Everything you need to know about cartridges

PRINCIPLES OF OPERATION

Magnetic cartridges (Moving magnet, Induced magnet, VMS)

In number, magnetic cartridges for Hi Fi use are clearly dominant. Their fundamental principle of operation comprises the effect caused by the movements of the stylus in a magnetic field, generating a current in the nearby coils.

Moving magnet

The most common magnetic cartridge is the moving magnet. Here, the magnetic field emanates from a tiny, fixed magnet that is fastened to the remote end of the cantilever. When the magnet is set into motion, which occurs when the stylus follows the modulations of the record groove, the magnetic field through the coil changes, and electrical voltages are generated in these coils.

Although a moving magnet cartridge uses a tiny, powerful magnet on the cantilever, the weight of the magnet will still be a strain on the cantilever, increasing its mass and reducing its ability to react precisely to transients in the music. (Fig. 3)

 

Fig. 3. Moving Magnet cartridge principle. The movements of the magnet produce
currents in the coils by induction.

Induced magnet

This type of cartridge must be considered a further development of the moving magnet type. With the induced magnet cartridge, it is possible to use a smaller and lighter armature on the cantilever because a larger, powerful, fixed magnet increases the moving element’s magnetic strength.

Compared to a moving magnet cartridge, the total mass of the cantilever can be reduced, thus improving transient reproduction. On the other hand, the cartridge’s weight is increased by the fixed magnet, which may render this type of cartridge unsuitable for use with tonearms which already have a high mass. (Fig. 4)

 

Fig. 4. Induced Magnet cartridge principle. The field strength in the small magnet is increased by the larger adjacent magnet. The cartridge functions otherwise as a Moving Magnet cartridge.

VMS

The latest development so far in the magnetic cartridge principle is the VMS, or Variable Magnetic Shunt.

The cantilever in a VMS cartridge can be made extremely light because it is not weighed down by a magnet. Here, the magnetic field emanates from a fixed ring magnet that encircles the cantilever, the rearmost part of which consists of a thin-walled armature of magnetic conducting material. When the cantilever is set in motion, the armature short-circuits part of the magnetic field, and a voltage is generated in the coils. The VMS principle not only makes it possible to reduce the mass of the cantilever to an absolute minimum, but the construction is such that the weight of the entire cartridge can be reduced making the VMS cartridge suitable for use with a large number of tonearms. The special construction of the VMS principle means that the magnetic operating point in the cartridge may be placed at the origin of the induction curve, where there is no risk of non-linearity that can lead to distortion. The VMS principle has made it possible to produce Low Mass cartridges with a weight of only 1.5 grams. (Fig. 5)

 

Fig. 5. VMS (Variable Magnetic Shunt) principle. The tiny armature of magnetic conducting material short-circuits the field from the ring magnet, and voltages are generated in the coils.

Moving coil cartridges

The first cartridges with Hi-Fi specifications were developed in the mid-forties and were of the moving coil design. In general, moving coil cartridges are more expensive than magnetic cartridges and they do not, therefore, enjoy the same popularity. However, the most demanding Hi-Fi enthusiasts remain loyal to the moving coil design because of its great linearity and lower distortion.

Compared with a moving magnet cartridge, the reverse principle is applied in the moving coil cartridge. Here, a powerful fixed magnet is used and the coils are mounted on the cantilever itself. When the coils move in the field of the magnet, they cut the flux lines of the magnet and voltages are generated in the coils. (Fig. 6)

 

(Fig. 6.) Moving Coil cartridge principle. The coils on the cantilever move in a powerful magnetic field, and voltages are generated by induction.

Once again, with a moving coil cartridge it is important that the moving parts be as light as possible. Therefore, there are only relatively few windings on the coils, and the output voltage from a moving coil is generally so low that it cannot feed a conventional amplifier without special steps being taken.

