Geoch says:
Dear Thuchan, whats the use of the greatest protactor if one can not manage to take advantage of the offered precision?
I would agree.
I have been following this thread after having my attention drawn to it by a client (who enjoys the "interplay") and was perhaps thinking of purchasing one, and asked my views.
My response was that there are a few issues raised which are quite serious (in the sense that any hifi issues are serious compared with world events).
Having been a former tonearm manufacturer, out of hifi for a good few years, I am surprised at the amount of woolly thinking still surrounding the whole issue of turntable set up. In this I include Dertonarm who puts himself forward as as a setup guru. It seems that here is still money to be made from people who are not aware of the issues surrounding setup.
So, I have a number of issues:
1. Reading the thread, I take issue with Dertonarm on his analysis of SME geometry and also on Antiskate. He is plain wrong on the SME, and vague on antiskate, and that makes me wonder how pertinent are his analyses of geometry. He is vague on the issues regarding 12" versus 9" arms and why this should make a difference. And why old full length records should be different from new full length ones.
2. He is unclear on the geometry issues. They are simple and have been known for years:
a. With a given minimum and maximum recorded radius and a given effective length, there is
b. a mounting distance (and therefore overhang (or vice versa if you like)) and a cartridge offset angle, which give either: a tracking error such that there is a minimum distortion at the outer, middle and inner radii(Lofgren A/Baerwald); or minimum average distortion across the record (Lofgren B).
In both cases, it depends on a given weightings for tracking error. Equally, there are other weightings one may care to apply to the tracking error. It appears that Dertonarm advocates a weighting that favours the inner third, but doesn't tell us the weighting he applies to the Lofgren equations (which give, as a starting point, the ways to minimise tracking error as opposed to distortion).
If he did so, we could all set parameters for any arm, and any record, following his recommendations.
3. I am concerned that there is a tendency to look at mounting distance accuracy and give numbers for this, without a similar figure for angular accuracy. It only takes a moment to realise that a mounting distance accurate to say 0.5mm is only as good as an equal accuracy in offset alignment. As someone who has experience in this area, I know that it is extremely difficult to hold accuracy to within 0.1 mm by eye, but a difference of a similar amount in offset, ie a misalignment 0.1mm either side of the optimum position for the stylus will give similar errors.
I would maintain that it is far more difficult to set offset to this accuracy than overhang. This is why no one gives figures for the accuracy of offset using their jigs (but, of course, they always seem to be accurate to 0.01mm in mounting distance using a digital readout...or whatever). This is also why the accuracy of overhang setting is at the mercy of offset. Any error in offset should have a correction in overhang. If your offset is wrong, your precisely set overhang/mounting distance is wrong too: albeit precisely wrong. Your mounting distance, with its error, whatever it is, say 0.5mm, might be accurate to 0.1mm, or 0.01mm, but it is still an error of 0.5mm...
To put it into perspective, if you happen to set your cartridge such that the stylus is 0.5 degrees off axis, that translates as the stylus being around only 0.08mm off to one side from where it should be. Half a degree can make a big difference - try it out in the VE spreadsheets. To get within 0.2 degrees would be better, but that means reliably detecting a misalignment of 0.03mm (0.0012")!
Then you have to consider if that is actually a good idea if you don't know how accurately your stylus is mounted on the cantilever, or how accurately the cantilever is suspended. If, as I have seen mentioned, cartridges are made with errors of a degree in these parameters, then where does that leave you?
Then there is also the small matter of the the angle of the cantilever when the platter is at rest compared to when it is revolving. If you can see a difference, it is at least half a degree out.
Then, if you are using effective length as an input parameter, VTF affects it (eg O.1mm from 0 VTF, which is where stylus position is gauged with the cartridge off the arm. Or again, the play in the mounting of the cartridge, which could cause errors of 1 degree, and 0.5mm.
The whole thing is a rat's nest of interdependent variables which, I suppose, keeps the online community, such as yourselves, well occupied!
Personally, this is why I prefer two point protractors. At least if your set-up is off from what you thought it was, (mounting distance, effective length, etc), you have a chance to notice the fact at the second point,
And if your cartridge/stylus is aligned correctly on both (that is, really aligned not wishfully "aligned"), you will be very close, irrespective of mounting distance, as the nulls are not dependent on that parameter if the cartridge has slots; or on effective length, if the mounting distance can be adjusted to suit; and, should an alignment different to the maker's be desired, the cartridge can twist a little,
4. I also have other issues with the marketing of the Uni-protractor.
The first, obviously, is who is Dertonarm? A person happy for people to take his word anonymously, make statements anonymously, and do a marketing exercise anonymously. Of course, presumably there are people who know him (as D, or Daniel? or Axel or what?) but for the rest of us he is just an anonymous person with no history. Does he have a shop? Is he simply giving a sales pitch? I don't hold with that.
I see that there are modifications, or extras, in the pipeline, presumably to sort failings in the original design. Given the fact that they are following close on the heels of the original, I presume their design was ongoing as the original was introduced, and are available as free upgrades to sort a failing in the original design, otherwise why wait to introduce a "better" device to set mounting distance or a special "azimuth template"? Why not include it in the original package? Or wait and introduce it later?
