Notes on The Belt Drive Turntable

Page first published in September, 2010


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Philips Belt-Drive 1950

The engineers of the Physics Research Laboratory (Natuurkundig Laboratorium - NatLab) of the Philips Company - in fact Philips Gloeilampenfabrieken in Eindhoven, Netherlands - often had the liberty to research, invent and design whatever idea they came up with. There are many inventions and patents registered on their name, and many are being used by other leading manufacturers. Also in Audio.
When in 1950 Philips started its record company named
Philips' Phonographische Industrie (PPI), there should be a proper machine for the playback of the new 33 RPM vinyl discs with newly recorded performances of conductors Willem van Otterloo and Paul van Kempen, pianists Clara Haskil and Cor de Groot, violinists Herman Krebbers and Theo Olof - to mention a few names in the classical music section - and of artists playing jazz and popular music. History tells that it was engineer Louis Christiaan Kalff who came up with a new turntable of modern design and a revolutionary transmission of the turning of the motor to the platter, a system that broke completely with the motors and transmission of the common 78 RPM worm wheel drive concepts. It is, as we know now, the first belt drive turntable ever. It was the Philips HX301a, two speed player.

The image above is from 'PHILIPS 100', the book published to commemorate the Philips Centenary "Philips One Hundred, 1891 - 1991".



I published a page about the Thorens TD-124 idler wheel drive turntable. I also published a page about the Technics SP-10 direct drive turntables (three versions).
A third method for driving the platter is by means of a belt made of rubber, or neoprene, a prepared thread, a length of recording tape, or whatever material that procures the necessary grip and does not show exaggerated elasticity.
So here are my notes on the belt drive turntable. - R.A.B.

HX301a Belt Drive

Since many music lovers would also continue to play 78 RPM shellac records in those days, the turntable (in fact a simple small record player), had two speeds: 78 and 33.33 RPM. RCA's 45 RPM 7 inch disc had been introduced in the US in 1949, but it would take some four years before it was adopted by the European record manufacturers. Therefor the Philips label had introduced a 78 RPM Minigroove vinyl disc with the size of the RCA 45 RPM 7" disc. Both popular and classical music was pressed on this format. In this way many people could already get acquainted with vinyl records and could be persuaded to buy the larger LP records instead of continuing to listen their old 78 RPM shellac discs which were still manufactured in the early 1950s.

Idler Wheel

At the basis of the new machine was an idler wheel. But it was not the familiar wheel that shifted up and down a pulley with diameters for 33 and for 78 RPM. No, it was the motor, mounted on a separate triangular chassis, that was shifted from the left transmission wheel to the right and vise versa. So there was no movement or deviation caused by the drums which were at a fixed position. Another peculiarity of the construction of the Philips is that the belt does not run over the entire periphery of the platter, but touches only about a quarter of the platter's diameter and that may be some 10 cm (4 inches) in all.

Philips Featherweight Pick Up

Equally revolutionary was the Philips featherweight pick up arm (AG 4105) with matching cartridge (AG 3005), and that in a time when tonearms were heavy objects and cartridges were playing the heavy vinyl 'pancake' platters at a mere 10 gr. downforce.
At left the arm as it was portrayed on a 78 RPM record sleeve.