Nowadays, it is becoming more common to equip amplifiers in the higher price range with a special input stage for moving coil cartridges, but otherwise it will be necessary to purchase a transformer or pre-preamplifier before a moving coil cartridge can be connected to the phono inputs of an amplifier or receiver.

Other cartridge types

The aforementioned four operating principles for Hi-Fi cartridges are the most common and by far the majority of cartridges on the market today belong to one of these groups. Many attempts have been made to use other electrical transformation principles, and some of the prototypes have - albeit to a limited extent - found their way into the Hi-Fi specialist shops. These are electret, condenser, and Strain Gauge cartridges, which require a special transforming section and have so far not enjoyed much popularity.

STYLUS TYPES

The stylus is an extremely important component in a Hi-Fi cartridge. (Fig. 7)

 

Fig. 7. a. Nude diamond. The stylus is a whole diamond, specially shaped and glued or fastened to the cantilever. b. Tipped diamond. Here, a stylus tip of diamond is mounted on a metal shank.

It is usually made of diamond - the hardest material known - to give it maximum durability. However, the fact that it is of diamond is not sufficient in itself, for its construction and shape are also crucial factors in sound quality.

Many less inexpensive Hi-Fi cartridges use a so-called “tipped” diamond, where the diamond tip is mounted on a metal shank. However, such a shank may increase the stylus tip mass and thus impair the cartridge’s transient reproduction, in comparison with a cartridge that uses a nude, untipped diamond. There are several different diamond shapes to be found and the most important are described in the following paragraphs. (Fig. 8)

 

Fig. 8. a. Cutting stylus used for
the cutting of master discs.
b. Spherical stylus.
c. Elliptical stylus.
d. Fine Line stylus.

The spherical stylus

The spherical shaped stylus is the simplest and cheapest to produce and it is, therefore, the most common. Spherical styli can be recommended in all cases where robustness and economy are taken into consideration in the purchase of a cartridge.

The elliptical stylus

The elliptical shaped stylus bears greater resemblance to the triangular shaped cutting stylus that is used when cutting master records.

The elliptical stylus is able to follow the groove oscillations more accurately than the spherical type, and its distortion and phase error will, therefore, be less.

In the outer turns of the record groove where the diameter is the greatest, it may be difficult to hear the difference between a spherical and an elliptical diamond, as there is relatively good space in the groove for the highest frequencies. However, in the innermost turns of record groove, the wider radius of the spherical diamond makes it difficult for this shape to track the finer groove undulations. This can muffle the treble, and lead to audible distortion in difficult passages. There was a time when the experts disagreed about the choice between spherical and elliptical cartridge styli. However, this debate can now be considered resolved and today, very few, if any, elite cartridges are supplied with spherical styli.

Other stylus types

The introduction in 1971 of quadraphonic music reproduction from records based on the CD-4 system started a completely new development in the Hi-Fi cartridge field. Cartridges for CD-4 records must be capable of reproducing frequencies as high as 45,000 Hz. This was more than the models in existence at the time could manage, as even the contact surface of the elliptical diamond is too wide for a 45,000 Hz oscillation to be tracked accurately. A solution to the problem might have been a sharper grinding of the elliptical diamond to obtain a reduced horizontal contact surface. This would, however, increase wear on the record surface considerably. The Japanese scientist - Shibata - went in an entirely new direction and invented the special stylus shape that now bears his name.

The Shibata shape distinguishes itself by having the necessary small contact surface at the horizontal level for playback of the ultra-high frequencies found on CD-4 records. At the vertical level, the special shape of the stylus gives a wider contact surface than is the case with either spherical or elliptical styli. This means that a Shibata shaped stylus, in spite of its high frequency capabilities, gives less record wear than the traditional stylus shapes.

Various cartridge manufacturers have been inspired by the Shibata shape and now produce cartridges with stylus shapes that give the same advantages as the Shibata. These have names such as bi-elliptical, pramanic, quadrahedral, hyperbolic, pathemax, and Fine Line. Although CD-4 and other quadraphonic systems never really caught on with consumers, they have helped to speed up the development of stylus types that improve playback of stereo records in the form of a more precise treble reproduction, lower distortion, and less record wear.

