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Should the maximum anti-skate force be applied at the beginning/mid/end of the record as the stylus tracks across. I know its very little overall.
Edits: 11/29/16Follow Ups:
Due to this very same issue/s with anti skate and pivot arms. Ever since I got my ET-2 arm back in 2002 I have been happy without having to deal with this issue. I tried to use a pivot arm again but that anti skate issue came up again and I just gave up on them.
Linear Tracking arms have their issues too but once properly leveled and cable dressing addressed, they are trouble free. Now I'm talking about air bearing linear trackers not servo based trackers. There are some servo trackers that are better than others but sill have some issues.
Good to have the same sound at the beginning of the LP all the way through to the end of the LP without any inner groove distortion or wear.
Wow, you can say that again. I had an ET-2 on a VPI TNT back in the '90s, and "issues" abounded. Poor Bruce Thigpen of ET got an earful of my problems but could never solve them for me. Most troublesome was that the arm tended to stick ... and repeat ... somewhere in the lead-out grooves of damn near every LP I owned.
I ended up practically giving the arm away, AFTER which the buyer told me what the trouble was. BOTH the Wisa pump and Airtech surge tank were defective (How can a surge tank be defective? It leaked air). He said this was a common problem with these arms and he had bought more than a few at fire sale prices. Live and learn.
To get the table perfectly balanced and the arm balanced so it will float without pulling in any direction from the most outer to most inner positions in the arms range. With the ET-2 setup jig, it's quick and easy. Once that is done with all the other Alignments you are set for a very nice surprise in sound and soundstage.
I was starting to get that same problem as you with the arm sticking near the run out. First, I found my air tube to the arm was kinked, fixed that. Then it started up again a few months later. I sent Bruce a email and he gave me some suggestions. I ordered a air pressure gauge from him, that's when I found the source of the problem. The gauge showed the pressure was too low and was the Wisa pump. It was still working but seemed not be able to push the length of the tubing to my table with the DIY surge tank.
I bought the Medo pump and a regulator, set the pressure and never had a problem since and sounds way better than with the wisa pump. The spindle must be kept clean or there will be sticking issues later. All this sounds like a lot of work but it's not! I have been in turntable/music heaven ever since.
I'm finally in turntable/music heaven myself, so I understand the feeling.
How's the Lenco and Empire working out after the upgrades? I always wanted an Empire table just because it was a American made table that looks to be very durable.
I have a Garrard Lab 80 that I'm going to restore. I have the "Cake cover" for it too! I just need the part that locks down the arm when not in use and a new Idler wheel. Thinking of making a plinth for this too! This will be for my "vintage setup. I would like to get some Bozak speaker for this system but may just make some Multiway DIY JBL's since I have most of the parts for the project.
Inner groove distortion is not something you can eliminate with a linear tracking tonearm. It's a result of the LP spinning at constant RPM so the linear speed of the groove past the stylus becomes slower and slower as the cartridge moves inward. It's basically analogous to tape speed on analog tape recorders. For example, the linear groove speed past the stylus on an outer groove with 11.4-inchs diameter would be 19.9-ips compared to 8.9-ips for an inner groove of 5.1-inches diameter. It's possible that pivotal tonearms might exacerbate the problem slightly, but I've never had an issue with inner groove distortion on any of my pivotal tonearms. After all, most people align their tonearms so that one of the alignment null-points falls within the inner groove area.
Best regards,
John Elison
I agree. It depends on which source of distortion dominates as to how audible the distortion is on the inner grooves. For a correctly optimised pivoted arm or LT arm, tip scanning radius and SRA are by far the biggest contributors of audible distortion on the inner grooves given the combination of HF scanning loss and high levels of IMD introduced by a large enough error (which is actually surprisingly small IME) with very small adjustments in arm height making for audible changes on the inner grooves. On the outer grooves, the same magnitude of arm height shift is unnoticeable given the longer groove wavelength.
Having said that, given that I have many LPs that conform to the DIN radii (inner radius ~57mm not the IEC minimum of ~60mm), my Laser Turntable does give marginally better reproduction on the innermost grooves (54 to 58mm) on 7"s running at 33rpm and also 45rpm. This prompted my switch to a linear offset of 91.14mm (giving nulls at ~63 and ~119mm) rather than the IEC LO of 93.34mm, although I had to change headshell design to the Jelco/Sumiko HS12 design which is the only one I found that had long enough slots to accomodate all cartridges when adapting to the preferred geometry in the Technics arm.
Regards Anthony
"Beauty is Truth, Truth Beauty.." Keats
Hi Anthony,I'm not familiar with the IEC linear offset. Can you elaborate on that for me. I know linear offset is the average of the two alignment null-points and I know it's also the effective length multiplied by the sine of the offset angle, but I didn't know there was a specific linear offset standardized by the IEC.
Thanks,
John Elison
Edits: 12/04/16
Sorry I was being economical with the wording because I assumed you knew what I was referring to! You are correct, the tonearm geometry for minimum distortion is not defined in the IEC standard which is exclusively for record manufacture and cutting. Tonearm geometry is not relevant to the standard.
Most alignment gauges assume 66.1 and 120.9mm as the preferred inner nulls for IEC radii of Rmin = 60.325mm and Rmax = 146.05mm.
I personally feel that nulls of ~63.1mm and ~119.2mm (DIN radii Rmin = 57.5mm and Rmax = 146.05mm, LO = 93.14mm) give a better result towards the end of a side even for an IEC compliant LP since the rate of change of angular error towards 60.325mm is far steeper and I think this magnifies the other sources of error. The tiny increase in the maximum distortion envelope is of no consequence at the outer grooves, but the benefit is readily heard towards the end of the side.
Regards Anthony
"Beauty is Truth, Truth Beauty.." Keats
Anthony: I also deem Baerwald/Loegren A calculated for DIN playback radii a pretty good compromise on the whole. Iirc, usual outer radius for DIN should rather be 146,3 than 146.05 mm, though - so you'd rather arrive at ~ 63.1 & 119.3 mm instead.
But of course that's not the only pretty good compromise - for example, Thorens' original alignment for the TP28(ES) on the TD280(II/III) with null points at ~ 61.0 & 120.3 mm also isn't bad and even more inner-groove-friendly than Baerwald/Loefgren A calculated for DIN radii. Just a bit of a pity that they only supplied a single-point cardboard protractor with the original accessories. On the other hand they even supplied a tiny mirror - and quite a few of those little plastic distance plates...
