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

Showing 1 response by mulveling

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.