The vinyl turntable support disc is very important for quality playback because it is in direct contact with the record, affecting the pickup needle through it.
One of the most important requirements for a baseplate is the stability of its rotation speed. The rotation speed for most modern recordings must be strictly 33 1/3 rpm. Deviation from this value is extremely undesirable but much worse if this deviation is not constant, but is periodic in nature. In this case, the sound begins to "float", which is clearly visible to the ears. To prevent this unpleasant phenomenon, the majority of manufacturers of high-class players tend to make their discs massive enough. A heavy disc serves as a flywheel and is much less susceptible to external factors that affect the stability of its rotation speed. Since the support disc is a rotating object, the stability of its rotation is affected not so much by its own mass as by the moment of inertia. To increase its thickness, the discs are often made heterogeneous (thicker at the edges) or a special notch at the edges of the disc, which is filled with heavier material. This solution allows the required rotation stability to be achieved without the catastrophic increase in the total weight of the disc, which would inevitably lead to increased wear of the support bearing.
In addition to the high inertia, the disc must be very precisely manufactured and perfectly balanced so as not to become a source of vibration itself.
In order to withstand external vibration as well as the parasitic oscillations caused by the needle movement on the surface of the plate, support discs are often made of materials with good vibratory properties, such as carbon fiberglass, vinyl or acrylic.
In many players, a special mat made of felt or rubber is placed on the surface of the disc. The mat provides additional vibration isolation between the disc and plate and prevents the disc from coming into contact with the plate, which is completely unacceptable if the disc is made of metal.
Unfortunately, materials with good resonance properties, as well as felt and rubber mats do not always have sufficient rigidity. Simply put, they are quite malleable. In some cases, this can lead to loss of articulation, especially at low frequencies. It is not possible to give a general recommendation here and to determine how good a particular support disc is only by listening to it in an experimental way.
In order to ensure optimal contact between the plate and the support disc, many manufacturers offer the use of an additional clip. We are not going to look here at vacuum clamps, the principle of which is based on the constant pumping of air out of the space between the disc and the gramophone plate, because it seems to me, to put it mildly, controversial. Closer to the people are the clamps, which are simply a massive load that is put on the spindle over the plate, a threaded clamp that is screwed onto the spindle, as well as a clamp with a special latch that allows it to be fixed on the spindle of sufficient length.
In order to reduce the detonation level when the disc is rotated to a minimum, it needs to run as smoothly and easily as possible. This task is performed by the support bearing. The bearing should not have any backlash, and given that the discs are often very heavy, it should also be sufficiently wear-resistant. One of the most common bearing designs is a steel axis, which is attached to the disc at one end and inserted into a metal (usually bronze) "cup" and rests on the ball lying on the bottom. The balls can be made of different materials but must retain their wear resistance during the entire period of use. The surfaces of the ball's interface with the disc axis should be well lubricated and ideally smooth in order to provide the rotating disc with minimal resistance and not become a source of additional vibrations.
In order to withstand external vibrations as well as to dampen the parasitic vibrations caused by the needle movement on the surface of the plate, support discs are often made of materials with good vibratory properties, such as carbon fiberglass, vinyl or acrylic.
In many players, a special mat made of felt or rubber is placed on the surface of the disc. The mat provides additional vibration isolation between the disc and plate and prevents the disc from coming into contact with the plate, which is completely unacceptable if the disc is made of metal.
Unfortunately, materials with good resonance properties, as well as felt and rubber mats do not always have sufficient rigidity. Simply put, they are quite malleable. In some cases, this can lead to loss of articulation, especially at low frequencies. It is not possible to give a general recommendation here and to determine how good a particular support disc is only by listening to it in an experimental way.
In order to ensure optimal contact between the plate and the support disc, many manufacturers offer the use of an additional clip. We are not going to look here at vacuum clamps, the principle of which is based on the constant pumping of air out of the space between the disc and the gramophone plate, because it seems to me, to put it mildly, controversial. Closer to the people are the clamps, which are simply a massive load that is put on the spindle over the plate, a threaded clamp that is screwed onto the spindle, as well as a clamp with a special latch that allows it to be fixed on the spindle of sufficient length.
In order to reduce the detonation level when the disc is rotated to a minimum, it needs to run as smoothly and easily as possible. This task is performed by the support bearing. The bearing should not have any backlash, and given that the discs are often very heavy, it should also be sufficiently wear-resistant. One of the most common bearing designs is a steel axis, which is attached to the disc at one end and inserted into a metal (usually bronze) "cup" and rests on the ball lying on the bottom. The balls can be made of different materials but must retain their wear resistance during the entire period of use. The surfaces of the ball's interface with the disc axis should be well lubricated and ideally smooth in order to provide the rotating disc with minimal resistance and not become a source of additional vibrations.
Finally, it is necessary to mention such an important element as the disc drive. To rotate the disc, vinyl turntables use low-power and low-speed electric motors that have a minimum of their own vibrations. The speed of rotation of the electric motor should be constant, therefore in players of high enough class, the quartz stabilization of speed of rotation is applied. Depending on the design of the player, the drive can be direct, roller and passive. In the direct-drive version, the disc is placed directly on the motor shaft. The advantage of this design is the reduced level of detonation since there are no intermediaries between the motor and the disc that can affect the stability of rotation. The disadvantages here are very serious. Firstly, the motor is a source of vibration and in the case of direct drive, they are all transferred to the support disc. Second, the motor emits a magnetic field that interferes with the voice coil, which is in close proximity to the motor.
A roller drive in which the disc is driven by a roller connected to the motor shaft is practically not used in high-end equipment.
The most common in Hi-Fi players is the passive drive. In this scheme, the motor is connected to the support disc using a special passika, usually made of rubber or less frequently of silk thread. The passive drive dampens the vibrations generated by the electric motor, which are transmitted to the support disc via its shaft in a direct drive construction. In addition, the motor is located far from the voice coil and does not affect its magnetic field. In some top-of-the-range players, the motor is generally placed on a separate chassis, thus completely isolating it from the support disc and the base of the tonearm. Naturally, this design can only be implemented using a passika. The downside of this drive is that the passive is made of an elastic material and can, therefore, cause the disc to become unstable. However, this is not very important for solid discs of quality players. Working like a flywheel, they smooth out this instability.