Greetings from Munich!
Manfred / lini
Did you know that linear offset can not define an alignment? It is simply the average of the null-point radii. Consequently, there are an infinite number of null-point pairs for any given linear offset. The only way to accurately describe an alignment is to specify its alignment null-points. For example, the linear offsets for both Lofgren A and Lofgren B alignments are exactly the same for a given modulated groove envelope.
As you know, the IEC modulated groove envelope has an inner modulated groove radius of 60.325-mm and an outer modulated groove radius of 146.05-mm. Lofgren A null-point radii for the IEC modulated groove envelope are 66.00-mm and 120.89-mm with linear offset of (66.00 + 120.89) / 2 = 93.445-mm. Lofgren B null-point radii are 70.29-mm and 116.60-mm with the same linear offset of (70.29 + 116.60) / 2 = 93.445-mm. Stevenson's alignment for the same IEC modulated groove envelope has null-point radii of 60.325-mm and 117.421-mm with linear offset of (60.325 + 117.421 / 2 = 88.873-mm.
Since linear offset is simply the average of a set of null-point radii, there can be an infinite number of pairs of null-points associated with any given linear offset. Therefore, linear offset cannot be used to define a specific alignment. Moreover, there is no single linear offset associated with a particular modulated groove envelope.
Best regards,
John Elison
Do you realise how predictable you are?
You slavishly regurgitate the same old stuff about tonearm alignment without actually reading the posts to which you are replying.
I was very specific about applying Lofgren A alignment for defined min and max modulated radii according to the IEC or DIN standards. Therefore for specific min and max radii, a unique set of null points satisfy the minimum distortion envelope which correpond to a specific linear offset.
"Since linear offset is simply the average of a set of null-point radii, there can be an infinite number of pairs of null-points associated with any given linear offset."
...but only one unique pair which satisfy the equations for minimum tracking distortion...which define a linear offset with respect to a null point. This is how the alignment protractors work! You don't need to know the effective length or overhang. As long as you have the linear offset defined, you can use any tonearm which has been arbitrarily whacked into the arm board as long as you have enough play in the offset and overhang.
"Therefore, linear offset cannot be used to define a specific alignment."
Read your SME arm specifications.
"Moreover, there is no single linear offset associated with a particular modulated groove envelope."
See above. Also that statement is true ONLY if you choose to ignore the requirement for minimum tracking distortion.
"Stevenson's alignment for the same IEC modulated groove envelope has null-point radii of 60.325-mm and 117.421-mm"
You should probably read his paper again. You are quoting his "universal" Design 1B which has an Rmin of 54.8mm in the table. His modulated radii are 54.8mm to 145.3mm....which "magically" give a solution which is identical to a Lofgren A solution for Rmin = 54.8 to Rmax=145.3 since the formulae are the same.
Now I understand why you insist the so-called Technics alignment is essentially the same as Stevenson. You seem not to understand that Stevenson made the distinction between "typical" inner radii vs MINIMUM inner radii (Rmin). His design 1B was intended to be optimised for all 3 record sizes. Design 1A was considered more favourable for LPs. This gives nulls of 63.5 and 119mm.
Now, how about commenting on the original aspect of my post which was suggesting that shooting for the standard nulls related to the IEC modulated radii does not achieve best performance on the inner grooves and furthermore simply aiming to minimise horizontal tracking error does not achieve best overall performance until ALL parameters have been optimised since different sources of error begin to dominate the resultant distortion. Tracking error is comparitively insignificant compared to the IMD introduced due to stylus profile, SRA error and VTA error. HTA doesn't help, but it certainly isn't the dominant source.
Regards Anthony
"Beauty is Truth, Truth Beauty.." Keats
> Now, how about commenting on the original aspect of my post which was suggesting that shooting for the standard nulls related to
> the IEC modulated radii does not achieve best performance on the inner grooves and furthermore simply aiming to minimize horizontal
> tracking error does not achieve best overall performance until ALL parameters have been optimized since different sources of
> error begin to dominate the resultant distortion. Tracking error is comparatively insignificant compared to the IMD introduced
> due to stylus profile, SRA error and VTA error. HTA doesn't help [and] it certainly isn't the dominant source.
To begin with, I have never recommended minimizing horizontal tracking error (HTA). I believe that after selecting the most appropriate modulated groove envelope, applying Lofgren's "A" alignment method is the best approach. Lofgren recommends minimizing harmonic distortion resulting from HTA rather than minimizing HTA directly. He developed two methodologies, one to minimize instantaneous distortion and another to minimize RMS distortion within the modulated groove envelope. I prefer minimizing instantaneous distortion rather than RMS distortion although the RMS distortion curve does have application, just not across the entire modulated groove envelope. That would create excessively high instantaneous distortion in the outer and inner groove areas. However, the RMS distortion curve is an excellent tool to show the fallacy of Stevenson's alignment methodology for the inner groove area.
Stevenson erroneously believed that placing the inner null-point at the innermost groove resulted in the lowest amount of inner groove distortion. However, by calculating RMS distortion within just the inner groove area, it can be shown that lower inner groove distortion will be achieved by placing the inner null point in the middle of the inner groove area rather than at the very end of it.
With regard to your final statement about other sources for distortion, you said, "Tracking error is comparatively insignificant compared to the IMD introduced due to stylus profile, SRA error and VTA error. HTA doesn't help [and] it certainly isn't the dominant source." If what you say is true, all this means to me is that those other considerations are just as important or possibly more important than HTA. I don't see how that reflects on anyone's choice of their favorite horizontal tracking error alignment method. Am I missing something?
Thanks,
John Elison
Sorry for the hiatus, I've been on vacation in an area with an intermittent data connection.
Now where were we...
Just to clarify an important point first, you seem to imply that I have an axe to grind over preferred alignment (Technics or otherwise). For the record, I don't. In fact I apply Lofgren A for different Rmin and Rmax according to the records I wish to optimise my various cartridges for using the Technics arm. For example I have cartridges specifically optimised for 7" and 10" records, DIN compliant LPs etc. The aim being to minimise the distortions as far as possible for transcription.
"I have never recommended minimizing horizontal tracking error (HTA)."