It begs the question of whether it was a design not properly thought through in the first instance, or, cynical marketing, unless upgrades are free as per car recalls for faulty parts.
It appears he has sold some 40 of these protractors. Its prime function is to set mounting distance. Anyone who can do some basic arithmetic can buy a digital caliper for 10 euros and set their arm mounting distance to within 0.1mm (if they can be bothered to be conscientious enough, which applies to any set up - you can spend an hour, or you can spend five minutes setting up your arm and cartridge; you can use a two point protractor or a fancy Uni-P or Feickert; but if it is a shit set-up, it's still a shit set-up...
Sorry for the length of this post, but if you've made it to here, well done, and hopefully you've got something to think about.
Comments welcome...
Regards,
John |
Downunder
Yes - I am that unmasked man...
J |
Peter: Earlier in the thread you asked a question regarding SME and arc protractors (3.11.11) Surely with arms like these the crucial thing is to determine the effective length as accurately as possible and then set the appropriate pivot-to-spindle distance, again as accurately as possible." Thom then goes on to miss the point and talk about another issue which fact you then gently draw to his attention. Then Dertonarm says: But back to the SME V, which was when introduced anticipated like no other tonearm ever before or ever after.
The SME V is unique in the sense that it's offset and effective length (at least its designers thought so and intended it to be that way...) are fixed and pre-determined. Problem is, that SME Ltd. took for granted that each and every cartridge manufacturer would strictly follow IEC standards regarding stylus-mounting slots distance. Which of course they did not.
Now there is the legendary SME slide base to allow sliding the whole tonearm back and forth. That way the arm kind of "moves to the wanted alignment spot".
In theory....
The fact that the fixed offset angle of the fixed headshell isn't really a feature which eases things in any way did not really appeal to the SME engineers in their strive for setting the technical frontier in tonearm design." Now, apart from the tone (hopefully humorously intended, but easily taken as arrogant and disrespectful) and the assumptions regarding the motivation for the design, there are two very elementary errors: the first is assuming that the SME has a fixed offset and fixed effective length. It has a nominal offset, and nominal effective length. The misunderstanding here arises from conflating cartridge offset angle and headshell angle. In the SME the headshell angle is fixed and decided by the geometry selected by the designer (Baerwald/LofgrenA IEC). Once this is decided, another dimension follows, namely, linear offset (LO), and this is then a constant for the hardware and given by the effective length times the sine of the cartridge offset angle. When a cartridge is fitted it retains the headshell angle (within the limits of the mounting hole clearances), and consequently the linear offset remains unchanged. So if you mount a cartridge with say a 12mm mounting hole to Stylus (MH2S) as opposed to one of 9mm MH2S the effective length increases and the cartridge offset decreases, and with a 6mm MH2S the opposite occurs. There is no twisting cartridges unless there is a misalignment within the cartridge (can of worms left unopened...). Only the base needs to be adjusted to supply the correct mounting distance (and therefore overhang) to align the two nulls. I hope I have explained this well enough. It is something over which even some well respected tonearm designers appear to get confused...try drawing it out on paper. The second error is assuming that any standard for cartridge mounting hole to stylus distance was implicit in the design. In fact, the opposite could be argued, as this parameter is only relevant in setting up an SME if you use an arc protractor, which is arguably not as universal as a two point, (which can be used with any arm and cartridge) and with the SME is easy to use, owing to its clever sliding base. To use an arc with the SME V you need to measure the effective length accurately (or as accurately as you can) then obtain and adjust the mounting distance until ideally the two nulls are squared off as per Baerwald/LofgrenA IEC. . Dertonarm says "The SME V is a super strict 9"/Baerwald IEC-standard tonearm. The "super strict" 9"V and the V12 share the same geometry, ie Baerwald/LofgrenA IEC. TPerhaps the V-12 is super strict 12". (I believe the 300 series are actually DIN as opposed to IEC, which should actually appeal to DerTonarm, as he, correctly, in my view, advocates a more general alignment to allow for inner radii less than the IEC standard) You can't really align him a Loefgren or Stevenson curve with good results." Lofgren B IEC is simply a matter of sliding the base slightly forward - no fiddling with the cartridge screws. Dertonarm said in another thread re SME (ironically given the 300 alignment mentioned above) "The SME 300 series is one of the very few tonearms which does come with a kind of "fixed" geometry in ALL parameters. Given its unability to adjust offset, overhang (we can just move the base - which we shouldn't ... - NOT the cartridge ) and effective length, it surely is a fairly unique sample...
...SME took for granted all industry standards of its day (early 1980ies) and said:
"well, if all cartridge designers do obey to and follow the standards given and if all LPs are cut following the new IEC standard, then evrything will be perfect with our new tonearm - it will be the "best tonearm in the world"............"
But the world is an imperfect one and many people do want to go their own ways.
The new SME surely was the LEAST UNIVERSAL tonearm ever designed .......
