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Turntables

TURNTABLES

Our quick and simple guide to the modern LP spinning turntable.

garrard-401-on-slate-plinth

 

The turntable spins the (vinyl) disc at 33rpm (revs per minute) or 45 rpm.. A few offer 78rpm for older shellac discs.  Broadly speaking, the types are classified by drive system, and each drive system has a characteristic sound. Popularly, 'turntable' means both turntable and arm together, as a package, often with a cartridge, as above where a Garrard 401 turntable sits on a slate plinth, with SME3009 arm and Shure V15 cartridge. Otherwise,we refer just to the motor unit in this section.


IDLER DRIVE

idler-drive-2

An idler wheel sits between motor and platter, acting as a ‘gearbox’ to give 33 and 45 rpm. It is a ‘tight’ coupling system that transmits motor deficiencies, such as poor speed stability and rumble, to the platter. The corollary is that it equally transmits good characteristics, so works well with a good motor. Classic exemplars are the Garrard 301 and 401 that have the sonic pace and power of an express train. Idler drive is the oldest of the systems and not used anymore, even though it can be made to work well.


BELT DRIVE

belt-drive-2

Adopted to tune out motor deficiencies, a compliant rubber belt connects a pulley on a motor to the platter. This decouples the motor, suppressing rumble, cogging and much else. It also allows the platter to float on a sub-chassis, to isolate it from both the motor and outside disturbance, a system first used by Acoustic Research of the USA and Thorens of Germany. Platter mass dominates, so start up can be leisurely and running torque modest, but the sound is clean and airy, if often a little weak on temporal grip. Widely used, it is inexpensive and effective.


DIRECT DRIVE

direct-drive-2

The platter sits atop the  spindle of  a low speed d.c. servo motor that runs at 33 or 45rpm. There is no intermediate drive system.The servo is often locked to a crystal oscillator acting as speed reference. First mass produced in the late 1970s, in Japan, direct drives died when CD arrived, except for the Technics SL-1200 and Vestax DJ turntables, both available today. Fundamentally, it works well, setting accurate speed and keeping a tight grip on speed - and this is audible. Complex, it was a big company engineering exercise, often less than  perfect in detail. The Technics SL-1200 is a popular modern choice and a very effective turntable for hi-fi use.


PLINTH AND ISOLATION SYSTEMS

Early turntables like the Garrards were simply mounted onto a wooden base, for use in radio studios, or onto a simple wooden plinth for the home. Acoustic Research in the USA conceived the first belt drive turntables in the AR18 and Thorens of Gerrmany produced the massively popular TD-150. In this system  the platter and arm  sit on a sprung sub-chassis, isolated from external vibration, as well as the motor. This works, but the bouncy sub-chassis makes cueing difficult and, bouncing at 5Hz or so, was set in motion by suspended wooden floors that tend to bounce close to the same frequency.


The Japanese have traditionally used mass to isolate their turntables, preferring very heavy plinths. Similarly Garrard idler drives need substantially built and therefore heavy plinths. Cue mechanisms are easier to use and mass does provide isolation from vibration, but such plinths are cumbersome and need strong support.

 

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