general tonearm design question


Many popular tonearms are designed with with the fulcrum for the vertical axis at ~70 degrees (e.g. Rega, SME), rather than perpendicular (e.g Origin Live).

Doesn't the former design cause the needle to track to the outer groove as the counter weight swings downward?

...or does the cartidge/tube somehow counter this?

Would a counter weight mounted at 90 degrees to the fulcrum, yet the arm tube set at 70 degrees be the solution to this, or am I wrong?

(The reason I started wondering about this was due to the varous Rega counter-weight mods. I would think that a lower center of gravity would exacerbate this problem. Furthermore, wouldn't a lower center of gravity only be effective on a uni-pivot design?)

your thoughts?
128x128popluhv

Showing 1 response by armstrod

Nsgarch and Dougdeacon both give great answers here, and I agree that having the vertical bearing axis perpendicular to the armtube rather than the cantilever is a flawed design.

Here's the part I don't understand. Go to Origin Live's Web site here:

http://www.tonearm.co.uk/index.htm

and scroll down a bit. There's a top view view of all the OL tonearms. Except for the least expensive model (an unmodified Rega RB250) all of their arms have the vertical bearing axis perpendicular to the armtube, not the cantilever. Their most expensive arm is something like $5-6K, so building at right angles shouldn't be needed for hitting the price point. I'm guessing they think the design affords some advantage, but I can't see what that might be. I'm puzzled.

David