This is a great resource for figuring out stuff like this: http://www.cartridgedb.com but this time I'll save you the trouble. Your cartridge has a pretty low compliance, even for a moving coil (10, compared to say Transfigurations at 15, or vdH at 30) and weighs 9.8gm. Your Sig TA has an effective mass of 9.5gm, which is borderline-low for such a stiff cartridge suspension. Here is the compatibility chart for your TA and cart: http://www.cartridgedb.com/resonance_from_arm.asp?adesc=VPI%20JMW%209%20Signature&amass=9.5If you read down the left side until you come to 10, the compliance of the te Kaitora, and then read across to the cart weight + mounting hardware column (figure 9.8 gm + 1.5+ gm for mounting bolts and nuts, total = 11.5 -12 gm) you will find yourself (barely!) in the 'green' zone at 11Hz, which is the natural resonance of your arm/cartridge combo. Lower (like 8Hz) would be better but you're SAFE for all but the wildest, loud, low-frequency tracking conditions! With a cartridge with as stiff a suspension as yours, you probably should not need any fluid damping at all. Even a slight amount could slow down bass transients. As for AS, line contact styli (like yours) develop very little friction in the groove because of their shape, and therefore the arm tends not to "skate" toward the spindle with any significant force. If you feel more comfortable, twist the wire until the floating arm just barely creeps toward the outside of the record and that will be plenty ;-) |
I actually do not use any with my 12.7 or JMW 9" arms. The amount suggested is often wrong and it is impossible to apply the correct amount all across the record. When I do use it I try to use as little as possible. Use Denon 304 on the 12 and 103 and AT OC9 on the 9". |
IMHO the wire on the Signature arm is to stiff for the twisting method to work. I use the VPI anti-skating gizmo with just a bit of anti skate applied and no twist of the wire either way. |
Thanks to all for the advice.............I have read that the damping fluid is ineffective unless it is actually in contact with the internal part of the tonearm that sits on the pivot point is this correct? Thinking about it...........this does sound logical, However, it contradicts most of the other comments I have read about damping fluid. |
In general - "skating force" is not linear. It is general with modern styli much less than it used to be in the 1970ies. Several respected tonearm designers (Pierre Lurne, Mortensen, ...) do recommend not using anti-skating at all and for good reason - applying a steady and linear "anti-force" upon a non-linear force is not a good idea at all......
Dampening - if you REALLY need it, the cartridge/tonearm match is less than optimal in terms of its mechanical parameters.
In general - less is more with both issues.
If you apply any dampening fluid, do use as little as possible and do use fluid which is NOT like honey but more like water......
If you apply antiskating at all, do set it as little force as possible - 1/2 of what is recommended by the manual will be enough and more than that.
The higher the VTF - the lower the antiskating ! |
Great posts that are spot on! |
Agree with all the above.
With regard to your question, on most unipivots that offer fluid damping in the bearing well, the fluid must actually touch the upper (movable) portion of the bearing to have much audible effect. Just damping the well isn't going to do much. I haven't played with the damping on a JMW, but if your well is tall enough to allow it, that's the right idea.
That said, I'd heed Nsgarch's sage analysis regarding damping with this particular cartridge/arm combo. Your bass and dynamics response are borderline now. Even a little damping might impair them noticeably.
Of course you could try it and hear for yourself. Just remember, once you've added enough fluid to touch the upper (free) part of the bearing, adjust in TINY amounts. Dertonarm's suggestion to use thinner fluid than what's considered normal makes excellent sense (again, because of your arm/cart combo).
|
When you lift your arm off the well you should see a string of oil coming off the tonearm base. That is if you want damping. I would suggest using the damping oil that came with your Scout. Again if you want damping. Use a syringe to suck out any extra.
Anti-skate is arm/cart dependent- try it with your set up to see what is best. With my VPI 9 arm twisting the wire was perfect, with the VPI 9 Mem arm it is not. |
Hi,
The lemo connector has a small amount of anti-skate bias, even when not twisted. Twisting it (counter-clockwise, I think?) will increase the anti-skate force.
I experimented with the anti-skate on this arm, both via the lemo connector and the anti-skate assembly. The difference I heard was minimal. I only heard a noticeable difference when way too much anti-skate was applied. The soundstage moved off-center and the sound became smeared.
