Thales - The One And Only Tangential Pivoted Tonearm

Inventors and technicians all over the world have made many suggestions on how to solve the  problem of optimal  LP record tracking. Just dealing with minimizing angular tracking error is the subject of dozens of patents. Few of these ideas have ever been translated into reality because  their complicated mechanisms, subject to friction and resonance, destroy any advantages that tangential tracking might bring.

However, Thales combines an elegant theoretical solution with an uncompromising technical implementation. Manufacturing its more than 100 parts uses the most modern process engineering in Switzerland. A watch manufacturer in Winterthur fabricates and assembles the micromechanical parts, in which twelve sapphire jewels in bearings reduce friction to an absolute minimum. The materials employed are carefully selected, measured and tested.

Thales is not a mass-market product. Each pick-up arm is individually numbered and matched to its related turntable. Meticulous tuning as a result of extensive listening sessions raises the performance of the pick-up arm to a level where we can enjoy the magic of the music and the fascination of the technology in equal measure.

Why construct a tangential pick-up arm? Aren’t the terms "tangential" and "pivoting" mutually exclusive in classical pick-up arm geometry theory? Here is some basic geometry and its worldwide resultant development. As you see, the advantages of both principles can be reconciled and allow a previously unattained quality of analogue sensing.

Angular tracking error
A decisive factor in pick-up arm geometry is minimizing the «angular tracking error», which determines construction and design. In the following, the origin and consequences of the angular tracking error are briefly portrayed. When making the master, the cutter, which is mounted on a linear slide, is actively moved over the rotating turntable so that the cutter is always at right angles to the radius and is, therefore, always tangential to the record groove.

The cutter vibrates along with the music signal, in the horizontal plane (lateral cut) as well as the vertical (vertical cut) when creating stereo masters. The forces that appear while cutting a master can only be kept under control by using short, stable construction methods. The most obvious solution is a linear guide as near as possible to the cutting point. Other conditions apply when playing the record. The pick-up must always be centered above the groove and forms, together with the arm, an inertial vibratory system for converting the groove cut into an electric signal. Passive, groove following methods are optimal.

The conventional pivoting pick-up arm places the pick-up on a circular path around a pivot bearing. Thanks to the lever arm between sensing and turning point, bearing friction results in only slight lateral forces. It isn’t possible to reach the entire record surface tangentially because the pick-up follows a circular path.

Using the right settings (position, length of the pick-up arm, projection) gives two places at which the pick-up is tangential (zero crossing) and provides a maximum deviation of approximately 2°(SME-V) from the tangent. This deviation is called angular tracking error.

This angular tracking error causes nonlinear falsification of all lateral-cut signals. The pick-up is not tangent to the groove and the analogue signal suffers what is called angular distortion. The amount of this distortion depends on the size of the angular tracking error, the music signal and on the size of the current groove. The insight gained from Baerwald and Löfren's extensive mathematical analyses allows us to deduce the ideal pick-up arm geometry with the minimum effective distortion. The length of the pick-up arm, its offset and the position of its pivot in relation to the centre of the turntable play a decisive role.

A Century of Solutions
Since the invention of the phonograph in 1887, many different solutions have been adopted to reduce or minimize distortion resulting from angular errors. The most widespread solution used today is from the first patent for a tangential approach in 1923.The pick-up, in exactly the same way as master cutter, is moved linearly across the record. Both active and passive systems exist.

In a passive system, the pick-up arm is supported so that it can move as freely as possible to minimize the lateral forces acting on the pick-up arm. Current examples of passive systems are Kuzma Air Line (air bearing) and the SoutherTQ-1 (roller bearing using quartz rods).

In active systems, the pick-up arm is also linearly guided and has a drive motor. The pick-up arm is no longer passively pulled by the record groove. Generally, the pick-up arm is fixed on a pivot-mounted carriage allowing a small amount of angular movement. Sensors measure the angular deviation and correct the position of the carriage. Theoretically, a small tracking error is still occurring but it is constantly minimized. There are other patents whose pick-up arms don’t move gradually but with constant active motion. These systems continuously control the carriage speed. Examples of active systems can be found, among others, at Revox and Pierre Lurné.