It is for sure the one tonearm which gives almost no possibilities to adjust to specific cartridge needs or to different arcs." I make no claims for SME universality, but all the above is simply laughable, or misleading. So, Peter, it looks to me like you are setting up the SME correctly. The only issue is that you should use Baerwald/LofgrenA IEC nulls. If you mount your cartridge as accurately as you can in the headshell, then align to the nulls you should be very close. If you have measured your actual effective length, and thereby obtained a mounting distance for the alignment, you can use an arc to check. Hope all this is of use. John |
T Bone From your all your posts on this thread, you have obviously thought all this through, and I appreciate your comments. First let me say I ploughed through the thread prior to posting and read all the arguments with all their points, both relevant and off the wall. I also looked at related threads. I don't have an axe to grind, other than the one called clarity, and I am the first to admit I might not be as clear as I could be at times. To take your points: 1. I have seen no vagueness of analysis on 12" versus 9". Basically he doesn't say why he considers Baerwald/LofgrenA IEC a 9" as opposed to a 12" alignment - the nulls are the same - and confuses the issue with the comments regarding record radii by talking about old records. I'm not saying he's wrong, just that the two things then get connected disproportionately. What I was asking was if he saw a difference between old and new records with full sides - is that a factor. I have old records with very long run out groove, and new ones with the opposite. What he should have been clear about at the beginning was that the issue is primarily about where the minimum radii are in any particular collection and what each person wants to do about it. That is as you say, step one, and I agree. Average out the radii in some way, or use a deck as Nandric wittily suggested, with four arms set for different minima, or whatever. In which case there are no standards, but different nulls and you get a protractor to suit each. You said Standard geometry using standard assumptions does not always produce lowest possible distortion except in the case when the record has the same dimensions as the standard assumptions AND one does not prioritize low distortion in one part of the record over another. I don't disagree. I just asked that he should have been specific rather than vague. 2. In other words, is he just saying: "use a minimum radius of 55mm", (say, or 57 or whatever), or is he effectively saying: "I played around with the spreadsheet and found nulls which work best with both DIN and IEC", or is he saying "I have a theory which says that the existing weightings are inappropriate because there is D% more distortion due the added effects of X and Y and Z, and here is what I think the weighting should be.to compensate - use this to insert into the Lofgren equations to calculate the best alignment for your record collection". That to me, is being vague, or obtuse, deliberately or not. I'm not looking for "new math", just asking for clarity regarding the existing old math. I have looked through the thread and admire your persistence in bringing some sort of sense to the scene, and I take all your points regarding Darkling Dert's alignment being the way it is. I don't disagree with him, or say he is wrong in what he is taking as his parameters and objectives, but until your intervention it appears that he wasn't up for clarifying things. Presumably, he had reasons for that, personal, commercial, legal "foral", who knows. 3. You said I think all of us, including the dastardly Dertonarm, get that minute changes and ball-busting accuracy requirements for one or two of the parameters will necessitate the same accuracy requirements for ALL the geometric inputs (though inner-most groove by its very nature must have some flexibility because one does not newly align (or set up a new headshell) for every particular length). I wasn't talking about being so anal as to change alignment for every record, nor saying that DerT wasn't concerned with accuracy, but drawing attention to the fact that he didn't share any measure of that concern in terms of how accurate was his offset angle adjustment method. As you well know, if the angle is off by half a degree, never mind more, all that precision will leave your alignment different from what was intended, and generally not in a nice way. You said: As an aside, as far as I can tell, the supplied lengths and angle for your signature tonearm don't match the null points noted in the manual. The null points for all my RP1 arms as I recall, were 63.5 and 119.5. with a minimum radii of 58/146 - basically Baerwald Din, rather than IEC, as I had more records with that characteristic, and it seemed a good option - in that regard I concur with DerT. I think he is correct. And I would agree that a different alignment approach can pay dividends. Not having seen the supplied protractor, I can only presume it was in fact like a jig so that people could set their cart perfectly straight without deviating from appropriate offset angle, and then the overhang would fall into place shown on the protractor. I don't get this, T Bone. No jig was supplied. The protractor was a two point, and the effective length was a nominal 230mm, the offset, a nominal 23.5degrees, with a linear offset of 91.5. Mounting distance was therefore variable as it would depend on the effective length with cartridge (see SME comments to Peterayer above) Using the accuracy as stated, one would not have come up with the same null points as you did, which means that anyone using a protractor other than yours would have been off Baerwald by a decent bit, even if they had managed to get the offset angle and mounting distance perfect. Could you be more specific? I'd have thought that would be more applicable to arc protractors... as long as there is play in the cartridge mount you can get a Baerwald IEC or Lofgren without any problem -just adjust angle and mounting distance as necessary. You'd need a two point protractor, though. 4. I don't know Dertonarm, and perhaps I could dig up some info on him, if I had to (the internet is a wonderful thing, but time consuming). My point was that I don't think I should have to. If I was selling something, I'd be happy for people to know who I was, and where I was - it's not an issue for me - although perhaps I'm just a bit behind the times and it's more acceptable now, in a forum, on ebay etc. Anyway, you knew exactly who I was, without any digging, and, by now, anyone else who wishes will know a great deal. As to the protractor, other people challenged him on the subject, and rather than complain about being attacked, he made it. He is now offering it out. Good for him, I hope he makes his money back, but he isn't doing anything different from a host of others who try their luck at the hifi business. Is it more expensive than a laminated piece of cardboard? Yes. Is it for everyone or is necessary for achieving good sound? No. But neither is a gold-plated tonearm with diamonds on the headshell. A slightly cheap shot - I don't know you and, with you, I have no beef, T Bone, but perhaps I deserve it. If I have been a bit too critical in some areas and if I've caused offence, I apologise, But reading the thread, there were some obvious things that needed to be said. And I agree that gold plate and diamonds aren't obligatory, however, you may have given our man, Diamante Dert, an idea for a more limited edition... |
Thuchan
If Dertonarm has a reputation (whatever it may be and for whatever reason) hopefully he deserves it. That doesn't mean one should accept everything he says is correct when it patently is not, and is not a matter of opinion.
