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Those were the Days...



Ortofon A/B and SPU Moving Coil Cartridges
Decca London Moving Iron Pick Up
Tannoy Vari-Twin Phono Cartridge

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Crystal and Ceramic

In the early days of the Lp, records were played with a crystal or a ceramic pick up (or phono) cartridge. Crystal pick up cartridges have the advantage that they can be connected directly to the line stage of the amplifier. The output is high and no correction is necessary. Just two valves and a high efficiency wide range loudspeaker unit deliver a loud and clear and dynamic sound, though the high frequencies are not refined. The use of these pick ups was widespread, in spite of the fact that Ortofon had introduced the first moving coil phono cartridge right from the beginning of the Lp era in 1948.

ORTOFON MOVING COIL PHONO CARTRIDGE
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 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. On top of that boron and beryllium are very stiff, their resonance frequencies are in the ultra high region far from the audio band.
Aluminum is a far softer material with a lower transmission rate of the sound and has also some benefits in relation to the midband, but generally the distortion is somewhat higher. At right part of an advertisement for the A and C cartridge in 'The Gramophone' of May 1957.

The Principle of the First Ortofon Moving Coil Mono Cartridge of 1948

Shure's model M3D tracks with pressures as high as 6 gr. and as low as 3 gr. - picture taken from the April 1966 issue of High Fidelity Magazine

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. These could have been marketed then if the playback equipment would have been available to the general public. However, the stereo disc was presented in September 1958.

The first company to manufacture a moving magnet cartridge was AKG from Austria. In 1957 Shure Brothers introduced their first M1 Studio Dynetic cartridge which was also a moving magnet design. 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 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.
From then on 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 Moving Coil Principle

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 with the cantilever. Before storing it in the beautiful red box, a transparent cover protects the needle assembly of the cartridge.

 

Ortofon SL15 / SL-15 Cartridge
Ortofon SL 15 ELL is a further development of the Ortofon SL15 cartridge from around 1968 and had a beautiful step up transformer to match the impedance of the cartridge (2 Ohms) and the output impedance of 15 kOhm to connect perfectly well to the input impedance (load impedance) of 47 kOhm of the (pre-)amplifier. (These two images courtesy Don Sellers, USA).
These cartridges were replaced by the SL15, SQ 15 and later by MC20 and MC10, before the 2000 and 7000 were introduced.
Below are the most important specs.

 


DECCA MOVING IRON PICK UP CARTRIDGE

In the early stereo days, some odd, but very remarkable designs were introduced. One of these were the moving iron cartridges made by Decca Special Products. The design was derived from the earlier cartridges in the Series 4, developed in the mono era.
The first stereo cartridges were designed especially for playing the new Decca Full Frequency Stereo Sound recordings (FFSS). The later Garrott versions were Deccas, modified by the Garrot Brothers in Australia. Aalt Jouk van den Hul re-tipped several Decca Gold cartridges with a long, nude version of the special Van Den Hul tip.

Different

The engineers of Decca followed a completely different track than Ortofon (MC) and Shure (MM). Knowing that the signal will deteriorate somewhat if a long cantilever is used, they devised a way to practically retrieve the signal just above the groove. To achieve this, the Decca engineers positioned the generator (coils and magnets) as close to the surface of the record as possible, only leaving the necessary room for the diamond tip, but not more than approximately one millimeter but always in such a way to prevent the housing from touching the groove guard or the record's surface.
The first cartridges were mono cartridges with one coil.

Philosophy
Did Ortofon connect a long vertical coil to the cantilever to move in between the poles of a magnet, and did Shure connect a tiny magnet to the end of the cantilever to move in between coils, Decca's men choose as generator a piece of iron to move between magnetic poles close to or within a fixed coil. They choose for this concept right from the start when they designed their first ffss cartridge.
They gave the iron piece an angled shape. Slight flexing was possible in both the horizontal and the vertical plane. By clamping the rear end in a block, it stayed firmly in place to guarantee a correct azimuth at all instances (if it had been precisely adjusted in the arm in the first place).
In that way they avoided the small piece of rubber that in MM and MC cartridges constitutes the pivot and at the same time functions as a damper to control the movements and resonances of the cantilever and its tip and of the coils wound on the tiny core. It is this rubber that greatly influences the signal and is responsible for a certain weakness in the lower mid region. If this small piece of rubber can be left out, than the signal can be as pure as it possibly can be.
Note: There is just a very thin piece of rubber glued on the horizontal part of the iron. This is to prevent that the tie back cord pulls the iron against the horizontal coil when the diamond tip is not in the groove, i.c. is not scanning. But it is not altering or deteriorating the signal.
The early Deccas generated some hum if the coils are close to iron platters and in case the motors were not well screened off.
The Decca engineers did master this problem. They also looked for better magnetic materials and they made the armature extremely stable by forming it and cooling it at - 196 degrees Celsius. They even lowered the weight of the cartridge to a mere 4 grams, which extremely low.

