Angling for 90° - tangential pivot tonearms

Some explanation about the RS-A1 tonearm by the designer below.

It has a curious set up by using underhang so it's very much the same concept like the Viv Lab Rigid Float tonearm.

As the subtitle of the article suggests, it is more about "minimizing unnecessary forces affecting tonearm" than about tangential tracking.



The structure and the features of RS-A1 Tonearm

minimizing unnecessary forces affecting tonearm

1. Inside Force
2. Down Force
3. Arm Resonance

by Shirou Horii



What is happening?

1. Cantilever gets bent

Most of today's tonearm comes with offset angle to compensate the tracking error and set with about 15mm of overhang. This setting inevitably causes a strong inside force and to compensate that, they come with an inside force canceller. However, the amount of inside force dramatically changes according to the frequency and amplitude and a static cancellation system is not effective.
Please check your cartridge if the cantilever remains correctly on the center of the cartridge body. Older your cartridge is and higher the compliance of the cantilever is, more likely that you'd find the cantilever is bent.
This phenomenon is the result of the transformed damper caused by the inside force. If it's slightly off centered from the dead center of the magnetic circuit, it's not a serious problem as long as it stays within the linearity of the magnetic circuit and damper, but the inside force is always changing, shaking the cantilever left and right, adding unnecessary modulation to the signal.
To solve this problem, either we forget about the tracking error and use a pure straight arm, or employ linear tracking system.
Since the effect of the distortion caused by tracking error is easy to calculate geometrically, it is easily understandable. But the actual effect of the tracking error is not as serious to the sound as many of you imagine. You can check this easily by changing the angle of the cartridge. Western Electric arms, 1A, 3A, 5A, all comes with straight arms. I wonder if they already new about this issue.
Overly concerned with the tracking error, the designers of the arms with offset angle fail to see the larger picture.

2. Down force occurs too

Offset angle doesn't only exist in horizontal plane. It also exists in vertical plane. As you can see on diagram 1, there's an extra force pulling the arm down. This means that, according to the change of the groove formation, the arm itself goes up and down in relation to the surface of the record, adding modulations to the output of the vertical element which controls the stereo effect.

An externally hosted image should be here but it was not working when we last tested it.



3. Needle talk


Have you ever played a naked mechanism of a music box? You can hardly hear it's playing. But once you let the mechanism touch something, not only hard wood, but a piece of cardboard or a cookie box, suddenly the volume increases and you can hear even lower resisters.
Needle talk is caused by the same reason. With such a small needle of a cartridge (quite a bit smaller than the reed of the highest note of a small music box), there shouldn't be any audible sound. The reason we hear an unexpectedly large sound is that somewhere in the resonant chain of cantilever-cartridge body-head shell-arm-arm base is amplifying the initial vibration of the cantilever.
The amount of the needle talk is dependant to the compliance of the cantilever, rigidity of the cartridge body, the structure of the head shell and the arm, etc. Less the amount of the needle talk and clear the sound of needle talk, better the combination.

The concept of RS-A1

On designing RS-A1, I wanted to present a solution to the above problems, which may not be a perfect one, but at least one that is reasonablly effective.

The problem (1) is caused simply by the offset angle, so making it a straight arm is the simplest solution. Of course, the less tracking error it has, the better, so the practical length of the arm should be as long as possible. With RS-A1, the distance between the needle tip and the center of the arm is about 230mm and by setting it the way shown in the diagram 2, you get the minimum tracking error.
If you replace an arm with offset angle (with the 220~230mm of practical length), which supposed to have an overhang, to a straight arm of the same length, it'll have an unnecessary overhang and a shorter practical length when set according to the diagram 2, creating more tracking error.
A pure straight arm also have an advantage on sound by not creating a dynamic distortion in principle.

diagram 2

An externally hosted image should be here but it was not working when we last tested it.


