to be clear, i've never claimed any specific tonearm as best, only the 'best i've heard'. what i wrote; the very best arms i have heard are the Durand Talea 1 and Talea 2 in my system, in other systems, and at shows. i would also add the Continuum Cobra to these 2. i've heard the Cobra 5 different times at audio shows. i never said or intimated i'd heard most or all tonearms. i've heard quite a few if i include various shows. i did offer my opinion that i felt strongly that unipivots will turn out to be the ultimate tonearm design approach and stick by that. |
This is what I posted:
+++++ " Do you think that a bearing friction as low as 4mcg. ( like in the Technics EPA-100MK2 ) permit that ride-free condition?, IMHO certainly yes.
Which advantage has any unipivot against a fixed bearing tonearm like that one ? , IMHO none other than disadvantages: you speak of " the micro and nano wiggling ... " and is that micro/nano work the one that unipivots IMHO not solve yet. " ++++++ and this was posted by Hiho:
+++++ " The problem with unipivot is, obviously, not about lack of movement but TOO MANY planes of movement, " +++++
any tonearm designer is freedom to choose the pivot bearing type and this fact is out of discussion.
IMHO a unipivot design is the " worst " choice for a pivot tonearm because its inherent unstability that's a main subject to permit not only that the cartridge rides the grooves but that that same unstabilities ( in all planes. ) add minute distortions on the cartridge/tonearm quality performance ( I'm not talking here if you like or not those distortions, this is not the subject: what you like or I like has no importance here. ).
The first issue in a unipivot design is try to fix what can't be fixed and I mean fixed not almost fixed.
I asked: what advantages gives an unipivot/dual point tonearm against a fixed bearing design ( gimball, jewell or what ever )on that specific regards?, my answer is none but disadvantages.
Do you think that the cartridge ( at microscopic level. ) only moves in horizontal direction?, certainly not it moves in all directions and all those cartridge random movements only excited the unipivot unstabilities more.
Maybe you think that the side-weight, oil damping and weigth a top is enough to fix the problems in an unipivot but certainly no.
In the other side and this is my opinion as an audiophile: why choose an inherent faulty type pivot bearing and try to fixed when exist other pivot bearing types where you have to fix nothing?, makes no common sense to me especially that can't gives us any advantage even if its unstabilities are truly fixed ( ideal world ). So: in favor of what can we choose unipivots tonearms to achieve performance cartridges levels of excellence.
Yes, a cartridge quality performance level does not depends only in the tonearm bearing type and at " random " through the tonearm design could be that those unipivot unstabilities bearing inherent distortions on playback could be more or less hide, but still there.
A cartridge ask for a extremely fast tonearm response to the different movements ridding the LP grooves, you can imagine a race car in a circuit where stability on the road curves ( one after one after one all in different directions. ) is a must to have:
in the race car there are several parameters/factors/car build characteristics that help the car stay on the " road " it does not matters how " agressive " were those "road " directions changes " ( at high velocity where the driver has control on that speed. ) in the other side the cartridge/tonearm has no control over " recording velocities " and the cartrridge movements are at random: in a fixed bearing pivot tonearm the cartridge is secure because has no single " free movements in all planes " as an unipivot that can't recovery fast as need it/asked by the cartridge, those very tiny movements that styll exist on unipivots/dual preclude to attain what the cartridge asks in the same way and with the applomb of a fixed bearing tonearm type. A priori the unipivots/duals have no unstabilities because those unstabilities were already fixedbut dear gentlemans that " fixed " was at macroscopic level not where really matter that's at microscopic stylus tip ridding grooves.
To all that we have to add all the LP imperfections as LP's hole off-set and several waves on the vynil ( between others. )
If some of you with unipivots/dual and fixed bearings tonearms have a method/process to detect trhough real music LPs different kind of distortions then you can be aware of the tonearm bearing distortions between an unipivot/dual and a fixed bearing tonearm design because this specific subject. The added distortions exist but not easy to detect with out specific tests.
Now, from the point of view of what we like everything is 100% subjective and each one of us have different preferences on tonearms, but this is not the subject.