 

Fig. 9. A record groove showing the angles of different stylus types in relation to the groove when tracking the modulation. a. cutting stylus. b. spherical stylus. c. elliptical stylus. d. Fine Line stylus. The elliptical and Fine Line styli are able to follow the groove modulation more accurately than the spherical

KEY SPECIFICATIONS FOR HI-FI CARTRIDGES

It would be wrong, or at least risky, to choose a cartridge on the strength of its technical specifications alone. Good technical data are, of course, necessary for good sound, but even the most detailed data sheet gives only a rough indication of the sound of the cartridge, and says very little about hie a particular cartridge will suit a person’s taste. The choice of cartridge is further complicated by the fact that it is not sufficient merely to aim at obtaining the best possible technical data. As it is necessary to consider a cartridge in relation to the tonearm on which it is mounted, thought must also be given to the tonearm’s characteristics so that problems of resonance or mistracking in playback are avoided. Therefore, it may be necessary to compromise certain of the cartridges specifications in order to gain other advantages.

In the following paragraphs, we will discuss the specifications that have direct influence on the cartridge’s practical performance in a Hi-Fi system. Many more specifications may be included in the data columns of cartridge brochures and the most general of these will be discussed briefly after the key specifications: frequency response, channel separation, compliance, tracking ability, and output voltage.

Frequency response

As with the other links in the Hi-Fi chain, the cartridge must be capable of transmitting the entire frequency range. This means that reproduction of the frequency range from 20 Hz to 20,000 Hz must be as linear as possible. It is important here to note the difference between frequency range and frequency response. (Fig. 10)

 

Fig. 10. Frequency response diagram for a good (A) and an inferior (B) cartridge. Both cartridges cover the same frequency range, but (A) has a more linear frequency response.

A frequency range of 20 Hz to 20,000 Hz merely tells that the cartridge is able to give a signal at and between these frequencies; whereas a frequency response of 20 Hz to 20,000 Hz +/- 1dB indicates that the cartridge’s output signal will vary a maximum 2 dB across the entire frequency range. A 1 dB variation in sound level is marginally discernable.

The manufacture of a cartridge with a completely flat frequency response is extremely demanding on construction, production and quality control. Such a cartridge is, of necessity, relatively expensive. Where magnetic cartridges are concerned, the frequency response figure stated can only be achieved when the cartridge operated with the recommended load impedance. This load always consists of two elements: a resistance and a capacitance. For stereo cartridges, the load resistance is nearly always 47 kohm, with 100 kohm for CD-4 cartridges. On the other hand, the recommended load capacitance has not been standardised, and can vary between 100 picofarads (pF) for CD-4 cartridges and 500 picofarads for some stereo cartridges. If too high a load capacitance is used, the treble will be subdued. If the capacitance is too low, the treble will be too sharp. Some amplifiers are fitted with switches for both load resistance and load capacitance, and the correct combination can be found with the help of listening tests. In other cases, however, it is wisest to receive advice from a Hi-Fi specialist shop so that optimal matching between cartridge and amplifier or receiver can be achieved.

Channel separation

A good channel separation, i.e. the cartridges ability to keep the two stereo channels separated throughout the entire frequency range, is essential for good and stable reproduction of stereo records. Channel separation is normally only stated at 1000 Hz, where values of 25 dB or more are not unusual.

When assessing the quality of a cartridge, it is useful to know its channel separation throughout the entire frequency range, for example by consulting a graph. (Fig. 11.).

 

Fig. 11. Frequency response and channel separation for a good (A) and an inferior (B) cartridge. Not only has (A) a more linear frequency response, it also has a wider channel separation over a wider frequency range.

A high channel separation figure in the treble range is particularly advantageous, as the stereo image in recordings will be reproduced with greater clarity.

