hobbyists's views for hobbyists
Those were the Days...

The early Ortofon mono moving coil cartridge was quite a heavy one. It showed already an important trait of the later Ortofon phono cartridges: the short aluminum cantilever.

The advantage of a relatively short cantilever is that the movement of the diamond tip is translated into a signal already very close to the surface of the record. The vibrations do not have to travel through a longer stem (cantilever) which can influence the frequency characteristic of the signal and introduces some distortion. To avoid distortion, most aluminum cantilevers used today have a bend.

In many modern cartridges and especially the high-end cartridges the cantilever's material is boron or beryllium. The movement of the tip is translated with great accuracy because sound travels very fast in these materials. The main reason being that boron and beryllium are very stiff, their resonance frequencies are in the ultra high region, far from the audio band.
Aluminum is a much softer material with a relative lower transmission rate of the sound and it has also some benefits in relation to the midband, but generally the distortion is somewhat higher. Below at left a picture of the A-B 45 -33 head. At right a scan of part of an advertisement for the A and C cartridges in 'The Gramophone' of May 1957 a few months before the stereo LP was introduced. The stereo LP was officially launched in September 1958.

It is amazing that over a relatively short period of time the further development of the Lp attained an ever increasing quality. The groove guard was introduced in 1954 and better vinyl was gradually made available. The process of galvanizing the lacquer was refined. The dynamics were increased and the frequency band attained greater linearity. The sound was getting more refined.

In this respect the improvement of the tape recorder and the development of better cutter heads, lathes and lacquers was crucial for recordings to have a higher fidelity.

Already five years after the introduction of the Lp format, the first commercial stereo recordings were made by Remington Records Inc. in 1953 and RCA followed the next year. These could have been marketed then if the phongraph playback equipment would have been available to the general public. However, there was the stereo tape recorder. The stereo disc was presented and made available to the record buying public in September 1958 for the first time.

The first companies to manufacture a moving magnet cartridge were Elac (Germany), AKG (Austria) and Shure Brothers (USA).

Some 10 years ago I had a short correspondence with a Dutchman who migrated to the US in the mid 1950s. He had designed a moving magnet cartridge that was patented, but Philips did not want to manufacture cartridges along this priciple as they had their gramophone players equiped with ceramic transducers. Then - according to this former Philips-engineer - he left the company and migrated to the USA (as many Dutch people did at the time). Then Shure studied his patented design, made a few alterations to avoid patent infringement and started producing moving magnet cartridges.

In 1957 Shure Brothers introduced their first M1 Studio Dynetic cartridge. When the stereo phonograph record was launched, Shure came up with the M3D Stereo Dynetic phonograph cartridge. This development and the introduction of the SME pick up arm designed and manufactured in the UK greatly have contributed to the acceptance and the success of the stereo Lp, even though the catalogs still listed the mono equivalents of new stereo recordings and still many mono records were sold. Shure developped and improved their cartridges to an extreme level. From the M3D they developped M-44, M-77, and the various V15 cartridges. This is what John Borwick in The Gramophone of November 1969 had to say when he was reviewing the Shure M75 II series of cartridges:

"Shure Brothers Inc. includes some of the top audio brains anywhere. Their work on pickup cartridges has brought listening pleasure to countless music lovers and given their competitors a difficult challenge.
Very soon after stereo records came on the scene, the Shure M3DM was launched as an early example of the moving magnet principle adapted to twin channel 45°/45° reproduction. How right this basic design was can be judged by the M3DM's continued popularity right up to the present day and by the family of a dozen or so more sophisticated Shure cartridges which have grown up to match the upward trends in pickup arm, amplifier and speaker performance."

For a long time alreaqdy the crystal pick up was only used in small budget systems and in portable gramophones. Popular brands of crystal pick ups were Acos and Ronette.
Other manufacturers too developed all sorts and types of moving magnet cartridges. There are many more famous names like Elac, Pickering, Goldring and Stanton. Ortofon introduced their SPU cartridges (stereo) and their top of the line arms and step up transformers to match these moving coil designs.

Ortofon SPU Cartridge

At left you see the innards of a very old Ortofon SPU cartridge from the early days of stereo.
At first inspection it seemed that someone had soldered the connecting leads to the four pins at the back instead of using clips. On top of that the pins had come loose and could be turned very easily.
I had to take off the housing to check if the wires of the coils were still connected to the pins inside the cartridge. They were.

Although the rule is "Never solder connecting wires to the pins of a cartridge whatever the type", in the case of the SPU soldering was done in the factory for connecting the output of the cartridge directly to the small step up transformer which was placed in the headshell right behind the cartridge. The lower left image shows the cartridge and the step up transformer. (Picture courtesy Arne, USA.)

 

The drawing shows the principle of the cartridge: coils moving in a magnetic field. All parts and also the arrangement (the topology) are of course of great importance. They determine the quality of the signal being picked up: strength, frequency characteristic, harmonious build up, and the level of distortion.