Setting the arm

In general, 1/3 from the inner groove (position B) will work best
choose a position where you get 0 tracking error at one point between outer and inner groove


center of the arm rotation



The solution for the problem 2, extra down force, can be simple too. Setting the vertical rotating center on the extension of the line between the tip of the needle and the vibration center of the cantilever (extension of the vertical tracking angle) will solve this problem. The vertical tracking angle should be the same as the cutting angle of the cutter. It is currently standardized as 20°. However, in early stage of stereo recording, it was set as 15°, and most of the LPs made in that era were cut by this standard. The famous Shure V15 was named for this reason. I'm not sure when exactly it was changed to 20°.
Once you draw a schematic though, you'll realize how steep this 20° angle is. To realize this with the supposed length of the arm, it has to be almost 15mm higher, and if you try to keep the height as it is, the arm length becomes too short, creating maximum of 13° tracking error. So what I ended up is a compensation between the two and the angle is set at a bit over 16°

The problem 3 appears as a common needle talk, but I think it is an essential problem about tone arm design. What gave me the solution on this matter is the rotating head shell that I designed 3 years ago. It succeeded in principle to separate the cartridge from the arm mass on horizontal vibration. Most of the musical signal was cut into the horizontal plane, so the rotating head shell worked quite effectively to minimize the needle talk.

RS-A1 was designed to realize above 3 principles in a simple design to allow the cartridge of its maximum potential. My basic concept was to go back to the basic relationship of what vibrates and what supports it.

An externally hosted image should be here but it was not working when we last tested it.


The structure of RS-A1 is quite simple as you can see in above picture. Avoiding knife-edge, or ball bearing support and making it with one point support simplified the whole structure.
The material is aluminum for the arm and the base and stainless steel for the strut, counter weight and the armrest. The arm is held to the armrest with a small magnet attached inside the arm.
The head shell is a rotary head shell. It can be taken off by loosening the nut at the bearing and is replaceable. You have to work carefully not to leave it loose, but the procedure itself is not a difficult one.
The finger hook is unconventional that it extends 90° off from a conventional design. It is designed to maintain the left-right balance. Once you get used to, it is very easy to use. However, if you'd like to change the angle, you can do it by loosening the screw under the arm. It would change the balance in strict terms, but not as much as to disturb the practical use.
Setting of the tracking force is British Decca-International style. With the common method of moving the weight forward after setting the static balance, the distance from the weight to the vertical fulcrum changes from what it once was when the static balance was set with the weight of the cartridge, thus making the scale inaccurate and unreliable. By having sub-weight on the back of the arm when setting the balance and taking it off afterwards, you get a very accurate tracking force. However, all cartridges come with an instruction for the tracking force with some range, so it doesn't need be completely exact. RS-A1 comes with 0.2, 0.4, 0.8 and 1.6grm sub-weights so that you can select between 0.2grm and 3.2grm tracking force with 0.2grm step.
How to run the signal wire is where I had to think hard. I wanted to keep the rotation sensitivity high, so decided to use the same fine wire used on the rotary head shell. The loose wire left out at where the strut meets the arm is not necessarily to keep the rotation sensitive, but to make changing the cartridge easy. Since the head shell is the fixed design, you need to take the arm off from the strut and turn the arm over when changing the cartridge.
The output of the cartridge is connected to the terminal with attached lead wire. Then each wire run through the 4 separate thin aluminum tube (for shielding) inside the arm to the output terminal. The terminals are made by Switch Craft, which has a reputation of having good sound.

The sound

My own impression is, in a word, "ease", especially at the fortissimo, which was a tough hurdle for LP reproduction. RS-A1 produces lively presentation with ease, as if the tracking ability has greatly improved, where other arms had a hard time and resulted in congested sound. Well, "you can't really tell until you hear it for yourself" is my rule when judging the sound; so hopefully, you hear it for yourself sometime soon!!

transration by Yoshi Segoshi


Please bear in mind the only reason I am bringing this RS arm up is that the design of the headshell can be modified to turn a conventional pivot arm into a tangential tracker a la Garrard Zero 100. If the GZ100 is not so flimsily built, I would just modified that. I have one and it's a piece of garbage. The idea is good but the execution is horrid.

Here's some criticism by one user of the RS arm from another forum. To be fair to RS Labs, the user initially expected that arm to be self aligned! The headshell pivot point is right above the stylus tip so I just don't see that's even possible. You need an extra force to move the cartridge body, hence the idea of adding an guiding mechanism for it to be an LT arm.

