Skivspelare (vinyl) - diskussioner och köpråd /Mod

Turntable drive systems
Many platters have a continuous series of strobe markings machined or printed around their edge to provide optical pulses to these speed-control systems. Viewing these markings in artificial light at mains frequency produces a stroboscopic effect, which can be used by the operator to verify rotational speed.


[edit] Idler-wheel drive system
Earlier designs used a rubberized idler-wheel drive system. However, wear and decomposition of the wheel, as well as the direct mechanical coupling to a vibrating motor, introduced low-frequency noise ("rumble") and speed variations ("wow and flutter") into the sound. These systems generally used a synchronous motor which ran at a speed synchronized to the frequency of the AC power supply. Portable record players typically used an inexpensive shaded-pole motor. At the end of the motor shaft there was a stepped driving capstan; to obtain different speeds, the rubber idler wheel was moved to contact different steps of this capstan. The idler was pinched against the bottom or inside edge of the platter to drive it.

Until the 1980s, the idler-wheel drive was the most common on turntables, except for higher-end audiophile models. However, even some higher-end turntables, such as the Lenco, Garrard "Zero" series and Dual turntables, used idler-wheel drive.


[edit] Belt drive system
Main article: Belt-drive turntable
In a belt drive turntable the motor is located under and to the side of the platter and is connected to the platter by an elastomeric belt. Belt drives brought improved motor and platter isolation compared to idler-wheel designs. Motor noise heard as low-frequency rumble was much reduced.

The design of the belt drive turntable allows for a less expensive motor than the direct-drive turntable to be used. Also, the elastomeric belt absorbs motor vibrations which would otherwise be picked up by the stylus. The Acoustical professional turntable (earlier marketed under Dutch "Jobo prof") of the 1960s however possessed an expensive German drive motor, the "Pabst Aussenläufer". As this motor name implied, the rotor was on the outside of the motor and acted as a flywheel ahead of the belt-driven turntable itself. In combination with a steel to nylon turntable bearing (with molybdeen sulfide material inside for lifelong lubrication) very low wow, flutter and rumble figures were achieved.


[edit] Direct drive system
Main article: Direct-drive turntable
Direct-drive turntables drive the platter directly without utilizing intermediate wheels, belts, or gears as part of a drive train. The platter functions as a motor armature. This requires good engineering, with advanced electronics for acceleration and speed control. Matsushita's Technics division introduced the first commercially successful direct drive platter, model SP10, in 1969 and it was replaced by the Technics SL-1200 turntable, in 1972. Its updated model, SL-1200MK2, released in 1978, had a stronger motor, a convenient pitch control slider for beatmatching and a stylus illuminator, which made it the long standing favourite among disc jockeys (see "Turntablism").


[edit] Direct vs belt drive
Although most high-quality turntables use a rubber belt to drive the rotating platter from an electric motor, the Rockport Sirius, for example, uses a linear induction motor with no physical connection to the platter. The direct-drive turntable, for example, the abovementioned Technics SL-1200, became popular in the late 1970s.

Many turntables, such as the Rega Planar series, use a fixed plinth with the motor and bearing attached to the same flat surface, usually constructed of wood, metal or acrylic, others use a "suspended sub-chassis" design, where the platform allows the stylus to track accurately relative to the surface of the record whilst being protected from external vibrations. The platter, sub-chassis, armboard and tonearm mechanically form a closed loop, and sit on top of dampers.

The evaluation of the "best" turntable design is very subjective and often based more on listening experience. Technical measurement is fraught with difficulties: first there is the difficulty of measuring small parameters, secondly there is disagreement about relevant parameters to measure.

Audiophile grade turntables start at a few hundred dollars and range upwards of $100,000, depending on the complexity and quality of design and manufacture. The common view would be that there are diminishing returns with an increase in price - a turntable costing $1,000 would not sound significantly better than a turntable costing $500; nevertheless, there exists a large choice of expensive turntables although the popularity of the vinyl replay medium has been surpassed for some time.

http://en.wikipedia.org/wiki/Direct-drive_turntable