Ct, In the absence of any friction at the pivot point, yes there is no need for any external force to move the arm wand/cartridge across the LP surface. However, in the real world, there is never zero friction. Thus we first had the Rabco SL8, referred to by Ralph, which used a servo motor to nudge the pivot each time the arm wand moved in tiny arcs at the stylus contact point; the Rabco makes a series of tiny arcs all across the LP surface, the servo motor makes noise, yadayada. Arguably, it's not even a true SL tonearm. The Goldmund TF tonearm is naught but a very expensive copy of the Rabco idea. We also have the Souther tonearm which operates in concert with a "dished" platter (marketed in recent years by Clearaudio), so that the cartridge "falls" toward the spindle whilst riding on a rail. The most pure form of the art is the air bearing type, which at least strives for zero friction. But since that is impossible, side forces are created, as described by Ralph. In addition, one must fuss with air pumps, etc. But certain examples, like the Terminator, can be very good. I don't need to own an SL tonearm or turntable in order to know these things. What about you?
The only full bore turntable/SL tonearm available now comes from Germany, I think, but I cannot recall its name. Another German company, Brinkmann may also make one.