I have responded to T Bone - see above.
Regarding opinions, I may have have been a bit too straightforward in expressing some of mine, and for any offence given, I apologise. But there is no point in ignoring mistakes - I've certainly made enough of those in my life, and was the better for having them pointed out to me...
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Thanks Peter
Glad you found it clearly stated
J
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Thuchan, I didn't say you, personally, accepted everything Dertonarm said. I was making a general point. I am always willing to discuss things, and admit when I'm wrong, the operative words being "discuss" and " wrong". you said The (analogue) world is like it is, some good developers and failed ones.
Mostly the failing guys do have a motivation to define the world and tell the succesful developers what they seem to have done in a wrong way.
believe me, I do know producers of tonearms and even turntables who do understand the theoretical implications of proper alignment but they do not really care about it. Success or failure in hifi and good and bad developers do not necessarily correlate. Making money from a product doesn't mean it is good, merely that a lot of people buy it, and vice versa. My, and many other's, experience is that often a good product can fail because someone who can influence the market decides it should fail - it's all part of the way markets work... probably best to stay out of it (or, vice versa, as given by your example above,...!) J |
Dertonarm Glad to see you have responded to my post (via T Bone). Why did you do that? I am willing to discuss the SME issue directly. You said Given the fact that the mounting hole in the SME V is not really intended to allow anything like a "cartridge offset angle" (which in tonearm geometry not really exists at all - other as by wishful thinking)... please read my post to Peter re the conflation of headshell and offset angles and why this is confusing.I am assuming you mean cartridge mounting. ...one can assume that it's designer did so by good reason... That is a fair assumption, but only if you give a fair analysis of why they might have done it that way. ...As this mounting hole is (to the regret of many of it's owners past and present - including me ..) not really an elongated one either... Patently not, given it has no slots. Why would this be? ...the effective length is - at least in theory and designer's intention - pre-determined as well... No. The alignment chosen, ie Baerwald/LofgrenA IEC, is predetermined. The effective length is nominal. ...Setting the "cartridge offset angle" other than the offset angle of the tonearm's headshell does produce an additional break-down torque in the tonearm's static model - i.e. an additional force vector.
This is a plain mechanical fact - thanks to Isaac N. ...;-) .... This is vague. What do you mean by "break down torque" and why would it be additional if the overhang remains the same? The stylus merely rotates, the groove tangent remains the same, therefore the vector towards the centre remains the same. The only change could be due to the stylus, which may or may not increase the force along the groove tangent depending on the stylus profile. (re Issac Newton - I have heard he had a great hifi, but maybe Einstein's was better on the super fast transients... (just a joke)) That additional break-down torque does of course influence the skating force. In what way, by how much? Now you get to the point: Now is the SME V designed and constructed strictly following Löfgren A IEC (Baerwald)?
According to it's designer's it is.
According to it's technical parameters it is too.
Can one adapt the SME V to different alignments by moving its slide carriage? It was not intended to adapt to different alignments, but to different position of stylus relative to the mounting hole of the SME V. Granted, though Lofgren B IEC is much easier than with a slotted headshell - no need to loosen the cartridge, just slide the base. ...The moving of the SME carriage does alter P2S and adapt's the effective length to different distances - in cartridges - between the mounting hole and the stylus. Correct Thus being able to retain the original Löfgren A IEC alignment is was calculated to. Thank you for agreeing. But why not just say you were wrong, or had expressed yourself badly, previously? As Piet Hein, the Danish scientist/philosopher/poet said: The road to wisdom?
Well, it's plain
And simple to express:
Err
And err
And err again
But less
And less
And less. |
T Bone I take on board all your points, and, as it happens, I agree with Dertonarm on some points. I just wish he would stop obfuscating and avoiding admitting he has completely missed the point on others. Regarding reasons for different weighting, check out Keith Howard's piece in the features/reference section http://www.stereophile.com You said you couldn't get the numbers to match and something had to give. Something always does. In this case, the theoretical world. I never saw the point of giving numbers which were impractical for set up. Thirty years ago, no one set their tracking angle and the rest, to three decimals.No one does today. The numbers were rounded up for a nominal effective length of 230. The important word is "nominal". I should have perhaps laboured the point more, but that was back when tonearm geometry was perhaps better understood, and the issues concerning the choice of design - sliding vs fixed pivot, slots versus holes etc, were better appreciated. How are you doing with the SME (or rather, sliding base) geometry? I'm going to post an explanation separately. You said Your point about 'just adjust angle and mounting distance as necessary' is EXACTLY right and appropriate given the imperfections we each bring to the table when we mount a tonearm/cart, but that is the art, not the science (and most of the critiques of Dertonarm's ideas and protractor on this thread are on the science, not the art, of tonearm setup, and his product I would think is specifically addressing ease of getting the art right - because the science is gotten right by anyone who gets the algebra right). If his device makes setting up easier I'm all for it, but not if it is less accurate. That was my reason for posting originally. He doesn't say what the accuracy of his device is, compared, for example, to a paper two point. Now I don't know how accurate a paper two point is, but I do know it is more accurate than the easier one point - two nulls are always better than one, as they allow an obvious a way of double checking. And in any case, as Dertonarm has said in the past:
But the alignment of the zero (points) is the raw basic on which everything else builds.