Of course that I can be wrong on the whole subject or maybe I could missed something but today this is my take.
Regards and enjoy the music,
Raul. |
I don't know why people get so worked up on this gimbal vs unipivot debate. Raul, you really take the cake. I have both kinds of tonearm and, again, I have no dog in this fight. I enjoy tonearm design and it's fun for me to think about these things but I'm no dogmatist. I maintain audio to me is a hobby not a religion. Let me start with the positives of a unipivot design. A tonearm needs to move in at least two planes, horizontally and vertically. A unipivot can do that easily with very little friction and no bearing chatter in a single fixed bearing point, which to me is a very nice advantage. It also forces the resonance to travel in one direction, into the bearing and into heat. But every rose has its thorns... It also by nature exhibits torsional movement that affects the azimuth during play. If all records are perfectly flat , perfectly same thickness, and perfectly centered, there should not be azimuth rocking even in a unipivot arm. The same with a car on a perfectly flat straight road then the car would not even need steering. Since records are not perfect, the arm has to hold the cartridge to travel the grove of mountains and valleys. In a "controlled' unipivot design that allows what Mike called some "wiggle room" is not necessarily a bad thing to some designer. Just like cars have suspension for uneven roads with the occasional bumps and nasty potholes. I am not defending this is exactly the case but I at least allow this possibility. In the quasi/pseudo-unipivot with non-compliant/rigid secondary bearing like the Cobra, Copperhead, and Vector, the "unstabilities" that Raul refers to does not even exist. Modern unipivot tonearm designers are well aware of the azimuth instability, hence the emergence of new breed of unipivot tonearms in combating this problem. They stick to unipivot because they believe the positives outweighs the negatives. All they did was to spend the time, resource, and effort into addressing the issues at hand. And what's wrong with that? Happy listening! -------------------------------------------------------------------- P.S. For a good read on the topic, let me quote passages from Dick Olsher's now classic review of Graham 1.5 tonearm from 20 years ago, that its points are still valid today. It starts with the role of the tonearm in an analog system to the Graham solution. Obviously Graham didn't solve all the problems with the original design otherwise he wouldn't proceed to design the Phantom. The perfect tonearm
The role of the tonearm has been compared to that of the enclosure in a loudspeaker. In this analogy, think of the bass driver as representing the cartridge. The first important point is that it is impossible to assess the driver's performance without considering its interaction with the cabinet. The cartridge/arm combination should be viewed in the same light. The arm's effective mass should be compatible with the cartridge compliance to produce an optimal low-frequency resonance. Just as enclosure wall flexure and resonances may color a speaker's reproduction, so can arm resonances influence the overall frequency-response and time-domain behavior. Arm resonances, both lateral and torsional, should be minimal and well-damped.
From the perspective of the cartridge, the arm is essentially a "monkey on the back." As the stylus negotiates delicate groove modulations, the cartridge has to literally drag this monkey, kicking and screaming, down the groove spiral. Bearing friction at the arm pivot, sufficient to impede the motion of the cartridge, gives rise to distortion because frictional forces along the groove wall increase as a result. Thus, low bearing friction is an automatic prerequisite for a good arm. For a magnetic, velocity-characteristic cartridge, the differential velocity between the stylus and cartridge body gives rise to the output signal. Should the arm rattle the cartridge, the signal's amplitude and the system's frequency response will both be affected. This can happen when the arm bearings are loose and "chatter." Unfortunately, for conventional bearings of the gimbal or ball-race design, the requirements for low friction and tightness (no chatter) are contradictory; some compromise must be struck between the two. In other words, the tighter the bearings, the greater the friction.
The dynamic behavior of the arm is critical to overall performance. Real-world records are eccentric and warped. Trying to negotiate such a record subjects the arm to lateral and vertical accelerations. By far the most serious practical problem is that of negotiating a small-radius warp. As the stylus starts to climb the uphill side of the warp, the cantilever is compressed upward, which may significantly increase vertical tracking force. This is bad enough in itselfincreased VTF accelerates record wearbut the cantilever may be displaced upward to the extent that the cartridge enters the twilight zone of nonlinearity: either because of suspension overload or operation in the fringe of the magnetic field.