I currently use the optional anti-skate with no weights on it. It makes no difference that I've ever been able to hear consistently, but it tracks the test record better and so I would assume it's probably better in terms of groove wear.
The great improvements I've made with this arm were the result of a) dialing in VTF/VTA, and b) nailing the alignment with a Mint LP protractor.
I've never tried using the damping fluid. Just seems too messy.
Regarding Srwooten's post, if you don't have a syringe handy, a Q-tip works too.
Cheers.
Tom |
Skating force is a 'twisting torque'. It occurs only in tonearms that have an angular offset built into them to help minimize tracking error - making it zero at two points across the record instead of one point (which would result if there were no offset.) The amount of the skating force is the result of the friction force (or drag) of the stylus in the groove times a lever arm. The length of this lever arm is the length of a line drawn from the stylus, pependicular to the axis of the cartridge, to the point where it intersects at 90 degrees with a line drawn through the pivot of the tonearm. Since this relationship remains constant, regardless of the stylus' position on the record, the skating force remains essentially constant across the record. I say 'essentially' because there is some very minor variation in the force-of-friction as the velocity of the stylus-in-the-groove slows down toward the center of the record. ANTI skating force, when applied with a spring, can be made to compensate for this (VERY slight) variation, as in SME arms. However, the weight-on-a string method or the twisted-cartridge-leads method will work just fine. Whether AS has an effect (or not) depends on the design of the cartridge. Stiffer suspension material and/or lower VTF reduce the need for AS. Further, the larger the size and strength of the magnetic field in which the coil is immersed, the less AS will make a difference/improvement.
Increasing the VTF will ALWAYS increase the skating force/torque because increasing the VTF increases the friction of the stylus in the groove. The fact that line contact styli produce so much less friction (compared to conical and elliptcal styli) is why moving coil cartridge makers (using line-contact styli) are able to use higher VTF's and stiffer suspensions necessary for the generally superior performance of MC cartridges.
With MM cartridges the situation is reversed. True they customarily track at 1/2 the VTF of MC cartidges, and many of them now employ line contact styli. However, because of their extremely compliant suspensions, it's easy for just a little skating force/torque to pull their tiny magnets out of alignment with the field coils.
. |
Thanks again for all of the comments.......much appreciated.
Tom,
When you set the vta was it done by sight i.e. with the lined card as suggested by vpi, or by ear after this and If you turn the vta wheel clockwise does this lower the arm? I am currently on my second Mint...the first one cracked as I was taking it off the platter spindle. |
Skating force is a result of the offset of the polished area of the stylus in perspective of the groove wall. During the journey of the tonearm cross the record side this offset becomes zero 2 times - the zero tracking error point - and is depending on the tangential error angle (which changes all the time - becoming more and less again during the journey from and towards a zero error point).
Less derivation from tangential zero error = less skating force.
Skating force too is influenced by misalignment of the stylus in the groove and - to a VERY high degree - by the total contact area. Larger contact area (= modern line contact) is far less force on the groove wall with a given VTF as the skating is a by-result of VTF divided through contact area.
In summary:
- less derivation - offset - from tangential zero = less skating force.
- super precise vertical alignment of stylus in groove = lower skating force.
- larger contact area of stylus = lower skating force.
- old - conical or elliptical - stylus = higher skating force compared to line contact or similar.
MOST IMPORTANT: skating is NOT linear, but a force which gets higher, lower, zero and higher again.
Trying to compensate such a force with a linear anti-force is......... well....... no good idea.
"Correctly applied" anti-skating would fix the problem in 2 short moments of the record side and produce a new problem for most (98%...) of the rest.
Then there still is the (objective and empirical by observation ...) "fact" that most tonearm/cartridge- combo featuring very high VTF (2.5 grams +) do indeed produce LESS skating force .........
Thats why Ortofon did not care for antiskating at all in its 12" tonearms w/SPU cartridges and why my FR-66s runs smoothly w/ FR-7fspec. without any anti-skating....... |
God bless America. Dertonarm has a right to express whatever ideas he feels are true ;-) and on any subject. Besides, they say laughter is the best medicine. So I say 'Good luck' to him! |
Indeed - God bless america.
Especially so in our troubled times.
Thanks to him, that not all americans always go for the most simple model in everything......
