Uni-Protractor Set tonearm alignment

Perhaps it might be a good idea to go back to basics. There are two aspects to this issue. One is to acknowledge what the force is and how it originates. Second to see how it manifests itself on a record deck.

While we might call it antiskate, or bias, or whatever, the force which pulls the arm inwards is not specific to tonearms. It can apply in any situation where there are two forces opposing each other.

To illustrate the simple example of a linear tracker. (Those of you with linear trackers can start practising your smug grin.)

Say you hold one end of a short rope. You are the Tonearm bearing. You put a conical blob of blutak in the middle of the rope - the Stylus. Your wife holds the other rope end. She is Friction.

Friction acts on the Stylus by pulling it along the groove in a direction directly opposed to the Tonearm bearing. It reacts by holding on and pulling back. The rope is straight. The Stylus remains unmoving in the middle. As friction moves to the side, Tonearm bearing follows every move (hopefully).

Now a Pivoted arm.
Friction takes a different tack. She pulls at an angle. Tonearm bearing reacts against Friction. It is immovable. It holds on to the Stylus. but the rope wants to straighten, and Stylus will be pulled sideways, unless......

Help arrives. Another pal called VTF, stands on the Stylus. now it's harder for Friction to pull Stylus sideways. Then yet another pal, Antiskate, comes in and pulls the Stylus in a direction which stops the rope straightening, just enough to stop the Stylus moving without pulling it in the opposite direction.....

Ok, this is simplistic, but relevant. First, note that we have no mention of cartridges, only the stylus which is simply the name for a point on our rope. The angle we talk about is the angle formed by a line from pivot to stylus and stylus to groove. Which is not quite the same thing as cartridge offset.

Forget about cartridge offset for the moment and just imagine your arm with no cartridge, just a sewing needle on the end where the stylus would be, and then follow its arc on a record. Follow it beyond the inner groove, beyond the label, beyond the spindle, and out the other side. See how the angle between pivot, needle, and groove changes. Think of the rope story and in what direction the arm will be pulled. 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..

That is the basis of the antiskate issue. Does it exist as a force. It exists, yes, it definitely does. But why some people prefer no antiskate, that is for them to say. My arms had an antiskate mechanism, using lever and thread, which allowed for varying the force, and the ratio to some extent across the record, or it could be removed completely. But it was not any more sophisticated than that (It could even have been used to apply a reducing force like the Morsiani,though I am not aware anyone ever did, and not a negative antiskate as in their example of the blank disc; I think there's something wrong there.)

It would be possible to design a cam system given different leverages so as better to follow the average variation, though not the instantaneous.

Whether you can adjust for it totally and in every way, I doubt. As there are many other factors involved in the friction calculation. Some people are more sensitive to its effects than others. Personally, I always tried to compensate for it. I was concerned with its effects on imaging, soundstage etc

Regards, T_bone: If I understand your point then an alignment with zero overhang would result in all relevent forces coming into balance at the spindle, progressively increasing overhang would bring "stasis" at incrementally greater distances from the center?

Peace,

@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,