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Two Protractors - Only One Aligns

So I've got a Technics SP10ii with an SME 312S tonearm and an Airtight PC-1 cartridge.  I had MINTLP make a custom protractor for the 312S, and it aligns just fine.  Recently I acquired a second tonearm (Musical Life Conductor SE 10" Cocobolo) - a very uncommon tonearm with essentially no documentation available.  Since the MINTLP states that it is fitted to only my SME312S tonearm, I defaulted to using a generic turntablebasics.com cartridge alignment tool. I was told that the pivot-to-spindle (PTS) length for the Conductor SE should be 235mm, but again, there is no written documentation. With the TTB tool, I could not get alignment at any PTS length, and I varied it from 225 to 270mm. Frustrated and confused, I pulled out the MINTLP protractor, and was able to align the cartridge at a PTS length of 250mm (FYI, the effective length is roughly 265mm, though hard to measure with the tonearm in place).  Then, in the spirit of scientific inquiry, I checked the alignment of the 312S using my TTB protractor and NO DICE - it was telling me that the cartridge was out of alignment (contradicting the MINTLP).  What the heck is going on here?????

I know there are more than one different alignments people use (Loëfgren, Baerwald, Stevenson, UNI-DIN, etc.) - but between the two null points on the TTB protractor the stylus was off by around 10mm.  That is way too much to be explained by variable alignment methods, right? And since I had success with the MINTLP protractor, I would like to call it good, except for the warning on the MINTLP ("BEST Tractor is tailor-made for a particular tuntable tonearm setup. Using it on any other setup will result in error and do harm to your cartridge").  I don't get that either.  Aren't the null points the null points, regardless of which tonearm you are using on a particular turntable?

Those with a high degree of vinyl experience - please chime in if you can.  Thanks, Peter
peter_s
wlutke
294 posts
 
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.  
lewm
6,770 posts
 
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 OP
1,088 posts
 
@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...
lewm
6,770 posts
 
Because of the adjustable headshell offset angle on your tonearm, I think you will still want some detailed information from the company that makes it. Like what exactly is the intended pivot to stylus distance, and what exactly is the intended pivot to spindle distance?
peter_s OP
1,088 posts
 
@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. 
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