Spiral Groove Centroid tonearm

I'm going to try and not be promotional here. If I fail at my attempt, I sincerely apologize. I want to reinforce what Jonathan mentioned about the overhang alignment arrangement when using the Centroid and the new Delos or Kleos. In the case of the Centroid, we include an alignment system that provides exact stylus to pivot positioning of the alignment protractor using the locator hole on the headshell, which will also accommodate for the particular cartridge height (which will change the stylus to pivot point distance) with a height adjustable locator pin mounted on the protractor. When using the new generation Lyra Delos or Kleos, the alignment protractor isn't really needed unless you want to perfectly align the cantilever to the protractor within the deviation of the screw diameter to the headshell slot spacing. Don't get me wrong, zenith is a critical alignment, but I find that visually aligning the cantilever to a protractor is usually only good for a consistent zero point from which to do the final dial in by ear. There is a patent on this locator hole system but the patent is really only to maintain a standard. I know that Allen Perkins invites all cartridge and tonearm manufacturers to use this system in an effort to standardize and make set up easier. Credit must be given to both Jonathan and Allen for their conceiving and executing on this system. It is in the spirit of furthering the art and not market competition. To answer the questions about the Centroid and azimuth stability, the goal was to significantly reduce the moment of inertia and therefor its effect on the cartridge cantilever/suspension system. It is a classic unipivot and the stability goal of the arm is actually in the name. Allen has designed the counterweight to place the center of arm mass at the pivot point (where the pin and jewel cup meet) . In other words, the arm functions on the centroid of the mass. (Centroid; def. - That point about which the static moment of all the elements of area is equal to zero) Of course, the center of mass will move relative to the pivot point depending on the position of the counterweight. The Centroid has a stainless steel counterweight that is quite heavy and wraps closely, forward, and low around the pivot point in such a way that very little movement is required to accommodate a wide cartridge weight/stylus pressure range up front. With the center of mass always located extremely (extremely) close to the pivot point, the moment of inertia is very low and the stability of the system, in all planes is very high...when the stylus is at the record plane. The very low and consistent moment of inertia due to the consistent proximity of the center of mass to the pivot point provides a system that allows for the use of low weight/high compliance and high weight/low compliance cartridges. I'm afraid I've already stepped over the boundries in my explanation so I had best stop here, and I'm sure I've just raised more questions than answered those above. There are a good many details beyond this description that I think are more appropriate for a manufacturer sponsored information site. Again, my apologies of I've come across as promotional.
cheers, Stirling Trayle

I failed to mention...
Mark Doehmann, Director of Research and Development at Continuum Audio Labs must be noted as well in regards to the concept and discussion that led to the stylus locator hole system mentioned above. I believe Allen, Jonathan, and Mark were sitting around after a trade show chatting about things analog and this was one result. Woulda been fun to sit in on that one...

Hiho, thanks for your comments. Regarding the alignment precision of the stylus locator system described above, I can assure you that it will get you very close. To use your ball park analogy, if the ball park stadium were a bulls eye with the pitching rubber being dead on center, this system will put you on the pitchers mound. From there, cartridge manufacturing variation will require you to find the rubber by ear.

The Centroid does have VTA adjustment, however it cannot be done on the fly. The set screw you see on top of the arm adjusts the the arm body position on the pin of the bearing (and is quite stiff to turn) so adjusting VTA does not alter the pivot point relative to the record plane. The distribution of the mass relative to the pivot point is critical in a unipivot and indeed if distributed incorrectly can exacerbate any resonance or record warp issues the arm has to deal with. For instance, if deliberately disturbed, the Centroid quiets down extremely fast due to the inherently stable nature of the distributed mass and it does not continue to rock. The azimuth is adjusted using a stainless set screw set into the side of the counterweight. The set screw is rather large, is set up high near the pivot point, and buries very deep into the weight . Like the heavy counterweight itself, it requires very little movement back and forth to accommodate any azimuth adjustment required. Damping is provided by using a silicone fluid pool with a variable height set screw to provide a wide range of damping effect, or none at all. On the Centroid model that mates to a Spiral Groove turntable (called the SG Integrated) the fluid pool is integrated (machined) into the arm board and the set screw is threaded into the arm body. For Centroid arms not bound for a Spiral Groove table, the Centroid Universal Integrated arm will have a very lightweight but stiff control plane that simulates the Spiral Groove armboard in function, providing the damping fluid pool, arm rest, mechanical cueing device, anti-skate support, and RCA block. The Universal Integrated is designed to be light enough to be mounted on lightly sprung decks such as the Linn LP 12. The Universal Integrated will mount with a single bolt and will have the facility to adjust the pivot point height to match the record plane of the turntable while still allowing for independent VTA adjustment, albeit it not on the fly. Mounting jigs and tools will be provided to dealers to ensure that the pivot point will be accurately positioned at the record plane of the particular turntable being worked on. The application of anti-skate force can also be a problem for a unipivot. The Centroid anti-skate is applied with a hanging weight connected to the arm body. Where the thread connects to the arm body is height variable so no matter where you have set VTA, you can always position the point at which the anti-skate applies force on the arm is centered at the pivot point and will not tug the cartridge out of azimuth. Additionally, the curve that the string follows is such that it tracks with the variable skating forces across the record and applies an equally variable and therefore uniform anti-skate compensation all the way across the record, which I think is pretty cool.

As far as i understand the design, forces on the cantilever are minimised during record warps and off center movement. This is controled by mass and not stiffness like in a conventional arm. The arm may look less stable when it tracks a record but when you look more carefully it followes the flow of he groove quite easily. Considering it´s delicate look it is surprisingly long. Effective length is 10.5", a good compromise between accurate tracking agle and stiffness. The materials are carefully chosen including the wiring, the solder and the plugs. Earthing and RFI rejection has been optimised.