In this sense - good luck to Nsgarch too. |
|
Hi Wes,
When I set VTA, i did it by ear only. Didn't even look to see if it was parallel. It's pretty easy to hear when you've got it right. The sound kind of pops into focus. Bass and treble become balanced. Bass is taut, not sloppy. Treble is clean, not strident. When you're off, either bass (too low at the tonearm base) or treble (too high) will dominate and exhibit the sloppy/strident characteristic.
Later on, I saw a post here recommending the 3 x 5 card method (Thanks, Stan). I tried it and found that my arm was exactly parallel to the record surface.
I haven't done it in a while, but I thought that turning the VTA wheel clockwise raises the arm at the pivot point.
Cheers. |
Thanks for that Tom............ |
Dertonarm has stated the facts as I have always heard them. If it was that easy to apply the correct force then why, for example. did the Grace 707 bias control give twice the necessary force? It was a well designed arm. I have never heard that a given amount of bias compensation would be correct all across the record, the setting is always a compromise. That said, the compromise I chose is not to use any. |
Stanwal, first of all the Grace 707 is a vintage tonearm calibrated for MM cartridges, not MC which require far less AS. The rule of thumb in the MM days was that the AS should equal the VTF, and even at that, how much sideways AS force (in grams) was applied was definitely NOT the same as the actual weight on the string. Skating force is expressed as torque (foot-pounds, or centimeter-grams in the case of tonearms) and is the product of friction (in grams of drag) TIMES the (virtual) lever arm created by the tonearm offset, in centimeters; and is easily calculated if you know the amount of drag of the stylus in the groove (admittedly hard to determine without proper instruments ;-) The lever arm length is a result of the tonearm dimensions and offset angle. Those two factors don't change, regardless of where the tonearm is positioned. To be fair, the amount of groove friction actually CAN change (but only very slightly) between the beginning and end of the record as a result of the slignt difference in linear velocity (the speed of the groove under the stylus) between the outside and inside grooves of the record -- not enough to make a significant difference in AS force required. I suppose if one wanted to get REALLY nit-picky, one could also mention that louder passages produce more friction than softer passages. But that's pretty much it in terms of the causes of skating force (torque.).
With all cartridges except those with the stiffest suspensions, as long as you can see the cantilever from the front of the cartridge, it's quite easy to set AS force visually. I always did it that way with my MM Shure cartridges. You just lower the stylus into the groove while watching the cantilever from the front. If it deflects to the right (relative to the cartridge body) you need to add AS force. If it deflects to the left, AS needs to be reduced. No deflection of the cantilever when the stylus hits the groove means the skating force is balanced out. It could also mean that the skating force (even without AS applied) is not enough to alter the relationships in the cartridge's generator (usually because the suspension is stiff enough to resist the skating forces) and so you would HEAR no difference with or without AS applied. Nevertheless, with no AS applied, the inner groove wall of the record would wear faster than the outer groove wall ;-)
. |
Nsgarch explanations are based on the original patent description of skating force and the anti-skating applied. And its too is not a matter of MM-cartridges vs MC-cartridges. Their different basic mechanical characters do contribute some details to the behavior, but not essentially so.
This general patent description from over 60 years back - while not entirely incorrect - is an incomplete model and is simplifying a quite complex issue. All anti-skating devices designed for tonearms are based on this patent description and a simplified model which gives the impression that skating is a constant force which can be nulled with a correct applied counterforce.
Well - it is a neither constant nor linear force and it is depending on tonearm length (with the resulting offset being more or less depending on effective length), stylus shape, size (especially so by older elliptical/conical styli, which do create a "double-side-contact" towards the inner grooves! )and alignment, groove cut, VTF, groove-compliant VTA and tonearm geometry aligned for (2nd zero close to inner grooves give another benefit here... see our sadly deleted tonearm geometry thread from early summer...... if you saved it in time).
As I said before - this is NOT a simple model.
I still believe that it is rather smart not trying to counter a highly variable force with a constant applied anti-force. It is obvious, that there are only very few seconds of the 20-35 minutes of a record side in which the counter-force is really correct and nulling the skating force of the moment. During the rest of the time the anti-skating applies a more or less unwanted side force of its own - just going in the opposite direction.
With the standard "skating vs. anti-skating"- model we have a model which is incomplete and the consequences drawn from it were wrong.
