Vinyl Record Player Tonearm / Pickup Arm

The tonearm or pickup arm on a vinyl record turntable is the arm mounted to one side of the actual turntable holding the cartridge and guiding it across the record.

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

The tonearm or pickup arm is a key element of any vinyl record player turntable and system.

The pickup arm or tonearm is the arm on which the pickup cartridge is mounted. It is pivoted slightly off to one side of the actual turntable, and enables the cartridge to be placed over the vinyl record and move with the position of the groove.

The geometry of the tonearm is very important because it ables the cartridge and its stylus to follow the vibrations in the groove as exactly as possible.

Although in its very basic form, the tonearm may be seen as a rod extending out over the vinyl disc for the cartridge, there is a lot more to it than just this. It plays a vital role in enabling the best performance to be achieved.

Anatomy of a Tonearm

The tonearm consists if several elements, all bound within the overall tonearm structure. Each needs to be optimised to ensure the best performance can be achieved by the pickup cartridge.

The various elements in the tonearm or pickup arm include:

Tonearm Tube: is the main arm, typically crafted from lightweight yet rigid materials like aluminium or carbon fibre. Rigidity is crucial to prevent unwanted vibrations from affecting playback.
Head-shell: This detachable component at the end of the tonearm holds the cartridge and allows for easy swapping and alignment.
Counterweight: This weight on the opposite end of the tonearm from the head-shell balances the weight of the cartridge and tonearm, ensuring the stylus tracks the record groove with the correct pressure.
Bearing System: This allows the tonearm to move freely in both horizontal and vertical planes.
In the horizontal plane it must allow the head to move across the record surface with minimal friction, ensuring smooth and accurate tracking. The bearing system must provide very free movement at all times with less than 50 grams and preferable a maximum of 20g being required at the stylus to move the the arm across the disc.

Vertical movement must be possible to accommodate any warp int he record, which is hopefully minimal, and also for set down and pick up for cueing at the beginning of the disc and removal at the end.
Lift Mechanism (Cue Lever): This allows the head to be gently lowered onto the disc, minimising potential damage to the stylus and record. It also allows for the head to be raised on completion of playing. Many turntables have a mechanism that automatically raises the arm and turns off the motor when the head reaches the centre of the disc.
Bias compensation / anti-skate mechanism: The rotary friction of the vinyl disc system results in a force that tends to pull the stylus towards the centre of the disc even when it is blank. This results in additional pressure on the inner wall of the groove in the disc and this could result in more wear on this surface.

To offset this, a bias compensation mechanism is incorporated into the tonearm assembly. This can be achieved in a number of ways. Sometimes small weights are used in a thin cord, others use a small weighted lever and others can use a magnetic system. Typically these are adjustable so that the required compensation can be set up.

Tonearm geometry

When the master for a vinyl disc is cut, the tracking cutter traverses across the blank with the cutter remaining aligned with the groove at all points in the disc.

While some very high end turntables may be able to emulate this, most have an arm which extends out over the disc.

The error in the angle is known as the lateral tracking error, and it gives rise to distortion, and in particular second harmonic distortion. This can be estimated from the formula below:

δ = \frac{28.73 ϕ V}{r}

Where:
δ is the percentage of second harmonic distortion
φ is the tracking error in degrees
V; is the peak recording velocity in cm/s
r is the radius from the centre of the disc in cm

From this it can be seen that the offset can give rise to a significant level of second harmonic distortion.

In order to reduce the distortion and ensure the most faithful reproduction of the original sound, it is necessary to ensure that the tracking error is minimised.

If a straight arm is used, then this forms a tangent to the disc, i.e. it is aligned wit the groove at one point over the whole of the playing are of the disc.

However if an offset is made n the arm by "bending" or offsetting it near to where the cartridge is mounted, then there are two points over the playing region of the disc where the head is in alignment with the groove.