I didn't suggest that you were. I agree, minimizing the peak/weighted distortion is the desired goal - using the Baerwald approximation for 2nd harmonic distortion, the distortion is directly proportional to (peak recorded velocity * tan(HTA)) and inversely proportional to the groove speed so I would consider it virtually equivalent to say that minimizing the peak weighted distortion amounts to the same thing as minimizing the HTA with respect to the groove radius although I do appreciate that they ARE different.
Where I think the standard arm geometry optimisations don't give the full picture is that the estimated distortion assume a peak recorded velocity equivalent to ~0dB (ref 1kHz). Stevenson uses 10cm/s which is +3dB with respect to the 7.07cm/s (5cm/s RMS) for 0dB ref 1kHz, 11.2um, but this figure of 10cm/s is the reference level used for some test records (AT use this IIRC?). If we take a threshold of 3% as being audible due to HTA alone, then that is equivalent to a peak level of +12dB or a peak of ~30cm/s (ref 1kHz). Yet, the distortions on the inner groove with a tiny error in SRA are audible (at least to me) at much lower recorded velocities. Anyone who adjusts arm height for record thickness will know just how audible small adjustments that amount to fractions of an arc can make. The question is why this is so audible given the miniscule adjustment? Purely stylus related IMD?
Assuming the geometry was indeed correctly optimised for, say, LofgrenA with DIN min and max radii, then we would expect something in the region of 0.7% distortion as the peak weighted maximum. If we consider the 3% threshold as an audible limit, then the factor increase above 0dB to get to this 3% threshold is ~4.3x or ~+12.7dB increase in recorded velocity.
Hence I assert that the other contributing sources of distortion (SRA, tip profile/wear etc) must be more significant than HTA alone. Secondly, if you look at where the gradient of HTA becomes steepest with respect to groove radius, it seems apparent to me that this will make the distortions more obvious/detectable at the inner grooves given the ever increasing distortion for small changes in the radius and that a more desirable option is to reduce the gradient of HTA wrt groove radius at the end of your preferred record size. Hence establishing the tonearm parameters for a slightly smaller Rmin (i.e DIN radii) will yield superior results, not so much because the HTA was reduced at the inner groove, but because the rate of change of HTA error with respect to groove radius is also reduced at the Rmin for (say) an IEC compliant LP.
This is what I believe Stevenson was considering with his proposed Designs (1A-C).
"Stevenson erroneously believed that placing the inner null-point at the innermost groove resulted in the lowest amount of inner groove distortion."
I disagree for the reasons given. Additionally, I believe this to be a subtle misinterpretation of his paper. Here is his "Table 2" with the units changed to "mm" as I prefer metric units(!) You will notice that the Minimum Radius (Rmin) for Design 1A, which Stevenson intends to favour LPs, corresponds quite closely to the minima specified in the DIN standard. What he did was to choose Xinner/Xo at a "typical" minimum and NOT the absolute/extreme minimum which is what all the calculators like Conrad Hoffman's arc protractor and the VE calculator do, which is presumably where you get the idea that Stevenson chooses the inner null at the minimum radius. Granted he does explicitly write in the paper that he chooses Xo=Xinner, but he subsequently writes that "the values for Xinner are representative values for the minimum distance from the record centre and Xmin denotes the minimum distance in exceptional cases, being the minimum value obtained for Xinner from measurements on a batch of records of different makes and different types of music." If he really did choose Xo=Xmin as the calculators all do, then Table 2 would look very different would it not?
Additionally, he is presenting an optimised "universal" solution for 3 record sizes taking into account that a 7" will likely be running at 45rpm and therefore more tolerant of greater HTA as the increased groove speed will lower the estimated distortion back to an equivalent maximum value as for the LP at 33rpm.
Regards Anthony
"Beauty is Truth, Truth Beauty.." Keats
..
Sometimes the Kogen paper needed to be taken out into the sunlight every now and then as a reminder to the unwary. ;^)
Attached is an old discussion on that subject...
https://forum.audiogon.com/discussions/zero-antiskate-vs-stylus-wear
This is a wonderful article about skating force. In my opinion, skating force is the worst factor to degrade sound for a pivot arm. The popularity of pivot arm is the most tragic thing for LP playing back. There are so many factors to impact skating force and skating force is not a constant force. But anti-skating is a constant force. Therefore, nobody can get the anti-skating right.
http://www.audiomods.co.uk/papers/kogen_skatingforce.PDF
Edits: 11/29/16 11/29/16
> Therefore, nobody can get the anti-skating right.
While that may be very true, there are different magnitudes of "wrong" and using no antiskating at all is the greatest magnitude of "wrong" you can have. This is very easy to prove with microscopic examination of worn styli.
Best regards,
John Elison
John,I don't disagree with these two points.
1. Anti skating device DOES NOT degrade sound. Skating force degrades sound.
2. It is better to use anti skating device and pick a reasonable value for anti skating.
Edits: 11/29/16
Just a point....I hear a difference in staging et al with/without a/s. I don't hear it with headphones, but there is a solidity I hear w/o a/s applied that is attractive. The option to use or not use is all for us to apply....but there is a sound difference.
Sorry! I forgot you were pro antiskate.
Best regards,
John Elison
I recall seeing an article by Thorens (I believe) discussing anti-skate. The only part I can remember stated the force was not constant across the playing surface. JE's description seems to support that. But how could one ever have a pivoted arm which corrects for the appropriate portion of the LP?
Maybe that is one reason why Harry Weisfeld prefers to ignore anti-skate? ;^)
"The piano ain't got no wrong notes." Thelonious Monk
M3lover.....actually, the VPI anti-skate device can be adjusted so that the greatest force is at the beginning, middle, or end of the record...or anywhere in between. The device can be pivoted so that the most horizontal position of the arm/weight, can be had anywhere on the record one would like. When not horizontal, the weight of the arm/and its rubber weight will gradually be supported by the pivot depending on its position meaning less or more pull on the arm.
I had not seen that VPI AS device. It reminds me strongly of the AS mechanism on a Kenwood L07J tonearm, supplied only with the L07D turntable. Threading it is a pain in the arse, if you have to set up the tonearm from scratch.
Lew...no threading issues.. It is only a pia to remove it once installed..it requires setting up the arm again to remove or install. You need to remove the rear counterweight which requires VTF, and Azimuth to be recalibrated. A new modification of the arm is in the works...an extra pivot (easy user installation) so that azimuth could be retained in the initial setup.