We would need a variable anti-skating force based on the tangential curve of the given tonearm. This antiskating force would then be inverse to the tangential curve and would indeed null the skating force if properly aligned.
Several questions in tonearm geometry today are long set aside as "complete", but are based on models which were simplified and as a result of this simplification did not give the correct results.
But so far we are living with these - less than optimal - results.
Partly due to laziness, lack of knowledge, partly ignorance (this is not meant to offend anyone !!), partly ease of use. |
Dertonarm, my explanations are based on the Laws of Mechanics introduced by Sir Isaac Newton July 5, 1687, and which remain true and in use to this day. You can point to all the little nuances which you assert would have an effect on the basic design, but they are so small as to be irrelevant. You seem to want to make things as complex as possible, which makes any useful solution impossible of course. Nonsense!
As I said before, I have no problem with your expressing your ideas, but remember, without any scientific proof or technical underpinnings, that's all they are: thoughts, and whimsy ;-)
Anti skating in it's basic form is a very useful concept, if only to prevent uneven record wear and reduce surface noise in the left channel. To those who think anti-skating is of no value, or just TOO COMPLICATED to implement (dear, dear!), I say, "don't worry, be happy" or better yet, get a 16" tonearm with no offset ;-) |
Newton would smile.....
Again Nsgrach - your simplified model does not meet reality.
It is obvious and a simple fact that the skating is altering - ever seen any skating in the zero point ?
The offset is changing - and so is the amount of skating force.
You are calling for simplicity - this is a very simple fact.
Where is your problem ? |
HP speaks on Oct. 3, 2009: A lot of systems don't sound like music," said Harry. "They sound like hi-fi. When I go to Carnegie Hall, I sometimes close my eyes and try to pretend I'm listening to a hi-fi system, so I can see what I'm missing." Some of the great designers continued to issue great gear even as their hearing declined with age, because they were designing to what they heard in the concert hall. Hence the importance of a life reference, the experience of acoustic music performed in an excellent acoustic.
Harry also reminded us that his magazine was the first to hire women reviewers, and that women's hearing is superior in the crucial 48 kHz range. One of the very few women present (were there more than two?) then spoke, noting that she had to flee a number of rooms at RMAF because the sound was too bright. I wonder if she saw me asking people to either turn the music down because it was too piercing, or following in her footsteps and making a quick exit It is always the same: When you don't understand what you hear...but even HP can't change it anymore. |
NSGarch:With all cartridges except those with the stiffest suspensions, as long as you can see the cantilever from the front of the cartridge, it's quite easy to set AS force visually. I always did it that way with my MM Shure cartridges. You just lower the stylus into the groove while watching the cantilever from the front. If it deflects to the right (relative to the cartridge body) you need to add AS force. If it deflects to the left, AS needs to be reduced. No deflection of the cantilever when the stylus hits the groove means the skating force is balanced out. It could also mean that the skating force (even without AS applied) is not enough to alter the relationships in the cartridge's generator (usually because the suspension is stiff enough to resist the skating forces) and so you would HEAR no difference with or without AS applied. Nevertheless, with no AS applied, the inner groove wall of the record would wear faster than the outer groove wall Although I don't profess to have anywhere near the expertise in these matters of several of the protagonists in this thread, Neil's statement above seems to me to be the common sense bottom line, regardless of the fact that any anti-skating setting will be a compromise to a degree that will vary with position across the record. NSGarch: The Grace 707 is a vintage tonearm calibrated for MM cartridges, not MC which require far less AS. The rule of thumb in the MM days was that the AS should equal the VTF, and even at that, how much sideways AS force (in grams) was applied was definitely NOT the same as the actual weight on the string. FWIW, I have over the years used several MM/MI cartridges on multiple turntables and arms (mainly a Grace F9E Ruby and a high output Grado Reference Sonata on a SOTA Sapphire with Magnepan Unitrac tonearm), and using the visual alignment method I've consistently found that the optimal setting was about 2/3 of the setting recommended by the tonearm manufacturer for the particular vtf. Regards, -- Al |
Al, thanks for the reinforcement. You obviously have more insight/experience than you want to claim ;-)
Tonarm, I really have nothing further to say to you ;-(
Neil |
Hi guys,
this developing argument reminds me somehow of what Søren Kierkegaard (19th century Danish philosopher) who once said: "If you get married you'll regret it, if you don't get married you'll also regret it, and if get married or do not get married you'll regret it.
