At the introduction of the LP record turntable manufacturers were already well on the way to optimising the idler drive turntable. The emphasis was on maintaining platter speed and consistency of performance with the heavyweight pickups that were designed to play shellac 78rpm records at tracking weights in excess of 10 grams. This additional load on the turntable required the design of high torque motors and efficient methods of transferring rotational energy to the platter
The golden turntable designs of that time were made by three promininent manufacturers, Garrard, Lenco and Thorens. With the advent of the LP the design of pickup arms entered a new era with cartridges that could track under 3 grams weight using jewel based styli and exerting less 'drag' on the record. However it has not been well understood until recently that the transfer of energy to the record is still of major importance.
The reasons why idler drive turntables, such as the Garrard 301, are so sought after, and fetch such high secondhand prices, are not just down to nostalgia for the engineering quality of the past. Sound quality from these turntables is demonstrably better than their low-torque, belt drive counterparts, and for good reason.
If you consider that the energy that the cartridge receives from the record groove is purely due to the rotational energy in the record and, therefore, platter then the efficacy of idler drive becomes an obvious advantage. With no slipping or stretching belts between the motor and platter, the idler drive transfers motor torque to the record in the most efficient way possible from a suspended motor.
So why did belt drive catch on in the first place? To understand this we have to look at the history of hi-fi equipment sales in the '60s and early '70s. High quality hi-fi equipment was sold by specialist hi-fi shops who offered a complete service to the customer. This included housing the customer's choice of equipment in a smart wooden cabinet, of which there was a choice of styles. In order to accommodate a range of turntable 'motor units' (as they were then called), the suppliers of these cabinets utilised thin, plywood motor boards which could be cut easily with a fretsaw.
Now consider the effect of mounting a heavyweight turntable like the Garrard 301/401 on such a thin, resonant board. And imagine the compounding effect that putting such a resounding board and motor in a wooden cabinet. What you have is an efficient low frequency resonator excited by motor noise, feedback and building subsonic interference. No wonder these units rumbled!
If one refers to the manufacturer's recommendations for mounting, however, these cast a very different view of achieving the best sonic performance. The original Garrard 301 manual, for example, recommends a 'substantial' motor board.