Jonh, Thanks for your detailed explanation! Good-looking tonearm from a trusted company with a solid reputation, but wrong geometry ... strange world ...
L.
L.
Ortofon RS-309D geometry
I'm curious about the geometry used by Ortofon for this tonearm. The published specs are the following:
Mounting distance = 311 mm
Effective length = 326 mm
Overhang = 15 mm
Offset angle = 19 degrees
According to the calculator at Vinyl Engine, the resulting null points are 64.787 mm and 147.484 mm, the latter being outside the playable area on the LP surface. Maximum distortion is 0.831% and average rms distortion is 0.564, both of which are quite a bit higher than Stevenson, Baerwald, or Lofgren B geometries with an effective length of 326 mm.
I'm think of using this arm as the second on a 2-arm table. Current users seem to really like it, I really like the idea of being able to swap between SPUs and regular MM/MC carts on a 12-incher with easy VTA adjustment. But the geometry and distortion numbers are giving me pause. Should I even worry about them? If I change the mounting distance to get closer to Baerwald null points and distortion when using regular carts, will I lose the ability to use SPUs because of their fixed position?
I'm a bit perplexed as to why Ortofon would choose what seems like such an odd geometry, especially one that seems to increase distortion by quite a bit. Perhaps I'm misreading something. Any comments are welcome, but especially from current RS-309D users.
Thanks,
Bill
Mounting distance = 311 mm
Effective length = 326 mm
Overhang = 15 mm
Offset angle = 19 degrees
According to the calculator at Vinyl Engine, the resulting null points are 64.787 mm and 147.484 mm, the latter being outside the playable area on the LP surface. Maximum distortion is 0.831% and average rms distortion is 0.564, both of which are quite a bit higher than Stevenson, Baerwald, or Lofgren B geometries with an effective length of 326 mm.
I'm think of using this arm as the second on a 2-arm table. Current users seem to really like it, I really like the idea of being able to swap between SPUs and regular MM/MC carts on a 12-incher with easy VTA adjustment. But the geometry and distortion numbers are giving me pause. Should I even worry about them? If I change the mounting distance to get closer to Baerwald null points and distortion when using regular carts, will I lose the ability to use SPUs because of their fixed position?
I'm a bit perplexed as to why Ortofon would choose what seems like such an odd geometry, especially one that seems to increase distortion by quite a bit. Perhaps I'm misreading something. Any comments are welcome, but especially from current RS-309D users.
Thanks,
Bill
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