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.




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.

          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.

          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