Two Protractors - Only One Aligns
@lewm is referring to Dietrich Brakemeier at Acoustical Systems, http://www.arche-headshell.de/about-us/ could be worth reaching out to the US Distributor who sold Musical Life, Tom Vu at K T Audio. He is now the principal at Triangle Art http://triangleart.net |
@lewm That is the rub! The company is no longer in business. I guess I need a contact in the German audio industry to track down the manufacturer - no luck googling thus far. I will operate within normal ranges. The pivot to stylus distance can only vary by a small amount, which means the P2S range is pretty tight as well. |
@lewm Thank you! I think I’ll sell my TTB on ebay! I was just going online to purchase a Feickert when I saw your post coming in! Paid the extra $$ for 2-day delivery so I can get this thing wrapped up over the weekend. Just checked the retail price for the TTB. $20. I think I’ll give it to a budding vinylphile... |
Peter, Based on the info you provided, you own a $5800 tonearm. Such an expensive tonearm certainly does merit the cost of a Smartractor (if you want universal applicability) or a dedicated Mint LP. (Plus also you apparently own an SME 312S; nothing to sneeze at.) Because of its issues (difficulty of aiming to the pivot and parallax created by the distance between the mirrored surface and the grid lines), I would say the TTB is not up to the level of your tonearm. (Also, any play between the spindle and the spindle hole on the TTB is yet another potential source of error.) If you don't want to spend on a Smartractor or limit yourself with the Mint, I would also recommend the Feickert Protractor. Either Smartractor or Feickert will work now and forever for any tonearms you may ever buy. I own both a UNItractor, big expensive brother to the Smartie, and a Feickert. My TTB stays in the drawer. |
peter s, You said; "But shouldn't the alignment lines be parallel to the grooves if they occur at null points? This makes the cantilever parallel to the grooves." Yes. It's the grooves that are not parallel to each other at the two null points. As the stylus tracks past the outer null point, the stylus tracing angle turns too far inward. As the stylus approaches the inner null point the groove angle turns inward even faster (nearer record center) and catches up with the stylus tracing angle at the null. Overhang staggers the null points (a line cannot be drawn from the Spindle through both null points) to make this possible. As the effective length of the arm increases, the arc gets shallower and shallower and the overhang is decreased, bringing the arc closer to ninety degrees to a line drawn between Pivot and Spindle - until you have no arc, no overhang and a linear tracking arm. |
@wlutke I get what you are saying:
As the stylus traces the flatter arc, the stylus tracing angle changes less in relation to the grooves. The Mint inner and outer null alignment lines will be more near parallel to each other to compensate. Overhang may be different in order to compensate as well.But shouldn't the alignment lines be parallel to the grooves if they occur at null points? This makes the cantilever parallel to the grooves. I think what changes is the angle between the alignment lines and the stylus arc on the MINT. These are not perpendicular, and differ at each null point. If I am being thick, forgive me - I appreciate your help. Peter |
oldears ... these adjustments are only as accurate as the alignment of the stylus to the cartridge body.This is mistaken, and is an advantage of the Mint protractor. Like some others - such as the WallyTractor, the Mint aligns the cantilever itself, not the phono cartridge body. That is the purpose of the mirrored gauge. |
You have good advice from lewm. The mint is valid only for a given tonearm length and offset angle, provided that the stylus overhang distance has been set accurately. It is a convenience item. It is not more accurate than the TTB gauge, it is just easier to use; and it is invalid to use for any other tonearm length. If they do not agree, check the overhang distance. The TTB will provide accurate results for any tonearm, again if the offset angle has been manufactured correctly for the tonearm effective length, and if the overhang distance is set correctly. If all of these conditions are not met; it can provide a good compromise by twisting the cartridge in the headshell. Also, all of these adjustments are only as accurate as the alignment of the stylus to the cartridge body. |
peter s, You said; "By definition, the null points are the two points where the cantilever is tangent to the record groove, and this is not effected by the "curvedness" (or flatness) of the arc." As I stated, the null point distance from the record center does not change. As the stylus traces the flatter arc, the stylus tracing angle changes less in relation to the grooves. The Mint inner and outer null alignment lines will be more near parallel to each other to compensate. Overhang will be different in order to compensate as well. |