The aim of course is to retrieve the maximum signal from the groove by optimizing the mechanical technique (the functioning) and by the application of specific materials for the various components: coil wire, core material, magnetic material, rubber damper, cantilever, diamond tip, connecting wires, cartridge housing, and the distances between the individual parts and the arrangement (topology).

All these were as important in the early days as today where cartridge builders have chosen different materials and maybe a slightly different topology, but the main principle developed by Ortofon is still their starting point.

Shown here is a cartridge and when mounted in its shell it has a light gray, plastic cover with an opening which fits around the protruding coil assembly and the cantilever. Before storing it in the beautiful red box, a transparent cover protects the needle assembly of the cartridge.

DECCA LONDON EXPORT
Output: 7.5 mV per channel.
Frequency Response: 20 - 20.000 Hz. +/- 2 dB
Stylus Material: Diamond
Stylus Radius: 0.0006/7"
Vertical Tracking Angle: 15 degr.
Compliance Lateral: 12 x 10-6 cm/dyne
Compliance Vertical: 5 x 10-6 cm/dyne.
Channel Balance: within 1 dB
Inductance: 130 mH.
DC Resistance: 4400 Ohms per Channel.
Tip Mass: less than 1 milligram.
Playing Weight: 2 to 3 grams. Recommended 3 grams.

During the manufacture of whatever component, be it amplifier, loudspeaker, DA-converter or you name it, there are always slight differences between the ready products. For cartridges these differences are more or less noticeable in the linearity of the frequency curve and the values for crosstalk (channel seperation). The Decca London Export was in fact a Decca London cartridge but had better specifications. The frequency curve of an "ordinary" London was 20 - 20.000 Hz. +/- 6 dB, while the Export model's curve was better than +/- 3 (generally +/- 2 dB).

When manufacturing cartridges, tolerances are relatively large because winding the coils, manufacturing the tiny parts and components are all done by hand. That is why there can be some differences between two cartridges of the same type. Manufacturers often select from a production run those cartridges which answer to the tolerances of a specific checklist. From the same production run various categories can be selected which will fall into specific price brackets. Tolerances with Deccas are somewhat larger. There can be minute differences between tips and the moving iron.

Also the adjustment of the Vertical Tracking Angle can vary slightly from one cartridge to another. But this does not impair the working of the Positive Scanning configuration. A somewhat longer or shorter diamond tip does not influence the signal. Even a higher tip mass does not change the excellent rise time which is always better than the design with a long aluminum cantilever.
With the older Decca cartridges you can be sure to have a high output signal of 7.5 mV. The later models have less output all depending on the coils, shape of tip and magnets used.

Decca International arm

The Decca engineers designed a tone arm to match the Decca London cartridges.
It has specific features:

1. Frictionless unipivot with magnetic bearing. This reduces rumble. This was probably devised with the turntables of those days in mind: Garrard 301, Garrard 401, and Lenco/Goldring.

2. Optional fluid damping. If it is necessary to dampen the fundamental resonance of the cartridge-arm combination, the appropriate viscosity can be selected.

3. Magnetic Bias Adjustment. This design (later followed by other manufacturers) further isolates the arm completely. The arm is free as opposed to those arms which use threads and small weights.

4. Complementing sound pattern. As the review in Hi-Fi Choice showed, the measured frequency characteristic of the arm is different from most arms. This sound characteristic of the arm compensates for the frequency characteristic of the Decca cartridges. The arm is best suitable for the older Blue and Gray, MKV, and Mk VI, respectively. For the later Decca Gold and Maroon some prefer the Hadcock arm. The Decca International arm is not suitable for most non-Decca cartridges as trials with the Denon DL-103 showed. But then the silicon damping fluid was not removed.

5. Precise leveling of cartridge (VTA and Azimuth) and balance. The arm can be adjusted to very a high and very fine level to retrieve the complete signal out of the record groove.

In general the use of magnets for the arm bearing is not preferred by all designers. They do not go for rubber insulators either, for threads and weights in bearings, or other ways of de-coupling the pivot with the aid of a magnet. They prefer the "grounding" of the arm to the chassis or plinth right at its base.

A peculiar design was the Tannoy VariTwin (Vari Twin) or Variluctance Phono Cartridge which of course used the same principle as the Decca ffss pick up. The VariTwin was introduced in 1959 and it was followed by the Mk2 in 1965. For this cartridge Tannoy also had special styli for 78 RPM records with a specific shape and mass. The styli were easily exchangeable by loosening and fixing a screw at the end of the cartridge.

The Tannoy VariTwin is a heavy cartridge. It weighs some 12.5 gr. The simply stenciled leaflet does not state the compliance. It states the optimal capacitance of the 47 kOhm entrance of the phono stage, which is 150 pf. and keeps the resonance at 20 kHz. well under control. Frequency response is 30 to 15.000 Hz. The downforce was 4 gr. or less. In the mono days heavy, thick records were pressed which could sustain up to 10 gr. downforce.