On the downhill side of the warp the cartridge begins to lose contact with the groove. The effective VTF is reduced, which increases distortion, but the ultimate danger is that of complete loss of contact and groove skipping. What's required here is a nimble arm, dynamically able to keep the stylus in the groove while negotiating a roller coaster.
A figure of merit for assessing a tonearm's dynamic performance is the ratio of VTF to effective mass: the greater the better. This (with an important caveat) gives the maximum acceleration in gravitational "g" units that the arm can withstand before leaving the groove. The effective mass for the Graham arm is about 11 grams. Thus, with a VTF of 2.0 grams, the maximum safe acceleration is 2/11, or 0.18g.
What we have ignored so far in the dynamical analysis of the arm are the effects of damping fluid and arm-pivot restoring forces. Damping is normally applied at the pivot of the arm in the form of a fluid. Used in moderation, damping is a good thing. It is not a magic potion that will somehow convert a poor arm into a good one, but it does help an already good arm perform even better by reducing the "Q" of any resonances. Used in excess, damping can backfire by reducing the dynamic capability of the arm. Damping fluid resists acceleration and exacerbates the problems encountered by the arm while negotiating warps.
Another negative complication involves the action of restoring forces acting at the pivot. On some arms the pivot is located above the arm's center of gravity in what is known as a "stable static balance." The analogy suggested by Bob Graham is that of a high-wire artist balancing himself with the use of a large pole which bends at the ends to well below the plane of the wire. The pole confers stability by lowering the center of gravity below the "pivot point," in this case the artist's feet, thus opposing the decentering of the center of gravity. Again, this makes it more difficult for the arm to navigate warps. Once the arm is knocked out of balance by the warp, the arm attempts to steer back to stable balance regardless of what the dynamic situation demands.
The Graham Solution
Let's look at how the Model 1.5 addresses the various criteria for the "perfect arm," starting with the pivot design.
It may surprise some of you to find that Graham has chosen to go with a "unipivot" bearing. Nevertheless, a unipivot has a lot going for it: First, it is the simplest design. Second, it pre-loads the bearing surface to zero tolerance, and is capable of yielding the lowest possible friction in a mechanical design.
Bob sent me a videotape of a test he conducted where he pitted an SME IV against an undamped Model 1.5. Both arms carried the same cartridges and were statically balanced. Both arms were displaced vertically downward the same distance at the start of the test. The idea was to see which arm bobbed up and down the longest, as this would indirectly reveal the degree of vertical friction in the bearings. The SME pooped out after about 30 seconds. The 1.5 kept going for two and one half minutes before Bob stopped the arm for fear of having me fall asleep. He claims that the arm actually continues its pendulum-like motion for over five minutes.
Third, bearing performance does not drift out of tolerance, as there is nothing to adjust. Graham uses tungsten carbide for both the bearing cup and pivot. Both elements are said to be polished to stylus-tip tolerances. With a typical 7-9gm cartridge mounted on the arm, Graham calculates the loading on the bearing point to be in excess of 100 tons per square inch. With this sort of loading there is no play in the bearing to interfere with the transduction process. Finally, a unipivot design makes it easy to add damping fluid around the pivot point. Viscous silicone fluid (about 0.75ml) is used here to provide damping in both vertical and horizontal planes.
Older unipivot arms, such as the Formula Four, used stable balance with the pivot point well above the center of gravity of the system. In contrast, the 1.5 places the pivot point in the vertical plane essentially at the center of gravity of the assembly, hence in neutral balance. The pivot point is in line with the longitudinal axis of the arm tube, main pivot housing, and counterweight. Two outrigger weights are positioned to either side of the pivot housing and slightly below the pivot point to provide lateral stabilityotherwise the arm could tip over to one side or the other because it does not favor a particular rest position. The short lateral levers connecting the outriggers to the pivot housing create a strong stable balance along the line connecting them, thereby resisting torsional motion and keeping the arm in the correct upright position.