Oh, he also said: "If you hang yourself you'll regret it, and if you don't hang yourself.... :-)
Now replace 'anti-skate' for the 'married' or 'hanged' bit, and see what it looks like...
I'd say: you regret it :-)
Greetings,
Axel |
Nsgarch, I have no idea where you got the idea that the Grace was used with MM cartridges, it was sold as a package with the Linn LP 12 and Supex cartridge in England and I sold it with the 901 Supex over here. I also have no idea where you got the idea that MM and MC required different settings, I have followed the literature since the early 60s and never heard this. We are talking about a mechanical system here, how does the physical force pushing the arm know whether it is a MM or MC. Could you tell me where you got this idea? I have sold tables and cartridges for over 30 years and I never saw a mention of different compensation for MM and MC by any manufacture of either MM or MC. It was also applied SOELY on the basis of tracking weight, the test I quoted simply said that the bias force was off by a factor of two. This test was done by people whose knowledge of the subject far exceeds that of either you or I so you have either discovered something unknown to others or only true in your universe. Otherwise I would think arm manufactures such as SME would make some mention of it. |
Stan, the tonearm manufacturers are indeed now catching up with the essential differences between MC and MM cartrige requirements. Or to be more specific, the difference in the tonearm settings required by cartridges with line contact styli and previous types of styli. One example of this response by manufacturers is the SME IV.V which is made specifically with MC-with-line-contact-styli in mind. It's like an SME V, but comes without silicon damping (unnecessary for MC cartridges' stiff suspensions) and without hairspring VTF adjustment (also unnecessary for cartridges tracking in the 2 gram range.) Further, no current manufacturer of quality tonearms is silly enough to assert that the user just blindly set the antiskating force scale indicator to match the VFT setting. They all know better by now ;-)
As I indicated previously, the reason MC cartridges, or more accurately, cartridges with line contact styli, require so little antiskate compensation, is because they create so little skating force to begin with. Simply put, for each gram of VTF, a line contact stylus "drags" in the groove just a fraction of the amount that a conical or elliptical stylus would. And since 'skating force' is a product (read: multiplication result) of stylus friction drag TIMES the length of a (virtual) lever arm which is created by headshell offset angle. Therefore, lower stylus drag produces less skating force with a given tonearm.
If a tonearm has no headshell offset angle (like some of the old 12 -16 inch transcription tonearms) then no skating force is produced because there is no (virtual) lever arm for the stylus "drag" to act upon. However, with long tonearms, you still pay a small price in increased tracking error and a big price in tonearm resonance and inertial momentum (the tonearm wants to keep going UP after a record warp ;-)
If you want to have your cake and eat it too, get a linear tracking tonearm - no skating force, no tracking error, stylus rake angle (SRA) adjustable while the record is playing - and they do sound fabulous, I've had one. BUT, they ARE a hassle, needing (usually) an air pump, and constant checking. Or, as you might also remember from the 60's, the goin' up just ain't worth the comin' down! |
Dear Stan, you are of course right. We have seen - and still have... - MCs with VTF around 1.2 to 1.5 (v.d. Hul among others). MC do NOT have ad decretum lower compliance than MMs. The skating force is - among others - a result of VTF, offset of the stylus towards the groove wall and total contact area of the stylus. Its becomes less with increased effective length and resulting decrease of tangential error. It is null at any zero error point and becomes more and less with increasing tangential error and decreasing to wards the next zero point.
Simple model.
The force is never constant - and should therefor be addressed by an inverse force which is itself variable in conjunction with the tangential curve of the given tonearm.
Not really complex - it just needs more than a plain stupid constant anti-force.
But nothing in our days is so clear as not to be neglected and denied by some.
I am positive that maybe Raul in his new upcoming tonearm-design will address this issue.
Of course we can always simplify things and we see a strong movement in this direction ever since the last 2 generations.
Why ?
Because it makes things cheaper to produce.
More profit made - less brain needed.