To ignore anti-skate is very bad solution. It is very difficult for me to understand why VPI doesn't have anti skating device.
> It is very difficult for me to understand why VPI doesn't have anti skating device.HW believes that antiskating degrades the sound quality of his tonearms. I presume he also believes it degrades the sound quality of other tonearms, too. He bases everything on listening tests without regard for the physics of skating force.
I tested my SME III tonearm using headphones to listen while raising and releasing the antiskating weight and I couldn't hear any difference with or without antiskating. Therefore, I don't believe antiskating degrades sound quality on SME tonearms. However, I know from microscopic examinations of styli that not using antiskating causes significantly uneven stylus wear. In other words, one side of the stylus tip becomes significantly more deformed than the other side when not using antiskating.
On all my styli that I periodically examine with a microscope, stylus wear is always symmetrical on both sides. Consequently, I believe in using antiskating because I think it is very important in preserving my LPs as well as prolonging the life of my styli. I fully believe in the physics of skating force.
Best regards,
John Elison
Edits: 11/29/16
Jian.... great article .....vpi arms DO have a/s device.
Unless something changed (very possible, I'm not shopping for current arms), VPI arms don't come with a-s, but it is offered as an option. From what I've read, HW does not necessarily believe in them but offers the a-s device because of consumer demand.
I believe even his "twisted connection wires" was suggested for those who wanted something, rather than set up the arm with no counter force at all.
"The piano ain't got no wrong notes." Thelonious Monk
The a/s device is an option only as to use it or not.... no additional cost.
You are right. VPI does use anti skating device. I should state it more precisely.
"...vpi arms DO have a/s device"In fact they have two methods.
The device itself with the weight and the string plus "a twist of the wire" (the original way A/S force was applied to a VPI tonearm before the "device" was offered).
That's twice as many ways to apply A/S force as any other tonearm I'm aware of.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 11/29/16
The wire twist method is not reliable....the tension of the wire gradually relaxes....Discovery and Nordost have very different stiffness.
I'm sure that is true.
But it was the method prescribed for applying A/S force for all those years before the "device" was added.
I was just pointing out the irony that the tonearm, made by the guy that doesn't believe in A/S, has two ways of applying A/S.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
My shoot from the hip response is that max skating force would be generated when the cantilever is farthest from either of the two null points, assuming a conventional pivoted tonearm. This happens, again I'm guessing, somewhere in between the two null points, but it could also be true for the very end of the LP. So, for Baerwald or Lofgren, somewhere around the middle of the playing surface or at the innermost inner groove or both.
The constant aspect of skating force is proportional to the angle between the groove tangent at the stylus and a line through the stylus and tonearm pivot. Therefore, minimum skating force is generated in-between the two null-points where this angle is minimum.
For example, take a 230-mm effective length tonearm aligned for null point radii of 66-mm and 120.9-mm. The angle between the groove tangent at the stylus and the pivot-stylus line is 25.865-degrees at the outermost groove radius of 146.05-mm. That angle becomes minimum (22.853-degrees) in-between the null-points at a groove radius of 89.3-mm. Then the angle begins to increase again to the innermost groove of 60.325-mm where its value is 24.750-degrees.
In other words, maximum skating force occurs at the outermost groove and decreases gradually to a point in-between the null-points where it is 11.65% lower than at the outermost groove. It then increases gradually to the innermost groove where it is still 4.31% lower than at the outermost groove. However, its minimum value occurs in-between the null-points.
Best regards,
John Elison
John, Is it not the case that there are two aspects of conventional pivoted tonearms that contribute to lack of tangency?: (1) The fact that an overhung tonearm can never achieve tangency to the groove, except by virtue of the headshell offset angle, which, combined with observation of any of the accepted mounting geometries and variants thereof, allows for tangency to the groove at two points along the playing surface, and (2) even when tangency is achieved for such a system, there is still a residual skating force that results from the headshell offset angle itself; because at the two null points, the headshell places the stylus/cantilever at an angle to the pivot point.So, I would have thought (and did think), that the two null points represent skating force minima, because at those two points there is no contribution to skating force from the lack of tangency of the stylus/cantilever to the groove; it's all due to the headshell offset angle at those two points. Whereas, every where else on the LP surface, you have both sources of the skating force operating.
What have I got wrong? Thanks.
Edits: 11/30/16
> What have I got wrong? Thanks.The main thing you have wrong is that the headshell offset has absolutely nothing whatsoever to do with skating force. Its sole purpose is to minimize tracking error.
Skating force is caused by frictional drag on the stylus from the spinning record such that the direction of the drag makes an angle with a line through the stylus and tonearm pivot thereby exerting a torque on the tonearm.
If the direction of the frictional drag on the stylus were parallel and coincident to the line through the stylus and tonearm pivot, there would be no torque exerted on the tonearm and therefore no skating force. Headshell offset actually has nothing to do with it.
Look at the diagram below. The force vector Ft is the frictional drag on the stylus from the spinning record. It's direction is not in line with the stylus-pivot line. Consequently, it has two components, Fa and Fs . Fa is in line with the stylus-pivot line and creates no skating force. However, Fs is the component of Ft that creates torque on the tonearm and is responsible for skating force.
Edits: 12/03/16
John, I really don't need the lecture. I take it as a given that we both know that friction of the stylus in the groove is the force that results in the skating force. And my very question subsumed the bit about headshell offset angle and its role in generating a skating force (but not ALL of the skating force). So, I don't need the diagram, either. Please re-read my question; there is much more to it than you seem to assume.
With zero headshell offset on an overhung pivoted tonearm, would there still be a skating force? There would be, because the stylus/cantilever can never achieve tangency to the groove without headshell offset.
> With zero headshell offset on an overhung pivoted tonearm, would there still be a skating force?
Yes! Headshell offset has no impact on skating force. They are two completely independent issues.
> There would be, because the stylus/cantilever can never achieve tangency to the groove without headshell offset.
Yes, there would be, but not because the stylus/cantilever can never achieve tangency to the groove without headshell offset . Stylus/cantilever tangency and headshell offset have nothing to do with skating force.
I don't know how to explain this to you in a way you will understand. I thought the diagram would do the trick, but apparently not.