So, adding an arc in addition should certainly make it easier to set up (for a specific effective length) as the arc and the nulls must intersect, thus giving two opportunities to check offset. I don't have a problem with that, I think it is a good idea. If it is easier, great, fine, but is it more accurate...? Hopefully, if not DerT, then someone will tell us. J |
Jazzgene
Thanks for your comments. I find them helpful and illustrative.
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Geoch As Dertonarm has avoided the issue yet again, (he only seems to respond to posts on which he feels he can appear to be right) and (if your question was genuine and not to provoke) perhaps I can help. You said I have a question for you (and it is a genuine one, due to my ignorance) :
The Talea, Schroeder, Clearaudio Satisfy are designed with adjustable arc on their rudimentary headshell. The Simon Yorke has circular headshell which does not shows any preference in cartridge angle. Moreover, there are some circular cartridge bodies also! How does the Newton's law applies there? Newton (the famous hifi enthusiast), said that to all forces there is an equal and opposite reaction.Bear with me if you are familiar with the following, but I will say it for those that are not. The friction of the stylus against the moving groove causes a force which is aligned along the groove and reacts against the arm mount. The resultant would pull the arm inwards and out of the groove, were it not for a force reacting against it, so a counter force needs to be applied in some fashion. VTF supplies some of this force and the remainder usually as an antiskate device of some sort near the pivot. As you correctly state, Geoch, this force has to increase as the arm approaches the centre, because, while the overhang is constant, the radius decreases, therefore the inward force varies in proportion. All good arms have antiskate/bias, adjustable in amount and in degree. Longer arms need less antiskate, as they have less overhang. (There are arms with zero or negative overhang (underhang). These have very small skating forces, but, unless fitted with a mechanism to maintain the cartridge parallel to the groove, will have large tracking errors.) Whether a cartridge is cylindrical, cuboid, flower-shaped or whatever, is neither here nor there. It does not affect antiskate if correctly mounted. The bottom line is that there is only a vector towards the pivot from the stylus, and a vector from the stylus along the groove, These result in an inward rotation of the arm. It has nothing to do with cartridge offset angles, except inasmuch as the stylus contributes more or less to the frictional force along the groove, (eg elliptical versus conical) and certainly nothing to do with the cartridge body shape. I could explain further, but for now that is enough. So, the question of round headshells, rotating headshells is all baloney in terms of antiskate. The arms DT mentions may well not have a specified offset and therefore provide a facility for adjusting whatever offset is desired, which is a good thing (although the way they do it doesn't look as smart to me as he seems to see it, as none of them apply the rotation at or around the stylus where it would be most useful (and where, should I ever (no! no!) design another tonearm, put it - (there's a hint for DT if he's designing an arm...god forbid) Other stuff: About weird shaped cartridges (in my opinion the result of designers /stylists who have more interest in being different, than in good, practical functional design) Dert says they avoid a pre-determined offset angle and thus are much easier to adapt to different alignments (calculations) without trade-offs due to the alternation of a "pre-determined" offset angle by a cartridge's body aligned in a different angle. Well, he would say that, given his commitment to arc protractors: the more weird shapes there are, the harder it is to align using anything else. Cartridge manufacturers must be rubbing their hands at the prospect of being able to mount generators and cantilevers any old way... Dertonarm says Circular bodies further reduce the problem, which problem? he doesn't say, for it isn't antiskate. but - unless they follow the Ikeda or DECCA/London cantilever-less principle - there is still the line of the cantilever which should be in line with the offset angle. I hope every reader out there (with a Decca (or otherwise)) sees this error for what it is. The Decca does not have a cantilever in the accepted sense, but has the equivalent nevertheless - the armature - it is just not visible. So it must be aligned like any other cartridge. If it wasn't cantilevered one could mount it reversed - try that with your client's Decca, Dertonarm, and you'll probably get a slap round the ear for being so stupid... Also when we talk about cartridge offset angle, that term is usually accepted as encompassing the generator, cantilever and stylus, which ideally should all be in line. Errors here are an issue for cartridge designers and manufacturers. By all means line up to a cantilever, but that doesn't mean either the generator or stylus are lined up with the cantilever. Geoch, Dertonarm shows his ignorance and arrogance by his response to you. Instead of explaining something he asks you for your ideas, perhaps because he is not truly clear in his thinking, as in the case of SME arms. I realise your wisdom in avoiding getting too involved, but avoidance of bullying, for that is what it is, can lead to unwanted and unpleasant consequences, both here, in a small way, and, in the greater world, in a big way. |
Jazzgene,
I have not heard your arm, but if you tell me it's a good arm and you prefer it without antiskate, I believe you.
