Though everyone familiar with AR and Thorens turntables acknowledges the importance of the spring suspended subchassis to isolation of unwanted resonances, another critical component of this isolation is often ignored: the belt. Inherent in the fact that the three-spring suspension allows the sub-chassis to FLOAT, is the fact that an improperly sized belt will cause the sub-chassis to be aligned incorrectly. (Most often, an overly tight belt will pull the entire suspension towards the motor.)
In addition to its importance to proper fucntioning of the suspension, the correct belt size will also ensure there is constant velocity between the motor pulley and the drive platter. Any kind of slippage will result in speed variations. Finally, in the case of the Thorens, where speed change is accomplished mechanically, a high quality belt of the correct dimensions will ensure the proper change of speeds. You won’t find the belt riding midway between 33 and 45rpm.
To sum up, a high quality belt will allow independent motion of the subchassis, yet drive the inner platter at a constant speed by friction. It’s a complex balance that can only be achieved by a correctly sized belt of good quality rubber. (I wish you were here with me now so I could show you the difference in feel between a belt of good quality rubber and one that seems to be made of a poor synthetic rubber. The former has a suppleness and evenness of tension; the latter is slippery and lacks elasticity.)
It is almost comical to me how some folks will spend hundreds of dollars on the their cartridge, but then skimp on the quality of their belts. Come on, spending fifteen or even twenty-five dollars on such an integral part of your vinyl playback system should not be so hard when you have already invested so much. Would you rather spend it on a new motor caused by an overly tight belt stressing your bearings?”