Compliance

Cartridge compliance is an expression for the elasticity of the cantilever suspension. Compliance is measured in cm/dyn or µm/mN. In practise, compliance values for Hi-Fi cartridges lie between 10 µm/mN and 40 µm/mN, and a high degree of stylus elasticity is represented by a high compliance value. There is a close correlation between a cartridge’s compliance and its tracking force and tracking ability. The greater the elasticity of the stylus suspension, the lower the tracking force that is required for the stylus to playback powerful bass passages. Most record collectors prefer to play their records with a low tracking force, as this gives less record wear. The majority of cartridge manufacturers have, therefore, made great efforts to obtain the highest possible compliance values for their cartridges, with the result that some of the better known cartridges are bale to operate with a tracking force of less than 1 gram. Recent cartridge research has shown, however, that it is wrong to choose a cartridge merely on the grounds of a high compliance value.

When a cartridge is mounted in a tonearm it can be compared to an oscillating system consisting of a spring and a weight, where the compliance is the spring, and the tonearms mass is the weight. (Fig. 12)

 

Fig. 12. Oscillating system consisting a spring (c) and a weight (m). The spring can be compared with the compliance of the cartridge’s cantilever, while the weight represents the total mass of the tonearm and cartridge.

When such a system is set into motion, it will oscillate at a certain frequency - the resonant frequency - which is determined by the elasticity of the spring and the mass of the weight. Both high elasticity and high weight will give a low resonant frequency for the oscillating system.

When the cartridge plays back a record it will, of course, be influenced by the music that has been recorded whose frequency range extends from 20 Hz and over. As records are never completely flat, warps and other surface irregularities will also influence the cartridge in the frequency range around 5 Hz and below. It is extremely important that the resonant frequency for the cartridge and tonearm lies in the range between 8 Hz and 15 Hz. If the resonant frequency is below 5 Hz - 6 Hz, it will easily be excited by warps and other irregularities in the record, and in extreme cases the complete tonearm will vibrate visibly. Tracking ability will be impaired, reproduction coloured by the vibrations, and there is a risk of acoustic feedback. These problems plague many Hi-Fi enthusiasts who, with the very best of intentions, have chosen a cartridge whose compliance is too high in relation to the mass of the tonearm. On the other hand, modern cartridge/arm combinations with a resonant frequency approaching the audible range are scarce.

In the majority of cases, a new cartridge has to match a specific tonearm with a mass that cannot be altered by the consumer. Thus, it will be necessary to choose a cartridge whose compliance, together with the mass of the tonearm, gives an acceptable resonant frequency. If it is an absolute must that the cartridge have the highest possible compliance, it will often be necessary to change to a special tonearm in order to avoid problems in reproduction. In many cases however, by using one of the new Low Mass cartridges, the total tonearm mass can be reduced so much that it will be possible to operate with a compliance that is higher than would be possible with a conventional cartridge. In the section “Choice of cartridge” we will illustrate the correlation between compliance and arm mass with some practical examples.

Tracking ability

Tracking ability is an expression for the ability of the cartridge to track the high groove amplitudes at a given tracking force without losing contact with the record groove. Tracking ability can be expressed in two ways. In µm, by the oscillating ability of the stylus, or in mm/sec as measured by the speed of the stylus in the record groove. The former is the most general means of measuring and here, tracking ability is measured by playing a 300 Hz sinus tone that is adjusted at levels from 20 µm to 100 µm. As mentioned in the previous section, tracking ability at 300 Hz is decided first and foremost by the compliance of the cartridge, and should be sufficiently high to handle the full range of recordings. A value of 50 - 60 µm will be sufficient to obtain playback of all conventionally recorded records without distortion. Only special test and demonstration records are recorded with a greater groove modulation in the low frequency range.