Sorry,
John Elison
John is somewhat correct. There is always a frictional force generated regardless of the stylus being tangent to the groove or not. It's a function of downforce and contact area. Friction force is a vector. Friction vector can be resolved into 2 perpendicular components. One component, in the direction of the armtube, the other 90 degrees to it in the direction of the spindle (skating). However, if there was no offset and the friction force direction was along the armtube, there would be no component acting towards the spindle, thus no skating force would exist, like a linear tracking arm.
There is no such thing as being 'somewhat' correct. I am either correct or I'm not. In this case, I am correct because cartridge offset has absolutely nothing to do with skating force.In order for skating force to exist, there must be a frictional force component at 90-degrees to the line through the tonearm pivot and the stylus as shown by the vector Fs in the diagram below. Therefore, if total friction from the spinning record were in the direction of the vector Fa only, there would be no skating force regardless of cartridge offset.
In other words, suppose you move the base of the tonearm farther from the platter spindle so that the vector Ft falls along the line through the stylus and the tonearm pivot; then there would be no skating force because the vector Fs would no longer exist. Cartridge offset makes no difference.
Edits: 12/03/16
We are on the same page but you are forgetting that the magnitude of vector components changes with angle of the vector. So yes, the offset will change the magnitude of the skating force. That's why you were "somewhat" right.
No! We are not on the same page. Cartridge offset plays no role in the page that I'm on.Cartridge offset has nothing to do with the magnitude and direction of the three vectors in the diagram below. The only parameter that affects the relative magnitude and direction of the three vectors in the diagram below is pivot-to-spindle mounting distance.
The vector Ft is tangent to the groove at the stylus. This represents the magnitude and direction of frictional drag on the stylus. Vectors Fa and Fs are components of vector Ft .
If you allow the stylus to remain at the radial distance from the platter spindle where it now resides but you increase pivot-to-spindle mounting distance, vector Ft will become coincident with vector Fa and the skating force vector Fs will be eliminated. The angle of the cartridge at the end of the tonearm need not change. Only, pivot-to-spindle mounting distance need change. Of course, this will also change overhang to underhang, but the angle of the cartridge need not change whatsoever.
Just as there are two possible alignment null-points where tracking error can be zero, there is one possible null-point where skating force can be zero. It depends only on pivot-to-spindle mounting distance, not on cartridge offset.
I don't know how else to explain this so you will understand, but until you understand the truth we will never be on the same page.
Good luck,
John Elison
Edits: 12/03/16
Here you go chief. Change the angle and you change the value of the components of the vector. My last post on this subject, can't explain vector mechanics on an audio forum.
Here is my last post on the subject:If I leave the stylus in place but move the pivot of the tonearm such that its pivot-to-spindle mounting distance is increased to the point that the line through the stylus and pivot is coincident with the groove tangent at the stylus, then total frictional drag Ft is pulling directly on the tonearm pivot and there will be no skating force whatsoever. This situation occurs for this one tonearm position only. As you can clearly see, cartridge offset will have no effect on skating force whatsoever because the total frictional force Ft is pulling directly on the tonearm pivot point. The only thing that cartridge offset affects is tracking error.
Edits: 12/03/16
John: Problem with that example is that you're changing the game/context/scope, because the second alignment wouldn't represent one of the regular alignments for hifi anymore, so that the offset angle also wouldn't for the most part represent the deviation between the direction of the groove drag and the virtual arm axis anymore. So you're actually expanding the context/scope to a wider range of examples (in this case unusual, not necessarily sensibly chosen alignment geometries) - and then you certainly also can't expect a statement/claim, that was made with a narrower range of examples in mind, to still apply.
Greetings from Munich!
Manfred / lini
If you are arguing that cartridge offset in some way impacts skating force, then you need to prove it using legitimate physical relationships and valid vector analyses that prove a relationship exists between cartridge offset and skating force. All you're doing now is blowing smoke.You've seen my arguments and my vector diagram. Prove me wrong. The only thing you've written to date that makes any sense is:
> ...you're of course entirely correct, that the only requirement for skating force on the geometrical
> side would be a deviation between the direction of the groove drag and the virtual arm axis...I have never heard of anything called a virtual arm axis, but I take it to mean a line from the tonearm pivot through the stylus tip in the plane of the vinyl surface. Is that your definition? If not, you need to define 'virtual arm axis'.
Apparently, you previously thought I was entirely correct and now you seem to have changed your mind. Prove me wrong using valid physics. I think when you attempt to do that you will again see that I am right.
Thanks,
John Elison
Edits: 12/03/16
John: Yup, I use the term "virtual arm axis" for the horizontal 2D projection of the axis between needle tip and tonearm pivot, because that's shorter as well as to make it clear that I'm not talking about the longitudinal axis of the arm tube (unless both would happen to be the same, of course).
And I don't think that my equation above (total angular deviation between groove drag and virtual arm axis = offset angle + (+/-) remaining tracking error angle) requires any further proof, as that's pretty obvious. And I also don't think that there's any debating, that in a usual setup according to one of the usual alignment approaches (Baerwald/Loefgren A, Loefgren B & Stevenson) we have two null points at which the remaining tracking error angle is 0, so that at these two points the offset angle completely represents the deviation between the direction of the groove drag and the virtual arm axis, and that at any other point of the travelled arc within the LP playback range chosen for the calculation the offset angle still is the dominant component in that equation. So within the scope of that range of examples we can claim that the offset angle by and large represents the angluar deviation between the direction of the groove drag and the virtual arm axis.
Well, and hence I have to disagree with you, that the offset angle would have nothing to do with skating within the scope of that range of examples, as there obviously is a clear relation, while I at the same time agree with you, that the offset angle is not the general, fundamental reason for skating on the geometrical side.
And no, I haven't changed my mind - 'cause, as already mentioned above, we already had a similar discussion on the same topic a while ago, and my points haven't changed since that.
Greetings from Munich!
Manfred / lini
> I don't think that my equation above
> (total angular deviation between groove drag and virtual arm axis = offset angle + (+/-) remaining tracking error angle)
> requires any further proof, as that's pretty obvious.
I totally agree with your equation. And, because of your equation, I believe you are saying that skating force is based on total angular deviation between groove drag and the virtual arm axis. If that is your understanding, then we are in total agreement because I believe the same thing and I also completely agree with your equation for finding the total angular deviation between groove drag and virtual arm axis.
