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In Reply to: Setting Cartridge alignment using a Two Point Protractor posted by bkearns on February 07, 2001 at 03:58:40:
Don't most (all?) protractors, like my Cart-a-lign, allow you first to set the overhang by positioning the protractor over the spindle in a particular way? That is, at your Step 2.Once you set the overhang, you use the alignment point just to set the angle. If you've done it right it will be correct for the other alignmnt point. That checks your work. Or you need to make what should be only a small adjustment.
This simplifies the procedure considerably. If your protractor doesn't let you set the overhang first with some sort of precision I think you should get another.
Of course, as you note at the end, if you've already determined the overhang, you can use it for your next cartridge.
Follow Ups:
To set overhang directly, the stylus needs to be placed on a the line through centre of the arm pivot and the platter spindle. Many arms do not allow enough movement to do this.Moreover, for an arm with head-shell slots, to set overhang directly, you need to know the mounting distance (ie distance from platter spindle to centre of arm pivot). This should be measured, and the overhang calculated using the formula below. The manufacturers data is often (usually) unreliable.
Overhang = Sqrt(Lm^2 + N1*N2) - Lm ( ^2 means squared, * means multiplied by)
N1, N2 = inner and outer null radii respectively
Lm = mounting distance.
But you are right, if it is possible to set overhang firstly, it makes things easier, as there is no need to go back and forth between alignment points.
Best regards,
Brian
Brian
I think what you mean to say is that to set the overhang _according to its definition_ you need to place the stylus on the other side of the spindle.As I wrote earlier, it is set _directly_ by many devices, including the $15 dollar one referred to, without needing to place the stylus in any unusual position. Then, as you correctly note, it makes things easier and you don't have to iterate ad nauseum.
One of the reasons for bothering to enter this thread as I did was because it seems to me that all of this unnecessary and time consuming fiddling one has to do to use the so called "two point" method is the kind of thing that makes us look a bit strange and keeps people away from vinyl.
Sorry I misunderstood, I thought you were referring to another kind of tool, that has concentric circles marked on it, and fits over the spindle. That kind of tool can be used to set overhang directly.The tool you mention is based on the Geodisk. The Geodisk sets the arm effective length by using the arm pivot as a reference point. In my opinion that is an indirect method, as it relies on some preliminary adjustment. We could argue over semantics, but I think I made it clear enough in the original post what I meant by setting alignment directly. The merits of the Geodisk versus two point tools has been discussed before, check the archives. A full description of the Geodisk can be found in US patent # 4,326,283.
"One of the reasons for bothering to enter this thread as I did….."
Do me a favour: the next time you are loath to enter a thread I have started, then follow your instinct, and don't bother.
"the kind of thing that makes us look a bit strange and keeps people away from vinyl…………"
That is your hang-up, not mine; speak for yourself.
My first post was an attempt to explain clearly how to set up a cartridge using a two point alignment tool. If you have something to add on the subject then good for you, but if you want to make flippant comments, then why don't you find some other internet site to surf.
Best regards,
Brian
In keeping with the thread the "indirect" methods of setting overhang and angle like those jigs included with the Graham, Dynavector and some other arms allow for much easier and far more accurate setting of the cartridge alignment. They are in fact more direct and accurate if the instructions are followed which also set the pivot to spindle distance prior to directly setting overhang.
Sounds like a good idea, particularly the jig to set the correct mounting distance. It is a pity every arm manufacturer doesn't do the same.Best regards,
Brian
If you want to use your obvious geometrical skills and teach people to set their alignment with one hand tied behind their back, I guess that's OK, even if I don't understand why.I never thought that adjusting cartridge alignment is an end in itself, only a means to better performance. Different strokes, I guess.
What I mean by "direct" is that you set it once, and it's done! Not an iterative process that can go on and on.
The toolS I mentioned are based on geometry, as is the Geodisk I'm sure.
I'm sorry if you are offended; no offense was intended.
I entered the thread to demonstrate that there is a fast and easy way to do it as opposed to a slow and difficult one. New people discover this site all the time so it might be useful, I thought, that people should know there is an easier way so as not to be discouraged from aligning properly.
I shall stay on this site, thank you, and since each author is identified in the listing, please feel free not to read my posts.
