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On 18/12/2011, Dan Nelson wrote:

> How about those straight arms that must have been 2' long on RCA
> transcription turntables ? With a pick up that would play vertical and
> lateral and a conical stylus it would appear that any tracking
> misalignment would be nominal and have little effect on playback
> response. No one has mentioned these and like long arms...... Astatic
> even made a straight arm that was at least 12-14" long. dnw
> 
What matters is the angle between the pickup cartridge and the line from
the stylus to the main bearing. The shape of the arm between the stylus
and the bearing is irrelevant - it can deviate from the direct line in
any way you like.

The angle is calculated to give the necessary offset for minimum
distortion. As the (pivoted) arm travels across the record, the correct
angle gives the least possible deviation from the ideal tangent to the
groove.

If the bearing is a pair of bearings, the axis between them should be at
right angles to the main line. But it can be a unipivot, with no axis -
and minimal friction.

There is one possible disadvantage to using a straight tube - it would
be more liable to resonance than an S-shaped tube. Damping with some
rubber can help with this.

There are advantages to using a tapered tube, wider at the bearing end -
but it is harder to manufacture.

Regards
-- 
Don Cox
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