In the treble range it is the effective stylus tip mass - and not compliance - that determines tracking ability. A 10,000 Hz tone can be recorded so powerfully on a record that the cartridge has to make accelerations of more than 2,000 G in order to reproduce it correctly. (Astronauts experience an acceleration of 7G when their rockets take off from the earth’s surface). To be able to perform such rapid movements, the stylus must have a minimum of mass. If it is to reproduce the 10,000 Hz tone mentioned above at a tracking force of 1.5 gram, the effective stylus tip mass must not exceed 1 milligram. Better quality cartridges use a microscopic, nude diamond stylus, which can bring the effective tip mass down to 0.5 milligram or less. Cheaper, more robust cartridges generally use a bonded diamond that comprises a diamond tip held by a metal shank, which does increase the stylus tip mass somewhat.

CHOICE OF CARTRIDGE

In the introduction of this brochure, we discussed in general the choice of the right cartridge for the right Hi-Fi system. In this section, our aim is to describe the technical requirement and restrictions that are involved in the interplay between the cartridge and the remainder of the Hi-Fi equipment.

Compliance and tonearm mass

Choosing a cartridge would be a simple matter if all cartridges could be used without problems in all tonearms. This is not the case, however, as even the finest and most expensive tonearms are not necessarily suitable for all cartridges. The majority of tonearms are quite robustly designed. A high degree of rigidity is necessary if the tonearm is to be able to stand up to possible careless treatment. This means that a typical tonearm, with headshell, has a mass of between 15-25 grams. To ascertain the total arm mass, the weight of the cartridge should be added to this value.

When looking at the graph (Fig. 13.) showing the relationship between tonearm mass, cartridge compliance and resonant frequency, it will be noticed that the mass of the tonearm narrowly limits the value of compliance that the cartridge may have in order to give optimum reproduction.

 

Fig. 13. Diagram illustrating the relationship between cartridge compliance, tonearm mass and the resulting resonant frequency. If the compliance is 20 µm/mN, and the mass is 20 gram, the resonant frequency will lie around 8 Hz.

If we take a typical tonearm with a mass of 20 grams and onto this mount a cartridge weighing 5 grams, the effective tonearm mass will be 25 grams. To achieve a resonant frequency of 10 Hz, it will be necessary to choose a cartridge with a compliance of 10, a value that the majority would consider to be very low. The lowest acceptable resonant frequency of 7 Hz makes it possible to use a compliance value of up to 20.

A truly lightweight tonearm with a mass of 10 grams together with the cartridge in the previous example will have an effective mass of 15 grams. Here, a cartridge with a compliance of 15 would be ideal, and a compliance of 35 would also be acceptable. If a cartridge with a compliance as high as 35 is to operate under ideal conditions, the total mass ( as indicated by the graph) including cartridge would be 7 grams. If the cartridge itself weighs 5 grams, then the mass of the tonearm must be no more than 2 grams! By accepting a resonant frequency of 7 Hz, it is possible with this cartridge to operate with a total mass of 15 grams.

The examples above are intended to illustrate that a cartridge with a high compliance (i.e. higher than 35) should only be used with extremely light and delicate tonearms. On the other hand, this type of tonearm is seldom ideal for cartridges with low compliance. Experiments and listening tests have proved that low compliance cartridges in many lightweight tonearms can easily cause resonances in the audible range. A typical example of such a cartridge is the moving coil, which should always be mounted on a relatively sturdy tonearm.

Measuring the tonearm mass

The majority of tonearm manufacturers today appreciate the importance of tonearm mass in record playback, and several firms now give this information in the data sheets for their turntables or separate tonearms. In many cases, however, it will still be necessary to measure the mass of the tonearm before a cartridge with the correct compliance can be chosen. As arm mass is only significant at very low frequencies, it will be sufficient to simply weigh the mass of the arm as it is registered at the stylus tip of the cartridge. This is done by firstly removing the tonearm’s counterweight - a simple operation that can be carried out without the use of tools on practically all turntables. Then a small spring balance or beam scale weight is fixed to the cartridge headshell as close as possible to the stylus tip. The weight can then be read off. The surest way of measuring the effective tonearm mass is to weigh the tonearm with cartridge mounted. Otherwise, it is necessary ti add the cartridge’s weight to the measured weight. (Fig. 14.).

