Uni-Protractor Set tonearm alignment

@John,

I might install the VPI after market Anti-skate weights again just to re-confirm what I heard the first time.

The thing is if the anti-skate force differs from the beginning to the end of an LP, how can a constant weight compensation like the VPI weight on a string work correctly on the entire LP? It can't, I would think.

Dear T_bone, yes, different alignments do alter the shape of the tracking error curve. However - it is always a bundle of effects which you can't actually isolate from each other and their dependences. The more "flat" a tracking error curve becomes, - it goes hand-in-hand with longer effective length and less offset angle. All these do influence the skating force. A zero offset angle (tonearm and cartridge body ..) would result in zero breakdown torque and thus any remaining skating would just be a function of friction due to contact area size. That would diminish even further with increased VTF. But even in a zero tracking error point - i.e. "null point" (strange blend of german and english here..;-) ... ) there is still the breakdown torque of the tonearm itself as the ever dominant source for skating.
You are right - a skating force "curve" across a record's groove will never be linear. Not with a pivot tonearm ( not even with the Thales).
The groove's radii change - so does the friction on the inner groove's wall. The tracking error decreases and 2 times and increases 2 times during the groove.
IMHO the most suitable way to handle this practically was always the same: - 12" tonearm w/low offset angle, low compliance cartridge with high VTF, lateral balanced pivot tonearm.
In other words - all measures taken to minimize breakdown torque so to minimize the evil at the source. Better to minimize skating to a value negligible then to fight a constant war with lots of friendly fire (anti-skating...) and no aspect to win.
That way of mine does of course limit the choice of cartridges and tonearms.
As my prime choices in both categories do however qualify in all points to this schemata I am kind of lucky..... ;-) ...
In any case - it is a path as suitable as some other.
It just suits my personal way of addressing problems at the source rather then seek painful cures for situations which have already evolved way past practical solutions.
Cheers,
D.

Dear John,

You didn't answer my question, or might missed it. How should anti-skate work in a pivot designed tonearm ?
From outer groves to inner groves :
1. decreasing
2. increasing
3. decreasing then increasing
Or none of the above.

Regards,

Mesael

Sorry.

I said

The angle changes towards the centre not varying much, but under 7cm radius, the closer to the spindle it gets, the greater it becomes, until at 0 it is a right angle..

What this means is that the inward force trying to rotate the arm stays more or less constant within a few percent reducing slightly following the tracking error curve of the arm (not the tracking distortion curve) which varies across the record. Depending on the overhang used and the arm effective length, at the inner null the force starts to increase rapidly.

So it would appear that the ideal would be to follow this curve, reducing slightly then increasing.
However, it has been shown that there are other factors which increase the friction force as the radius decreases, which would skew this result and make it more likely that the force should at least be constant then increase, or even gradually increase all the way across the record

When I designed my arm that's what I did, as I thought that, like tracking distortion it seemed to be worse towards the inner grooves, and less of an issue further out, and should be weighted that way. But it was all "suck it and see". So, really, a tonearm should perhaps give the user the option of trying different things.

The actual amount of antiskate needed is very much dependent on stylus profile and downforce. With enough downforce the stylus will never meet a modulation large enough for it to lose contact with the outside wall, or even throw it up out of the groove. However there will still be unequal forces on each side of the groove unless there is some kind of compensation.

As Dertonarm says, a longer arm has less skating force than a shorter one.

But it is still there, and it has to be dealt with somehow - you can't just sweep it under the mat....

Dear John,

Thanks for your response, I appreciates.