For a tonearm setup according to one of the usual alignment approaches (Baerwald/Loefgren A, Loefgren B & Stevenson) there will be two null points at which the tracking error is 0 and between the null-points tracking error will be negative while outside the null-points tracking error will be positive. Therefore, you really don't need the (+/-) sign in your equation. You can simplify it to read:
(total angular deviation between groove drag and the virtual arm axis) = (offset angle + tracking error angle)
I totally agree with this equation and I believe it holds under all conditions. Well, I know for a fact that it holds under all conditions because I've done the math. You can do the math, too. And because skating force is based on (total angular deviation between groove drag and the virtual arm axis), the particular value of the cartridge offset angle really doesn't matter . In other words, (total angular deviation between groove drag and the virtual arm axis) will always be equal to (offset angle + tracking error).
The following graph shows a Lofgren A tonearm alignment for a tonearm with 230-mm effective length, a mounting distance of 211.947-mm and a cartridge offset angle of 23.971-degrees. The blue curve is tracking error and the (total angular deviation between groove drag and the virtual arm axis) = (offset angle + tracking error).
.
The graph below is the exact same tonearm as depicted above but with cartridge offset angle set to zero-degrees. Effective length and mounting distance are identical to the graph above and (total angular deviation between groove drag and the virtual arm axis) is also exactly the same as the tonearm graphed above because it still equals (offset angle + tracking error).
John: First of all, thanks for sacrificing some of your time for reevaluating my thoughts/statements. And yup, I thought we were in agreement right from the start regarding the general, fundamental geometrical reason/requirement for skating, anyway.
I just wasn't happy with your "has nothing to do with" due to the relation I saw. And I thought one could cut people some slack, when they would say that the offset angle would be the (geometrical part of the) reason for the skating, when looking at a "usual example", due to that not being all that wrong - although I'd surely also be happier, if people would be more exact and rather say something like: "In this case the offset angle represents/visualises/indicates the geometrical requirement for the skating for the most part, and the remaining tracking error angle only adds or subtracts a bit from that. But the general, fundamental requirement would rather be the deviation between the direction of the groove drag and the virtual arm axis - and if there is an offset angle, that's just one part of that deviation. So, if one would imagine a completely straight arm at the same spot, the skating would be just the same, but our deviation would then be fully represented by the tracking error angle instead, just like it would be fully represented by the offset angle of our arm with offset angle on the two null points."
And yup, one could surely scrach the "(+/-)" - I've just put it there to indicate that the tracking error angle has a direction/is a signed value, which has to be considered/the sign of which has to be correctly assigned for a correct result.
Greetings from Munich!
Manfred / lini
P.S.: On a side note, if you've got some patience left for me, maybe you would also like to reevaluate my comment in that stylus-shape-related thread a while ago about estimating the influence of height change on SRA/VTA, that it would depend on whether the axis for the vertical pivot was angled according the the offset angle or not, whether one would calculate the angular change with arcsin (height change / (effective length x cos (offset angle))) or rather with (height change / (effective length / cos (offset))) (see link to thread below!) - 'cause I still think that's correct.
I reevaluated the stylus-shape related thread and the equation is correct as posted. You have to multiply effective length by the cosine of the offset angle.Best regards,
John Elison
Edits: 12/06/16
John: Could you explain, why you think that? Because to me it would rather seem that this would only apply, if the axis of the vertical pivot is angled perpendicular to the offset angle - whereas with the axis perpendicular to the arm tube in my view it should rather be the effective length divided by cosine of the offset angle, as shown in my little illustration. I'll repost it below for convenience - remark: Hook-shaped headshell arrangement chosen for simplification, i.e. so that the virtual arm axis is the same as the actual arm axis and the actual offset angle the same as the offset angle of the headshell.
Greetings from Munich!
Manfred / lini
> Because to me it would rather seem that this would only apply, if the axis of the vertical pivot is angled perpendicular to the offset angle
You're right! That's the situation I was addressing--a tonearm like the SME V with an offset vertical bearing.
I think you might be right about the other situation in which the bearing is not offset to match the angle of the cartridge. Moving the arm up-and-down would alter azimuth in addition to changing SRA/VTA. Therefore, you might be right about dividing effective length by the cosine of the offset angle because the change in SRA/VTA would be less than the angular change in the virtual arm axis.
Good luck,
John Elison
John: Yup, in the "non-angled" arrangement there would certainly be a certain degree of tumbling on height change.
Greetings from Munich!
Manfred / lini
> I thought we were in agreement right from the start regarding the general, fundamental geometrical reason/requirement for skating, anyway.
I thought so too and I would like to explain how I would calculate skating force to see if you agree. I will use the force vectors from the diagram below. As such, Ft is the frictional force of the stylus against the moving groove in the direction of the groove tangent at the stylus. We would need to know the coefficient of friction for the stylus in the moving groove to calculate Ft using the following equation.
Ft = VTF x (coefficient of friction)
Once the value of Ft is determined, we can calculate skating force Fs by multiplying Ft by the sine of the angular deviation between groove drag and the virtual arm axis .
Fs = Ft x Sin(angular deviation between groove drag and the virtual arm axis)
Let me know if you agree so far.
> I just wasn't happy with your "has nothing to do with" due to the relation I saw.
There is no question that the relationship you saw is valid and your equation is valid. I realized that immediately, which is why I didn't challenge your posts explaining that relationship to Lew . However, I have a problem understanding your insistence that cartridge offset and tracking error are necessary parameters for calculating skating force because I don't know how to derive tracking error without first calculating (angular deviation between groove drag and the virtual arm axis) . That is why I believe that knowing a cartridge's offset angle and tracking error angle are unnecessary for calculating skating force.
The only way I know how to calculate tracking error is by using your equation rearranged in the following way:
(Tracking Error) = (angular deviation between groove drag and the virtual arm axis) - (Cartridge Offset Angle)
The only way I know how to calculate (angular deviation between groove drag and the virtual arm axis) is by using trigonometry (the law of cosines) to solve the pivot-stylus-spindle triangle for the complement of the angle at the stylus, which IS the angular deviation between groove drag and the virtual arm axis . This is why I feel that knowing tracking error and cartridge offset are unnecessary for calculating skating force of a pivotal tonearm.
After all, the goal is to find the angular deviation between groove drag and the virtual arm axis and I don't know how to do that using your equation because I don't know how to find tracking error without first using the law of cosines to calculate the angular deviation between groove drag and the virtual arm axis .