This is why it’s good to have a single-point universal like the GeoDisc in your toolkit. Also I use the SMARTractor, another single-point true universal (with multiple curves to choose from) which is definitely more precise, but also much more expensive. And I’ve used a Mint LP (2-point) to good effect, but it’s frustrating to have to buy a new one for EACH setup (yes you really have to). The simple GeoDisc should work quite well with your unusual tonearm, because the center pivot point is so easy to visually sight - when you can’t clearly "see" the pivot point, the GeoDisc doesn’t work very well. The GeoDisc is based on the Loefgren A IEC curve (i.e. Baerwald), which is quite common and generally works well. Your P2S distance should ideally be set based on the tonearm maker’s recommendation, but if it’s a little off in reality, a true universal like the GeoDisc or SMARTractor will compensate for that (as long as you have enough leeway in your headshell slots), whereas the Mint LP will give you an increasingly erroneous result as you stray further from what the Yip thought the P2S should be. With a Universal - if you find yourself "short" on the headshell slot length (towards the front end of the shell) then the P2S distance is probably too big, and vice-versa. In theory the MintLP for a specific setup will be more precise than even a SMARTractor (and I must admit the Mint has FAR better lines for cantilever alignment), but in reality this advantage will often be negated by P2S distance not being in EXACT agreement (again, unlike a universal, the Mint will not adjust for discrepancies here). I don't think it's uncommon for the P2S distance to be off by 1mm (or more) from where you requested the holes drilled into a blank armboard - maybe with a fixed ecosystem like a Rega you can be more confident in its published P2S distance. And the back-and-forth iterations between the two alignment points is a bit more time consuming, and can be a tad frustrating at first. |
@lewm Sorry I missed your post at 8:05am before writing the one above. I will need to see if the stylus follows the arc on my MINT - but it probably won't, because I'm using a 10" tonearm and the MINT was set up for a 12" tonearm. The arc HAS to be different, and this is why less error occurs with a longer tonearm. But this doesn't mean that meeting the two null point requirements is not sufficient for getting proper alignment, right? Although I know that I am close, I haven't yet fully confirmed that I can meet both null point requirements with the MINT without rotating the protractor. |
@lewm Is this to suggest that a dedicated protractor is needed for every possible effective length? See my post above. If that is the case, the TTB would be misleading. Must have something to do with pointing the orientation line on the TTB to the pivot point. But even when I come close to doing that, my alignment with the TTB sucks. I think the unique thing about this "Musical Life Conductor SE" tonearm is that I can alter the P2S, the offset angle, and effective length (3% range). My question stands: if I can match the two null points with the correct angle so the cantilever is tangent to the grooves (defined by the protractor grids), is it OK to rotate the protractor during alignment? |
@wlutke I get what you are saying, and agree that the arc should be flatter for a larger P2S (or a longer effective length). However, if the null points are the same for both configurations, perhaps this doesn't matter. By definition, the null points are the two points where the cantilever is tangent to the record groove, and this is not effected by the "curvedness" (or flatness) of the arc. I think the difference is that a flatter arc will create less error at locations away from the null points. That is why a 12" tonearm is preferred over a 10" tonearm. I found a good turntable geometry calculator on this website. This calculator shows that for any given P2S, the zero radii are the same. What changes is the effective length and offset angle required to meet the null point requirements. For example, calculating the zero radii for a 250mm and 290mm P2S, I get the same zero radii (63.32, 119.63) with the following differences: P2S 250 290 Eff. Length 264.79 302.84 Off. Angle 20.25 17.61 I guess the cool thing about my tonearm is that the offset angle is adjustable, because the headshell is attached at only one point and can be rotated. Thus, if I am able to find a P2S that works for the effective length of the tonearm, I can adjust the offset angle accordingly. Early indications suggest that I can accomplish that with the MINTLP - but I haven't confirmed that yet. Where I get confused is applying the protractors. My MINT and TTB protractors both have the same zero radii (67 & 121 mm) which differ slightly from those calculated above (don't know why, maybe different calculation method). But they are clearly offset from one another in a different manner. So if I could lay them on top of one another, the two null points would not line up, even though they use the same zero radii. That probably reflects the difference in P2S, and the TTB must have some assumed value of P2S. The problem is that both protractor manuals state that you should fix the protractor - so that the differing offset makes it either possible or impossible to match the two null points on the protractor. If the only requirement is that at each zero radius the cantilever is tangent with the grooves, couldn't I simply rotate the protractor and use the lines on the mirror to make sure that the angle is correct? |