The RS Labs headshell does not work as reported! There are numerous problems with this design. For one, the theory is wrong, a headshell with a pivot at the stylus tip will not self align. I tried several different configurations and found also that the headshell does not self align regardless of where the pivot is moved forwards or backwards relative to the stylus tip.

Secondly, even if it did work, the cartridge leads impose far too much bias on the headshell to allow free movement. I tried several different leads too, long and short. I found that if you twist and pull the leads so that the headshell is roughly aligned as intended, then it sort-of stays that way. But the process is very approximate.

Besides the above, there were a number of other issues, the design is just not very good: the pivot has too much friction, and if you loosen it, there is too much slack. In any case, what I really wanted was to experiment with alternative alignments, to see what were the advantages of the different options. My next step is to have a similar headshell machined, allowing variable offset with the stylus at the pivot.

I tried underhang, and the result was the same. I can't recall exactly if I did an experiment without any headshell leads, but I did satisfy myself that the headshell does not self align.
 
M.Kelly is largely right. And what are opinions on "needle talk" article?
Quote:
3. Needle talk
Have you ever played a naked mechanism of a music box? You can hardly hear it's playing. But once you let the mechanism touch something, not only hard wood, but a piece of cardboard or a cookie box, suddenly the volume increases and you can hear even lower resisters.
Needle talk is caused by the same reason. With such a small needle of a cartridge (quite a bit smaller than the reed of the highest note of a small music box), there shouldn't be any audible sound. The reason we hear an unexpectedly large sound is that somewhere in the resonant chain of cantilever-cartridge body-head shell-arm-arm base is amplifying the initial vibration of the cantilever.
The amount of the needle talk is dependant to the compliance of the cantilever, rigidity of the cartridge body, the structure of the head shell and the arm, etc. Less the amount of the needle talk and clear the sound of needle talk, better the combination.
 
There is a lot to be said about using things the way they are supposed to be used, designed to be used, and expected to be used. That is what standards are all about. The cartridge is not designed to be freely-rotating at the end of a tonearm. We can immediately predict bad things, like tracking distortion when the cartridge and arm misalign.
Some circumstances are a little more involved, such as distortion due to VTA misalignment. All cartridges are designed so that their top edge is supposed to be parallel to the turntable surface. This is the expected arrangement, and should always be followed at first. It only requires obeying the mounting-height and VTF (vertical tracking force) instructions.
In reality, some adjustment may prove valuable. Unlike Segoshi-san’s statement, the VTA standard never really took hold on a large scale. (source: Martin Colloms' Hi-Fi Choice books and cartridge tests from about 1978 onward in Hi-Fi News & Record Review). VTA varied from about 13 degrees to 40 degrees (the latter used by a popular line of B&O cartridges). The CBS-100 test record was made with a 15 degree cutter, e.g. The Shure V15 pickups started with 15 degrees (as did the Stantons) and finally settled on 20 degrees.
To top it all off, preamplifiers started being manufactured without tone controls (all of them weren’t bad; the John Curl-designed Mark Levinson controls were outstanding). VTA experimenters found that, among other things, changing the angle varied the tonal balance. (Screwing around with loudspeaker crossover settings could do the same).
So now we could use things in ways they weren’t designed for, to compensate for odd conditions. The results could vary from nil to very large (notice that that could be very good or very bad), but at least the user had a measure of control.

Thinking through the entire audio chain is hard, but necessary. If you have good tone controls, don’t risk ruining the vinyl groove with excessive VTA (a little is OK); use the controls. And don’t mess with speaker controls unless you know what you are doing.

A note: Elsewhere in this thread I have indicated why I don’t like straight-line trackers (SLTs), but they must be acknowledged for two things:
(1) Set-up is vastly simpler than most other tonearms with respect to side-thrust (bias); and
(2) Their use (and short arms) brought to market disc flatteners, from plain weights to vacuum hold-down designs. This also increased awareness of vinyl warps and their effects on VTA tweaking.