Therefore, my question to you is: "Can you teach me how to calculate tracking error without first calculating the angular deviation between groove drag and the virtual arm axis ?"
In the tonearm geometry spreadsheet I developed 20-years ago, I use the law of cosines to solve the red-green-blue triangle in the diagram below for the angular deviation between groove drag and the virtual arm axis . This would be the angle at the stylus subtracted from 90-degrees, which is the complement of the angle at the stylus. By graphing this angle throughout the full range of tonearm movement and then subtracting the cartridge offset angle in accordance with your rearranged equation, I was able to plot tracking error . Unfortunately, I know of no other way to derive tracking error, so if you can show me a different method, I'd be very interested in learning.
You can find my Excel Tonearm Alignment Spreadsheet at the link below. I will review the stylus-shape related thread in your link and get back to you, perhaps by email. Thank you for putting up with me throughout this lengthy discussion.
Best regards,
John Elison
John: Oh, that would rather be a misunderstanding, I guess - 'cause I wouldn't insist that the offset angle and the remaining tracking error angle would be required for such a calculation at all, as that would rather seem to be a detour compared to directly determining the total angular deviation. So I'd think we'd agree there, too.
However, using the offset angle would of course seem convenient for a quick estimation in a particular "usual" setup, for which the offset angle is already known - which would already seem good enough for me, 'cause to me the more problematic part/factor for an exact calculation of the skating force for a particlar point on the travelled ard would rather appear to be the friction coefficient. Because, iirc from school physics, those friction coefficient tables in the physics books typically only cover the somewhat idealised case of polished, flat surface against polished, flat surface - and I'd also assume a certain dependance on temperature and thus also on the speed and the pressure in practice, depending on the particular material combination. Hence I wouldn't very feel comfy with such an exact calculation anyway, unless I'd have an Orsonic Lateral Pressure Detector or a Dual Skate-o-meter at hand for verification...
Greetings from Munich!
Manfred / lini
P.S.: Sorry, can't have a look at your spreadsheet yet, 'cause I'm currently still using an old notebook, that's only intended to be an interims solution, so that I've hardly installed any additional software, also including any sort of office suite. And what you should probably also know, is that I'm not that great in math and physics anyway. I just used to be pretty good at school, and can still work fairly well with the basics I still remember - but as soon as things become more complex, I'll be lost pretty quickly due to the lack of practice and further knowledge. So you'd better expect too much of me, as my tool-kit in that regard is pretty limited.
You should realize that believing the angle between the groove tangent at the stylus and the virtual arm axis is dependent on cartridge offset is simply a limitation of your own thinking. While it's true that the groove tangent angle to the virtual arm axis is the sum of cartridge offset and tracking error, there is no dependency involved. In other words, you don't need to have cartridge offset to have an angle between the groove tangent at the stylus and the virtual arm axis. Furthermore, your inability to separate the two means you probably don't understand either.
A good analogy might be the equation 2 + 2 = 4. This is a true statement, but the number 4 is not dependent on the number 2. The number 4 exists on its own. Therefore, if you tell me the number 4 is dependent on the number 2, all I need to say is, "How about 1 + 3 = 4?" There's no number 2 involved in 1 + 3 = 4.
If there is any dependency involved in tonearm alignment, cartridge offset is dependent on the angle between the groove tangent at the stylus and the virtual arm axis. It's definitely not the reverse. Cartridge offset is man made whereas the angle between the groove tangent and the virtual arm axis is based on geometry. In fact, you really need to know that angle before deciding on the appropriate cartridge offset. At any rate, the angle between the groove tangent and the virtual arm axis exists on its own without any need for cartridge offset.
If you want to derive the angle between the groove tangent and the virtual arm axis, you need only analyze the pivot-stylus-spindle triangle using the law of cosines. If you solve for the angle at the stylus and take its complement, you will have the angle between the groove tangent and the virtual arm axis. You can then graph this angle from the innermost groove to the outermost groove in order to determine the most appropriate cartridge offset. Consequently, if there is any dependency involved, it's cartridge offset that's dependent on the angle between the groove tangent and the virtual arm axis -- not the other way around.
Best regards,
John Elison
... but not being a native speaker I fear I can't explain any better to you what I mean. So I'll leave it at that.
Greetings from Munich!
Manfred / lini
It's perhaps not appropriate to add to this branch of the thread at this point, but I do think it's misleading to say that cartridge offset angle even "represents" anything that's relevant to the skating issue and that it has a "clear relation", etc.But I can add that if the mounting distance of the arm makes a difference, as Johns showed, then the stylus-to-pivot distance makes the same type of difference, as the two distances hang together, as we know. Move the stylus tip closer to or further away from the arm pivot, and the angle of the groove-tangent and the tip-to-pivot axis is altered, at least a little.
So lateral adjustment of the cartridge does have some bearing on the skating issue, although it's about overhang only, not about the offset angle of the cartridge. Cartridge-offset and overhang operate independently: I could have made a less than good alignment with a wanted overhang and an unwanted cartridge-offset; the skating force would be the same as if I got the offset-angle right and kept the overhang.
Offset-angle is the angle between the cantilever/stylus assembly and the headshell, and I believe the headshell should be seen as having as little to do with this issue as the tonearm tube. For skating, it's only the locations of the stylus tip and the tonearm-pivot which contribute anything of substance to the matter, as far as lateral aspects of the tonearm are concerned.
Dragging cartridge offset into the skating issue is thus confusing the matter, as I see it, as its relationship to the issue is nonsubstantial and extremely indirect , no matter the math.
But perhaps I should have shut my mouth at this point :-)
Greetings from Oslo!
Edits: 12/04/16 12/04/16 12/04/16
Well, you're a little late to the ball game, that's for sure.
> Offset-angle is the angle between the cantilever/stylus assembly and the headshell
I don't think we are defining offset angle like that for this discussion. I think we are using the term 'cartridge offset' to apply to tonearms in which the cartridge and headshell both are attached at an angle to the stylus-pivot axis of the tonearm. The other situation involves tonearms without any offset so that the cartridge and headshell is attached in-line with the pivot-stylus axis, which rindolini calls the virtual arm axis. Here are some examples of tonearms with and without offset.
.
Based on what you've just written, you seem to be supporting my position that skating force has absolutely nothing to do with cartridge offset. The opposing viewpoint held by rindolini and rotarius claims that skating force is somehow affected by or even dependent on cartridge offset.
