Uni-Protractor Set tonearm alignment


Looks like Dertonarm has put his money where his mouth is and designed the ultimate universal alignment tractor.

Early days, It would be great to hear from someone who has used it and compared to Mint, Feikert etc.

Given its high price, it will need to justify its superiority against all others. It does look in another league compared to those other alignemt devices

http://www.audiogon.com/cgi-bin/cls.pl?anlgtnrm&1303145487&/Uni-Protractor-Set-tonearm-ali
downunder
@04rdking

It's okay if you don't understand it.

The Uni-Pro allows me to try out different alignments. I just didn't like the Lofgren IEC compared to the VPI. I will try the Baerwald IEC and the VPI specific alignment later this week. Perhaps I'll find one of them preferable to the VPI alignment.

Oh, I also want to add that the Uni-Pro is much more precise than the VPI jig. The VPI jig has a certain amount of play between the jig and the metal piece that moves to contact the pivot base. The parralax effect can throw you off on the vpi jig as well.
DT,
I would have figured that different alignments altered the shape of the tracking error curve (this is indeed the critique of using a Stevenson vs a Baerwald - that the tracking error curve is "worse" than the Baerwald over the whole of the recrod) and/or tracking angle curves as functions of radius, even if ever so slightly. If they did so, would the skating force curve not change as well?


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.