The outriggers manage to lower the center of gravity of the assemblybut only slightly in the vertical planeand the arm operates essentially in neutral balance with minimal restoring forces. According to Bob, if the arm is lifted a full 0.5" off the record, the generated restoring force at the stylus tip is only about 30 milligrams. Because the outriggers are so close to the pivot point, their effect on the effective mass of the arm in the vertical plane is minimal. However, they account for most of the moving mass in the lateral plane.
These same outriggers are used to adjust the azimuth. The weights are moved in and out along threaded rods that provide a precise and stable adjustment. A closer look at these weights shows that they are displaced from true perpendicular in reference to the arm tube. This is by design, and assists in preventing the cartridge from twisting while negotiating record warps.
_______ |
Dear Hiho: Things IMHO are really more complex that what you posted or to that DO review.
I like to " see " things not only more in deep but where things happen: stylus tip/tracking grooves. As I said what almost all people see as " solved/fixed " unipivot unstabilities are really only at macro level but not at micro/nano levels where the unipivot simple has no time to recovery to take and execute the next cartridge " order " where a fixed bearing design IMHO is the best " slave " and best friend the cartridge is asking for.
+++++ " the positives outweighs the negatives. " +++++, well IMHO a fix bearing tonearm design has no discernable " negatives ".
Btw, thw whole subject is not only azymuth unstabilities but any single one around in all planes.
Statements like this with out any objective explanation is in the best case a misunderstood on the unipivot bearing type behavior and is something like if I say ( talking on motion cars. ): " the cycles will be the way to go and the ultimate design approach and stick by that ":
+++++ " unipivots will turn out to be the ultimate tonearm design approach and stick by that. " ++++
why is that? what makes the differences sole by the tonearm bearing type?, here we can say: " hey I like it that way " and if said it: yes, why? and probably the answer will be: " I don't know but I like unipivots ".
I think we have to be or to take a little more serious our hobby or at least try or intent to understand it even if we like a different approach. Please remember that what we like is no important when we are talking in objective terms.
I'm not against Mike or other unipivot advocates I'm questioning that: " I like it " with out foundation in objective terms in that specific tonearm bearing pivoted design, with no single explanation.
Seems to me that for some of you this unipivot subject is the " today fashion " just like the 12" long tonearms that gives no real advantages ( but disadvantages ) to the cartridge ridding: just think that the cartridge needs extremely fast response from the tonearm that depends on the pivot and from the stylus tip distance to the tonearm pivot. A 10" tonearm has a faster response over a 12" ( everything the same. ): don't you think?, remember that a tonearm must works in favor of cartridge grooves ride as better and faster respond to cartridge needs as better that tonearm.
I'm not questioning that a cartridge/unipivot combination likes any one of us over a fixed bearing cartridge combination because this quality performance level depends on many factors where the pivot tonearm bearing type is one of those factors.
I don't know the whole method/process that Mike, you or any other person have to detect in a precise way distortions and to discern from where that distortion comes but I can say for sure that if we don't have that method/process to be aware about all what we have to say on the pivot subject has almost no validity other that " I don't know but I like it ".
I hope some of you have a better answer than that.
Anyway, I think that from my part was enough and in the other side the thread helps to know what each one of us " think " on the issue.
Regards and enjoy the music,
raul. |
As with most 'purist' audio concepts like 'valves vs SS'....'belt-drive vs DD vs rim-drive'.....'horns vs panels vs dynamic speakers'.....there is no one 'correct' solution or answer.
Rather, it is in the execution of a particular solution whereby a particular design may excel over another?
I have unipivots ( or dual pivots) like the Hadcock GH228, Phantom II and Copperhead.
I also have double gimbal bearing arms like the DaVinci 12" Ref Grandezza, Fidelity Research FR-64s and FR-66s and Micro Seki MA-505s and I have a double knife-edge bearing arm....SAEC WE-308.
You would think that if there were 'differences' inherent in the design philosophies of these arms alone...... they would be audible in side by side comparisons?
Apart from the Phantom II not liking high-compliance MM cartridges and the Hadcock not liking high-energy cartridges like the Titani, I find the differences between the various arms to be those of execution and quality.
There are far greater differences between cartridges than those between differently-principled arms IMHO. |
