Building a Tuthill/Reed 5A Tangential Tracking Pivot Tonearm

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directdriver

directdriver

Member
Joined 2005
super10018 said:
When we say “offset”, we may mean two different things.
Click to expand...

Conceptually they are the same thing. Let's look at the Reed diagram again.

Just imagine if the BLACK line (A3 to 1B3) is shortened to a dot and the RED line is lengthened all the way to point A3 and, voila, you have the Thales brand model Simplicity tonearm, another dual-pivot design, which came with magnetic antiskating device. So obviously the Reed 5A has less skating force than the Thales arm but does not mean it has no skating force at all. My belief is that until you can make the main fixed pivot 1P2 located exactly at point P3, you will always have some skating force, however little. Essentially having the moving pivot and variable offset at the headshell has the highest amount of skating force. And having it closer to the Thales locus at point P3 will have less. And having it exactly at P3 will have zero skating force, which result in an almost impossible design.

Apparently Reed thinks it's not enough to bother to need an antiskating device. However the Japanese blogger, who is skeptical of Reed's claim of no skating force, brought up a question in his post whether that knurl knob, added after the prototype version, above the main fixed pivot has anything to do with antiskating. Maybe it's just an end cap to protect the bearings. Just curious.


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super10018

Member
Joined 2010
DD,

I don't disagree with you. Both meanings of offsets we are talking about here are the same in concept. I expect Reed 5A doesn't skate just because the concepts are the same. Wally Tools already demonstrated that a regular pivot tonearm with offset angle doesn't skate as long as the overhang is negative and the stylus is on Thales circle. They didn't say it is on Thales circle. I did. They said in the video that the stylus is perpendicular to the spindle. But it is the same thing as on Thales circle.

Skating Study (Part 4 of 6) - Overhang 1 - YouTube

This 2nd video to show skating force.

Skating Study (Part 5 of 6) - Overhang 2 - YouTube

I did the same tests before Wally Tools. The test convinced me that Reed 5A may not skate because the offset built-in Reed 5A tonearm is conceptually the same as the regular offset that is just behind the headshell.

I don't know if Reed has some kind of secret device for anti-skating. I don't think so. My best guess is the cap is for keeping the bearing clean. Reed audio may think it needs to oil the bearing sometimes. In any case, I don't know what is for. If they use jewel bearings, I don't see the need for oiling.
 
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warrjon

Member
Joined 2011
If you look at that video they are using a Technics pivoting arm so when the stylus is tangent to the groove there is NO linear offset between the stylus and horizontal pivot, thus no skating force.

With a dual horizontal pivot arm there is a linear offset (1B3 to 1P2) to the second pivot the torque around that pivot (1P2 in DD's drawing), will cause skating forces unless that second pivot is unable to rotate due a servo.

DD is correct if 1P2 can be located a P3 there will no skating force.
 
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alighiszem

Member
Joined 2007
super10018 said:
I don't know what you are talking about.
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That was what I was afraid from.

super10018 said:
1, On the Thales circle, Reed 5A is on the Thales circle without overhang. It supposes to have no skating by their claim.

2, All regular pivot tonearms are beyond Thales circle with overhang and two nulls. They can be sin(90)=1, at null. By your model, once sin(90)=1. Fsk=Ffr. If Fsk=Ffr, does this mean there is no skating? However, all regular pivot arms skate at nulls, i.e., sin(90)=1.

All the tonearms are real. They are not imaginations.
Click to expand...

Overhang and Thales circle have nothing to do with skating. Exactly that was I wanted to illustrate with my formula. The only thing what counts is the angle of the tangent to the path of the stylus to the line between the stylus and the centre spindle.
If this angle is 90 degrees, than the stylus is on the label. Then of course the friction force and the skating force will be the same, but that has no practical value to the listener.
 

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super10018

Member
Joined 2010
Doug,

I am not going to use ball bearings and probably won't add a pre-loaded bearing either since the purpose of building such an arm is to approve if the arm will skate. Chances are the arm will skate. But I will still go-ahead to build it. Building air-bearing arms left me way enough small parts and material.

