Hi Photon46 In the cartridge setup instructions with the Vacuum State Guru protractor, Allen Wright says that after checking many cartridge alignments with final adjustment tunings done by ear, there is a consistent trend of finding settings about 1.27mm behind traditional Cotter points on an alignment arc. After spending part of last Sunday setting up an Ortofon Kontrapunkt H with a super fineline stylus, I ended up very close to those points myself. Don't get misled by vague statements which offhandedly negate or discard existing knowledge, and appear to have discovered something new in promoting a product. Another way of saying the quote above is: "If you try a Lofgren B DIN alignment you might find it suits your LPs better than the Lofgren A/Baerwald IEC (which is the usual alignment with nulls at 66 and 121), which is what I (the Guru) am doing, but not telling you." But that doesn't quite have the same mystique..... That is in effect what is happening with the new alignment - it is LofgrenB-ish - for a 230mm arm, it now has effective length of 228.73, overhang reduced to 16.78 and offset angle reduced to 22.87degrees. John . |
Hi Nandric, you said But there must be
the corresponding max. distortion at some other 'points'.
Well it seems to me that we should worry about those also.
I have never seen any numerical values for those in this forum. It may be the case that while I feel 'proud' about my own selection of the zero points my records are in a
sade state because of my choice? For most alignments there are three maxima (Stevenson being a special case). Typical distortion values for these are (for a 230 arm) 0.65% for the three equal LogrenA/Baerwald IEC maxima and 0.42% average across the side. For Lofgren B IEC the average is 0.38% but the maximum is now 1% at the innermost groove. For DIN alignments, there is more distortion when playing a DIN LP but less at the inner grooves when playing a IEC LP. This is why I chose a DIN alignment 30 years ago. Dertonarm's Uni-DIN alignment is a variation on this which reduces the inner maximum to 0.5% for DIN LPs and lowers the middle max to 0.5% while increasing the outer max to over 1%. John . |
Hi Thekong Dertonarm said the alignment I did choose actually minimizes distortion in the last 2/3 ( not just last 1/3) of the record groove's radius He should have said ...the alignment I did choose reduces distortion.... The alignment reduces it. It doesn't minimize it. It can easily be reduced further, but at the expense of an increase elsewhere, which is the point being ignored. Regarding changes in overhang and offset. For a 9" arm, if the overhang is increased by 0.5mm, and offset increased by 0.5 degree, they tend to compensate, as they also do when reduced by similar amounts. If one is reduced as the other is increased, the errors add and the distortion increases. So you could have made unintended errors in your setup and they could sound ok. Or not. As an illustration, if the overhang is increased by 0.5mm without the offset changing, you basically get Lofgren B, which may well sound better on your favourite album... John . |
Cocoabaroque, Are we not taking it on faith that the great masters of cartridge alignment(!)--Lofgren, Baerwald, Stephenson, etc knew what they were doing even though they disagree amongst themselves? You don't have to take anything on faith, it is not a matter of "faith". The only reason we can all actually talk about alignments and geometry and use the words to describe them is because Loefgren, (and Wilson before him in the 20's) spent many hours (without calculators or computers) to figure out from first principles how to minimise tracking error and then tracking distortion. Subsequently Baerwald, Bauer, Stephenson et al came up with variations based on those calculations, which have different perpectives, but in no way disagree. Rega doesn't use a "special" alignment. It is just not Loefgren A IEC. Stephenson IEC is simply a Loefgren A with inner radius around 54.8mm which places the inner null at 60.3mm, the IEC inner radius. Dertonarm is correct in saying that conditions change as the radius decreases, but the calculations for minimising tracking error are the same as they always have been. It is the distortion caused by that error that is the issue... Which is why he is advocating different alignments. But these alignments are still predicated on the Loefgren equations and merely reflect his preferences as to where the equations should be weighted. This can now be done by anyone and his brother, who (unlike Loefgren) has access to the excellent Vinyl Engine calculators. In the same way that Stephenson came up with his variation, we can enter minimum and maximum radii such that the shape of the distortion curve suits our purpose for the records we have. However, as far as I know, no one has yet come up with a formula which has been designed to use different weightings (other than those for average distortion (Loefgren B), or for minimising/equalising distortion peaks (LoefgrenA)) Whatever our reasons, in coping with tracing distortions caused by using modern stereo (versus old mono) stylii, Dertonarm and the rest of us are basically still using Lofgren A, with variations in input parameters. Although all this doesn't address the issue of how significant are errors in set up in relation to the distortions at particular radii. . |
Moonglum,
After the first 60 tries (yes you read that correctly) I was still unhappy with the final cart position which often ended up with an estimated 0.2mm offset from target in any given direction(!!!). I finally got the perfect result (and was only truly happy) after 70 tries...