 

Fig. 14. The mass of the tonearm with cartridge mounted can be measured approximately by weighing the tonearm without counterweight.

Another method of measuring tonearm mass is with the help of a special test record with subsonic signals (for example Ortofon’s test record DC 0001). Together with the dynamic compliance of the cartridge, which is stated by the majority of manufacturers, the effective mass of the entire tonearm system can be calculated either by using the following formula:-

M = 10 to the power of 6: (f² x (2p)² X C

Where M is the mass in grams, f is the resonant frequency in hertz, and C is the compliance in µm/mN

or, by reading the table as below.

Note that the tonearm mass calculated comprises the mass of the tonearm itself, the mass of the cartridge, and the mass of the headshell.

Ex.
a) The tonearm resonant frequency is specified as 10 Hz.
b) The dynamic compliance of the cartridge is known to be 15 µm/mN.
c) From the formula or table, the total mass of the tonearm system can be defined as 16.9 grams.
d) The weight of the cartridge is known to be 5 grams.
e) The tonearm mass (including headshell) can, therefore, be specified as 16.9 grams less 5 grams = 11.9 grams.

It is sometimes possible to reduce the effective tonearm mass a few grams by changing to a very light headshell, and this can be recommended when the cartridge used has a high compliance. Low compliance cartridges should be mounted in a more solid headshell, preferably of a cast light-alloy metal, to avoid resonances in the headshell, which will impair sound quality.

A greater reduction in total tonearm mass can be achieved by replacing a conventional cartridge and headshell by an integrated Low Mass cartridge with standard plug. Such a cartridge can weigh as little as 6.5 grams, which is less than the majority of headshells, and many cartridges. (Fig. 15.).

 

Fig. 15. Integrated Low Mass VMS cartridge for mounting on tonearms with standard socket.

Table for tonearm mass when the resonant frequency and compliance values are known.

 

Output voltage

A cartridge’s output voltage should be sufficiently high to utilize to the full the output power of the associated amplifier or receiver. Where magnetic cartridges are concerned, there are generally no problems in this respect as the majority give a signal to the order of 1 mV/cm/s. As the average groove modulation on modern records is in the region of 5 - 10 cm/s, a typical cartridge will give a signal of 5 - 10 mV, which is a good match for the input sensitivity of modern amplifiers, which are typically 2 - 3 mV at 1,000 Hz. A rule of thumb for magnetic cartridges is that their output voltage decreases in line with increasing quality. There are some advanced magnetic cartridges available with an output voltage as low as 0.4 mV/cm/s. Here, an input sensitivity of 2 mV in the amplifier is sufficient. However, such cartridge should never be connected to amplifiers with lower sensitivity, and particularly not older models, as the signal-to-noise ratio can be reduced, and it may be impossible to utilize the full rated output of the amplifier.

The majority of moving coil cartridges have an output voltage which is approximately 50 times below the level for magnetic cartridges. As a result, the output voltage from a moving coil cartridge must be amplified correspondingly before it can feed a conventional amplifier. There are a number of transformers and special amplifiers on the market today for this purpose, but as the output voltage from moving coil cartridges can vary widely from manufacturer to manufacturer, it is generally recommended to follow the cartridge manufacturer’s instructions in order to void matching problems.

As a result of their special construction, moving coil cartridges are particularly sensitive to hum fields from power transformers and turntable monitors. Transformers and special amplifiers for these cartridges are also sensitive to hum pick up. The majority of these hum problems can be solved by connecting the cartridge and its matching device as recommended in the user instructions. However, if the turntable used has a poorly shielded power transformer (which is the case with some direct drive turntables) it can be impossible to achieve reproduction form a moving coil cartridge which is completely free from hum.

