How critical is the exact placement of the tonearm

Less than 0.5mm is about right. You have some room to compensate by changing overhang via moving the cartridge back or forth.

Good luck!!

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).

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