Before a record player can be designed, some important principles must be understood. The most important of these is that the stylus or diamond tip of the cartridge must exactly trace the undulations pressed into the groove walls of the record. For this to happen, the pickup cartridge must be held absolutely rigid and stable, and the record must also be held absolutely rigid and stable. Then the only thing that is moving is the diamond tip, and as a result, the output of the cartridge is a perfect electrical replica of the shape of the groove with nothing added and nothing taken away.

That is the theory. In practice, the record is being rotated and so cannot be held rigid, and the cartridge is mounted in a freely moving tone-arm, which also cannot be held totally rigid. Nonetheless, the skill of the designer is to rotate the turntable at a constant speed whilst allowing it to have no lateral (side-to-side) motion and to design a totally rigid tone arm which allows the stylus to track across the record. The success of the designer in getting close to these ideals determines the ultimate performance and the quality of the musical experience.

Below are some tips on the basics to get you started. At the bottom of this page, you'll find a more comprehensive turntable set-up guide.

At first glance, it would seem to be a simple task to rotate a turntable at the correct speed, but in practice, several problems can be difficult to overcome. The turntable platter is mounted onto a shaft which rotates upon a bearing assembly. First, these bearings have to be extremely smooth in operation because any irregularities produce 'rumble', the effect of which is similar to that felt when driving a car along a gravel path. The small undulations cause the platter to move up and down an almost imperceptible amount. Still, the movement is detected by the stylus and added to the signal as a distortion.

Secondly, the bearing has to be very tight with virtually no slack, which would allow the shaft and platter to move from side to side. Again, any sideways motion would be detected by the stylus as a 'wow'; the sort of effect that would be heard on a sustained piano note as a crude vibrato.

For much the same reason, the turntable platter itself needs to be perfectly balanced and of uniform structure. Throughout the Pro-Ject range, you will always find very solid, often heavy main platters of varying types suitable for the budget and application of the design.

Obviously, the rotational speed needs to be held constant, and this is achieved using an AC synchronous motor, which, in the case of Pro-Ject's turntables, is often regulated by a DC-powered AC generator built into the turntable for clean, consistent power.

Of course, even the best motors have imperfections, and these include the small vibrations created within the motor bearings; small vibrations caused by noise and interference on the mains power lines and the so-called 'clogging' vibrations; a consequence of the motors having a finite number of poles giving an 'on-off-on-off' type of motion.

Any of these vibrations reaching the stylus could degrade the sound, so it is good design practice to decouple the motor assembly from the turntable platter by a belt drive using a carefully specified belt. The characteristics of this belt (compliance, surface finish, etc.) and the amount of tension determine the degree of isolation between the motor and platter. A high-mass platter will always smooth out any tiny remaining speed irregularities as a result of the 'flywheel effect', which causes the rotational speed to settle to a constant value.

Almost every object resonates. Tap any object and the “knocking” sound will be at a different note from object to object, because each has its dominant resonances. When an object resonates, it actually vibrates to a larger-than-usual degree and, of course, in a record player, any vibrations have the risk of being picked up by the stylus and added to the music signal.

For this reason, Pro-Ject use a variety of technologies throughout their range to ensure the plinth (the main structure of the turntable), the platter and other key components are extremely well damped or isolated to avoid unwanted resonances transferring to the cartridge. 

The design of a tonearm is a demanding task. Earlier, we said that a key design requirement is that everything be held absolutely rigid and stable. If a tonearm has any flexibility between its pivot point and the stylus, then any movements will be superimposed on top of the music signal, causing degradation. In practice, this means that the whole assembly should ideally be a homogeneous single piece which is rigid and free from flexing. Yet at the same time, this arm needs to have a low mass to work well with most modern pick-up cartridges.

Pro-Ject has met this requirement superbly on most of its turntables by employing aluminium and/or carbon fibre tubes, and almost always, they are effectively "one piece" tubes. These tonearm designs are as free from any flexing as possible, while remaining rigid and light - often with good electrical shielding as well.

Read the full turntable set-up guide here

Provided by Henley Audio