Simple story indeed. |
Stan, the Supex cartridge(s) you specifically refer to, have elliptical styli. In fact, Supex makes cartridges with either spherical or elliptical styli - no line contact styli! AND they all have medium compliance suspensions, and some even have high compliance suspensions, just like most MM cartridges. Add to the elliptical stylus, a recommended VTF of 1.8 gm and you have a recipe for high skating torque. So from an anti-skating adjustment point-of-view, those Supex are indeed more like MM cartridges. So I think you need to do your homework before making general assumptions like you did.
I also think it's a bad idea to assume, as some others here do, that there is such a level of complexity at work in this situation, that all efforts at resolution are hopelessly doomed. If one understands the basic forces at work, and especially their overwhelming magnitude compared to the little molehills some want to make into mountains, (to prove how smart they are?) it's really a simple matter to cancel 90% of them out. If you want better than that, as I said, get a straight line tracking tonearm.
As for implementation, would you rather have a 'simple' German car or a 'complex' British car? Hmmmm . . . . . ?
. |
Dertonearm,
I do not understand why you assert that skating force is "null at any zero error point". If you're saying that skating force is null at points of zero tracking angle error (e.g., at the Baerwald or Loefgren points), that is simply untrue.
Skating force exists ANY time the axis of the cantilever is not aimed directly at the pivot point of the tonearm. Therefore, EVERY tonearm with a fixed pivot point and an offset cartridge mounting angle encounters skating force at all points that the stylus is riding on a spinning record.
Don't take my word for it, and let's not argue theory. Just try this simple experiment: find a record that's ungrooved (flat) at the null points of your particular alignment scheme. Set A/S to zero, spin up the record (the faster the better) and drop the stylus at one of the null points.
Unless you're using a linear tracker or a pivoting arm with no offset angle I guarantee it will "skate" inward.
Once you've performed this simple experiment you will revise your theory, because it doesn't meet observed phenomena.
If I've misunderstood your assertion, please explain in other words if you can. I fear your current assertion is potentially misleading for the less experienced.
|
Dougdeacon...you're correct, but anti-skate decreases with velocity so that it becomes less and for all practical purposes, pretty much zero at the end of the LP. That being said, Highly modulated sections of the groove will create more skate than quiet sections all through the record. ...just clarification...I'm sure you know that. |
Hi,
anti-skate force is a ~99% function of the OVERHANG!... have I been missing something?!
Without overhang, no vector force, no skating force.
If you had "underhang" you'd create a vector force once again, but it is not of practical interest other then in the consideration of the vector forces.
Axel |
Dear Doug, lets not mistake the torque tension force (which is indeed a result off the offset angle at the headshell) or the J-/S-shaped form (featured on tonearms with detachable headshell) common on most pivot-tonearms (and seldom addressed....).
As many (not all) a tonearms do not feature any lateral balance device at all to counterbalance the torque tension of its armpipe, these all too often do indeed produce a movement on a plain record.
I have performed the test you suggested several times.
With my 12"+ tonearm and a cartridge with Q4-capable stylus the tonearm (... with correct applied lateral counter-balance and on a dead level TT) sits still (no inward move) at the 2 zero error points of the tangential curve.
Am I missing parameters?
Pure luck ?
Coincidence ?
Correct model ?
Whatever......
Fact is - as a selected handful (precisely...) of the bavarian routed A'goners do know very well - that sibilant distortion, inner groove distortion or "wandering images" are non-existent on the front-ends set-up by me.
And no - these aren't all FR-tonearms, but do include DaVinci, Kuzma 4P, Graham, SAEC, Micro MAX, Triplanar (to name the better of the pivot-designs).
9" to 12" which - by the way, Axel - can not really be distinguished in groups by their overhang.
And yes - exactly - what would we prefer?
A "simple" (but precisely designed and engineered - all too often forgotten as we are so accustomed to it - german car or a "complex" (....complex ? where ?) british one (and - oh, sorry - is there still any major british car brand NOT owned today (and improved in terms of reliability and performance by its new owner) by either BMW, Audi or VW .... Jaguar is owned by Ford isn't it?).....?
And yes, I know that the japanese cars are even more reliable - fact is that I still prefer 2-3 japanese born tonearms (which by the way did address the issue of torque tension producing lateral movement...) above any german designed tonearm. |
Stringreen
That is not correct, stylus friction follows the classic Amonton law so the friction is independent of velocity. This can be confirmed by a modification of the test Doug Deacon used to demonstrate that Dertonarm's idea was completely false.