From the manual it appears that VPI recommend using a higher tracking force than might be otherwise used. In my post I mentioned that downforce contributes to antiskate.
That the wiring can supply some antiskate, depending on how it is dressed, is mentioned too, in the manual. I don't know if you use this procedure, but these are methods of counteracting the skating force, without a specific antiskate device, so in that sense the arm has the means to do it, but you can choose not to use it, as with any arm.
Being longer than a 9" helps to an extent and the specific construction of the arm, being a unipivot, might lead to compensating forces in the rotational mode. The skating force is always present, though.
But if all the above mentioned things together mean you can do without a dedicated mechanical device to supply the antiskate, (spring/ string and weight etc), then that's a good thing, and the designer is to be commended.
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Jazzgene, You said ...Harry says in the manual that with every tonearm he's heard, it sounded better without anti-skate and heavier VTF. Perhaps so, but there can be issues with this method depending on the cartridge. The bottom line is that there is a force which tries to rotate the arm inwards and it is a consequence of pivoted arms. It's not my opinion - it's the way it is. The issue is what to do with the fact of it. That then becomes a matter of choice and preference for the designer and the user. |
Perhaps it might be a good idea to go back to basics. There are two aspects to this issue. One is to acknowledge what the force is and how it originates. Second to see how it manifests itself on a record deck.
While we might call it antiskate, or bias, or whatever, the force which pulls the arm inwards is not specific to tonearms. It can apply in any situation where there are two forces opposing each other.
To illustrate the simple example of a linear tracker. (Those of you with linear trackers can start practising your smug grin.)
Say you hold one end of a short rope. You are the Tonearm bearing. You put a conical blob of blutak in the middle of the rope - the Stylus. Your wife holds the other rope end. She is Friction.
Friction acts on the Stylus by pulling it along the groove in a direction directly opposed to the Tonearm bearing. It reacts by holding on and pulling back. The rope is straight. The Stylus remains unmoving in the middle. As friction moves to the side, Tonearm bearing follows every move (hopefully).
Now a Pivoted arm.
Friction takes a different tack. She pulls at an angle. Tonearm bearing reacts against Friction. It is immovable. It holds on to the Stylus. but the rope wants to straighten, and Stylus will be pulled sideways, unless......
Help arrives. Another pal called VTF, stands on the Stylus. now it's harder for Friction to pull Stylus sideways. Then yet another pal, Antiskate, comes in and pulls the Stylus in a direction which stops the rope straightening, just enough to stop the Stylus moving without pulling it in the opposite direction.....
Ok, this is simplistic, but relevant. First, note that we have no mention of cartridges, only the stylus which is simply the name for a point on our rope. The angle we talk about is the angle formed by a line from pivot to stylus and stylus to groove. Which is not quite the same thing as cartridge offset.
Forget about cartridge offset for the moment and just imagine your arm with no cartridge, just a sewing needle on the end where the stylus would be, and then follow its arc on a record. Follow it beyond the inner groove, beyond the label, beyond the spindle, and out the other side. See how the angle between pivot, needle, and groove changes. Think of the rope story and in what direction the arm will be pulled. The angle changes towards the centre not varying much, but under 7cm radius, the closer to the spindle it gets the greater it becomes, until at 0 it is a right angle..
That is the basis of the antiskate issue. Does it exist as a force. It exists, yes, it definitely does. But why some people prefer no antiskate, that is for them to say. My arms had an antiskate mechanism, using lever and thread, which allowed for varying the force, and the ratio to some extent across the record, or it could be removed completely. But it was not any more sophisticated than that (It could even have been used to apply a reducing force like the Morsiani,though I am not aware anyone ever did, and not a negative antiskate as in their example of the blank disc; I think there's something wrong there.)
It would be possible to design a cam system given different leverages so as better to follow the average variation, though not the instantaneous.
Whether you can adjust for it totally and in every way, I doubt. As there are many other factors involved in the friction calculation. Some people are more sensitive to its effects than others. Personally, I always tried to compensate for it. I was concerned with its effects on imaging, soundstage etc
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Mesael Sorry. I said The angle changes towards the centre not varying much, but under 7cm radius, the closer to the spindle it gets, the greater it becomes, until at 0 it is a right angle.. What this means is that the inward force trying to rotate the arm stays more or less constant within a few percent reducing slightly following the tracking error curve of the arm (not the tracking distortion curve) which varies across the record. Depending on the overhang used and the arm effective length, at the inner null the force starts to increase rapidly. So it would appear that the ideal would be to follow this curve, reducing slightly then increasing. However, it has been shown that there are other factors which increase the friction force as the radius decreases, which would skew this result and make it more likely that the force should at least be constant then increase, or even gradually increase all the way across the record When I designed my arm that's what I did, as I thought that, like tracking distortion it seemed to be worse towards the inner grooves, and less of an issue further out, and should be weighted that way. But it was all "suck it and see". So, really, a tonearm should perhaps give the user the option of trying different things. The actual amount of antiskate needed is very much dependent on stylus profile and downforce. With enough downforce the stylus will never meet a modulation large enough for it to lose contact with the outside wall, or even throw it up out of the groove. However there will still be unequal forces on each side of the groove unless there is some kind of compensation. As Dertonarm says, a longer arm has less skating force than a shorter one. But it is still there, and it has to be dealt with somehow - you can't just sweep it under the mat.... |
Jazzgene you said The thing is if the anti-skate force differs from the beginning to the end of an LP, how can a constant weight compensation like the VPI weight on a string work correctly on the entire LP? It can't, I would think. If your antiskate is the JMW 9 then the force will increase as the arm moves towards the centre if the little arm with the weight is horizontal when the arm reaches the run out. if it is literally a weight on a string, like the old SME, it can aso be set to apply an increasing or reducing force depending on the angle it makes with the arm, though this doesn't apply if the string run round the diameter of the pillar and the radius it is acting at doesn't change. Check the output wire and make sure it is not counteracting or adding to the antiskate. You can use headphones and a test record to check for distortion on one channel more than the other. If it distorts on the right, you need more antiskate.If the left, less. If it still distorts on the left with no antiskate, the wire is pulling outwards. Using a greater VTF stops the distortion by nailing the stylus in the groove, but it also increases the skating force because friction is proportional to VTF. If this was not so, our cars would go faster as the braking force increased... |
Thuchan
I often sweep things under the mat.... Most people probably do too. Especially the hard things, like precision in areas where it is hard to be accurate or measure reliably - antiskate is one, and, for me, setting cartridge offset is another.
