Rockport Technologies System III Sirius turntable and tonearm Page 3
The vacuum holddown electronics (and thus the vacuum lines) are also located in the box part of Payor's design, which isolates all possible sources of electronically induced noise in the shielded controller chassis. The three-dial air-regulator termination block sits at the bottom of the box. It pre-regulates the air coming from the compressor, and controls the pressure of the air sent to the spindle bearing and tonearm.
Andy Payor is understandably proud of the entire Sirius III design, but he's at his most defensive and protective when discussing his captured air-bearing, linear-tracking tonearm. As far as he's concerned, most so-called "linear" trackers are anything but. He feels "orifice compensated" air-bearing arm designs—the kind with tiny airflow holes in the rail on which the bearing slides—are characterized by "low central stiffness and self-resonance" and are too compromised to be considered state-of-the-art.
Payor thinks the word "bearing" should only loosely apply to what moves the arm in any of those designs; by definition, a bearing should maintain exacting geometry in the desired axes. "Floating" designs with air holes only on top simply cannot do this. Payor's position is that such designs cannot maintain precise tangency to a radial line across the record surface because of "bearing slop," or movement in all axes of motion, and so will microscopically meander across the record surface, and thus are not true linear trackers at all.
The same goes for mechanical "linear"-tracking designs, which have considerable movement along unwanted axes. The air-bearing scheme—comprising a stationary bearing and a moving rail—invented by Eminent Technology's Bruce Thigpen and used on his tonearm as well as on the Maplenoll and Walker Audio turntables, comes closer to being truly "linear" because the bearing can be more highly pressurized. But the rail's large horizontal moving mass creates another set of problems. And a true linear tracker completely eliminates a pivoted arm's inherent tracking error and skating-force vectors.
All of which, to Payor, means that his arm is the best currently available, and the true state of the art. Based on a groove-compensated captured air bearing, it certainly is the most brilliantly built. The ultra-high-precision design (sub-micron machining tolerances) uses a patented high-pressure, low-flow bearing that is essentially frictionless. For a complete description of the design theory behind this bearing, see my May 1996 review of the Rockport Series 6000 arm, but keep in mind that the Sirius III arm is a far more sophisticated edition.
The Sirius tonearm tube should be virtually inert, made of a constrained-layer-damped, 8-ply sandwich of carbon fiber and epoxy composite: four layers on each side of the damping material. Inside is a second tapered carbon-fiber tube, the space between the two filled with yet another damping material. The materials, construction, and aerospace pressure-laminating techniques create an armtube said to have the stiffness of steel, yet weighing only half as much as a comparable aluminum tube. This is extremely important, as low moving mass is critical to the performance of a linear-tracking arm. The entire mass must move horizontally.
The geometry of the design puts the bearing pivot point and the counterweight in the same plane as the record surface. This reduces frequency-modulation distortion and interchannel phase errors, and reduces tracking-force variations caused by vertical irregularities in the record. The benefits of having the pivot point at the record surface are not unique to the Rockport arm—the Immedia RPM2 does likewise.
The arm housing and integral damping trough are machined from a single billet of aluminum alloy and so form an incredibly rigid structure. The rail on which the bearing slides is held in place under pressure, its ends terminated by Delrin thrust seats and ceramic balls. With the proper silicone fluid level in the trough, the fundamental tonearm resonance caused by the cartridge/arm spring/mass system can be damped, and the arm can better follow groove eccentricities and vertical irregularities. VTA adjustment is simple, smoothly applied, and rock-solid repeatable. The other cartridge adjustments—overhang, azimuth, and VTF—are equally easy to accomplish. This is an arm that, once set, will never need tweaking.
Another single billet of aluminum alloy is machined to make the bearing mount, tonearm clamp, and counterweight assembly. This is a big improvement over the design of the Series 6000 arm: the structure is said to be 20 times stiffer than before, yet no heavier.
Finally, the tonearm wire is of custom-wound, specially insulated five-nines (99.999% pure) copper terminated with a pair of high-quality RCA jacks.