Science Meets Master Craftspeople - Thales Tonearm Technology / by Rom Beyerle

Our fine friends and master crafts people at Thales have added a new technology page to their already very informative website, please read on for a great insight into the mechanics of what makes their tonearms truly brilliant. Further reading is also available on their website for whitepapers and brochures on all their outstanding products, or simply arrange a time with us to come and audition them for yourself. 

IDEA

It all began when Micha Huber sought for a way to combine the advantages of a conventional pivoted tonearm and those of a linear tangential pick-up arm. The solution method is based on the well-known elementary school aid to construct a tangent: the Thales' circle. After much thought and calculations, a three-dimensional mechanical solution emerged that satisfies all the requirements placed on a modern pick-up system.

The long-cherished dream of geometrically correct tracking with low friction pivoted bearings became reality. A new patent was added to the dozens of existing patents that testify to this dream: CH 694567 Tangential Pivoted Tonearm, announced in May 2004.

DESIGN

Our philosophy is not only to find theoretical perfect solutions but also to realize them the most precise way and achieve continuous improvement in order to set new standards in music reproduction. Therefore, we invest into research and development constantly and we realized tangential pivoted tonearms with more complex mathematical background allowing more elegant mechanical execution.

Based on the experience that a turntable with its tonearm should be designed as one single unit, we have developed our own turntable-line which meets highest requirements. The portfolio is completed by our own phono- and line-cables.

TECHNOLOGY

 

 

TRACKING ERROR

 

While cutting the master disc of vinyl LP, the cutting-tool is hold on a massive support and guided linearly above the disc’s surface. This arrangement keeps the cutter-head rigid, even if high cutting forces occur.

cutting lathe

 

While tracking the LP for playback, it’s totally different properties: the pickup-cartridge should follow the groove as smooth as possible and even tolerate eccentric and wavy vinyl. Therefore, radial pivoted tonearms are established as they allow to reduce unintentional forces at the tracking point tremendously. However, this mechanically preferred solution ends up with a geometrical error, since the cartridge is not guided tangentially to the groove anymore.

This so called tracking error basically distorts the music signal in a non-linear manner. By using non-spherical diamond tips (f. e. elliptical), further consequences as timing error and channel-differences in the frequency-response occur.

GEOMETRY THALES ORIGINAL

The unique Thales-solution combines in an elegant way the advantages of the tried and tested pivoted tonearm with the absolutely tangential tracking. This construction for which a patent was taken out on the 8th of May 2004 reduces the perfectly tangential tracking to pivot points, while the pick-up cartridge is taken and aligned on the Thales' Circle.

 

All triangles ABC on the Thales' Circle around M are rectangular in point C. Thus BC stands rectangular to AC and therefore tangential to the groove (red) with the radius AC. Because the pick-up cartridge is mounted exactly under point C and in the alignment of the straight line BC the tracking is perfectly tangential in every position.

From this completely new solution the following advantages ensue:

  • No tracking error and no consequential resulting distortions
  • Minimal friction because of pivot bearings; no linear bearings; no active tracking
  • Short tonearm with little resonance
  • Symmetric inertia at the tracking point in all axles

GEOMETRY THALES SIMPLICITY

There is a small but mighty history in finding elegant solutions for tangential tracking of analogue records. Some of the inventors concentrated themselves on tetragon-geometry:

P. W. D. BURNE-JONES
GARRARD ZERO 100

P. W. D. BURNE-JONES

He announced in 1953 a patent with a tetragon tonearm where the cartridge was mounted in the middle of one side. Burne-Jones sold tonearms under his own name, and his idea was adapted several times.

GARRARD ZERO 100

This tonearm, published in 1970, is the best known solution working almost tangential. The cartridge tip was mounted exactly below a pivot-point. This idea made it possible to reduce the tracking error to +0.025 / -0.018°

Even if this solutions are not to be mixed up with the Thales-Original Solution – as the Thales is working on a triangle instead of a tetragon – the experience with the Thales geometry made it possible for Micha Huber to even optimize the tetragon solution and reduce the tracking error to 0.006° which is four times less than all solution published so far. This new geometry now made it possible to come very close to the perfect Thales geometry while using less parts and very elegant design.

GEOMETRY THALES EASY

The geometrical basis for the Easy tonearm is a novelty in tonearm-design. It’s the first solution by Thales where none of the bearing-points is located directly above the stylus. The clever arrangement of six bearing points creates three null points for the horizontal tracking error, plus a zero point for the variable offset angle. So, not only the tracking error is reduced, but the skating force as well.

SKATING FORCE

The skating force is so called because it causes the tonearm to glide over the record from the outside to the inside, so to say 'to skate'. This force which draws the tonearm to the centre of the disc ensues indirectly from the friction between the tracking diamond and the record. This friction force always takes effect in the direction of the tangent line. If the pivot point of the tonearm is not located on the tangent, the friction force is divided into two components: one takes effect in the direction of the pivot point of the tonearm, the other takes effect towards the centre of the disc.

FORCES

The force Ft results from the friction between the record and the tracking diamond. It acts tangentially. Because the pivot point is not located on the tangent, this force is divided into Fa which acts in the direction of the pivot point and Fs which is the skating force. The value of the skating force is not easily determined. It depends – first of all – on the music signal, further on the tracking weight, the circumferential speed and the tonearm and diamond geometry.

Therefore, even if the Thales-tonearms do track tangentially, their offset angle requiers compensation of the skating force. Since the offset angle for all our tonearms are lower than with normal tonearms, we do preset the compensation and it’s not adjustable for the client. For the different solutions, the compensation mechanism is solved as follows:

  • Thales Original: compensation-mass on a small lever, decreasing towards the inner groove because of decreasing offset angle
  • Thales Simplicity II: magnetical compensation between the two arm-tubes, decreasing towards the inner groove because of decreasing offset angle
  • Thales Easy: no skating compensation required, since the offset angle oscillates around the zero-point (straight arm)