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Re: [ARSCLIST] Anti-skating (was Mostly for laughs)
I see, but still don't like the idea of the record jerking the stylus in
and the bias jerking the arm out. I've looked at the difference
(visually) with and without bias, and it always looks violent when I
lower the cartridge with bias engaged. And after careful listening, I
found that the center image was where it was supposed to be without bias
(VS with it). With bias, the center image wanders as groove modulation
increases (increasing the skating forces momentarily). I know several
guys with good ears (Harry Weisfeld, the VPI guy, included) that don't
feel the gains for bias (lower distortion in one channel) outweigh the
drawbacks (a constant changing of skating force constantly changing the
geometry of the stylus). Of course, you can always by a linear tracking
arm. I did.
Phillip
Jos Van Dyck wrote:
Steven C. Barr wrote:
The phenomenon we refer to as "centrifugal force" is actually the
straight-line inertia of an object moving in a circular path
(or a portion of one).
Phillip Holmes wrote:
... The net result is that you exacerbate the misalignment of the stylus
in the magnetic gap. In other words, the needle/stylus is still pulling
in and you are pulling the cartridge body the other way.
Since the stylus/catridge doesn't rotate, there is no centrifugal force:
Fc = mv2/r, where Fc = centrifugal force, m = mass, v = speed, and r =
radius.
The root cause of skating force is friction between stylus tip and record
groove walls. Since the line between stylus tip and arm pivot is not
tangential (perpendicular to radius), the friction force is decomposed in a
vector towards the pivot, and another one pulling the arm inside (skating
force). Only a tangential arm (or one with infinite length) produces no
skating.
The anti-skating mechanism offsets the radial force vector, such that both
groove walls get equal pressure. Proper anti-skating adjustment can easily
be verified with a test record containing a heavily modulated sine wave
(e.g. 300Hz lateral @ +15dB). The anti-skating (bias correction) is
properly set up when distortion in both channels is equal. Without anti-
skating (or with too much), one channel will be more distorted.
The required anti-skating force depends on the friction resistance of the
groove, stylus pressure, stylus shape.
A stylus on a blank disk surface (without grooves) behaves differently from
the V-shaped groove.
Jos Van Dyck
NGM Archiving Solutions
centrifugal