Using your blank disc and having satisfied yourself that skating has nothing to do with null points, set the antiskate on the arm so that the arm remains stationary at 33 RPM. Now change the speed to 45 RPM and observe the result.
Axelwahl antiskate is properly a function of offset not overhang.
Mark Kelly
|
>>10-12-09: Stringreen
10-12-09: Stringreen
Dougdeacon...you're correct, but anti-skate decreases with velocity<<
Wrong again stringbean.
Mark Kelly has it right.
As does Nsgarch. |
Dear Mark,
use your test, whereby the tip of the stylus only touches the vinyl.
The contact area thereby sees no off-set, and simply assumes the shortest point between contact area and pivot = one of the vectors. Overhang to the spindle is creating another sector, with the spindle to pivot a third.
Thereby off-set is not involved, yes?
Axel |
another *sector* should of course read: another *vector*... |
Of course my idea is wrong.
But that is always the case.
After we have agreed upon that and set it aside, maybe someone is willing - or not..... no problem (at least not mine) - to visualize what is actually happening aside from dogmas, simplified models, laws (which aren't what they used to be either) and small hills which became mountains (ever seen the nice movie with Hugh Grant who climbed up the first and came down the later?).
With all those clear models around, I really wonder why there still are so many complaints and discussions about inner groove distortion, off-angle cantilevers, wandering images and sibilants which pierce the ear.
With all those great anti-skating devices around.
Strange. |
Axel,
Try your experiment using a pivoting arm having zero offset angle (like a transcription arm). Provided the cantilever is aimed correctly (i.e., directly at the pivot point of the tonearm), skating force will be zero. This will be true regardless of overhang.
Skating force is generated when we mount a cartridge at an angle in the headshell such that the cantilever is NOT aimed at the tonearm pivot (in a word, offset). Overhang has nothing to do with it.
Using that transcription tonearm (which has zero offset by design) you could still create an inward skating force by mounting a cartridge at an inward angle, just as on a regular tonearm that has built in offset. You could even create an OUTWARD skating force by mounting the cartridge at an outward angle. Again, you could do either of these regardless of overhang.
|
Axelwahl
You are assuming attitude is important but it isnt.
Consider the frame of reference of the tonearm with its pivot point as the origin and the arm lying along the y axis. The stylus frictional reaction force vector runs directly from the stylus tip in the direction of groove motion. The restraining force vector runs directly from the stylus tip to the tonearm pivot. The sum of these two vectors is the net force on the stylus.
The angle between the groove tangent and the x axis is the true offset angle. The stylus reaction force vector can be resolved into x and y components equal to its magnitude multiplied by the cosine and sine of this angle respectively. Since the x translational degree of freedom is constrained, the sum of forces in the x direction must be zero so the restraining force must be equal to the x component of the stylus reaction force vector.
For the y translational degree of freedom also to be constrained (eg the stylus not skip out of the groove) there must be a force which balances the y component, this force is either supplied by a reaction force on the groove wall or by antiskate.
IFF the force is supplied by reaction against the groove wall then the fact that that reaction force is not purely in the Y direction creates complexities but we can assume that the arm has been designed by someone who knew what he was doing so it has antiskate therefore we can ignore this: designing a pivoted arm with no antiskate is prima facie evidence of incompetence. The antiskate can be applied as a torque to the arm pivot or a force to a point somewhere on the arm, its all the same as long as the vectors resolve.
The argument from attitude rests on a falsehood which is that the stylus frictional reaction force somehow depends on the attitude of the stylus to the groove wall. A misalignment of say 10 degrees would result in a displacement betwen contact patches of about 25 microns for an elliptical stylus 7mil across, for a spherical sylus there would be no displacement at all since the contact areas between a sphere and a plane are always normal to the radius of the sphere.
This torque arm would result in a torque of about 0,5 uNm at 20 mN VTF where the actual skating torque is around 1mNmm, a difference of 2000 to one.
The issue which Id like to resolve is that of the influence of stylus shape. Amontons law for rigid bodies breaks down if one body is much softer than the other, which is definitely the case with vinyl and diamond. The breakdown takes the form of a pressure dependent coefficient of friction; the coefficient decreases with increasing pressure this seems counterintuitive but think about a car tyre: wider tyre, lower pressure, better grip. Since elliptical styli have greater contact pressure than spherical, the friction will be less for them and this was reflected in many tonearms having separate scales for elliptical and spherical styli back in the day. Check the owners manual for the Torens TD160 mk2 for an example. Since a line contact has, by design, a larger contact area the skating force should increase not decrease as our befuddled friend supposed.
