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