The drawbacks of linear systems lie in the high technical effort needed to minimize friction or to continuously correct the carriage's angular deviation. This often results in many components and delicate construction. Furthermore, active systems require that a small error always exist so that the angle can be corrected which means that they are always not quite tangential, even if only minimally.

The only non-linear solution that was mass produced was the famous Garrard Zero-100. A parallelogram construction with only pivot bearings which changes the pick-up's offset angel and thus can keep the tracking error angle at or below 0.5°. Similar solution methods are used by Burned-Jones and other, mostly two-armed, trapezoid constructions. Mathematically and geometrically, these solutions minimize the angular tracking error but failed to eliminate it. Thus, we shouldn't call it tangential sensing but rather an improvement in pick up arm geometry as a result of elaborate correction of the offset angle.

Thorens’ 1958 patent is a fancy, but in no way less interesting, solution. The pick-up also moves linearly across the turntable. A cleverly balanced vertical lever construction reduces these linear movements in the pivot bearings. Similar systems have been made by Japanese inventors, whose pick-ups are moved linearly using toothed levers. However, their construction is mostly horizontal.

Other attempts worth mentioning come from various Japanese patents. In these, a single pivoted pick-up arm is adjusted during the sensing process so that the sensing point is always located at the zero crossing, resulting in tangential sensing. This can be achieved in different ways: using cams (disc or track), by electromechanical updating or even with gears. In some solutions the length of the pick-up arm is adjusted, requiring continuous positional adjustment of the counterbalance weight. In other cases the pick-up arm's pivot point is moved along a specific curve depending upon the location of the pick-up. Such constructions are extremely complex and quickly call for technical descriptions that are more than 20 pages.

The Thales Pick-Up Arm
Despite all these various trains of  thought, the simple pivoting arm and the linear tangential arm have established themselves in practice. In many explanatory notes, these two versions are often presented as the only, opposed, solutions. It is often emphasized that the linear tangential arm is indeed the correct geometrical solution but that it needs complex bearings or controlled guidance which would cause more problems then it solves. Thales, the latest tangential arm uses a simple solution which can only be implemented thanks to well conceived detail solutions and appropriate high fabrication quality.

As the name says, the Thales tangential sensing pick-up arm is based upon movement and alignment on a Thales circle: All the triangles (ABC) on the Thales circle around M are right-angled to C. Thus, BC is always right-angled to AC in all positions and so tangential to the record groove with actual radius AC. Mounting the pick-up exactly under position C and aligning its path along BC (with variable BC length) results in tangential sensing. This method was granted a patent, number CH694567 on March 31st 2005.  

       Although sensing along the Thales circle seems, at first glance, simple and obvious, it requires close attention to various details. For example, to be consistent, changing the length of the leg BC must not contain a linear bearing, which is solved using compensating lever techniques. All mass measures are in the milligram range and meticulously handled so that the arm produces no lateral forces and that the burden remains constant. As in a conventional pivot arm, the Thales arm produces a frictional force between the record and the sensing diamond. This force is tangential (namely, along BC) which results only in torsion toward the disc centre.
(Skating force). This force is also a variable parameter which must be compensated. Only an uncompromising implementation allows the arm to play to such a high standard, justifying the investment in a new development. The Cardan bearings are vibration free and compactly constructed. Precise sapphire conical bearings, also in the adjustment arm pivot, ensure low friction. The pivot bearing above the pick-up consists of 25 individual components manufactured with very high precision (under 1μm), which guarantees free running and no play between the head shell and arm. All arms are machined from massive magnesium resulting in freedom from vibration and low inertia. The smallest part weighs only 0.009 gram and fits easily on a match head. As to its musical qualities: Listen for yourself, it’s worth it!

THALES–
THE ONE AND ONLY TANGENTIAL PIVOTED TONEARM