Pickup arm geometry showing head offset & overhang

One way of setting the design of the arm would be to set the points of zero tracking error at the beginning and end of the playing region, and this would give the maximum error in the middle of the playing area, but it would be less than the maximum error if there had been no bend or offset in the arm.

It is found that the distortion for a given tracking error increases as the effective velocity decreases. As the circumference of the groove is smaller at the centre of the disc, it means that the distance travelled is less at the centre and for a fixed revolution rate, this means that the velocity of the stylus over the groove is much less in the centre.

As a result it is better to arrange the system so that the first point where the tracking error is least is close to the end of the groove, but the second one is not at the outer edge but further in so that the distortion is equalised rather than the tracking error.

Typically the optimum positions for the zero tracking error are 65.6 and 120 mm from the centre of a 12 inch disc which has a radius of 152.4mm.

The optimum offset for a pickup arm calculated for the 120mm and 65.6mm zero points can be calculated from:

ϕ = \frac{5316}{l} degrees

Tonearm / pickup arm resonances and vibration

The tonearm or pickup arm should be free of unwanted resonances because these can colour the sound.

Whatever the construction, etc of the tonearm / pickup arm, some vibrations are transferred from the stylus to the cartridge and head-shell and hence to the arm.

It is found that at each interface, some of the vibration is reflected back and it ultimately reaches the stylus in a similar manner to sound reverberation and this will be converted into electrical signals by the head. This results in a form of reverberation being heard by the listener. Although the delay wil be short, it will alter the sound coming from the system.

In order to overcome these reflections, energy shunts are placed in some high end pickup arms between the interfaces to bridge the interface.

These can consist of fine brass wires that bridge the interface and enable the energy to be passed across the interface and prevent it being reflected back.

Arm wiring

It would be difficult to identify the different wires used in the pick up or tone arm. As a result a standard scheme for colour coding the wires is used.

The pick-up cartridge will be labelled with the connections: often L+, L-, R+, R-, thereby enabling the connections to be identified. It is essential to ensure that the phase for both channels is the same, otherwise the stereo effect will sound very odd.

Wiring Colour Code for Pickup Arm Wiring
Signal / Line	Wire Colour
Left Hand Live	White
Left Hand Screen	Blue
Right Hand Live	Red
Right Hand Screen	Green

Impact on Sound Quality

The tonearm or pickup arm plays a significant role in shaping the sound heard from vinyl record discs.

As can be understood there are various factors that shape the sound heard:

Tracking Accuracy: An unbalanced or misaligned tonearm can cause the stylus to mis-track the grooves, resulting in distortion, sibilance, and poor stereo imaging.
Resonance: Unwanted resonances in the tonearm can colour the sound, introducing unwanted coloration or muddiness.
Cartridge Matching: Different tonearms have varying effective mass, which needs to be compatible with the chosen cartridge for optimal performance. A mismatch can lead to inaccurate tracking or reduced high-frequency response.

Choosing a Tonearm

Most turntables come with a tonearm or pickup arm already attached. It is often part of the overall assembly. However some turntables, and especially those at the top end of the market allow a choice of tonearms

When selecting a tonearm, or seeing whether a particular turntable might suit and assessing its tonearm it is worth bearing the following factors in mind.

Turntable Compatibility: Ensure the tonearm is compatible with your existing turntable's mounting point and arm geometry.
Effective Mass: Match the tonearm's effective mass to the cartridge's compliance for optimal tracking and sound quality.
Features: Consider features like adjustable tracking force, anti-skate, and cueing mechanism based on your needs and budget.

Although most turntables have a tonearm fitted, understanding the factors that affect performance can enable the performance of a particular turntable to be understood and this may affect the choice of the whole turntable. These factors should certainly be part of the overall selection.

In addition to this, where a tonearm is not fitted, these factors can be of great importance in selecting the right one for a given system.

The tonearm, though often overlooked, is a crucial element in the vinyl playback experience. By understanding its anatomy, function, and impact on sound quality, it is possible to appreciate its role and make informed decisions when choosing or upgrading your turntable.