1953: Components 3-Speed Belt Drive + 25 lb. platter

While most manufacturers of turntables were designing their products along the principles of wormwheels (Thorens), idler wheels (Rek-O-Kut, Garrard, Collaro, a.o.), there was a small and hardly noticed company which produced a turntable that turned a heavy platter via a belt. That company was Components Corp., located in Denville, New Jersey. The design was quite revolutionnary. Apparently the engineers had discovered that only a heavy platter (in this case of cast steel weighing 25-lb=11.3 kg.) can procure a steady turning without being held back for not even one micron by strong dynamics and modulations in the recorded signal and was equal to the performance of the idler wheel transmission but without the inconveniences an idler wheel has. So smearing of transients was out of the question. The entire "turntable assembly is suspended on coil springs equipped with felt shock absorbers" to eliminate extraneous mechanical shocks and vibrations. To eliminate the transfer of vibrations from motor to chassis, they carefully suspended the motor. Mechanical and acoustical feedback was practically non existent. In order to change the speed of the Components Corp. turntable, one had to lift the large cover hiding the motor and belt and slip the belt to the desired section of the pulley as other turntables did more than a decade later. The best example was Linn LP12. In his report in High Fidelty Magazine (Vol. 3, No. 6 / January-February 1954) reviewer Roy Allison considered this a drawback. Strangely enough it took more than 20 years before the importance of the technique of this design was fully recognized and found its application in heavy high-end turntables.

Professional Features

The design and construction of the Components Turntable was well thought over and the denomination "professional" was fully justified. In order to minimize mechanical feedback, the motor had double shock mounting. The isolation was twofold. First the motor was de-coupled from its own, small chassis by four blocks as shown in the image at right and in the drawing below at right. Then this chassis was de-coupled from the main base plate by another four, round rubber silent blocks.

Then there were of course the other important features. The spindle was designed in such a way that records with large holes could be played without trouble. The long springs had felt damping. The shaft with single ball bearing was held in place by nylon sleeves. On top of the platter was a thick cork turntable mat (pad) for good protection of the surfaces. And there was the stepped pulley with the slightly rounded sections which kept the relatively wide belt from shifting during play. And there was the clever expanding collet spindle that cleverly centered records with oversized center holes.





In 1953 Thorens Turntables still had a gear box where wormwheels transmitted the rotation to the platter. And only later used a belt (in combination with an idler wheel) for the TD 124 turntable.

The TD124 page-Direct Drive

More Details

There are still a few Components Corporation turntables around. Kelvin Green did sent me a few pictures from the Components turntable that he had bought. He serviced it, polished the platter, put a neat grey mat on top of it, added a long tonearm, and wondered what the value would be. He did not have to wait too long for an answer when Mike "Gadget-Guy" Shaughnessy offered his Components turntable on eBay and sold it. Mike gave me permission to publish a few pictures from his auction. The images show the heavy cast platter with the extremely long spindle and much of the weight at the periphery, the rather simple plinth with switch, long bearing housing, and motor.


The Opposite: The Super Light Platter of the Acoustical 3100 turntable with All Balance Tonearm

The Acoustical 3100 turntable was also a belt drive turntable but did not sport a heavy platter. On the contrary. The platter was made of high density particle board and very light in weight. The motor was a sturdy, black Pabst Aussenlaufer type and there was a big capacitor which, when loaded, gave the platter a quick start. Therefor the frequency of the rumble stemming from the bearing and shaft was at a higher frequency (if compared to the rumble values of conventional players with more heavy platters) and did not interfere with the fundamentals of the audio band. Magnetic attraction to Moving Coil cartridges was avoided in this concept. By pulling or pushing the chrome plated knob at the left corner, the speed - 33 or 45 RPM - was selected.

Early Type All Balance Tonearm

The tonearm was of the balanced type which uses a spring for creating the down force. Such an arm does not jump out of the groove in case of a mild warp, but just keeps on tracking. If the side thrust (bias) has been set perfectly right, the turntable will play records correctly in practically every position. It does not need to be level (probably only for the motor and some other moving parts). At right the early arm with headshell. Below the Jobo 2800 with the later All Balance tonearm. The contacts to connect with the pins of the headshell were spring loaded and always provided maximum connectivity.



Acoustic Research and Thorens

The Philips HX301a, the Components construction, the designs of the later turntables by manufacturers Thorens (TD-124), Perpetuum Ebner, and Dutch trade company and turntable manufacturer Acoustical (Triotrack and Jobophone) all used a belt. The Triotrack had an idler wheel that touched a pulley, but from the idler wheel there ran a thick neoprene belt at the periphery of the platter. These were all still designed in the 1950s/early 1960s. These examples show that it was not such a big step for Edgar Villchur and Roy Allison (and it is said that Mitchel A. Cotter was involved as well) who worked at Acoustic Research, to design the floating chassis (independent sub chassis), the construction used for the Acoustic Research turntable. This drive system was copied first by Thorens and applied in their TD-150 and also by the English manufaturor Ariston in the RD11.

