the "maybe" part out when talking to him. :^) Basephysics - that's quite the moniker. I'm intrigued again, as I was with Parrottbee our OP(Original Poster). Is physics your line of work, hobby interest area ? Now Henry can confirm better, but if I recall he said that the timeline on the Raven turntable moved; but that it moved slowly and consistently. This implied that his turntable although not right at 33.3, maybe a little above (line going --->) this way or below line going (<-----) this way, the speed was still stable. So for purposes of enjoying records - just fine. Is that right Henry or am I blowing smoke out my ears ? Alas I don't own the thing. Also fwiw - based on Richard Krebs train calculations I would be very surprised if any movement can be observed from what is a "normal" situation for that turntable setup with its fixed tonerarm. So I guess it depends on whether Henry is game to play for us to find out ? On a personal note very much looking forward to Timeltel (Professor's) next thread synopsis :^) Cheers |
Halcro and Dover are correct although both muddy the waters slightly. Halcro, by explaining the principles of structural forces necessary to move a sufficiently large armpod and Dover by mentioning the speed-correction circuitry of a DD turntable. Neither point is relative to the Timeline and a moving armpod. A moving armpod will be displayed by the Timeline on a belt-drive turntable and idler both without servo control. The mistake being made is concluding that the Timeline is measuring rotational speed. It is not. The rotational speed is pre-dialled into its algorithm so that the flashing strobe merely confirms any deviations. The Timeline device actually measures 'movement' to a microscopic degree. That is why it is able to visually display the effects of stylus drag as 'movement'. As Dover points out, in a closed-loop system, any movement of the dependent particles in relation to another will be displayed by a device designed to detect movement. |
Chris. We all have songs lurking in our past that in some way stay with us. Re the number crunching. The figure given was for a perfectly inelastic collision. If the collision was perfectly elastic the new train speed would be around 99.99996 KPH. 0.00004% speed reduction. It just goes to show that little things can influence big things, even if they are 10 million times lighter. cheers. |
Richardkrebs "The song, I got U BABE". Yes Richard, but I rarely remember the good ones after I wake.......the nightmares ....tend to linger. I Got You Babe the song has some significance for me. I was 3? at the time, but I can still remember seeing this on my parents little circular screen black and white tv for the first time. I believe their show made a lasting impression on me. I say this because when my wife and I got married we went away to Palm Springs. Sonny had a restaurant there. We made a point of having dinner there one night and having our picture taken with him. Charming fellow. We were saddened later, not sure now how much later it was now after we saw him, to learn he had died hitting a tree while skiing. Thanks for the number crunching. |
This armpod definitely moves That is a 50cms/dyne x 10 (-6) cartridge on a JMW 12 tonearm. Theoretically it has no business on this tonearm and in fact this cartridge was not playable (too high compliance) when it was played on the same arm on my full plinth TT. Just saying...make what you want from it. I believe the Symposium jrs, managed to sink resonances. The result here was music that was quite listenable. A long time ago. My son 16 at the time is the camera man and gave me all of 10 minutes of his time to put cartridge on and do the test. Could not find a needed cartridge bolt washer so I improvised. Pls excuse the crude setup of cartridge. I now realize I should of just set the camera on the armpod and left it there. |
Further to the aboveDid I just awake....👀❓ |
Further to the above 02-10-15: RichardkrebsA basic understanding of the physics involved would help. Halcro's TT is a direct drive Victor 101. This turntable employs active speed correction using servos. The error correction detection can only measure the difference in relative speed between the base and the platter - those who have studied engineering, physics and mathematics at university would recognise that this a closed system. The POD exists outside the closed system, and as such if the POD is moving, the servo correction cannot be correcting for this outside force as it is not in the measurement loop. Therefore if the POD is moving, theoretically, it would reveal itself in the timeline test. |
Timeltel, Who can disagree that the first choice is the tonearm? I certainly don't. But I think the controversy surrounds the question of how best to mount a given tonearm in relation to the tt proper, assuming a priori that the choice of tonearm was suitable. And I think we're talking about a pivoted tonearm, not an SLT. Should the tonearm at its pivot be firmly mechanically joined to the tt bearing/platter, or should it be mounted outboard on a separate "pod" for optimal results? So, has Henry actually listened to a version of either of his tt's wherein the very same cartridge/tonearm combos are mounted to satisfy the "firm mechanical connection" group of us? I really don't think he's done that. And even if he did, must we accept his subjective opinion as gospel? Like you, however, I agree that whatever floats your boat is just fine, for all of us. |