Jim
 
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bambo

Member
Joined 2006
alighiszem said:
...
Overhang and Thales circle have nothing to do with skating. Exactly that was I wanted to illustrate with my formula. The only thing what counts is the angle of the tangent to the path of the stylus to the line between the stylus and the centre spindle.
...
Click to expand...
You may want to have a look at the very fine write-up by Klaus Rampelmann over at Vinyl Engine. He states:
"The skating force Fs is a function of groove radius R, overhang D and effective arm length L" which seems correct to me :cool:

You can find his downloadable article on 'Vinyl Engine'

Oh, and don't forget to enjoy your records!
greetings, Mark
 
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bambo

Member
Joined 2006
alighiszem said:
As is the path of the stylus a function of the above mentioned factors.

Thanks, Mark.
Click to expand...

Hi Alighiszem, I must admit that it is funny (at least, and indeed I do appreciate humor) to see my contribution being quoted as if super10018 made it... Is this an invitation to put you on my allergens list, or what? Your intentions are not really clear :confused:

best regards,
Mark
 
directdriver

directdriver

Member
Joined 2005
"Final remarks:

Since skating force is not constant across the record surface but describes a somewhat parabolic curve exact compensation is not possible: whatever the precision of setting the antiskating , the curve of the skating force will be intersected in two points at best.

From discussions on web forums it becomes evident that some people think that skating force is zero when the tracking error is equal to zero, as it is the case in the null points. This is true only for linear tracking arms, for pivoted arms this simply not correct. As long as the line connecting the stylus tip to the arm pivot is not tangential to the groove at the contact point, which is always the case for pivoted arms, a skating force is generated. For that very reason tangential pivoted arms like the Garrard Zero and the Thales still have anti-skating mechanisms."

-Klaus Rampelmann
Click to expand...

Hence Ray's string test and Conrad's stylus to pivot straight line theory.
 
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Straight Tracker

Member
Joined 2010
alighiszem said:
As Klaus Rampelman stated:

"As long as the line connecting the stylus tip to the arm pivot is not
tangential to the groove at the contact point, which is always the case for pivoted arms, a skating force is generated."
Click to expand...


Hi All,

The "groove" has nothing to do with tangentially tracking an LP.
The reference of tangential tracking should refer to a "concentric circle of random diameter between the limits of the start and the end of the modulated groove" I know it is a mouthful but it is a fact.

Sincerely,

Ralf
 
D

dtut

Member
Joined 2007
Ralf,

So for our purposes, the segment of a spiral the stylus touches is considered a segment of a concentric circle? That’s a very interesting and helpful approach which makes understanding tonearm movement forces much easier for me.

I hope the heat isn’t mistreating you.
 
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super10018

Member
Joined 2010
directdriver said:
Hence Ray's string test and Conrad's stylus to pivot straight line theory.
Click to expand...


Ray’s string test and Conrad’s condition are different from Klaus's statement.

Klaus Rampelmann stated: As long as the line connecting the stylus tip to the arm pivot is not tangential to the groove at the contact point, which is always the case for pivoted arms, a skating force is generated.

I will assume that he was talking about regular pivoted arms, i.e., a pivot arm with an overhang. Yes. He is correct. All the pivot arms with an overhang skate. Offset is irrelevant. No problem here. For a pivot arm with an underhang, his statement is incorrect.

Let’s take a DJ tonearm without offset but with an overhang. The DJ arm will pass the string text. If you pull the string, the arm won’t move sideways. The DJ arm will meet Conrad’s condition, too. A line through the headshell will intersect the center of the pivot. So, this DJ arm won’t skate by the conclusion of the string test and Conrad’s condition. In fact, the DJ arm does skate.

This why I said it before. The string test and Conrad’s condition can’t be used as the standard whether a tonearm skates or not.
 
directdriver

directdriver

Member
Joined 2005
super10018 said:
Let’s take a DJ tonearm without offset but with an overhang. The DJ arm will pass the string text. If you pull the string, the arm won’t move sideways. The DJ arm will meet Conrad’s condition, too. A line through the headshell will intersect the center of the pivot. So, this DJ arm won’t skate by the conclusion of the string test and Conrad’s condition. In fact, the DJ arm does skate.
Click to expand...

Nobody makes a tangential tracking tonearm to track only one or two null points or grooves.
 
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