No prize for 'close'. You only need care about precision to the degree you care about the quality of the 'sound' it can produce. If setting one up with precision is an issue for you, you'd probably be better served with other sources. Now if just getting to hear records with music you like is all thats important, buy an inexpensive table with few set up options to eliminate angst, and enjoy your music.
How critical is the exact placement of the tonearm
When mounting a tonearm how precise does one need to be?
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I don't believe anyone said the hole had to have that tolerance. There is play within the hole to adjust the arm to that tolerance which can be achieved with micrometers and other measuring tools. The actual drilled hole would have a much greater tolerance. Then again you would be surprised how accurate a drill press can be - let alone plowing it out with a Bridgeport if you wanted to get ridiculous. |
Zen, I design circuit boards. I deal with .001 inch every minute of every day. I have 3 points. 1) one wouldn't want that much "slop" in the hole size. Just tightening the arm would cause it to move more than that. 2) I'd bet you be surprised at how much runout the typical homeowners drill press has 3) at that size, the typical drill bit has a pretty large tolerance. IMHO, to get the hole that precisely located and sized, one would have to use a CNC controlled drill and a very expensive, high tolerance bit. Not to mention the fact that you are, usually, dealing with a fiberous material such as wood, or worse yet, mdf. Just my 2 cents. |
A drill bit isn't used to control center to center positioning of a pair of holes (or an array) when close tolerances are required. It is simply used to clear material out of the way in quick fashion for a more accurate method of machining. I wouldn't trust using a drill bit to maintain center to center positioning for tolerances tighter than 0.010" (.25mm) I'm not saying another machinist wouldn't TRY to drill 2 holes within that tolerance but I wouldn't. Sometimes you get lucky but it isn't worth the risk. Do it right the first time. |
Contrast these responses with the instructions for mounting the 47 Labs (or Miyabi?) RS-A1 tonearm, which is merely placed on the armboard so that the stylus is "about" a cm from the spindle! (I don't have an RS-A1, and these may not be the precise instructions, but they are quite casual about placement.) By all accounts and based on my one listening experience, the thing sounds just great. Go figure. |
Contrast these responses with the instructions for mounting the 47 Labs (or Miyabi?) RS-A1 tonearm, which is merely placed on the armboard so that the stylus is "about" a cm from the spindle! Lewm, the 47 Labs arm is quite different due to the rotating headshell. You cannot (or better you don't have to) adjust that arm for the standard Baerwald or Lofgren geometry anyway. The rotating headshell takes care of that. For a standard arm (with fixed headshell), if your spindle to pivot distance is far off, you cannot adjust the overhang correctly anymore and fulfill the standard Baerwald or Lofgren geometry requirements (two correct nullpoints across the arc). |
If you're close you can make up the difference with overhang adjustments most of the time. Once I installed a RB300 Tonearm on a Linn LP 12. The armboard on the Linn was drilled for a Linn tonearm. (I only did this as a stopgap until my new Linn armboard came that was pre-drilled for the Rega tonearm by the way) I think the two are different by 7 mm or so and the Linn arm hole is larger. I moved the Rega tonearm around in the larger Linn armboard hole until I was about 3 to 4 mm off. Then set the overhang so that it hit both marks and to my surprise it played just fine. No inner groove distortion, no odd sounding bass or high or mids or anything out of the ordinary. About 2 days later my new armboard arrived and I quickly replaced armboards and set up my table again. I can't say that I heard any difference at all. |
Hitting both marks on a two point protractor makes one very huge assumption. That is, the pivot to spindle is dead nuts on. If it is not, there is nothing you can do to correct for it as the tonearm swings the arc. Sure, you might hit it at one point and it might be close a little farther into the swing but at the opposite end you're going to be off. It is simple geometry. |
All, Dan and I have been hanging out elsewhere discussing the vitrues of arc-style protractors. I'm sorry to say that if you have not gotten your pivot to spindle distance error to well under .5 mm, that you've never heard your cartridge. Furthermore, you have to be an absolute wizard to accomplish this correctly with a two-point protractor. Yes, there are those among us who can do this, but we are far and few between. In that thread, there's a link to a provocative article on the Vinyl Engine site. Also in that thread, our good friend Palasr discusses a fellow in Hong Kong who will actually deliver an arc style protractor to you in about 10 days' time !! Palasr is very happy with this protractor, and at $90, considers it to be a bargain. It really doesn't make sense to cut and paste this volume of information here. If you're interested, click this link: arc style protractor thread. Cheers, Thom @ Galibier |
