Belt-drive turntable
Encyclopedia
Phonograph
The phonograph record player, or gramophone is a device introduced in 1877 that has had continued common use for reproducing sound recordings, although when first developed, the phonograph was used to both record and reproduce sounds...
turntable drives still being manufactured today, the belt-drive and direct-drive
Direct-drive turntable
A direct-drive turntable is one of two main phonograph designs being manufactured today. The other style is the belt-drive turntable. Each name is based upon the type of drive motor used...
systems; the names are based upon the type of motor system found in each.
In a belt
Belt (mechanical)
A belt is a loop of flexible material used to link two or more rotating shafts mechanically. Belts may be used as a source of motion, to transmit power efficiently, or to track relative movement. Belts are looped over pulleys. In a two pulley system, the belt can either drive the pulleys in the...
-drive turntable the motor
Electric motor
An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...
is located off-center from the platter, either underneath it or entirely outside of it, and is connected to the platter or counter-platter by an elastomer
Elastomer
An elastomer is a polymer with the property of viscoelasticity , generally having notably low Young's modulus and high yield strain compared with other materials. The term, which is derived from elastic polymer, is often used interchangeably with the term rubber, although the latter is preferred...
ic belt.
The design of the belt-drive turntable allows the use of a less expensive motor than the direct-drive turntable
Direct-drive turntable
A direct-drive turntable is one of two main phonograph designs being manufactured today. The other style is the belt-drive turntable. Each name is based upon the type of drive motor used...
. Also, the elastomeric belt absorbs motor vibrations which would otherwise be picked up by the stylus
Stylus
A stylus is a writing utensil, or a small tool for some other form of marking or shaping, for example in pottery. The word is also used for a computer accessory . It usually refers to a narrow elongated staff, similar to a modern ballpoint pen. Many styli are heavily curved to be held more easily...
.
Rotational stability
This is an absolute goal of audiophileAudiophile
An audiophile is a person who enjoys listening to recorded music, usually in a home. Some audiophiles are more interested in collecting and listening to music, while others are more interested in collecting and listening to audio components, whose "sound quality" they consider as important as the...
turntables, many of which are belt-driven. Problems with belt instability and deterioration in the past have largely been solved by use of modern elastic polymers.
Many belt-drive turntables having multiple speeds used a simple mechanical system to change speeds, using a mechanism to move the belt between different-sized pulleys on the motor shaft. It is difficult to design multiple-speed synchronous motors whose speed can be controlled electronically. Consequently, turntables with electronics providing speed control are nowadays most frequently used with DC servomotor
Servomechanism
thumb|right|200px|Industrial servomotorThe grey/green cylinder is the [[Brush |brush-type]] [[DC motor]]. The black section at the bottom contains the [[Epicyclic gearing|planetary]] [[Reduction drive|reduction gear]], and the black object on top of the motor is the optical [[rotary encoder]] for...
s. DC servomotors rotate in steps rather than continuously. This is referred to as 'cogging', and can add noise during playback. Helical armature motors can be used to overcome this. On some designs, the manufacturer prefers to ensure pitch stability by generating its own sinusoidal waveform to power the motor. Others attempt to achieve this by using optical sensors on the platter which feed back to the electronics to ensure the speed of the platter remains stable.
Belt-drive types
Some turntables, such as the newer versions of the RegaRega Research
Rega Research Ltd. is a high-end audio equipment manufacturer based in the UK. Rega was founded in 1973. The company's name was formed of the initials of its two founders . Historically Rega are best known for the Rega Planar turntable, but in recent years the company has diversified into a range...
Planar series, use a fixed plinth with a low vibration motor and bearing attached to the same flat surface, usually constructed of wood, metal or acrylic, without suspension. Others, such as the Linn Sondek LP12
Linn Sondek LP12
The Linn Sondek LP12 transcription turntable is produced by Glasgow-based Linn Products, manufacturers of hi-fi, home theatre, and multi-room audio systems...
, have a suspension.
Suspended-sub-chassis
The principle behind the "suspended sub-chassis" design is that the turntable is an inert platform that allows the stylusStylus
A stylus is a writing utensil, or a small tool for some other form of marking or shaping, for example in pottery. The word is also used for a computer accessory . It usually refers to a narrow elongated staff, similar to a modern ballpoint pen. Many styli are heavily curved to be held more easily...
to track the surface of the record accurately whilst being protected from external vibrations. The platter, sub-chassis, armboard and tonearm mechanically form a closed loop, and sit on top of dampers (usually three springs) which isolate the sub-assembly from its top plate and base. The motor, mounted (directly or indirectly) on the top plate, drives the turntable platter via a belt. The tonearm is usually sold separately, allowing for buyer choice and upgrades.
Bearings, mounted on the sub-chassis, generally use an oil film to lubricate between a metal ball-bearing connected to the platter by a spindle and the thrust-plate of the bearing's housing. More esoteric designs use an air bearing, where the spindle is supported by a high pressure flow of air.
Disadvantages
Over time the drive belt can wear or lose elasticityElasticity (physics)
In physics, elasticity is the physical property of a material that returns to its original shape after the stress that made it deform or distort is removed. The relative amount of deformation is called the strain....
, and begin to slip, causing variations in the platter speed. In addition, belt-drive turntables have much lower torque; the belt can also slip off the motor and/or platter spindle, and are thus not suitable for turntablism
Turntablism
Turntablism is the art of manipulating sounds and creating music using phonograph turntables and a DJ mixer.The word 'turntablist' was coined in 1995 by DJ Babu to describe the difference between a DJ who just plays records, and one who performs by touching and moving the records, stylus and mixer...
. DJs who scratch or mix
DJ mix
A DJ mix or DJ mixset is a sequence of musical tracks typically mixed together to appear as one continuous track. When a DJ mix or DJ mixset is recorded onto some medium, it is often referred to as a mix tape...
generally prefer to use direct-drive turntable
Direct-drive turntable
A direct-drive turntable is one of two main phonograph designs being manufactured today. The other style is the belt-drive turntable. Each name is based upon the type of drive motor used...
s.