Regards, all: I'm quite impressed by the depth of experience reflected in the comments above. Except that Gibson fellow. He's a hack and prone to gross exaggeration. Viridian suggests that the removal of the tonearm from the plinth tends to remove plinth based excitations from the tonearm. Atmasphere proposes precise coupling of the platter bearings and tonearm base, LewM seems to agree. Richardkrebs writes: "A skeletal design makes this goal more difficult to achieve since we are introducing the support structure, shelf, platform, into the equation. It effectively becomes the plinth. Related to this is the minimization of joints and material changes in the platter-arm loop." Ct0517 (hi, Chris) shares this experience "An exercise of Function over Form for me. The tonearm attached to the POD is a leading example of this. If for some reason one "hears" a mismatch in resonances, the ET2 (tonearm) provides resonances tuning capability." Halcro: "I simply use my ears and listen to actual examples BEFORE I blindly theorise." Henry implements a tweaked wall mounted shelf and considers it a plinth. There has not yet been proof offered of unwanted movement in the spindle/pivot dimension but neither should one deny the possibility. These things are known for certain: The greater the mass, the lower the vibrational frequency. Beams (tonearms) with a lesser mass vibrate at a higher frequency. Vibration takes place when a system oscillates under the action of disturbance. A system will vibrate at one or more of its natural frequencies as determined by its mass and stiffness distribution. Friction, viscous damping and mass acting as a vibrational sink influence the decay and amplitude of vibration. Damping has very little effect on eigen frequency of a system but is of some importance in limiting the amplitude of resonance. These resonances are influenced by the different boundary conditions of a tonearm. Our concerns are complicated if a tonearm is viewed as a semi-fixed beam with a "lumped" mass (cartridge) at the end. Boundary (reflected) resonances are observed at edges, shoulders and at the junctions of differing materials. Boundary resonances have been measured at levels greater than the original disturbance. We are now confronted by Young's modulus, the Eigen frequency of the system, the mass of the tonearm and the interaction of boundary resonances, all of which are capable of interacting and consequently generating additional resonances. Voltaire wrote "Best is the enemy of better". As observed in the past, not all roads lead to Rome but many will. Neither is there a single avenue to the great city. It would seem the first choice is that of tonearm, the remainder is a matter of tweaking for best outcome. As Henry said, much more directly, "I simply use my ears and listen to actual examples BEFORE I blindly theorize." Peace, |
Chris. I re calculated the train thing. Assuming the following Make it a 100gm sticky snow ball traveling directly towards the train at 100 KPH, to make things easier. Make the train, 1000 tonnes, also traveling at 100 KPH The snow ball hits and sticks to the front of the train. The train will slow to 99.99998 KPH, more or less. I accept that I may have an extra or too many 9's Conservation of momentum. You did ask! Re the pivoted arm/speed question. It makes sense, since the arm is moving forward relative to the radial line for some of its travel across the record. "The song, I got U BABE". My dreams, shall we say, are usually more exciting in content. Cheers. |
Halcro let us know if you hear the song - I Got U BABE when u wake up ..... Lewm LOL - Good one Lewm. Learn something new every day. Kind of sounds like a new dance to me ? Ok everybody off your asses and onto the dance floor, Lets all do the arm pod drag .... You shuffle across the floor with the front leg leading (closest to the TT)).... the back leg dragging... |
Halcro, Timeltel et al I have a hypothesis that surely explains that my friend Richardkrebs may well be correct. The hypothesis is that Halcro has inadvertently fabricated the worlds first Smartpod, that self corrects any stylus drag by moving in and out relative to the record to null any speed variation due to stylus drag. |
I want to stay out of this discussion, because it's all been said before, but I wanted to point out, with respect to the argument regarding whether the arm pod moves due to stylus drag, that the mass of the arm pod, no matter how great, is not the major determinant of its being moved by stylus drag. Rather, the major determinant is the coefficient of friction between the base of the arm pod and the shelf. (Think, if the shelf were made of ice and the arm pod was of the mass of a curling stone [38 to 44lbs, according to Wiki], the pod would move easily.) I am not pointing this out in order to take sides in the discussion. I really don't care whether the arm pod moves or not, because I don't use an arm pod. Second, I must agree with Richard, the Timeline says nothing about whether the arm pod moves. It only says that IF the arm pod moves, the mechanics of the tt (motor/servo/mass of the platter) are such that the Timeline read-out is unaffected. For all we know based only on the Timeline, the arm pod could be swinging around the whole circumference of the platter as if tethered to the platter, and the Timeline won't tell us this is happening unless the motor/servo/platter is not up to overcoming the resulting drag (call it "arm pod drag"). This is as obvious to me as is the opposite view to Halcro. |