One follow-up comment from Dan's 5/20 post ... The nature of a 2-point protractor is such that all but the most tortured souls will get one null point aligned perfectly and consider "really good" on the 2nd null point to be good enough. It is not good enough, but you will lose a lot of hair by working essentially in the dark to get "perfect" alignment on both points. In theory, with a two-point protractor, you can have a pivot to spindle distance error - as long as you have enough room in the headshell slots to compensate by changing the effective length of the arm along with the offset angle. In compensating for an error in pivot to spindle distance (drilling error), by moving the cartridge in the headshell slots, you are altering the other two Baerwaald parameters (assuming a Baerwaald protractor) to bring them back into line. Play with John Ellison's excellent spreadsheet ("Free Stuff" page on the Enjoy the Music website as well as a link to it on my Support page) and this will all begin to make sense to you. Note that the spreadsheet is driven off effective length and derives the pivot to spindle and offset angle. Depending on which parameter is known, you might have to run iterations to get your answer. I do this by setting the numeric precision to 4 decimal places (go to Format ==> Cells menu selection and select "number", set decimal places to 4). This is admittedly overkill but it allowed me for example to find the effective length that yields exactly 222 mm pivot to spindle distance. Now, there's a down side to arc protractors, and as Dan hinted, your pivot to spindle distance must match the one specified by your protractor. This presents an interesting challenge for owners of SME tonearms (SME iV, etc.) as well as Schroeder DPS and References. The challenge lies in the fixed mounting position of the cartridge in these headshells (from an effective length perspective). This is NOT a problem with the tonearms, but it does present a challenge for the user who wants to use an arc style protractor. For my Schroeder customers, I produce a series of 5 protractors of varying effective length in order to compensate. Because there is no standard amongst cartridge manufacturers for the position of the stylus relative to the mounting bolts, different cartridges will produce a different effective length with these tonearms. It's discussed in detail on the thread I linked to above. Cheers, Thom @ Galibier |
Thom- Unless I totally have the whole conceptual model of tone arm-cartridge-stylus geometry wrong (which could easily be the case) your comment about the Schroeder does not appear to apply to the M2, in which the cartridge carrier can move back and forth (and also pivot, damn it!). Pls confirm if you get a chance. |
You are absolutely correct, Swampwalker. The Model-2 has a slot in the headshell which allows you to adjust the effective length (pivot to stylus distance) of the tonearm. The DPS and the Reference are fixed in a hole which allows the cartridge to pivot but not slide back and forth. My guess is that Frank didn't like the structural integrity of a slot milled into the hardwood headshells. Playing with the Ellison spreadsheet will help you get the grok on all of this. As an aside, I was pointed to a compendium of tonearm specifications (not the Vinyl Engine website). I don't have the link handy, but if ddriveman is following this thread, I'm sure he'll provide it. Anyhow, the number of alignments chosen by the various manufacturers is astounding, and by no means limited to Baerwaald, Loefgren and Stevenson. In that document you'll find null points placed all over the map. Many highly regarded arms (Dynavector, et. al) have specified some unknown geometery. When I get a chance, I'm going to draw some arc protractors up for some of these geometries - to the extent that I have a tonearm on hand which I can "force" into these alignments. One of these arms is the Artisan that I carry. Way back when Ralph (Artisan) and I were evaluating the arm, we decided that we needed to have an easy means of providing the end-user with a reliable means of producing a known geometry. Ralph and I felt that an arc-style protractor would better help the user visualize and set up their cartridge. The visualization problem arises because the manufacturer's chosen alignment specifies an effective length that is almost 3mm short of what the 214 mm pivot to spindle distance would predict for Baerwaald. It also specifies an offset angle of about 1 degree less than what Baerwaald predicts. To achieve a Baerwaald alignment, a cartridge of average stylus position relative to mounting bolts, with a perfectly aligned cantilever would be some 2.8mm forward of the center of the headshell slots and rotated clockwise by about 1.25 degrees from being parallel to the headshell. All of these differences would likely confuse the user if they use their two-point Baerwaald protractor and begin the process by placing the cartridge bolts in the middle of the headshell slots and line up the front of the cartridge body so that it is parallel to the front of the headshell. I should most definitely return to this alternate geometry exercise to understand the intent of the manufacturer. There's been no rush, since "nuts on" Baerwaald has been very, very nice. Cheers, Thom @ Galibier |
