Understanding Vinyl Record Turntable Cartridges

Find out all about vinyl record turntable pickup cartridges: the different types, what they are, how they work and in fact all you need to know.

Vinyl Record Player Technology Includes:
Vinyl technology - the basics Turntable Pickup arm / tonearm Pickup cartridge Stylus technology

One of the important elements of any vinyl disc system is the cartridge or pick-up. Sometimes it may be referred to as phono cartridge or turntable cartridge.

The pickup cartridge is where the undulations in the grooves of the record are converted into the electrical signals to be amplified by the amplifier and passed into the speaker.

Vinyl record pickup cartridge — A typical vinyl record pickup cartridge

the turntable cartridge is a key element of any system, and its performance will have a major impact on the performance of the whole system - a poor cartridge will limit the performance of the whole system.

Cartridge body

The cartridge body is the part of the pickup cartridge that is seen. It houses all the internal elements and is usually made from plastic. It also includes the headshell mount, i.e. the interfacing to allow the cartridge to connect to the wiring in the tonearm, and also to be mechanically mounted onto it.

The headshell is located at the end of the tonearrm and may be an integral part of the tonearm, or an removable shell. Removable headshells are easier when adding a new cartridge, but some people feel all in one tonearm headshells are better.

When buying a new cartridge it is necessary to understand the interfacing to ensure the new cartridge will fit satisfactorily.

There are three main types of mount that are in use:

Standard / Half in ch mount: This is the most common form of mount. Two screws are used to fix the headshell and cartridge and hold the cartridge firmly in place.
P-Mount: For a P-mount system, the cartridge is directly plugged into the tone arm and then secured using a single screw. These cartridges tend to be longer and thinner than the standard mount cartridges.
Universal: As the name indicates this type can interface both standard and P-mount types, using an adapter to enable both types to be accommodated.

What is inside the cartridge

The vinyl record pickup cartridge is a complex assembly of precision-engineered components. each of them plays a critical role in transforming the microscopic grooves on a vinyl record into the music we hear.

here are the main elements:

Stylus: This is the heart of the cartridge, the tiny needle-like tip that makes contact with the record's grooves. Its tip traces the microscopic variations, translating them into mechanical vibrations for each channel.

As it is constantly in contact with the groove in the record, it suffers wear, and as a result it needs to be a very hard wearing material. Normally diamond is used, but years ago, sapphire was also used for some lower cost styli.
Cantilever: This is a slender tube that acts as the arm for the stylus, allowing it to pivot freely and follow the vibrations in the groove. It ensures the stylus stays in contact with the groove without skipping or damaging the record. Typically this is made from aluminium or boron because the cantilever needs to be light but rigid to transmit vibrations accurately. If there is too much mass then it will not enable the stylus to follow the groove vibrations, but if it is not sufficiently rigid then it will bend and not transmit the vibrations accurately.
Suspension system: Tiny dampers or springs cradle the cantilever, absorbing unwanted vibrations and keeping the stylus firmly following the groove.
Transducer assembly : This is where the mechanical energy from the stylus vibrations gets converted into electrical signals. There are several technologies and techniques that are used for this and these are detailed in a section below.

Pickup cartridge technologies and types.

There are several technologies and techniques that can be used within a pickup cartridge.

A number of different techniques an be used, and these have different characteristics, advantages and disadvantages.

However they all enable the variations in the grooves of the vinyl record surface to the transferred via the stylus and cantilever to be converted into electrical varying electrical currents that are a faithful representation of the original signal.

Today virtually all cartridges are stereo and separately pickup the variations in the two walls of the groove to provide the different stereo channels.

There are many different types:

Moving iron: In this type of pickup cartridge the armature on which the stylus is located passes through the centre of a coil which is enclosed between the poles of a permanent magnet. Any movement in the armature disturbs the magnetic field through the coil. This principle was used by virtually all monaural cartridges.
Moving coil: This form of cartridge is based around a pair of small coils which are mounted so that they can rock about the axis between the pole pieces of a magnet. The coils are mounted at right angles to each other so they each coil only responds to one plane of stylus movement.