And best regards to yourself,
Mel
Brian's piece covered two-point protractors. As he said, there are a few protractors, like Geo-disc, the Soundtractor, and the one you refer to, which do it in other ways. The one you refer to in your other posting (which certainly sounds like a good design) has two null points in addition to the sight line, which is a rare asset. The procedure is speeded up, while you still can check your alignment using the same protractor. It becomes a two-point protractor and a "sighting" protractor at the same time. I have a cardboard protractor called Polaris Plus which aspires to the same thing, but for some mysterious reason, the sight line is incorrectly positioned relative to the two null points (or the outer point is incorrectly positioned relative to the inner point and the line). Those who have (or make on the computer) a cardboard or paper two-point protractor might be able to draw a sight line themselves at the linear offset. The line should be placed (accurately, of course) at a distance from the stylus mark which equals the average of the two null points, e.g. 93.4 mm from the stylus mark in the case of points of 66 and 120.9 mm, and perpendicular to the axis from the spindle to the stylus mark (i.e. parallel to the gridlines). If two spindle holes and one grid are used, the line will even be valid for measurement at both points. I don't know the story behind the Cart-A-Lign line, which I think goes from the spindle to the arm pivot, but I suppose it's all right!The two-point protractor is more common and used by many, and will continue to be used by many. When the cartridge is actually aligned to both points and grids accurately, the cartridge is necessarily correctly aligned. By using both points and grids, the protractor achieves the same thing as other protractors achieve by other means. An advantage is that you are not dependent on having something to sight at in a precise way (so overhang and offset angle are instead set "directly", as Brian calls it), but the clear disadvantage is that it's *@&X! fiddly and can take a lot of time and patience. Brian attemps to help people by a method he believes can make this protractor a bit more effective.
The ultimate in convenience seems to be the arc-type protractor, such as the Wallytractor. Its only disadvantage is that it's made for one specific effective length.
> > I have a cardboard protractor called Polaris Plus which aspires to the same thing, but for some mysterious reason, the sight line is incorrectly positioned relative to the two null points. < <You'd think if the one thing you did was make cardboard protractors printed with critically positioned lines, you'd at least make sure you put the lines in the right place. I'm shocked! Have you called Martin Bastin about this? His name and phone number are printed right on the protractor.
Is his placement of the sight line at least consistent with a logical set of null points (that you disagree with), or did he just plain screw up?
My sight line is 92.0 mm away from the stylus mark when using Hole A. Are you saying I should just draw a new line parallel to the old one and make it 93.4 mm from the stylus mark?
Thank you, Helge!
Hi,First off, the 93.4 mm was tied to the example I used with null points of 66 and 120.9 mm; the Polaris Plus uses different null points, so the sight line should not be placed at 93.4.
Rulers differ slightly, but by comparing all of my rulers and measuring as carefully as I'm able to, I've come to 91.9 mm for the sight line, 63.9 mm for the inner point, and 120.5 mm for the outer. These figures must still be taken as approximations, as the measurements are not exactly done with laser or something. Also, the spindle holes may have been cut very slightly differently from sample to sample.
The instructions say that you can verify your alignment by using the outer point (i.e. spindle hole C) "if you wish". Every time I do this, the stylus will not hit the centre of the point, but is slightly too far forward. Maybe that's okay in practice if you know about it beforehand!
As far as I can see (and Brian Kearns believes the same thing), the sight line should be placed smack dab in the middle between the two spindle holes, which you can easily see that it isn't; it's closer to A than to C. A line like this is located at the so-called linear offset, which is the product of the effective length of the arm (no matter what this length is) and the sine of the offset angle (whatever that trigonometric stuff means). It also equals the average of the two null points.
With an inner point of 63.9 and a line on 91.9, the outer null point should be expected to be located at 119.9 mm. With an outer point of 120.5 and a line on 91.9, the inner point should be expected to be located at 61.9. With null points of 63.9 and 120.5, the line should be expected to be placed at 92.2. This assumes that the line is to be placed at the average of the two points (you just isolate X in the equations by multiplying and subtracting).
There are in principle three options:
Align as per the instructions, and accept that the real outer null point is at 119.9 (I have done this so far).
Align at the outer point instead of the inner, and accept that the true inner point is at 61.9.
Draw a new line (completely parallel) and use both points as they are.I'm posting from home, and need to look at some Excel stuff on my workplace machine..., but the first option seems to be the best of these. As Martin Bastin says, the inner point is the most critical (because of the notorious inner-groove distortion), so I wouldn't use alternative two, although this is what Geo-Disc does. Also, an inner point of 61.9 seems to be farther inwards that I would prefer. And in particular, the null points would be way too widely spaced. The latter point is possibly valid for the third option too. Bastin does write that the outer point is less accurate, but I don't know if he is referring to the same thing as we do. If so, why did he place the outer null point where he did?
