Raul, I apologize; the technical explanation for the underhung tonearm on the GT5000 is to be found on the "What Hi-Fi" review of the whole turntable, where the reviewer asked the Yamaha engineers for their explanation. He then had to translate the response from the original Japanese:
I thought I should ask Yamaha about its rationale for the tonearm length and the lack of anti-skating, and received a reply from no less a personage than Kiyohiko Goto, Chief Engineer at Yamaha Japan’s AV Division.
Regarding the tracking error he says: “A short straight arm has excellent tracking performance because the inside force is generated at the point of contact between a stylus tip and groove of vinyl and is always variable with the variate of the music groove. In the case of a short straight arm, its null point (= balanced point) is at the middle of the grooved area (so) the maximum tracking error is 10 degrees at innermost and outermost grooves. The distortion caused by this small error angle is inaudible because it is lower than both the tracing distortion and the residual noise. Furthermore, tracking error appears as phase shift between the left and right channels, and even at its maximum (10 degree) error the phase shift that results would be the same as caused by a difference in the distance from the left and right speakers to the listener of only 2mm. This also does not cause any problem for sound.”
As for the lack of anti-skating, he says: “A short straight arm does not require anti-skating because [at maximum error angle] if the vertical tracking force is 2g, the frictional coefficient is 0.3, and so the inside force (outside force) will be approx. 0.1g. In the case of a conventional offset arm with a maximum tracking error of 2 degrees, the inside force will be approx. 0.02g so the difference of the max inside force between a short arm and an offset type will be 0.08g at the maximum, thus the difference in force is very small.”
“On the other hand, when anti-skating is employed, because it applies a constant force it never cancels the inside force which constantly changes as its follows the music signal. The constant differences between the variable inside force at the stylus tip and the constant force by the anti-skating adversely affects the cantilever, hence the tracking performance is not stable. In a short straight arm the tracking performance following (the) music groove is excellent because the variable difference of force between the stylus tip and tonearm (cartridge) is not generated.
In my opinion, the real reason there is no anti-skate device is because AS would have to reverse direction by 180 degrees, before vs after the stylus gets passed the single null point achieved with any underhung tonearm. That would be difficult to manage. Whether AS per se is harmful for the reasons stated by the Yamaha engineer is a matter for debate. Whether distortion due to TAE is lower in magnitude than both tracing distortion and residual noise is an interesting claim that I am not equipped to critique. The bold type is mine in order to highlight that controversial claim. If the claim is valid, perhaps that explains why I hear no problem that I can relate to the extreme TAE, with my RS Labs RS-A1. In fact, the character of its sound across the surface of an LP, from outer to inner grooves seems more constantly the same than with conventional pivoted tonearms. This is only an opinion based on listening and with no measured data, of course.