I was playing with an angle protractor this evening and trying to see how repeatably I could measure an angle. Where it was possible to physically set the protractor against both objects it was easy, but by eye maybe within 0.5 degrees.... that is one place we need precision.
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As an aside: Halcro, you asked (16th April): although something tells me that whilst the UNIprotractor 'arm' is not centred on the Spindle, there might be some mathematical formula which, when the micrometer is wound down to its minimum position, could still be used to check Spindle to Pivot dimensions? I don't know how the device works, how it differs from the Dennesen, or what the various fine adjustment features are, but presumably they allow the device to be set up for Baerwald IEC nulls, (and whatever other nulls are supplied). If the principle is Dennesen, which it appears to be, then arm mounting distance (pivot to spindle distance) can be obtained by finding two dimensions: First: The distance to the arm pivot as measured along the axis of the perspex arm from the point where the null radius crosses it. Call this X. Second: The distance from the centre of the spindle along the null radius to the centre line of the perspex arm that terminates on the arm pivot. This distance varies depending on the alignment, and must adjust for each, but you don't have to measure it if the device can be set for Baerwald IEC as it is given by: Outer null minus Inner null, then divide by 2, Call this Y. (For Baerwald IEC this is 27.45. If the device is set for another alignment, then the same calculation applies with the appropriate nulls.) This gives a right angled triangle, so the mounting distance is given by: the square root of: X squared plus Y squared. This applies to the Dennesen also, of course, but only for the Baerwald alignment for which it is set up, unless modified. The accuracy of the method depends on how well you can measure the distance along the perspex arm to the pivot. It does beg the question, though, of why one would need to know the mounting distance, as the Dennesen principle allows correct alignment with any existing and unknown mounting distance. If the distance has been set wrongly for a particular arm, this would be corrected (for a slotted headshell) by adjusting the effective length and cartridge offset (assuming enough adjustment) to match the null on the protractor. . |
Halcro
I haven't used it, but I'm sure you are correct in assuming a different principle for the Feickert. If it has the facility to set or measure mounting distance, it is because it uses arcs which have to be referenced to a known pivot point.
You are correct in saying that headshell type cartridges having no facility for adjustment need to have the effective length of the arm with the cartridge fitted known or measured. Also the true cartridge offset angle (which will depend on the arm/cartridge combination) also known or measured. Then an appropriate mounting distance can be calculated, and precisely set.
Alternatively, using an arm with a known alignment, you can use (if it has the same alignment) a two point protractor to set up. By sliding the base the offset will be given automatically. Swapping different kinds of these cartridges would depend on them having the same headshell mounting collar to stylus distance.
You are also right in saying that swapping headshells could be problematic. It looks to me that swapping headshells between arms would require them to be set up initially with one headshell/ cartridge combination which remained set once the first arm was done, and which was then used to set the remaining arms with adjustment achieved at the bases of the others, assuming they were different arms.
The alignment chosen would have to also be the same for each set up, irrespective of the arm design, but the arms could be different lengths. Then any cartridge/ headshell combination could be set up to suit these alignments without moving the bases. This would depend on the headshells having slots, though the initial headshell could have holes as long as the arm used was designed to the chosen alignment.
I think that covers most of the difficulties..... please feel free to point out a simpler way, any mistakes or anything I've overlooked.
John
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Dertonarm: You said: If a phono protractor really is universal, it must automatically align regardless of the given mounting distance. I would agree with you in that, but I would disagree with you when you say that Setting the mounting distance is done before aligning the tonearm. It is a "conditio" already set before starting the alignment. This is only necessary when using a protractor which requires it - like yours - because, as you say, The UNI-Pro does follow the smart idea of Francis Dennesen and adapts to whatever P2S a given tonearm is mounted. As is the case with the Dennesen, arms with adjustable bases and fixed headshell mounts are awkward for your protractor. So it can´t really be called universal, as it only caters for arms with adjustment for effective length and offset at the headshell. In most cases the tonearm is already mounted when one starts to align the tonearm/cartridge All arms are "mounted" prior to alignment, but, as you are aware, not all arms have the pivot to spindle distance fixed at a specific measurement, but have the facility to adjust this, as in any arm on a pod or adjustable arm board, or the SME, and arms like it. It could be argued that a more universal version of the Dennesen would have adapted it to allow its use with arms such as these, as well as with different alignments. . |
Dertonarm: you said If however the user does wish to align the given tonearm exactly to the geometry (especially the offset angle) the tonearm was designed with, then knowing the P2S and setting it precisely (IF possible ...) is important.
