As tracking forces diminished, idler-wheel drives became more refined, but retained their resistance to stylus force drag. As time went on and VTF dropped to below 2 grams, it was thought stylus force drag could be combated by the simple use of [minimal] mass and rotational inertia, and not the brute force of rumbly idler-wheel drives, which were discredited for this reason, even though their rumble figures were in fact better than those of the then-rising Linn LP12. Properly set-up, idler-wheel drives do not rumble. In auditioning, the Lencos prove that in fact it does take a certain amount of [refined] brute force to counteract the all-too-audible problem of stylus drag, which belt-drives are ill-equipped to combat, their Achilles Heel being their belts and weaker motors. This is clearly audible in the transient attack of a Lenco, EMT or Garrard, and their tremendous bass reach (bottomless) and bass detail (which affects both air and imaging), and of course its perfect timing and speed stability under real-world conditions (actually playing a record).
The Lenco motor is a high-torque four-pole motor which spins at something like 1500 RPM , suspended from the metal chassis by springs, in a reversal of the spring suspension belt-drive, which fixes the motor but suspends the turntable.
The Lenco in particular has some design features which make it special in the world of idlers. First of all, it is nowhere near as well-built as as the Garrards, EMTs or quasi-idler Thorens TD-124s, which is one reason it is still not taken very seriously (the other being that it is still a relative newcomer). But not as well built does not mean not as well designed, and it is in design that the Lenco truly shines.
Since the Lenco is both oversized AND has a large proportion of its mass on the periphery, it has consequently more outward/rotational force than can be accounted for by simple mass alone.
First of all, the single-piece platters on the Lencos are oversized, which increases the centrifugal force: outward force is proportional to the distance from the axis of rotation and to the rate of rotation of the frame. Since the Lenco is both oversized AND has a large proportion of its mass on the periphery, it has consequently more outward/rotational force than can be accounted for by simple mass alone. In other words: it achieves more via design than most modern high-mass record players do by simple, expensive, mass alone. Engineers and turntable manufacturers seem to have forgotten basic physics: the mass immediately above the point of rotation – i.e. the main bearing – and closest to it, has zero rotational inertia (and so contrinutes not at all to inertia/torque), and minimal effect for a short distance from the point of rotation. These oversized platter designs are a waste of money, and place undue stress on the main bearing, which must be manufactured to compensate, and so increase the cost of manufacture (as for the massive platter), and undue wear, meaning a shorter life-span for the main bearing. The Lenco’s oversized – outwardly – platter is a far more intelligent and elegant solution, economically. Finally, in addition to this, the platters of the L78s and L75s are dynamically balanced, thus achieving excellent and steady flywheel effect to ensure stable speed. The platter design alone is an engineering tour-de-force.
But it doesn’t end there: the idler-wheel, unlike all other designs, runs vertically, not horizontally. It is held in place by a subtle spring, delicately, so as not to force motor noise and so vibration. Since the pressure is directed upwards, delicately, it does not press against the platter’s side, and so does not push or stress the main bearing. Even the motor is dynamically balanced, is massive, and runs silently on its lubricated bearings. The high-torque motor spins at roughly 1500 RPMs (compared to a belt-drive motor’s average 150-300) which pretty well wipes out speed variations by itself. The wheel contacts the motor spindle directly, while contacting the platter directly on its other side, thus transmitting most/all of that torque without any belt stretching. But since the platter is also a flywheel, it evens out whatever speed variations there may be in the motor. Since the wheel pushes upwards, the platter spins freely on its ball-bearing, like a ballerina on her toe. It’s a closed system (motor-platter, platter-motor) and speed variations brought on by groove modulations don’t stand a chance in this rig, and it is clearly audible.