Servo Controlled Arm

Again, why do it at all? I would file this under "gimmick". That's all I'm saying.

IMHO, of course. :-)

Why do it at all? Because a conventional 8.5" or 9" tonearm can have a tracking error up to 3 degrees compared to the linear arm error of less than 0.5 degree. So the "gimmick" would be to lower harmonic distortion. As for the comment on servo damping, dan_ed makes it sound more complicated than it is. The tonearm, cart/stylus, LP groove form a sytem which will resonate at one particular frequency which is variable. Detection of resonance is easy and almost instantaneous due to a very large increase in amplitude. With the servo detecting and changiing some variable, it keeps the sytem away from the resonance point. Theoretically, it should produce cleaner sound.

Rotarius...I think you are talking about the vertical "Biotracing" servo, which is quite separate from the linear tracking arm. Sony made pivoting Biotracer arms also.

By the way, I made a typo in my last posting. The spec tracking angle error is 0.05 degrees, not 0.5.

The Biotracer arm tracks very warped LPs with not the slightest problem. (That's why). If you lift the arm manually is has a strange "limp noodle" feel to it. The downforce remains constant dispite movement of the arm up and down as with a warped record. The downforce, VTF, is applied electronicly, so it can be tweeked while a record is playing. The arm itself is mass balanced (no downforce) and this minimizes sensitivity to vibration.

This time is about servo quasi-tangent arm. I think getting rid of anti-skating force on a linear tracking servo arm is at least ONE advantage over the conventional 9" pivot arm. It's not geometrically perfect but the tracking error is still smaller than a 9" arm. It's not a gimmick if executed right. I agree with Kirkus that the problem sometimes it's not the servo but the tonearm itself. I have a Pioneer PL-L1000 that uses a linear motor, like a mag-lev train, to glide and match the dynamic pivot movement of the arm, ie, it moves left AND right(!!), but the roller bearing quality is not on par with the motion and it's just not smooth and quiet enough, perhaps implementing with air bearing would do the trick but then again, one would compel to just simply use a conventional PASSIVE air bearing arm. I prefer the old Rabco way and simply move one direction and calculation the amount of offset and just let it roll. The Yamaha PX2 is quite successful in this regard and it sounds good. The Goldmund T3 is just a glorified Rabco, really.

I would like to see someone to come up with a servo gliding arm base so the user can mount the tonearm of his/her choice - perhaps attaching some sensors to the counterweight, arm-tube, or even at the cartridge position, for the servo system to detect the offset. This way the audiophile can use their favorite tonearm AND turntable. It will be a neat accessory. Gimmick? Maybe, but I bet it's fun. :-)