Like most discussions of opposing viewpoints in this forum, a resolution is rarely forthcoming. However, I appreciate your input.
Thanks,
John Elison
John: Iirc, we already had that dicussion a while ago - and to me it still would be more of a semantical discussion.
I.e., while you're of course entirely correct, that the only requirement for skating force on the geometrical side would be a deviation between the direction of the groove drag and the virtual arm axis, which we'd also have with an entirely straight radial-tracking arm, I still wouldn't concur that in the context of a radial-tracking arm with offset angle the offset angle would have "nothing to do with" skating. To me that would simply seem too strong of a claim, due to the relation/equation in my explanation for Lew above - namely that in context of such an arm the offset angle would by and large (entirely at the two null points or with a few degrees for the remaining tracking error to add/subtract anywhere else) represent that geometrical deviation.
Hence I'd think from a certain point of view one could indeed say, you're only correct in a way, as the offset angle as such certainly isn't the fundamental requirement on the geometrical side, but in the context of a radial-tracking arm with offset angle as example it is nevertheless related, as it for the most part represents that deviation between the direction of the groove drag and the virtual arm axis, which is the actual fundamental reason on the geometrical side.
And I also wouldn't quite concur, that a certain claim/statement can only be either correct or not correct - 'cause imo life is full of cases of context-dependent correctness/incorrectness. For example, in lot of claims/statements we as humans will typically automatically assume typical "planet Earth surface dweller conditions" as we are used to, like for example that we can expect ca. 10 N per kg.
Greetings from Munich!
Manfred / lini
> you're of course entirely correct,
>
> the only requirement for skating force on the geometrical side would be a
> deviation between the direction of the groove drag and the virtual arm axis
And, that's exactly what this discussion is about -- skating force.
> I'd think from a certain point of view one could indeed say, you're only correct in a way
Well, I think you should go back to the point-of-view that caused you to write the first two statements because that is the point-of-view I am concerned with in this discussion -- the point-of-view of skating force.
If you want to discuss cartridge offset, that's fine but it's a separate issue. Cartridge offset is used in conjunction with overhang to minimize tracking error in a pivotal tonearm. There are essentially two choices in aligning a pivotal tonearm. You can align it to minimize skating force or you can align it to minimize tracking error, but you can't do both. Nor can you eliminate either in a pivotal tonearm! There will always be skating force and there will always be tracking error in a pivotal tonearm.
If you strive to minimize skating force, tracking error will be significant. If you strive to minimize tracking error, skating force will be significant. The only way I know to eliminate both is with a straight-line-tracking tonearm, which is perhaps the best point-of-view for vinyl reproduction.
Thanks,
John Elison
Lew: You need to consider the direction of the tracking angle error. I.e., the deviation between the groove drag and the virtual arm axis represented by the offset angle is the dominant component, and the remaining tracking error angle curve adds or substracts an extra bit to/from that. That extra bit is on the positive side from the start to the first null point as well as from the second null point to the end - while it's on the negative side from the first to the second null point, reaching it's (negative) maximum roughly halfway between. So at the two null points our deviation angle just equals the offset angle, but the absolute minimum of our deviation angle would rather be reached somewhere about in the middle between the two null points. And so at least from the geometrical point of view one would expect minimal skating there. I'm not sure, whether radius-dependent modulation density/structure size might have an additional influence, though - not on the geometrical component, of course, but maybe on the friction component...
Greetings from Munich!
Manfred / lini
Thanks, Manfred. My point is/was that at either of the two null points, the component of the skating force that is purely due to absence of tangency between the cantilever/stylus and the pivot is cancelled by virtue of the headshell offset angle and proper mounting geometry, whatever one is chosen. This leaves a skating force only due to the headshell offset angle, as shown in John's latest diagram. This is why I wondered whether skating force is minimal at the null points. I certainly could be wrong (without having done the geometric calculation). For me to be correct, the skating force purely due to headshell offset angle would have to be no greater at the two null points than it is elsewhere on the LP surface. There's the rub.
Yup, Lew, and that's just the point: At the two null points the extra bit to add/subtract from the offset angle to get the total angular deviation between groove grag and virtual arm axis is just 0 - whereas our extra bit reaches its negative maximum about halfway between the null points, so that we get the lowest sum there.I.e.: Total angular deviation = offset angle + (+/-) remaining tracking error angle
At both null points: Total angular deviation = offset angle + 0 = offset angle
Somewhere about halfway between the null points: Total angular deviation = offset angle + maximum negative tracking error angle = lowest/smallest absolute deviation
So I guess a more helpful visual aid would have rather been a typical tracking error angle over playback radius graph, which you could for example create with JaS' neat alignment calculator over in the Tools section of VinylEngine - you'll need an account and to be logged in, though, otherwise you'd just see the numerical values, but neither the tracking error angle, nor the distortion graphs. See optional link for "random" example...
Hence my suggestion above to consider the direction of the tracking error angle: As soon as that turns negative, which it does between the two null points, it'll actually subtract from the offset angle and hence reduce the total angular deviation.
Greetings from Munich!
Manfred / lini
Edits: 12/01/16
Somewhat related might be the type of stylus design and it's relationship to audible differences due to skate/antiskate? I always fond my conical stylus seemed more "immune" to the effects of antiskate when compared to elliptical for example?
I usually dial in a little bit of antiskate and leave it alone.
John, may I ask whether the figures you give relate specifically to a theoretic model within the discipline of moments which I would therefore expect to relate to either a blank disc or perhaps an unmodulated groove?
Given the figures for the resultant skating force calculated to two decimal places, are they not somewhat spurious when given a real life situation where the actual skating force is also affected by (amongst other factors)groove modulation and friction, neither of which appear as factors in your calculation?
Regards
Pete
I didn't provide any calculations for skating force.
Skating force is caused by drag on the stylus from the spinning record. There is a constant aspect of the drag caused by friction of the stylus against the moving groove and there is a dynamic aspect of drag caused by the energy required to wiggle the stylus by undulations in the groove. I was addressing the constant aspect of frictional drag on the stylus from an unmodulated groove. Both of these aspects are easily measured using a special cartridge designed for measuring skating force. Unfortunately, I don't own one of those special cartridges.
Best regards,
John Elison
Thanks for the clarification and as so often I have learned something new from you. I didn't know about those measuring cartridges.
Regards
Pete
nt
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