Linn copied that idea from Ariston when Linn was just the manufacturer of the Ariston parts and only later decided to make their own turntable, LP-12. At top right the original chassis of the Thorens TD-150 with the interchangeable arm board which was later omitted in the TD 160, 166 and subsequent models. The chassis plate on which the motor was mounted was well decoupled from the floating metal cross with the three springs. The similarity of design in the later Linn turntable is evident.




A disadvantage of the floating chassis is that it can easily move in the horizontal plane. This is provoked by external shock. Specifically the drive belt in designs with light platters is responsible for this instability because it has a pulling effect on the platter and chassis. In most turntables this is counteracted by filling the vertical springs with plastic foam. But this dampening may have some effect on the general sound quality and in particular on the transient performance. In the Philips 202 Electronic turntable the movement caused by the drive belt is counteracted by a small spring mounted opposite the motor on the other side of the platter. This spring can be adjusted so the pull is neutralized and balances the chassis. The result is the desired stability.

Heavy Platters

The light floating chassis was a swinging affair especially when the springs were not damped well with pieces of plastic foam. This prompted The Audio Critic to say about the 1970s Linn LP-12 that it was "a banjo". This qualification was of course less valid for the later improved editions. The point was made: a turntable with a suspended chassis which is separated from the motor is only working well if the suspension does not interfere with the performance: then linearity of phase and a perfect transient response are the outcome.
So several audiophiles and manufacturers started thinking of further developing the performance of the belt drive turntable. The next logical step was to improve the transient response by giving the platter a much larger mass. In the mid 1970s designers started to use heavy platters as Components Corporation had shown already in 1953. The advanced technical production methods improved speed accuracy and bettered the rumble values as well. And now there was no smeering out of sudden and complex, loud signals featured by light weight platters. Light weight platters were there for the impatient who wanted a quick start up time. And heavy platters were the choice of the demanding audiophile and collector.

Platine Verdier

Already in 1977 the first Melco turntable was presented at the Japanese Audio Fair. Micro Seiki introduced heavy turntables also and by 1979 Jean-Constant Verdier - who is known for his involvement in the French ERA turntables in the 1970s - had his first Platine Verdier ready, initially proposed as a DIY kit in the French high-end magazine L'Audiophile. But lateron he started to manufacture the table in series and it evolved to the grand "Platine Verdier" which became the wanted item on the list of several serious audiophiles. Above at right you see the earliest Platine Verdier, that can be considered as a prototype but already with the spring suspension as shown in the photograph, and the 20 kg. heavy platter, supported by magnets incorporated in both base (plinth) and platter. The springs in the definitive Platine Verdier are of a very intelligent design.





Thorens Reference

Other manufacturers built heavy turntables too. Thorens designed the Reference (Referenz) turntable. It had a relatively heavy platter of 6.5 kg but an extremely heavy plinth filled with iron granulate which brought the entire turntable weight to 90 kg. The plinth was hanging on four steel cables connected to four leaf springs concealed in four cylinders (towers). The frequency of the suspension was tunable by 4 sliding knobs on the sides of the pilars.

Meticulous Design

Around 1980, French importer Diedrichs advertised in La Nouvelle Revue du Son while displaying the many parts that constitute the Thorens Reference. The image at right shows the die cast base (frame) with the top plate removed. Four chambers (compartments) are filled with iron granulate. In the center is the circular compartment that accomodates the spindle and bearing. There are strips at the four corners of the base to which the blade springs are fixed. Next to the base the platter with the acrylic strobe is shown. The strobe is secured by twelve screws. The bearing housing is visible below the O in the name THORENS. It reminds us of the housing for the bearing of the TD 124. The spindle is hardly visible in the lower part of the E in the name. Further to the right is the "box" with knobs which contains the electronics for the steering of the motor. Below these are the many parts, screws, rings, various arms on their respective bases, etc. Further down at left are three of the four leaf springs with the steel wire attached. At the bottom left is the motor with pulley and next to it is the belt. The adverstisment reads "La musique passionnement", Music with Passion.

