Vinyl Asylum Welcome Licorice Pizza (LP) lovers! Setup guides and Vinyl FAQ.

---

[ Follow Ups ] [ Post Followup ] Thread: [ Display  All  Email ] [ Vinyl Asylum ]

---

[ Alert Moderator ]

---

RE: Wally Tractor Universal... is it worth it?

Posted by flood2 (A) on September 28, 2016 at 16:25:31

In Reply to: RE: Wally Tractor Universal... is it worth it? posted by bcowen on September 28, 2016 at 05:41:44:

"Linear offset? I don't even know what that is."

It is the basis of tonearm design and alignment.

Imagine a right-angled triangle with the hypotenuse defined by the pivot/stylus distance and the pivot centre and stylus tip being 2 vertices. Then the opposite side is the linear offset (opposite the offset angle).
The linear offset is a constant which can be associated with a desired set of null points and is independent of the tonearm length. For example, if you wish to have 66.1 and 120.9mm then the linear offset will be 93.52mm. If you wish to implement the same null points as a Technics SL1200 (at 58.8 and 113.5), the linear offset is 86.16mm.

Whether you have a 12" arm or 9" or 7" arm (but who would want one that short!), the linear offset can be used to define the exact position of the stylus and the offset angle unique to the arm being aligned. Hence any pivot/spindle distance can be accomodated with a unique solution for overhang and offset whilst still achieving the desired null points.

"However, the whole point of using the protractor is to set the overhang so the stylus tracks the arc "perfectly" at which point the pivot-to-stylus distance will also be perfect."

Yes, that is an obvious statement. However, your argument is predicated on an assumption that the pivot/spindle distance is known "exactly" and that the printer was correctly scaled in both axes to give "perfect" dimensions, the spindle hole on the protractor was a perfect snug fit around the spindle with no slack and doesn't shift during use; as you swing the protractor back and forth to set overhang you risk enlarging the spindle hole.
Do you see where I'm going with this?

There is no such thing as an "exact" measurement. Everything has a tolerance and all you have done is introduce an additional uncertainty as you attempt to find a solution that minimises the deviation from the arc.

"I have absolutely no problem getting the stylus to track the arc from end to end with a high degree of accuracy."

Good for you! It is highly unlikely that you hit the arc perfectly (which as mentioned before assumes the pivot/spindle distance was perfect as well) except by sheer luck. It is very easy to prove this to yourself with a compass and drawing two circles on a line representing the effective length; the first being the correct radius for the arc and the second such that the second circle radius hits the end of the line representing the stylus tip but with a shifted "pivot" position on the line. Obviously the larger the radii the smaller the deviation, but if you do small circles to magnify arc differences, you will have a better understanding of the errors.

Now the REAL question is whether any of this really matters? Probably not....
:)



Regards Anthony

"Beauty is Truth, Truth Beauty.." Keats

This post is made possible by the generous support of people like you and our sponsors:

Amplified Parts

---

[ Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2024, Audio Asylum, all rights reserved ]

---

[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]

---