SUPPLEMENTARY SPECIFICATIONS

The specifications discussed in the foregoing are the ones that appear most often in brochures and articles. In addition, however, more technical publications give supplementary specifications, and the most important of these are described below.

FIM

Frequency intermodulation is a form of distortion that occurs in a cartridge when it is required to reproduce two or more tones simultaneously. A high value of FIM will give the cartridge a raw, metallic sound. In a quality cartridge, frequency intermodulation distortion can be kept below 1% when the recommended tracking force is applied.

Vertical tracking angle

To achieve good tracking ability and channel separation, it is important that the record be played back at the same vertical angle as it was cut. Nearly all cartridge manufacturers today give their cartridges a vertical tracking angle of 20°. This is done on account of the proposal put forward to standardize the vertical cutting angle at 20°. The cartridge’s vertical tracking angle is defined as the angle that arises between the surface of the record and the straight line drawn from the diamond tip to the cantilever’s point of rotation inside the cartridge. Deviations from the correct vertical tracking angle will increase FIM distortion.

Equivalent stylus tip mass

The components that together comprise the equivalent stylus tip mass are the diamond, the cantilever and, depending on the design principle, the magnet, armature or coils, and the damping rubber bearing; although the contribution of the latter to the equivalent stylus tip mass is not constant, and depends on the frequency. At the lowest and medium range frequencies, it is the compliance that has greatest influence, whilst at high frequencies, it is the mass of the moving system that dominates.

It is important that the equivalent stylus tip mass must be as low as possible, in order to get the natural resonance of the system above the audible range where it can, to an extent, be kept under control by correct cartridge loading.

The weight of the cartridge

In order to be able to ascertain the natural resonance for a given cartridge and tonearm, it is necessary to know the weight of the cartridge. As all tonearms can only be balanced with cartridges having a weight within a specific range (for example, 5 - 11 grams or 2 - 8 grams), it is necessary to check whether a given cartridge matches a particular tonearm in this respect also, and, of course, vice versa.

As a rule, the best record reproduction is obtained with cartridges that have as low a weight as possible, and this should, therefore be taken into consideration when choosing a cartridge, tonearm and turntable.

Pinch effect

The gramophone record is cut with a triangular shaped cutting stylus, whereas the stylus that plays back the record has a different shape. The difference in shape between the cutting stylus and the cartridge stylus results in the so-called “pinch effect”, which is particularly noticeable in playback with a spherical diamond. As the groove does not have the same width throughout, the spherical diamond will be forced to make vertical movements while at the same time tracking the groove information. If the playback is in stereo, these vertical movements by the cartridge will result in unwanted signals in each channel that are out of phase. These unwanted signals will be heard as distortion. Pinch effect can be reduced by using a stylus with a shape that resembles the cutting stylus, for example elliptical or Fine Line styli.

Phase distortion

As a result of the difference in shape between the cutting stylus and the playback stylus, the tracking point in playback will move constantly, so that the two channels are not reproduced at precisely the same time, but with a low level of phase distortion, which will disturb the direction in the stereo image, making it difficult to pinpoint the individual instruments. This form of phase distortion is particularly pronounced when using a spherical diamond. Specially shaped styli like the Shibata and Fine Line give least distortion of this kind.

HF distortion

Distortion in the treble range occurs when the radius of the diamond is wider than the record groove’s radius of curvature. Even though the stylus may track well, it is unable to reach right out into the high frequency tips, and reproduction in this range may be distorted. As in the previous case, it is the spherical diamond which gives the highest distortion, while Fine Line and Shibata shapes give less distortion on account of their narrow profiles at the horizontal level.

CARTRIDGE MOUNTING

It is not usually difficult to mount or replace a cartridge. The cartridge body itself is fastened to a headshell or mounting plate by two screws on 12,7mm spacing (½”) spacing. Many Hi-Fi turntables and tonearms are also equipped with internationally standardized headshells with bayonet sockets, making it easy to change between cartridges mounted in such headshells.