Leaf Springs

With the Reference turntable Thorens introduced the leaf spring suspension, a technique that has been used in the automotive industry for ages. The leaf spring is fixed in the base of the turntable. To it is attached a steel wire that is fixed in the top of a cylinder. By turning the knob at the top it is possible to adjust to a perfect level. By sliding the knob on the side up and down it is possible to vary the effective length of the steel wire (between A and B) and this will alter the frequency of the factual resonance of leaf spring and wire.


Heavy platters became fashionable. Not only in belt-drive turntables. In 1981 the Technics SP-10 Mk3 was introduced with a platter three times the weight of the platter of the SP 10Mk2. Another heavy direct drive turntable was the Kenwood L-07D. Now many direct drive turntables were also adorned with heavy platters, sometimes as heavy as 50 kg! But such heavy turntables were only produced in small quantities or were just manufactured as one of a kind to be shown at fairs and demonstrations.
These turntables became an inspiration - not only to many manufacturers but to many a hobbyist as well - and remained so even after the introduction of the Digital Audio Compact Disc, the CD. That was when I designed the Basic 1 Turntable in 1980 following this new trend. It was designed by me in cooperation with Alexander Smit.

The Basic Turntable 1980

A few specifications:

* Platter machined from aluminum.
* Platter weight: 9.25 kg.
* Spindle: TD-124 bearing and bearing housing with ceramic thrust plate.
* Motor: TD 160 AC motor with added light bulb indicating if the motor is on.
* Precision pulley with 2 carefully calculated steps for 33 and 45 RPM respectively. Much later the motor and electronics of a Thorens TD-125 with variable speed replaced the simple AC motor.
* Plinth: rectangular box made of polished plates of
serpentino (amorphous stone), filled with a mixture of sand and lead particles (grain). The motor was housed in a separate box of serpentino, but no filling was added.
* The total weight of the turntable: 40 kg.
* After much experimentation the suspension was on 4 heavy springs. The springs were made by a specialized manufacturer taking the weight of the total turntable into account. Furthermore a specific diameter of the springs was chosen as well as the shape and the amount of torsion needed to arrive at the desired strength for the best decoupling and the fundamental resonance frequency of 5 Hz.
* Individual arm supports were machined for a variety of arms: SME Series IIIS, Micro Seiki MA505, Mission 774, etc.

The result is a turntable that reproduces the music with an uncanny silence, lowest distortion, a black background, and extremely high precision, as if the music signal originates from a studio master tape being played on a professional reel to reel tape recorder. This description is valid for all turntables with heavy plinths which support more or less heavy platters, although there can be subtle differences between the various concepts. Even relatively cheap tonearms performed much better with the Basic Turntable.

The mention of these data is to let hobbyists know that it is quite possible to design a high quality turntable oneself.

Audio Fairs

One of the interesting things of visiting high fidelity shows is that you can learn a lot from other knowledgeable visitors, but above all from manufacturers, importers and also designers of loudspeaker systems, amplifiers, turntables, CD players, and all sorts of paraphernalia that matter. During visits to the 'Festival du Son' and 'Les Journées de la Haute Fidelité' in Paris in the late nineteen seventies and nineteen eighties, and visits to Munich in Germany (High End Association) and other places, there were always many products that would spark the interest of visitors, dealers and distributors alike and all for a variety of reasons. When visiting a show in Paris in the late 1980s, I witnessed the introduction of the Confluence loudspeakers designed by Christian Gerhards. In all of his loudspeaker designs he used passive filters with 6 dB slopes and as you know, 6 dB slopes provide phase coherence. It was possible because he carefully calculated the volume of the low-mid driver in relation to the parameters of the unit and in relation to the tweeter. Remarkable was that he also made 3-way systems and he succeeded in creating a wonderful sound. Hearing his designs in conjunction with Jeff Rowland Research amplifiers was a sheer pleasure. Frequency characteristic and dynamics were without fault.

