Uni-Protractor Set tonearm alignment

Hi Dev, not yet. Delayed by "real world business commitments" which consumed all my time ...;-) .... hope I can list it tonight.
Cheers,
D.

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

John,
Could you please expand on your comment regarding the SME V arm? I have one of these and currently use the two-point MintLP protractor. What is faulty about Dertonarm's statements about the SME geometry? Thanks.

John G,
A few comments...

#1) I have nothing to say on his or your comments on antiskate and SME. I have seen no vagueness of analysis on 12" vs 9". Given what you say later in your post, it is pretty obvious you have a simple explanation (but you did not give your analysis either). I think if it is obvious to you, it may also be obvious to others. It is to me. If you have additional complex analysis of the differences, please share. I think 'analysis' of 'why' old full-length records should have different innermost and outermost grooves is kind of a moot point. They are different (at least mine are). If one has looked at enough records, one may notice patterns among periods, recording companies, cutters, etc. I think that noting the difference and applying math to it to achieve better set up where desirable is easy, and I think that is what he has done. 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.

#2) I don't find him unclear on geometry issues at all. As far as I can tell, he has stipulated everything you have written. He shouldn't have to as the math does not change. He mentioned in these fora, that given his parameters and listening preferences, he had found a better way (than the manufacturer's stated geometry, or standard Baerwald geometry using manufacturer's stated effective length) to set up a particular tonearm. Others pestered him on it, and he politely refused to be harassed. The effort spent by one person in particular on harassing him about this subject could fill a small magazine issue, and may have closed down two threads. I thought it would do this thread in, but he left some hints about it, and I did some analysis to figure out Dertonarm's 'geometry' including the "weightings" you speak about. It took me about 10mins to come up with it. If you did not read the analysis above, the short version is that assumes IEC records, and is basically a cross between Stevenson's 'tilt' and Lofgren A's curve shape. It achieves lower average distortion in the place where he wants to achieve lower distortion (second half of the record), and achieves sharply lower average distortion in the last 10% of the record for long records than either of the standard setups, especially when those tonearms/carts have been set up for DIN. It is, as he has stated, entirely a matter of choice based on his record selection and his priorities on where on the record he wants to hear his distortion (or lack of it). It is decidedly not 'new math'.

#3) 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). If you read his posting history, it is blatantly obvious he shares your opinion. On the other hand, bad implementation of offset angle is bad - on any geometry on any tonearm.

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. 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. 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.

#4) If you read his posting history, you can glean a fair bit of his history (who he is, what he has done, etc). A little bit of digging and you can find more. I don't know him personally but have discovered a little on these threads and more elsewhere. Without doing the digging on you, one would not know who you are either. 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. 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.

If you have but one or two tonearms, it may not be for you. If you have a half dozen, it may be cheaper than buying a half dozen protractors specifically designed for those half dozen arms. One could obviously make one's own 'mirrored' protractor using a CAD program, printing on clear plastic and mounting that on cardboard with some aluminum foil in between. But that is beyond most people who don't have CAD design experience. I don't have anything better than SketchUp, which is kind of a PITA to use, and I figure that if I don't like mine, I can probably sell it and not lose too much money on it. And in the meantime, I will have a cheaper tonearm-specific protractor for my more than half-dozen arms than I would if I bought just one. And I will have a universal protractor which will work on other tonearms. And I expect that it will be easy to use so that my conscientious set up will take less time and back pain than it would otherwise. I know nothing of the extra goodies/modifications yet other than what he has written, so cannot comment. You could send him an email and ask him yourself.

John Gordon , you are new to Audiogon. This is your first thread´s reply which is ok. I am wondering about your conclusions which run on a string, IMHO the only intention to undermine Dertonarm`s reputation. I am not going into detail, T_Bone did in a very persuasive way. If you are really an expert on tonearm design you may have a different approach to this topic as you used it.

Best & Fun Only
Thuchan