Belt drive turntable

In all turntables a motor spins a metal disk at a constant speed. On top of the rotating disk (platter) is a slip mat and on top of the slip mat records are placed to be played. The slip mat can serve two functions. In the past to slip mats were rubber and used to hold the record in place so that it would not rotate independently of the platter. Nowadays the slip mat is used to reduce the friction between the spinning platter and record. This way a DJ can scratch the record while the platter continues to spin underneath. The stylus is a small needle that glides along the grooves of a record and picks up the variations in groove depth and/or lateral movements, these are then converted into audible sound.

There are manly two types of turntables still being manufactured today, the older style belt drive or newer direct drive systems; the names are based upon the type of motor system found in each.

In a belt drive turntable the motor is located under and to the side of the platter and is connected to the plater by a rubber belt.

The design of the belt drive turntable is simpler than the Direct drive turntable which makes it cheaper to build. Also, the rubber belt absorbes motor vibrations which would otherwise be picked up from the stylus. These advantages, however, do not balance the many short falls of the belt drive design. There are many problems with the belt drive turntables as well. Over time the belt can become loose and begin to slip, causing variations in the platter speed. Belt drive turntables have much lower torque. This leads record to be much more susceptible to outside forces. The contact between the stylus and record causes a frictional force in the form of torque, as the stylus angular path gets closer to the center of rotation the force decreases. Thus, at the start of a record, the stylus contact could actually decrease the speed of the record by up to 3%, while at the end of the recording, the distance from the center is much less. The torque is much smaller and will have little or no noticeable affect on the speed of the record. The belt can also slip off the motor and/or plater spindle. When the platter is being physically manipulated by DJs, belt drive turntables often respond poorley. This mean that DJs who sratch or mix generally prefer to use direct drive turntables.

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