Extraordinary 'Mercure'

In an adjacent room another remarkable design was demonstrated: the 'Mercure' turntable ('platine tourne disque' or 'platine td' as the French say). It was an exceptional belt drive concept designed by Jacques Marteau. A basin was filled with mercury (quicksilver) and the platter was supported by this heavy liquid which has no crystal structure but a very high density. The platter had no axis, spindle and bearing housing. It was held in place by the belt which was guided via four wheels. The strong neoprene belt had a grip on the platter on four "sides" and thus the platter was kept well centered. The turntable was equipped with an arm which was built along the same principle: a mercury bearing. In the arm a Denon DL-103 was mounted. The amplifier was a professional Tannoy. The loudspeakers were Tannoy Dual Concentric Westminsters. The demonstration was extraordinary. The tonal balance, the absence of mechanical noise gave an uncanny realistic sound and lifelike atmosphere to the piano, drums and bass of the jazz players. The toxic mercury in the first edition was eventually replaced by oil of a certain thickness (viscosity) chosen in relation to the weight of the platter.

Above an edited image originally from "La Nouvelle Revue Du Son" as it also appeared in 1995 in "Het Beste uit Audiopinie".



The drawings illustrate the principle of the 'Mercure' turntable.

Mr. Yamamura and the Melco Turntables

A few years earlier, in 1981, I stumbled upon the Melco turntables which were for the first time on display in Paris. I had an interesting conversation with Mr. Be Yamamura who developped audio components and turntables. With his firm Belco in London he imported these heavy Melco turntables which boasted of platters weighing up to 35 kg. In comparisson Verdier's platter weighs 20 kg. But there were also lighter Melco platters 3533 (20 kg.) and 3520 (12 kg.). They could be mounted on different frames (3202, 3233, 3253, and 3256). The Melco 3560 is the heaviest system. Mr. Yamamura gave me the specifications and an image of the Melco 3560. When I showed him pictures of the Basic Turntable which we had designed and built, Mr. Yamamura and I talked about the various aspects that come into play when designing and building a turntable.

Platter Damping and Constant Speed

In the process Alexander and I had experienced all sorts of construction problems that needed specific solutions: damping, decoupling, mechanical and acoustical feedback, constant speed, etc. Mr. Yamamura told me that the damping of the heavy platters of the Melco turntables was achieved by applying a coat of resin to the inside of the platter, the same as used on wooden floorboards. Alexander and I had used a very thin bituminous sheet and carefully had put this on the inside. We were always listening to what the effect would be, even of a minor alteration. It became clear that by using this material, not the entire surface should be covered but that gluing four strips of a certain width brought about the desired effect, keeping the speed of the sound but at the same time eliminating the effect of a bell.





Micro Seiki

Micro Seiki proposed a similar belt drive turntable on 3 feet: RX 3000. And later also the more heavily constructed specimen and the extreme ponderous tables in the 5000 and 8000 series. At right the simpler Micro RX 3000 which used the motor, pulley and speed selector of the BL-51. The platter of the RX 3000 was of course heavier than that of the BL-51 which did not reach the 20 kg mark as in the Melco 3000. Below is the RX 3000. At right is the RX 5000 with the 16 kg heavy gunmetal platter.