Important only if one wants to avoid an additional breakdown torque and thus another source for skating force in a pivot tonearm with a fixed offset cartridge mounting.
With tonarms like the Schroeder, Reed or Talea however we won't run into this problem at all. Didn´t you suggest starting an antiskate thread? But since you have brought the subject up, in what way do the Reed, Talea and Schroeder differ from other arms? The Talea and Schroeder appear to have a facility to alter the effective length,(as does any other arm with a slotted or movable headshell) and they have a facility to alter the headshell angle. What is the difference between this and altering the angle in a normal headshell? The Reed has a normal slotted headshell except for the model with its little azimuth adjusting device. What´s the difference? I would honestly like to know. And I am intrigued to know what are these mysterious additional breakdown torques which the above arms don´t have. Unless you can explain where else it comes from, the only torque acting to rotate the arm inwards is generated by forces acting on the stylus in reaction to downforce and friction. More downforce, more friction; more friction, more inwards torque. No downforce, no friction.; no friction, no torque. Using more downforce doesn´t make the inwards force disappear, just that the force acting downwards is enough to allow the stylus to track without distorting. The imbalance of forces on inner and outer groove walls hasn´t gone. John . |
Dertonarm Allow me to return the rattle that you have thrown from the pram: You said: you don't really want me to tell you what additional breakdown torque is and why it does of course influence the skating force. If I didn´t wish to know I wouldn´t have asked. I´m always willing to learn something new and if you have something new to say, I´m willing to hear it. It is just that you seem unwilling or afraid to actually say anything at all - commercial reasons? You said If you think skating force is just a phenomenon of friction and downforce - fine, certainly no problem with me. I didn´t say that. A neat attempt at misrepresentation. You said If you muse about the model and draw yourself a good and precise force vector model of a pivot tonearm, you'll figure out. I have done. A long time ago. And since then I have re-considered my original thoughts and am willing to continue doing so in the light of new facts. You said: I did suggest starting a "antiskating thread" - I didn't say I want to start it nor did I say I want to participate in it.I have no questions regarding skating force in tonearms. But a lot of talk and precious few answers, it seems. You said: Regarding the UNI-Protractor and it's "universal" use.
Apparently you haven't worked with it so far and haven't understand it's principle either. Otherwise none of the comments in your last two posts would have been made. I think you´ll find it was I (not you)who briefly explained earlier the way your protractor works. I don´t know if you´ve done this elsewhere, but you don´t do it in your audiogon advertisement. Neither do you credit, or even mention, Dennesen at all in your ad. You say I don´t understand the principle you used. I understand it only too well. cheers . |
Dertonarm Again, since you were the one who brought it up, you said: If you think you can do better - go ahead design it. I already have - as soon as I saw the pics I knew you had missed the basic principle of the Dennesen, and, by extension, the underlying concept, which goes back to Percy Wilson in 1924. Anyone who understands the principle could, with a bit of thought, see how you could have made your protractor more universal, more precise, and easier to use, without compromising the existing features (and you can admit having used it for 25 years, yet haven´t seen this!) You said: So far your comments have shown little more than poor judgement, a fairly high aggression and very little understanding of the subject. Yes, bad judgement in expecting anything other than obfuscation. Aggression? Scarcely. Understanding? I can only promise to try and be more understanding of your explanations. You said: I welcome your attempt to put your name on the wall again and to prepare the road for yourself for a soon-to-be return to the audio market.
No problem with me - as far as I am concerned you are certainly welcome. Thanks, spoken like the true salesman you are. But, unlike yourself, I have no plans to market my add-on to the Uni-Protractor, to compensate for its non-universality. (Nor my new 12" FR66-killer zero antiskate adjustable effective length, dynamically balanced, irregular-pseudo-elliptical headshell arm, (or even my headshell mounted miniaturised preamp which uses the power gained from negating various mysterious breakdown torques to enable a single run of fine cable from the cartridge to the power amp...)) You said: I might react to a post by you from time to time only, but so far very few actually did ask for an answer or a comment. Most were simply lacking content and seriousness. Luckily my last post had two straightforward questions for you to answer, so you might start there. As you must have missed one of them, and misunderstood the other, I´ll repeat: in what way do the Reed, Talea and Schroeder differ from other arms? The Talea and Schroeder appear to have a facility to alter the effective length,(as does any other arm with a slotted or movable headshell) and they have a facility to alter the headshell angle. What is the difference between this and altering the angle in a normal headshell?
The Reed has a normal slotted headshell except for the model with its little azimuth adjusting device.
What´s the difference? I would honestly like to know.
And I am intrigued to know what are these mysterious additional breakdown torques which the above arms don´t have. Cheers again |