Hysteresis

There is a second aspect of great importance. The core of the coils in a Moving Coil Cartridge should be very light. Problems occur when thin and light pieces of metal are used for the core. The downside of this is that it will have hysteresis, which means that the coil interacts with the core and will become a motor with a changing hysteresis and the subsequent distortion (though minute) which has a changing and unwanted effect on the signal. Hence in a few designs of some manufacturers a tiny plastic cross was used on which the coil wire was wound.
Cartridges with moving magnets do not have this problem but show other weak points. A moving iron cartridge just makes use of the effect which a piece of iron in a coil has.


The design of the Full Frequency Stereo Sound (ffss) cartridge uses two pairs of magnets and three coils. One magnet for the pole pieces of the two 'vertical' coils (the drawing supplied by Decca shows only one coil). And there are magnets placed left and right of the single lateral coil for generating the lateral movement of the armature.
For the lateral movement the pole pieces of the horizontal magnets were placed left and right of the tiny piece of iron to which end the diamond tip was connected.
The iron was placed inside the lateral coil. So the system becomes a motor. This coil was placed right above the magnet poles.

It would have been theoretically logical if for the vertical movement just one coil would have been used and placed around the horizontal part of the bent iron cantilever which is parallel to the record's surface. This would mean that the coil with a magnet had to be positioned farther away and closer to the clamp holding the garrote in order to leave ample room for the lateral coils. In that configuration the parallel part of the iron needed to be much longer, in fact too long. The Positive Scanning (as the Decca engineers called the working of their design) would not have been possible.

Furthermore some lateral movement or a bending mode could have been the result and would have deteriorated the signal. There would be a delay in time also. And, the movement of the iron piece is there at a minimum. Unless, of course, very tiny coils in conjunction with a step up device would be used.

No, the best solution was to position the magnet and coils which generate the vertical movement, right above the angle of the iron piece which serves also as cantilever. At that point the vertical movement is the largest. There was no other way for detecting the vertical variations as close to the record's surface as possible.

When playing a record the horizontal and vertical movements continuously vary the gaps and thus generate the signals. The lateral (horizontal) movement is a torsional movement and the vertical movement is a bending movement.

The configuration 3 coils made it necessary to derive the stereo signal by adding and subtracting the signals. Even then the minute changes induced by both the horizontal and vertical movements of the iron part deliver a strong signal due to the large coils and strong magnets.
In order to keep the diamond tip in place (so it could not move forward) a tie back cord (garrote) is used.

The result is a clear and very realistic sound reproduction as no other design can deliver. The only drawback is the low vertical compliance which necessitated a downforce of up to 3 gr. in the Decca Blue, and in the earliest models even more downforce was required.
Later the Mark V and VI, the Maroon, the Gold and Super Gold were introduced when the functioning of the system was further improved by reducing the mass of the moving iron so it would be more flexible laterally and also somewhat vertically (higher compliance) without impairing its stiffness. Also new magnetic materials were used. This resulted in the possibility of incorporating elliptical styli and in the beginning of the nineteen eighties of fine line diamond tips. The outcome: an extended frequency band and the downforce could be reduced to 1.7 to 1.9 gr.
All Decca cartridges can be re-tipped Services are offered by The Cartridge Man in Great Britain and by Aalt Jouk van den Hul in the Netherlands.


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.


Tolerances and Positive Scanning

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.

 

TANNOY VARIABLE RELUCTANCE PHONO CARTRIDGE
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.

The cantilever is a long piece of metal that is fixed at one end with a bolt. On the other end figures a substantial stylus which asks for 4 gr. of playing weight. But since records in the mono era and in the first ten years of stereo were pressed from a harder and stronger vinyl, such weights were no problem. The Tannoy stylus could easily be exchanged for a new one or a special stylus for playing 78 RPM shellac records.
As in the case of the Deccas with their Positive Scanning ability, the advantage of the Tannoy design also the advantage of reading and translating the signal as close to the groove as possible. Here also the long cantilever which is the drawback of most modern cartridges is omitted.
The innards of the cartridge are not explained in the leaflet. And since I am reluctant to open the cartridge, the exact configuration and functioning remains a mystery.


Frequency Response: 30 - 15.000 Hz. +/- 1.5 dB
Output: 7 mV per channel.
Load: 50 kOhm minimum, 100 kOhm recommended.
Inductance: 350 mH.
Maximum Termination Capacity: 150 pF (correcting at 20 kHz.)
Stylus Material: Diamond
Stylus Dimensions: 0.0007 Compatible (Standard), 0.0005 Stereo only (to special order)
Tracking Pressure (Down Force): 4 grm. or less.
Standard 1/2 Inch Fixing Holes.

In modern days the variable reluctance principle with its very precise information retrieving is not at all forgotten and old fashioned.
It is Leonard Gregory from Great Britain who manufactures the MusicMaker III (based on a Grado Signature cartridge body), working along the principle of variable reluctance, but with all the benefits of modern times technology and materials.

Want to know the technical specifications of cartridges?
Go check THE CARTRIDGE DATA-BASE

R.A.B. November 12, 2004 - Images and specific drawings by Rudolf A. Bruil

Cartridges acquired from the collection of
the late Jan Th. Endenburg and the late Karl Föllmi from the Netherlands.
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Audio&Music Bulletin - Rudolf A. Bruil, Editor - Copyright 1998-2007 by Rudolf A. Bruil and co-authors