As said, these well constructed belt driven machines with heavy platters inspired manufacturers of direct drive turntables to equip their top turntables with big platters that perfectly helped to equalize the rotation from pole to pole further and bring their specifications to an even higher level. At right is a Technics direct drive turntable with an extremely large platter of 40 cm (15.7 inches) in diameter weighing 50 kg. The platter had a stroboscope consisting of long ribs lit by the lamp at left. It was reported that the turntable had 5 fixed speeds - 16 2/3, 21 1/5, 33 1/3, 45, and 78 RPM. The exact half of 45 RPM is 22.5. The reviewer must have made a mistake and he should have mentioned 22.5 RPM. All in all a versatile machine with extensive possibilities and speed adjustments. This machine with the 12 inch EPA tonearm was proposed for professional use by record companies. It was presented in 1979 at the Tokyo Audio Fair and the machine remained just a prototype. It led to the Technics SP-10 Mk3, the dd turntable with a 10 kg heavy platter designed for the demanding consumer. If compared to the Kenwood L 07D the latter had a platter weight of 4.5 kg.

The Poor Man's Reference?

The Thorens Referenz was only obtainable for the well-to-do and were manufatured in small numbers and only by ordering the heavy machine. Thorens allowed a prospective owner to choose a different color instead of military green. Thorens produced another high quality turntable which incorporated some of the features of the Reference.

Subplatter with a Long Spindle

But the most striking feature was that the platter rested on a subplatter similar to the construction used for the TD 150, 125, 126, 127 and others. However the spindle was - for practical resons - much longer. Choosing for the sub platter was somewhat economical. The total weight of platter and sub platter however was 8.1 kg which was 1.6 kg heavier than the platter of the Reference. Of course it was a high quality turntable in the Thorens tradition, but because of its price and construction, it could also be referred to as "the poor man's Reference".

Improving Speed Accuracy

Mr. Yamamura also talked to me about the idea of improving the accuracy of speed by means of a flywheel. In principle the speed accuracy could be bettered by topping the pulley of the motor with a thin and not too heavy, yet large flywheel with the bulk of the mass at the periphery. However it is not advised to put extra weight on the spindle of a small turntable motor. Therefor the solution is to put the flywheel, which acts as a large pulley, not too far from the motor and drive it with a belt. From there a belt or thread is than used for the transmission of the flywheel to the platter.

Mr. Iwata

That was exactly what I had seen in the French magazine L'Audiophile (First Series, No. 3 from 1978). In that edition the reader found an article written by Jean Hiraga with the title "Les recherches de Monsieur Iwata". It showed and described the system of Mr. Iwata of Osaka. Mr. Iwata had built gigantic loudspeaker systems with in total 36 speaker units for the lower register, and he had designed and calculated the shapes of various horns for mid and treble, all driven by a multitude of valve amplifiers. Naturally the units had a high efficiency. The evaluation of the loudspeaker system was that it may be less correct as regards to a linear frequency response, but that the listening experience was impressive and it was reported that it gave a display of a large space where performer, singer and orchestra were present in an extremely realistic way.


Mr. Iwata had built a heavy turntable and had used a lot of lead in the platter. On top of it he had built a peculiar tonearm. The image in L'Audiophile showed that Mr. Iwata's turntable was obviously in continuous flux and had not yet reached its definitive state and probably never would. The rotation of the motor was transmitted via a belt to a larger "pulley" which stabilized the speed and eliminated shocks provoked by the poles. And from there a string drove the platter. A flywheel can have all sorts of shapes and sizes. Today this principle is incorporated in various high-end designs like a few tables of VPI.

Shapes and Sizes

It goes without saying that also for the flywheel a high quality spindle and bearing has to be used. There are various possibilities for making a flywheel. Best is to experiment and determine the shape and size in elation to tyhe platter and the design of the turntable base.




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Page first published in September, 2010

Lenco Platter and Spindle, Wooden Plinth (Thick Particle Board with Veneer, covered with Thin Side Panels),
Aluminum Base Plate for Solid Connection Between Spindle and Arm Pivot,
Feet From an Old Sony Turntable, 2-Speed Motor, Audiocraft Tonearm

These images speak for themselves.

Page first published: December 2010.


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Audio&Music Bulletin - Rudolf A. Bruil, Editor - Copyright 1998-2011 by Rudolf A. Bruil and co-authors
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