Simple argument. However minimal the force or friction in a cartridge we can and do have stylus drag. That being the case a pod not fixed will be pulled with the drag in the absence of an equal and opposite force. Whatever the theories I am not a pod fan due to the fact they seem mechanically clumsy. They can be knocked inadvertently and appear to be a bit of a pain to locate. Shoot me down if you disagree but I don't like the idea of a moving part not being fixed down in any way. |
Audiogon log - Feb 11 - about 9:30 am EST. Time has clearly moved I have been transported to the next day - but its the same cold dreary looking winter day. As I sit down with my morning JAVA instead of logging onto to Banks lifeline to see if money still exists to pay the pile of bills that are in front of me, I am compelled to log on here to see if time really has moved on. There, a phenomena has occurred - I have been transported back in time to the Copernican thread. I am feeling like Bill Murray in Ground Hog day But wait. It is a little different this time. Some of the people are still the same,; but some are different. And there is a difference this time. Yes, its there. A sense of humor among the players. There is hope. Base on this glimmer of hope instead of stepping away and going about by business I am compelled to add more to the madness. ******************************************************************************************* Halcro/Richard et al Well everything is indeed moving around me yet I am grounded to the earth, and even though It appears to be still, giving me a sense of calm, there are signs of movement all around. Sun position in the sky and its physical effect on my body temp. So this is real indeed. Back to the fascinating turntable which we must now break into its main parts to make my point. Firstly I don't own a Timeline and never will because its information is only measuring one aspect of record play - some info on the table speed itself. It is not providing data on how the stylus is moving/vibratiing. It is not providing data on tonearm movement (up and down, left and right as it tracks the record) Am I wrong ? Now Richard that was an interesting post you made. Way back in high school we were tasked with this question.. Looks like you are comparing linear speed versus rotational speed of a record player. Based on this formula linear versus rotational speed calculator lifted from the internet, are you able to do your calculation and tell us what the movement really is ? I was always terrible at formula in school. Here is a crazy thought... could this movement you are referring to, be temporary (out of shape movement) like when vinyl heats up when played, and they it cools down and goes back to form ? Hmmmm..... What do you think ? How else to explain that an armpod after extended time and play still rests on the same spot ? back to those bills soon. Just one more question. I will ask Richard but welcome comments from everyone. The record for sake of argument spins at constant speed 33.3 - 45 rpm. this means its outside speeds are faster, with bigger grooves to track. The inside ones, slower speeds, smaller tighter grooves, more difficult to track. My pivot arms have all made this clear to me - audibly. A CD solves this by varying its speed as it plays. The music starts on the inside groove and goes out. on the inside a CD can spin 200 rpm and as quick as 500 rpm as the laser beam approaches the outside edge. I can't measure this and take the experts word on it. Getting to the question. Richard, back more than two years ago now, your friend Dover presented what he called a POSER on the ET2 thread. I ask you how measurable is this movement you allude to; and can its effect on the music be considered the same as what follows. Maybe ....the human ear can't detect it - which would mean for this "audio hobby" it is irrelevant ? Help, my Pivot Arm is Running too Fast
OPINIONS welcome ? |
Halcro Let's say, just for fun, we replaced one of your very nicely designed arm pods with a block of foam rubber and we mounted the arm on it. The foam is just stiff enough to carry the weight of the arm. On your TT... This set up will play music It will pass the timeline test. Are you saying that this pod will not move?😊 Cheers |
Richardkrebs, The Timeline works by detecting stylus drag which is caused by friction. To make an armpod move via the stylus/tonearm it must be solely by the friction (stylus drag) which is your hypothesis.... You need to understand and appreciate things like the mass, density and the inertia of the tonearm pod. Then you need to understand the disposition of the centre of gravity of such an item and the shear stresses which need to be transferred through the cartridge/tonearm to the fixing plate to then be converted to a bending-moment force sufficient to overturn such a mass about its centre of gravity. Before any of that occurs....the frictional forces of the stylus in the record groove will have ground the record to a halt...and possibly into the dust... But common sense will make this obvious to even lay folk.... |