This thread is a gold mine of creative thinking, for whatever goals the users deem worthy. The ideas and refutations can be equally valuable, but some can be dismissed more easily than others. You know who you are!

Andy
 
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Could you direct me to the post where you wrote that?

I believe he was talking about post#449.

Hi DD,

I have some questions about the driven-platform tonearm many contributors seem to favor. If the pickup is not offset from the arm, the benefit is no side-thrust (aka bias, skating force). The arm mount will be clock- or servo-driven to maintain tangency between the cantilever and groove. This sounds familiar.

The big problem with the SLT is its need to move all that mass (pickup, arm, mount & counterweight). The frictionless designs don’t work well, requiring high-compliance pickups to follow a non-tangential spiral and low-compliance pickups to avoid damage to themselves and the groove. The pickups in feedback-controlled versions do their deviate, correct, deviate, correct, deviate tango continually with some additional baddies, and so forth.

The driven-mount proposal (as I understand it) will have the same problem. The feedback loop will be necessarily slow and can’t be speeded up because it must accommodate eccentric records, variable-groove cutting and warps. It will continually lose perfect tracking and side-thrust immunity.

The problem is that, in the record cutting process, the lathe is driven to the desired location. The electronics preview the sound and control groove spacing accordingly.

In playback, there are no preview abilities. Nevertheless, a lightweight pivoting arm can follow all the pathway squiggles without difficulty. This bears repeating: the groove is telling the arm, via the cantilever, where to go. It is virtually instantaneous.

In the above SLT, the groove is telling a reluctant pickup to move its cantilever out-of-tangency and haul mass (sorry!). In the MPT (Moving Platform Tonearm), the arm is being driven to an expected location with no feedback whatsoever that it is correct. NB: the tighter the servo window, the worse the complications can get.

Granted, nothing is absolute and errors may be “small enough.” What (else) am I missing?
 
Hi Andy

My apologies for sloppy wording.

Sincerely,
Andy Wolff

There is no need to apologize. I simply wanted to know your reasons.
You cannot make improvements on existing designs unless you know what vinyl enthusiasts like and don't like.
I hope to expose my new tone arm later this year in these pages. You will find that I did away with all of your objections.

Sincerely,

Ralf
 
Hi David

ST

Will you exhibit this year at CES?

Regards
David

I am not in the financial position to exhibit my tone arm. I made a transparent display case for my tone arm and carried it throughout the show to see if I could find someone interested to manufacture it. If I get the time tomorrow, I'll take a picture of the tone arm and post it.

Sincerely,

Ralf
 
I hate to see this thread go cold.

2wice: I hoped someone more numerate would respond to your post.

If you zoom into the pivot track in any of your plots, the dots form a figure shaped like a comma and don't follow the arc. I got that same shape, or something very much like it, tracing the track of a point behind the pivot and in line with the wand on a mock up I built. Forcing that point to follow an arc resulted in tracking error at the stylus.

Do you have a design for your arm? And will you be posting it?

Regardless, good luck with it.
 
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That also bugged me and I spent lots of time trying to find the equation of the path the dots trace. I did find it but only after learning a branch of maths unknown to me before. It is an arc from an ellipse so I had to abandon that model. I was able to plot another arc using an offset circle without a cam as needed by the ellipse. If viewed at scale now the arc traces the circumference perfectly, only when you zoom in very deep can you see a slight deviance.
The design is complete but I'm worried that it works very well and someone else gets to monetize it before me.
 
Monetizing own invention is the most challenging part. Taking in account that independent inventor is the most discriminated category in modern society, not protected by government at all. Without huge resources to protect/ promote and manufacture his product, there are minimal chances to capitalize even most innovative and ingenious design... There are some exceptions, basically among people, who already invested many years to make a name and build some connections...
 
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Somehow your drawing differs from the original patent drawing in important points, i. e. in the point where the elongations of the tonearm intersect.

Hi alighiszem

That cat was skinned by another person with another method.

I started with a right angled triangle and then used matrices to rotate and translate that triangle so that the short side of every triangle goes through the spindle, in increments of 0.5 degrees.

Is there anything that you see that might cause the stylus not to be tangential to the spindle, so that I can fix it please?