Speaking of adjustable, SME tonearms allow adjustments of pivot to spindle distance. I have such an arm (a Pluto -- not an SME). The funny part is, unless someone gives you the exact pivot to spindle distance, you're stumped if you move the base of the arm... To make things even more exciting, my arm's instructions, for example, spec 219mm pivot to spindle & 23degrees offset angle... Well, it's either one or the other -- but not both (per Baerwald). What shoudl I choose??? |
Yes, Greg ... With the SME architecture you're "stuck" with a fixed offset angle (to the extent that your cartridge screws have some play in the headshell holes). This essentially means that the cartridge manufacturer's production tolerances dictate the offset angle, as well as the tonearm's effective length (due to the position of the stylus relative to the mounting bolt holes). The fact that you can nicely alter the pivot to spindle distance on their way-cool adjustment track means that you can set the pivot to spindle distance to agree with this effective length which is dictated by the stylus position. This leaves us with one "uncontrollable" parameter - offset angle. I need to do some empirical reserach on the importance of offset angle. Different offset angles move your null points, but given that we're talking about perhaps +/- a degree (due to manufacturing tolerances), this may not be such a big deal. We've certainly learned that tracing a perfect arc (getting pivot to spindle and effective length to agree with each other) are critical, and the SME design provides you an excellent means of achieving this. This offset angle thing is an area I plan to investigate, along with all of those alternate proposed geometries. Cheers, Thom @ Galibier |
Thom, I am not sure whether I under stand this correct though: If I read the post on vinylengine it seems that the problem of spindle to pivot distance is only a problem with arc protractors (if the spindle to pivot distance is wrong one gets the wrong arc across the record, the wrong null points and higher distortion. What I don't understand: If I use one of the standard two point protractors to adjust the nullpoints correctly, am I not close? Of course if my spindle to pivot is slightly off, I may move the cartridge in the slots and the only effect is that the effective arm length has changed slightly. There really is no preferred effective arm length and and the distortion curve is pretty close since it is fixed by the null points and the variation in effective length is small. What am I missing in the geometry? Why no align then for the two null points correctly. Is it just that an with arc protractor, it is easier to see any alignment errors? But then you can never determine the effective length more accurately than spindle to pivot distance anyway. Both methods seem to have similar errors built in. Thanks for all your clarifications! Cheers, Rene |
Hello All, There is a minefield of information on this thread for newbies. It does explain however, that when I put a different type of allignment tool on my Rega P3 many years ago, I couldn't get the geomtry right. Anyhow, that arc protractor sounds helpful. Does anyone have a link for that Gent in Hong Kong who makes one for under $100? Also, where does that old Mobile Fidelity alignment disc (the one that was the size and shape of an LP) fit into all this? Is the Mobile Fidelity disc Baerwald geometry? Is that disc an accurate enough tool to use in the correct alignment of arm and cartridge? |
Hi Rene, You didn't miss anything. You are correct that there is no preferred effective length (as long as you are not using an arc style protractor which is drawn for one and only one set of parameters). The benefit of a two point protractor is that with enough diligence, flexibility in the headshell slots, etc. you can get a perfect alignment irrespective of your pivot to spindle distance being off - as long as you have enough movement in the headshell slots to adjust the effective length and offset angle to match your "wrong" pivot to spindle distance. With an arc style protractor, the price you pay for ease of visualizing and solving the problem is that the pivot to spindle distance must be very close to perfect, because the arc is drawn from the theoretically correct arm mounting (pivot) point. Dsa - A few posts up, I have a link to an arc protractor thread. In that thread, Richard posted a link to the protractor fellow. He loves it even more than his "original" arc protractor. Cheers, Thom |
Hong kong guy Arc protractor link http://www.mintlp.com Very easy to deal with, fast turn-around. Not sure I've got the alignment right yet; its pretty tough when you wear progressives and are really far-sighted, but it appears to be well made and the instructions are not bad. |
