No big deal. Go to turntablebasics.com and look at their table of mounting dimensions. As long as you have enough adjustability in the tonearm mounting slots you can adjust the overhang and the angle to get correct alignment. For 249.5mm P-S the overhang should be 15.51mm and the angle 20.65deg. For 239.9 mm P-S the OH should be 16.09mm and the angle 21.41deg. Recall eff length = PS + OH. They make a very good protractor.
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Why would moving the cartridge forward in a headshell with elongated slots “look ugly”, and who cares? Do you know what is 10mm ? Try to move a cartridge 10mm forward than usual, it most cases it’s impossible to move that much. The difference between alignment methods is within 2-5mm max, no one have to move a cart 10mm forward in normal situation. And we are talking about different detachable headshells. On a tonearm with fixes shell the slots are much shorter. I have over 30 different headshells and very few of them (with overhand adjustment like AT Technihard) will allow me to move a cartridge 10 mm forward than normal position which is usually in the middle if the slots. 5 mm is ok, 10 mm forward is too much and in this position headshell is behind the 1/3 of a cartridge body - this is ugly. Normally a cartridge body is under headshell. Most of the audiophile are excited about ugly things, but in my opinion OP can change the armboard instead and everything will be perfect if he could. |
Whether exactly correct alignment could be achieved with the OP‘s situation is definitely a good question. I share your opinion that most headshells would not have that much adjustability room. But that is different from saying not to do it because it would be ugly. Whether exactly correct alignment is critically important is also another question. |
Lewm you brought up the question that 1st popped in my head. Could you move it 10mm and still have 2 null point. With the calculator on vinyl engine you should be able to solve with the variables he knows. He could also go to vinyl asylum and ask John Elinson (sp) he has his own spread sheets. He could figure this out quickly and will recommend to play by the rules. As a side note I have been playing around with 2 of my 14 inch arms with no offset and 1 null point. Seems to be a little more dynamic. If the average distortion is higher it is not apparent. Need to really sit down and listen and go back and forth. Took up Kayaking last year so haven't been building and listening much. Enjoy the ride Tom PS. I like the looks of a cartridge all the way forward in the head shell. Although I don't remember the OP asking about this issue. |
Dear @mrearl :"" Suppose I have a tonearm that wants to be mounted 250mm from the spindle . "" first that all is not that the " tonearm wants ", that could be the manufacturer spec ( normally the manufacturer gives the tonearm EL. ) and nothing more than that. If you need to mount from the spindle at 240mm what you are doing is changing not null points but tonearm effective length, overhang and off-set angle. So what you need is that the tonearm/cartridge new alignment be made it with a new overhang and offset angle. A shorter effective lenght gives you a little higher overall distortion levels that maybe you can't even be aware of. Here the parameters value you need for 250mm and you can choose between those 3 alignments: https://www.vinylengine.com/tonearm_alignment_calculator_pro.php?arm1=Arm+1&l1=ps&a1lv=250&a... here for 240mm: https://www.vinylengine.com/tonearm_alignment_calculator_pro.php?arm1=Arm+1&l1=ps&a1lv=240&a... If you use a good protractor then normally there will be no cartridge mistraking. Btw, it does not matters the changes in tonearms EL the null points inside each type of alignment: Lögren A or B or Stevenson always are the same. In 1938 Erik Löfgren stated over his calculation equations to find out the cartridge/tonearm overhang, off set and the alignment null points where the input parameters in his equations were and are: tonearm EL, innermost groove and outer most groove distances and the equations outputs: overhang, offset angle, null points and by difference P2S distance. Regards and enjoy the MUSIC NOT DISTORTIONS, R. |
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