The user instructions for the turntable or tonearm in question should always be followed carefully when mounting a cartridge. A few general tips are given below.

1. When possible, the cartridge’s stylus unit should always be removed while mounting takes place.
2. Always use fixing screws that are as short as possible. Screws that are too long will only increase the tonearm mass.
3. Colour code for cartridge connecting wires. (Fig. 16.)
   White - left channel (L)
   Blue - left channel ground (LG)
   Red - right channel (R)
   Green - right channel ground (RG)
   
    
   
    

   Fig. 16. Connecting pins and colour code of a typical Hi-Fi cartridge.

4. The cartridge lead wires should be fixed to the contact pins carefully with the help of a pair of pincers, making sure that the clips are making a tight contact. (Fig. 17.). They should be crimped, if necessary, to make them tight. The wires for each channel should also be wound together to avoid hum pick up. This is specially important in the case of the moving coil cartridges.
   
    
   
    

   Fig. 17. Cartridge wires are mounted carefully on the connecting pins using a pincette. Where possible, the stylus unit should be removed while this takes place.

In the majority of headshells, the cartridge can be adjusted in order to ensure the least possible tracking error and distortion in playback. This adjustment can be made with the help of a tracking alignment protractor, as illustrated below, where the cartridge stylus is placed on the spot marked X, and the sides of the headshell follow the lines on the protractor. (Fig. 18)

 

Fig. 18. An alignment protractor is used to find the correct distance from stylus tip to tonearm pivot. When the cartridge’s longitudinal axis is parallel with the horizontal lines, tracking error will be at a minimum.

Tracking force and antiskating

The majority of cartridge manufacturers give a tracking force range for their cartridges, i.e. a high and low limit for the tracking force. Many also give a recommended tracking force which will be suitable for most situations. If in doubt, it is wisest to let the cartridge operate with at least the recommended tracking force, as records wear faster when played with too low a tracking force than with too high a tracking force. Specially demanding records may make it necessary to adjust the tracking force to the maximum value, or maybe even more. However, the cantilever suspension will be damaged very quickly if the cartridge is used for longer periods with a tracking force that is higher than the stated maximum; and on warped records, there is a risk that the cartridge’s stylus unit will knock against the record.

The purpose of the antiskating adjustment in quality tonearms is to create an even contact force for the cartridge stylus on both sides of the record groove, thus keeping distortion and record wear at a minimum. Where the antiskating scale is calibrated in grams, the adjustment should, as a rule, be the same as the tracking force adjustment. However, it may be necessary to experiment with antiskating in order to limit distortion during playback of powerfully modulated records. Distortion which appears in one channel only may be due to improper adjustment of antiskating force.

CARTRIDGE MAINTENANCE

A cartridge is a highly developed miniature precision instrument which should be treated with care so that it can maintain its technical specifications.

Even the slightest particle of dust on the diamond can increase playback distortion and record wear. Therefore, the stylus should be cleaned after each record playback with the help of a suitable soft brush. If the dust on the stylus is mixed with grease or the remains of a record cleaning agent, it may be necessary to moisten the brush with propyl alcohol or a special cartridge cleaning fluid.

Many Hi-Fi specialist shops have cartridge clinics, where cartridges may be inspected under a microscope for wear, and possibly tested with the aid of special test records or electronic measuring equipment. Every cartridge should be inspected in this way at least once a year.

In normal circumstances, a cartridge’s stylus unit will least for 2 years in a private home without music reproduction being impaired or wear on records being increased to any extent. However, both the cartridge stylus and cantilever suspension will wear considerably faster if the records are badly scratched or smudged with dust and grease. In extreme cases, a badly scratched record can tear the diamond tip from its stylus mounting.

Finally it is always a good rule to snap the guard over the stylus whenever the cartridge is not in use.