To minimise the mass of the moving assembly, most coils have very few turns and this means they have a low impedance, and the output is very low in amplitude. As a result, they need high gain amplifiers to accommodate this. Some cartridges have coils with exceedingly fine wire to give a higher impedance and output voltage.
Moving magnet: For this form of vinyl record cartridge a lightweight cylindrical magnet is joined to the cantilever.. The assembly is pivoted at the remote end from the stylus to enable free movement. The magnet is surrounded by four yoke pieces spaced at 90° intervals. The opposite pairs of yokes are arranged to form a magnetic circuit through each of one of two coils. In this way, movement from one wall of the vinyl record, i.e one channel induces a field in the appropriate pair of coils giving rise to an induced current in the associated coil.
Induced magnet: This type of pickup cartridge is very similar on concept to that of the moving magnet. The main difference is that a stationary magnet induces a field into the armature which is moved by a cantilever. It partially overcomes the issue of the mass introduced by the magnet being incorporated into the armature assembly, although modern light weight magnetic materials have largely overcome this issue.
Variable reluctance: This technique is rather ingenious and uses the reluctance or 'resistance' to a magnetic field offered by an air gap as the basis of its operation. One pole piece of a magnet is split through a pair of coils to two pairs of faces. Close to these, there is a ferromagnetic moving element which is linked to the stylus. Any movement varies the air gap between the ferromagnetic element and one face and this results in field changes that are picked up and converted to electric signals.
Ceramic: Ceramic cartridges were all the rage for low end autochanger record players of the 1960s. They use the piezoelectric effect to convert movements from the stylus into electrical signals. They provide a high output level and have a further advantage that the output is proportional to the amplitude rather than the rate of change as with magnetically based pickups. This considerably simplifies the input circuitry because less amplification is required along with no need for any equalisation. However a high input impedance is required for the following amplifier - figures of 1 MΩ are typically needed. Lower levels tend to cause loss of bass response, and if they are fed into an magnetic input socket with a lower input impedance, then the equalisation will very approximately compensate for the bass loss.

Of the variety of pickup cartridges, the ceramic one used to be popular many years ago for low end record players. Today, the main choice is between the moving magnet and the moving coil.

Moving magnet ones tend to fill the more budget conscious end of the market, but moving coil ones, which give a much lower output and need a compatible preamp often fill the top end. Costs for high end moving coil pickups can extend into the cost region of several thousand GB pounds, US dollars, or Euros region.

Tracking weight / force

A precisely calibrated weight applies just enough pressure to keep the stylus engaged with the groove without causing excessive wear. Too light, and the music skips; too heavy, and the record and stylus suffer.

Turntables will normally have an adjustment on the tonearm to enable the tracking weight for the cartridge / stylus to be adjusted.

Also for those wanting to make accurate adjustments, small measuring instruments to measure the tracking force are available.

Specifications

When selecting a suitable cartridge for a system there are several different specifications that might be important in determining which cartridge to select.

A number of the highlight specifications are included below.

Frequency response: As the name indicates, this is the overall frequency response of the vinyl cartridge pickup. Often the response is given for the -3dB points, i.e. where the response has fallen by 3 dB.
Mount type: This is the mount type for the vinyl cartridge. It is essential to ensure that the tonearm can accommodate the type of mount for te cartridge.
Channel unbalance: The channel unbalance is the difference in level between the left and right channels from the cartridge. Typically this is measured in decibels and typically should be less than about 3dB.
Channel separation: This is the isolation between the left and right channels. It is not possible to get complete separation because it is never possible to get 100% mechanical orthogonality between the two transducers needed fort he left and right channels. It should typically be better than about 20 dB, or preferably much better. This ensures that the two channels stereo at the output of the speakers or headphones have sufficient separation to give a good stereo image.
Recommended tracking weight or force: This is the recommended tracking force required for the proper operation of the cartridge. It is typically measured in grams. If insufficient force is applied by the tone arm then the stylus will not be able to remain within the groove. This will result in audio distortion and possible damage to the record. Specifications may give an acceptable range and a recommended more exact figure, e.g.playing weight range: 1.5-3.5g, and recommended playing weight: 2.5g.
Record speeds: As vinyl records can revolve at 33 ⅓ (for albums), 45 (typically for singles of EPs) or 78 revs per minute (for vintage records), it is necessary to ensure that the cartridge is compatible with the speeds that will be encountered.
Load impedance: This is the impedance presented by the input to the amplifier or preamplifier that connects directly tot he cartridge. Typical figures might be in the region of tens of kilohms. The popular Goldring G800 cartridge from the 1970s had a specified load impedance of 47 - 100 kΩ
Output level: As the output is normally dependent upon the speed of movement of the stylus, the output is often specified in terms of an output voltage for a given stylus velocity. Again the Goldring G800 was specified as a 5mV out for a 5cm/sec stylus velocity.
Stylus type: As the styli do not have an indefinite life, it is important to know that replacement styli can be obtained and what the correct type is.

The specifications for the various cartridges will reveal the basic performance that the unit will provide.

However before buying one, it is also well worth reading a number of reviews of the cartridge to understand how they perform on real vinyl records. Although the specifications will tell a lot, they cannot give a full representation of the performance of these high precision items.

The pickup cartridges used for vinyl records are high precision items. Although some can be obtained very cheaply, they are still precision items that have used the technology and expertise of many years of development. The higher cost items provide very high levels of performance and are able to provide the levels of performance required for high fidelity audio systems.