Mark Kelly
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Hm,
I still don't get it, call me stupid alright :-)
Put any (hypothetical) 20, 60, 90 deg. off-set angle on a POINT contact only stylus (I'm not talking distortion right now) just spinning on a blank vinyl -- what effect will you notice as long as the point contact to pivot would be the same?
No difference at all is what I stated earlier.
(no 'spade' is getting dragged through some sludge or a groove at this test!)
The stylus' point, sliding over smooth (no groove!) vinyl, will want to align the arm wand in a straight line *pivot to centre of rotation*.
Now increase the over-hang and then what happens?
The more overhang, the longer the frictional force's lever. It will pull the arm wand harder in line (pivot to centre pin) = more skating force? I think so.
Or no change at all? I do not think so.
In deed, what means off-set angle with regard to a 'round' point (contact stylus tip) any way?! - as long as the over-hang length is not affected?
Axel |
Doug
I find your argument a little confusing. If one did as you say and merely twisted the cartridge in the arm while keeping the alignement of the arm WRT the groove tangent the same, you would create very little force, as my post above explains.
The force you do create would be because the cantilever was bent out of alignment and the suspension is trying to force it back. This force is very small compared top the true skating force and with good alignment it is even smaller.
Mark Kelly
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Oops
The Xs and Ys are reversed. Consider the arm lying along the X axis with the Y axis pointing down and it comes out right.
Sorry about that
Mark Kelly
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Mark: I'm interested specifically in what your thoughts are on antiskating as it relates to stylus profile.
If I'm reading you correctly, elliptical styli should require less antiskate than spherical and line contact should require more than elliptical-please correct me if I'm wrong and misunderstanding your post.
Despite all the reading on (in theory) how little antiskate may actually be needed, I've found that my Denon 103R (with its stock spherical stylus) sounds best with an antiskate setting that is very close to the 2.6 gram tracking force.
I'm in the process of having another 103R retipped with a line contact stylus and am curious as to what, if any, changes I may have to make with antiskate when that cartridge comes back. Would you expect that, like the stock 103R, one retipped with a line contact would require antiskate set to approximate tracking weight? Thanks in advance. |
HDM
The reason tonearm manufacturers put a scale on the antiskate corresponding to VTF is that the skate force is directly proportional to VTF, not that it equals VTF.
The constant of proportionality has already been factored in and the manufacturer based this on "average" vinyl composition and a typical contact area.
The difference between your old stylus and your new stylus will depend on the degree of polish on the diamond and the actual area of the contact patch. Note that with line contact styli the actual area changes with VTA so VTA and antiskate interact. BTW This is the only rational explanation of the effects of VTA I know of.
This also shows that even if one confines onesself to the realms of actual verifiable physics the situation "on the vinyl" is quite complex. There is nothing in audio which can't be explained with physics, its just that we haven't worked out all the physics yet. One thing is certain, if an explanation for an effect defies the known laws of physics than that explanation is wrong.
Mark Kelly
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Mark, could you walk me through a real life example of Anti_Skate setup with your own arm and cart? |
Hi,
funny, talking with my 'learned friends' I find *experiment most ALWAYS precedes scientific explanation...* :-)
I just now proved to myself by simply sliding my SME V arm forward from its ~ 18mm overhang to some more without changing VTF = 1.25g and anti-skate 1 on the arm scale which keeps the arm in balance on the blank area of my test record.
Slide the arm enough forward (increase overhang) and ---- the skate force increase enough to now pull the arm to the centre.
Now let's consider a cart like my Windfeld with more then twice! the VTF (2.6g) and the result should be even more telling.
Greetings,
Axel |
Perrew
Unfortunately I can't do that without revealing details of my tonearm's geometry which are not yet ready for publication.
Sorry.
Axelwahl
You have changed the offset angle (because the SME overhang adjustment works by moving the pivot not the cart)
Mark Kelly
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Mark, I understand you dont want to do that but could you desribe with some other tonearm?
Tks
Par |