Richardkrebs, The timeline test is showing that your TT is working correctly but do you honestly believe that its servo has some sort of preview of the upcoming modulation and reacts predictively? Of course not, it REACTS to a slow down and corrects.This is what I mean..... You present not a shred of scientific evidence to prove what you say or disprove what the Timeline shows.... Yet you reach a positive conclusion stated with precise conviction.... I do not understand how the time line test proves that the pod is not moving? All it is measuring is the platter's speed.If this is true....I fear that you do not understand the basic physics of the question you pose..... |
Halcro. Ok to answer your criticism's of my posts Most DD TTs use a synchronous motor with some type of feedback or a non synchronous motor also with feedback. In each case, if all is properly functioning the motor is COMPELLED to rotate at the correct AVERAGE speed. It depends upon the drive design how it reacts at smaller time increments. I have witnessed this incremental speed change by proxy on a Goldmnud studio by scoping its power supply. There plain as day was a distorted view of the music that was currently being played. Clearly the PS was not stiff enough but that is not the main point here. There can be only one cause of this modulation of the power supply. The platter is momentarily slowing in sync with the music and the motor/ controller assembly is reacting to this by drawing more current to correct the speed drop. The timeline test is showing that your TT is working correctly but do you honestly believe that its servo has some sort of preview of the upcoming modulation and reacts predictively? Of course not, it REACTS to a slow down and corrects. These errors are happening in real time, but it's average speed is correct. The platters inertia alone is insufficient. I did these tests 20 years ago and they proved to me, back then, that stylus drag exists. Then their is the subjective test. A frequent comment from my customers who have had MK3's upgraded is that the speed stability is improved yet the MK3 passes the time line test. I do a lot of work on the speed sensing mechanism in the upgrade so this observation does not surprise me. We should not need remanding that our hobby is subjective by nature. I do not understand how the time line test proves that the pod is not moving? All it is measuring is the platter's speed. |
Then I discovered his own Apolyt table used armpods.LOL Chris...😃 Audiophiles are just funny (strange) people..... Even rational university-educated audiophiles can make claims and statements without submitting one shred of corroborative evidence..... And the sad thing is....these statements (or really beliefs)...are often accepted by the masses and treated with the same gravity as solid evidence-based science...😥 Take for instance Richardkrebs who the Professor (Timeltel) humourously taunts... Now I like reading Richard's contributions here and he has undeniably made contributions to the turntable playback system (particularly in regards to Technics SP10 DD decks)....but 1) Perfect DYNAMIC speed stability. No drive system meets this and passing the (in)famous timeline test is zero guarantee of dynamic speed accuracy, only average speed accuracy.here we have an educated, trained professional stating that a repeatable and accurate scientific test should be ignored because it does not tell us what occurs BETWEEN every record revolution.... All manner of inexplicable and unimaginable oscillations could be occurring BEFORE the laser flash of the Timeline hits the exact same mark EVERY revolution...👿 But Richard need not provide any evidence himself of such malicious oscillations.... The fact that he can IMAGINE them is good enough to spread doubt and discredit the only scientific device which was able to prove conclusively that Stylus Drag was a fact...in fact..👀 Emboldened by the audiophile armour of theoretical hypothesising.... If this heavily modulated force is sufficient to slow a weighty platter of considerable inertia, would it not also be able to "tilt" a free standing pod even, if it is substantial?He forgets that the very device which he disparages (yet which proves the existence of Stylus Drag)...is also the device which answers conclusively his unsupported questioning of the free-standing pod....for if there were any movement in the pod itself or the tonearm (as the Professor rightly reminds us)....the Timeline laser would unmask it mercilessly...😜 And so for once...justice is done...👍 |
Cool - I like parrots, and try to avoid bees, but understand their importance on earth. I remember going at it pretty good with Dertonarm on that Copernican thread. He made no sense to me at all. No sense of humor at all, and he was always arguing against armpods. Then I discovered his own Apolyt table used armpods. Henry, I'd insert some emoticons here showing utter amazement, but alas my Lenovo Windows 7 laptop is incapable of doing this. :^( |
Hi CT I just love Parrots and Bees - nothing too sophisticated about that. When I use my real name I have always had some bizarre report from Hong Kong telling me about starving children needing $1000 usd in 24 hours to a foreign bank account. Sorry for taking offence in the earlier post. I am also fiddling around with some cheaper DD's so I may experiment with other plinth materials - who knows - I only have so much time on my hands to potter around like a maniac |
02-10-15: Timeltel Hi Timeltel (professor) - I am a music lover / part time audiophile. If I have a question regarding cartridges, your posted opinions are the ones I look for. You are a cartridge expert in my view. Please excuse my grammar in this morning's post :^( |