Bottom line, now that I've re-read your OP and gone to the website. First of all, don't expect the Mint you own to work with this tonearm unless the specs are identical to those of an SME 312S. Seems your new tonearm is 10-inch effective length and the 312S is 12. Not good. By fiddling with offset angle, you might get it to "work". |
I agree with wlutke. Nearly all other tonearms have a fixed angle headshell offset, unlike yours. The P2S (pivot to spindle) distance, effective length, and the headshell offset angle are intimately related and chosen for whatever geometry the designer of the tonearm had in mind (usually Baerwald, Lofgren, or rarely Stevenson). This is why the MINT protractors are unique for each tonearm. If by chance two different tonearms work with the same P2S and headshell offset and effective length, then a protractor made for one will work with the other. By adjusting the headshell offset angle on your particular tonearm, you may be able to cheat a little on this rule of thumb, but I think the tracking angle error in between the two null points might suffer. (I would have to sit down with a pencil and paper to figure that out, and I don't want to.) While I've never seen a Mint protractor, I believe it is an arc type, which is to say the stylus must ride on an arc drawn on its surface. If you can get your stylus to do that, with the Mint placed over your spindle of course, that might be valid. The TTB assumes a priori that you have mounted your tonearm with exact correct P2S and that you can then align the spindle-mounted TTB with the pivot by eye, which I think is fraught with error, and I do own a TTB which I never use. Slight errors in aiming the TTB at the pivot can result in large errors of alignment. I also noted that the TTB is a few mm thick, and the mirrored side is on the bottom, whereas the marker lines are on the upper surface of the glass. That also is a potential source of error due to parallax. I'll have to go back and click on the URL to see how your tonearm is constructed. Sounds like it might be a copy of a Dynavector DV series. |
peter s, Sorry, I found your OP a bit confusing, I thought your Mint was made for 250 mm. Never-the-less, the Mint arc is specific to the P2S. A Mint arc for 290 P2S will have a flatter arc than one for 250. The null points have the same distance from center in each case but the arc between them cover a different number of degrees. Think of an arm 10 feet long. The alignment grid lines at the outer null point would be nearly parallel to the alignment grid lines on the inner null point. On a ten inch arm they are not. The null points are not in line with the spindle but on an arc that overhangs the spindle. With proper magnification - at least 16x or so for the Mint- the problem will become obvious on your smaller scale. |
@lewm One thing that is unique about this tonearm is that I can change the P2S over a wide range without moving the mount, as the arm that leads to the pivot swings. This can be seen on the link in my first post. Thus I can change the P2S from 230-270mm. I can also change the overhang by +/- 4mm with the slot on the headshell, and I can change the offset angle significantly since the headshell is only attached with one bolt. With all this adjustability, I may be able to line up the proper offset angle and null points with the mint protractor made for my unique tonearm combo. Does this make any sense? |
@lewm - I’m surprised at how inaccurate the TTB is. I tried multiple P2S values and I couldn’t get close for any of them. After lining up the outer null point, the inner null point was always at least a centimeter off. @wlutke - are you saying that there is no universal 2-point protractor - that all protractors must be made based on the P2S and the effective length of the arm? How is it that TTB seems to be selling a universal protractor with no mention of fitting to these parameters? Does it have to do with pointing the guide line to the pivot point? Can someone direct me to a reference that I can read to familiarize myself with the math and geometry of this situation? |
@wlutke The MINT was made for a 12-inch tonearm that has a P2S of 290mm. Is it possible that a 12"/290mm combination has the exact same null points as a 10"/250mm combination? I haven't yet achieved a perfect alignment with the MINT and the 10" tonearm, but preliminary results lead me to believe that I likely could. |
peter s, The arc on your Mint has a radius that works only at 250 mm P2S. Both null points cannot be aligned simultaneously with ANY error in the P2S. I chased a sibilance problem for a year before realizing this (original VPI JMW 10 arm - spec is 250 - yes, I was a newb). P2S was 2 mm off. If you are aligning both null points precisely, your P2S is not 265 mm, but 250. If the null points cannot line up perfectly/simultaneously with the lines, the P2S needs adjustment or a single null point type protractor can be used. |
PS - even though the tonearm is 10", if the effective length is 265mm (10.8"), perhaps it is not surprising that the PTS length that works is 250mm. When I google PTS lengths for other 10" tonearms (not many hits) I see values ranging from around 228 to 232mm. When I look at 12" tonearms, I see values on the order of 295mm. (this is also where my SME is set). Using proportionality between 230 - 295, a 10.8" tonearm would have a value of 256mm. So it seems I am in the ballpark. I starting to not trust the TTB Protractor!!! |