That's correct, Dsa. The proprietor, Yip, makes the protractor for the tonearm parameters you specify. I had given him the numbers for the protractor I need without the name of the tonearm and table. I guess he is building a database as he asked for these before accepting my order. Another thing that came out in the thread on Thom's forum is that you will also need to specify the spindle hole diameter. Yip does cut to high tolerances so keep that in mind with the spindle hole. Oh, I also like the way he personalizes them. Yip also asked if I wanted a lupe he recommends for seeing what is going on while adjusting with his protractor. I ordered one since I liked the look of it and feel I can never have too many tools for seeing what I'm doing. What I like about the arc-style protractor is that you have a single tool that allows you to get the pivot to spindle right at the same time you get the cartridge alignment right. It is possible to get things right with most any 2 point protractor, but you would still need a tool and method to measure the pivot to spindle to get it really, really close. So if you are getting accurate results with a 2 pointer, that's all you need. In my case, I didn't realize how off I was until I tried the arc-style. I was clearly off the arc. Once I got things adjusted closer and re-checked using my 2 pointer, I found I was off by less than .5 mm with pivot to spindle. But the difference in the sound of reproduced music was noticeable, especially in the articulation of consonances. Well, that's what I noticed first. I suppose the benefit is to all micro-dynamics. Getting this adjustment closer to theoretical perfection provides for just that much more of an "in the room" presence from practically every LP I played since. There is probably still a small error in my setup but I'd say it is limited to the width of the printed arc. Once Yip's protractor arrives I'll adjust things again. |
Swampwalker pointed out the importance of Eyeball-to-Stylus distance, which is critical but often, umm, overlooked! Like him, I wear progressive lenses. Unlike him, I am quite nearsighted. Being able to see even the smallest styli from an E2S of 5" or less is helpful. Of course I need a hand finding the turntable... I've never used an arc protractor and don't feel a particular need for one. All my tonearms have allowed for overhang adjustment in the headshell and I've never had a problem visualizing which direction to adjust overhang when using a two-point protractor. To match overhang (and thus eff. length) to whatever pivot-to-spindle distance the arm is mounted at, just check the cantilever angle at each null point. If your eff. length is wrong the cantilever will be swinging through too many degrees or arc or too few (think of it as splay-footed or pigeon-toed, respectively). If the cantilever is swinging through: - too many degrees of arc (splay-footed), make your eff. length longer - too few degrees of arc (pigeon-toed), make your eff. length shorter I know this isn't intuitive for everyone so an arc protractor could be a good solution. My guess is that it would take me longer. I can tweak the position of a tiny cartridge more finely than I can tweak the position of my armboard, so + or - 0.5mm for the arm mounting position works fine for me. Different strokes... Re: SME - I know more than one IV/V owner who's drilled out the cartridge mounting holes slightly. Not much, just enough to allow for a degree or two of adjustment to cantilever angle. Seems like a reasonable idea, especially since few cartridges are perfectly made. |
I agree, Doug. It's not that one protractor is superior to another. All should work very well if they are used properly. But one could work better for someone versus another style protractor, depending simply on which may seem to be more user friendly. However, getting back to original question, the placement of the tonearm is still very critical to get right no matter what protractor one uses. I guess I don't in either Swampwalker's or Doug's "eyesight camp". My eyes have gotten bad in both near and far sight over the years. Good thing there are also great optical tools available as well as great protractors! It really is an excellent point. I think it is easier for me to see of the stylus is on or off the arc. Once I have that, squaring up to a single point is simple. As long as I don't move the cartridge screws too much forward or back, things are good. But re-checking the alignment with the arc after squaring the cantilever up is still a good idea. Just as with the two point protractor, it is an iterative process. |
After using various other types of alignment tools my Wally universal is a set and forget item. I did not have any idea how far off my adjustments were till using the Wally tool. You cant miss following the arc curve for your arm type. It would be great if a group of vinyl users got together getting one for joint use as most arm arcs or inscribed on it. It took a little time with Wally but well worth the trouble. |
Thom, Different offset angles move your null points, but given that we're talking about perhaps +/- a degree (due to manufacturing tolerances), this may not be such a big deal.Well, the wrong offset angle should increase your degrees of tracking error... so, as you've noted many times, we STILL ain't really hearing the cartridge (or the arm+cartridge combo for that matter). Really if we could only get these things correct to begin with, analogue life would be so much simpler:)! |
Hi Radrog, I think that everyone is in agreement that you can get there from here with any tool. The issue is (a) how an individual interacts with the tool - how intuitive it is to use, and (b) how much effort it takes. To date however, I have to add that everyone who has tried an arc-style protractor will never go back. I'm sure that there will be an exception to this at some point. Hats off to Wally for his out of the box thinking years ago. Cheers, Thom |