Interesting to hear your take - I would imagine that +/-0.2mm is pretty good and that 0.5mm is more typical. I have played around trying to estimate how accurately I could set the offset angle, as I think that is the real unknown when it comes to talking about accuracy, and reckon +/-0.25 degree is the variation. However, no protractor manufacturer, as far as I know, actually says either how accurately their protractor is made, or how accurate, precise and repeatable are the setups typically achieved with their device. In particular, regarding offset angle. So, is a Mint more accurate than a Denessen, a DB, a Wally tractor, a Feickert? How to measure this? |
Dertonarm, Löfgren just used euclidean geometry.... He was however unquestioned the first to muse and care about giving phono playback an optimized geometric solid basis. As you say DT, thankfully we can stick to Euclid and don't have to concern ourselves with Riemann. Re primacy, I believe it was Percy Wilson who published the first analysis of offset tonearm geometry and Loefgren accounted for the factor of decreasing radius as a contribution to distortion. As you say, "every analog audiophile should be grateful for his attempt." I agree when you say
his preferences and weightings aren't as universal applicable as they were in 1934/38.
My point was simply that the weightings for skewing the tracking error equations haven't changed. What has happened, as you are well aware, is that we can now easily change the input parameters to the same good old equations and find, as you have done, an alignment that is preferable, and then specify appropriate nulls. But these nulls are not related to the actual inner radius of the records, that is, there is no formula that I have seen published, where I can enter an actual inner and outer radius and come up with say, Uni IEC, or any other null based alignment. John . |
Dear Nikola, I find it harder to see (and hear) things as time marches on. But I try. As you say, the protractor is only as good as the widest tolerance. Which is my point. As DT says, spindles vary, by 0.25mm. So there we actually have a number. But he asks Why use a super accurate protractor?
Simply because it helps to get the best (read: best sonic performance) out of your cartridge/tonearm. So super accurate means that "best" is sonic performance, as opposed to physical performance. In other words to continue DT's analogy, if Michael Schumacher could drive his Ferrari with the old beetle tyres faster than Dertonarm using the expensive ones, then are his tyres better than DT's? Would we buy them? Wouldn't we rather look at the description of the tyre's performance? The reasons we might choose it for a Ferrari, why it might be suitable. The analogy here is to the protractor's performance. How accurately can it set up the arm. Will it be within 1mm, 0.5mm, 0.1mm in overhang? Will it be within 1degree, or 0.5, or 0.1? Mounting distance? And how repeatable is it? I'm not saying Dertonearm's protractor isn't precisely made, or can't give good results, just that neither he, nor anyone else, gives a specification for protractors, one of the few areas in hifi where that is the case. If it was an amp, would manufacturers get away with saying how loud it goes depends on how well you set the volume control? Perhaps if someone said it was precisely made? Or said it looked impressive? Or maybe I'm getting too old and too cynical. John . |
Dertonarm
I hope you have an enjoyable holiday, and, of course I agree with you that everyone should choose their alignment according to their record collection - would that were always the case. And for your collection you have chosen correctly. We have never disagreed on that.
Now on to other matters, and perhaps I shall manage a holiday at some point, though some would say, though I'd disagree, that I treat all my life as a holiday.
Regards,
John |
Hi Dan_ed The Mint Protractor you refer to, accurate to the 2nd digit of a millimeter does that mean to 1/100 of a mm? And what did you mean by ...aligning horizontal azimuth and effective length with any precision This is one of my points that, while there are figures for how precise the protractors are made regarding linear dimensions, there is nothing regarding angular ones. Even in the case of the Graham jigs mentioned by Moonglum, there are no numbers, so we don't know by how much things are improved by using the jig, ie how much angular adjustment is required. Or ultimately, by how much the stylus is out of alignment on the cantilever, how much the cantilever is out of alignment with the generator, and how far that is out re the body. Of course that is a big ask...! You are totally right regarding the rest of the adjustments - I agree that a protractor is only part of the set up process - and the other parameters can have big effects. John . |
Hi Tonywinsc
As Tobes says, you would have to use a mirrored protractor for the reasons he states.
For the SME 309, it should be LofgrenA/Baerwald DIN.
But importantly, it should be a TWO point protractor, not an arc, as you will have to make adjustments at the arm base rather than the headshell.
As an aside, this actually is interesting because it raises the possibility of using the SME base for measuring the variation in cantilever/cartridge body alignment. as the alteration in overhang/mounting distance for a given effective length means a specific change in offset angle. It also offers a practical way to measure typical accuracies by comparing the difference in base position for repeated setups by different users without altering the cartridge position.
The accuracy that the stylus can be positioned independently on an arc can be measured, and the variation from that position in the alignments can give a number for the offset accuracy...
Anyway, back to work...
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Hi Tobes, if you want to know more re SME geometry, see this link for my take on why SME doesn't need this facility. SME GeometryThere are some serious misconceptions and misunderstandings regarding their choice of geometry, which have led to erroneous comments from many quarters, including arm and cartridge designers who should know better. Given the vagueness in cartridge specs regarding stylus to mounting hole dimensions, I would be loath to assume in practice that the actual arc of the arm would be as calculated, based on published data for the arm and the cartridge, and consequently it would not necessarily match exactly that of the Mint, which is pointless if its arc is as accurate as claimed. In any case, with the SME, as with slotted headshells, there is still the possibility of twisting the cartridge by a small amount (or more, by using smaller diameter screws) to align the cantilever. regards, |