An inner point of about 63.9 is not "incorrect" anyway; it gives you a good performance on the inner grooves, but, relative to the 66/120.9-alignment, at the cost of more distortion elsewhere. It's a kind of compromise between the Rega-style alignment and the 66/120.9-alignment. I will see what the outer point is doing to this, what it adds to the distortion pattern.
I have a (new, cleaned) record with a more sibilant vocalist than usual, and the sibilance grows during the middle portion of the record, and may seem to reach a high somewhere around the middle peak distortion point, while I think it's better at the very end (about 65 mm). I'm thinking that the balance could be too much in favour of the innermost grooves, but that's speculation for now.
I haven't called Martin Bastin.
The Polaris Plus is really excellent in many ways: The stylus mark is a small circle, not a black dot or a cross. There are plenty of gridlines, including crosslines for aligning the front or back of the cartridge. There is a line for aligning the cantilever, and a nice touch is that this line is positioned slightly to the side of the circle; in this way, you can view the line behind *and along* the cantilever. The infamous sight line is fairly thick, just right for the pillar of my Nottingham Interspace arm. It's also long.
OK, Helge, I'm with the program now. The only thing I didn't follow was:"With an outer point of 120.5 and a line on 91.9, the inner point should be expected to be located at 61.9"
I assume it's just a typo, but "61.9" should be "63.3," right?
In any case, I see now that this is just as much art as science, and that the null points you choose can be tweaked according to where you want the most (and least) distortion. (It is odd though that the Polaris gauge wasn't made internally consistent by drawing the sight line right in the middle of Holes A and C.)
,k
Now I have used the spreadsheet... Following is a table for distortion based on a calculator made by Brian Kearns. See previous message.First is distortion at 62 mm (arbitrarily chosen to represent the inner grooves), then maximum distortion between the null points, then distortion at the outermost groove (146 mm).
1. Hole A + old sight line: 0.19, 0.66, 0.66
2. Holes A + B + new line: 0.19, 0.67, 0.64
3. Hole B + old line: 0.01, 0.74, 0.66
4. "Standard" 66 + 120.9 mm: 0.4, 0.61, 0.62
5. Hi-Fi News: 0.29, 0.63, 0.65
6. Enjoy the Music: 0.89, 0.6, 0.45Following the instructions (no. 1) will yield a slightly lower distortion between the null points than drawing a new sight line right between the spindle holes (no. 2). On the other hand, distortion in the outer groove (146 mm) will be slightly higher. Many records start around 145 mm, and the middle grooves are more important than the outer grooves (due to more compressed undulations on the groove walls), so I'd say that following the instructions is the best. This
alignment is also okay, I guess, although the outer null point should ideally be slightly further inwards, at least at 119.6 or 119.7 mm. Option no. 3 (using the sight line with hole C instead of hole A) gives a far too high distortion on the middle grooves.It can also be seen that the alignment with null points of 66 and 120.9 gives a higher distortion on the inner grooves, but lower on the middle grooves. I have also joined the values for the Hi-Fi News protractor (not at all bad, IMO) and the Enjoy the Music-protractor (favours the outer grooves!).
Mel, life would be easier if all protractors allowed you to set overhang first independent of angle but most don´t. The Wallytractor does and apparently the one you have most most others don´t.And yes you are right overhang is everything and the classic two point protractor does not make it an easy task.
For the grand sum of $15 you can currently buy a device that not only lets you set the overhang first, but provides a mirrored surface so that you can line up the cantilever in the preferred manner.Look at http://www.turntablebasics.com/
(a site with which I have no connection-this device has been favorably reviewed by an inmate-do a search)Like many such devices including the late lamented Cart-a-lign, lining it up so that it points to the tonearm pivot can be difficult at first. I have always managed by shining a strong penlight at the pivot from over the TT spindle. If the pivot is surrounded by a cylinder, that will provide a thin vertical bright line which makes it easier to aim toward by lining up the "line up" line on the protractor and the pivot.
Alternatively you can glue a thin piece of wood (like 1/8" ply), plastic or cardboard stock cut long an narrow so that it reaches (or almost reaches the pivot) and extend the "line up" line almost to the pivot.
All of this is easier to do than to read about, and makes setting up the overhang almost instantaneous and adjusting the cartridge tracing angle a breeze.
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