Spiral Groove Centroid tonearm



Anyone has any experience with this new design? It has a rather brief rave review along with the Spiral Groove turntable in the latest Stereophile. It seems like an exciting analog product in recent years, along with Thales arms. Allen Perkins is a respected designer and I am intrigued by his tonearm design and wants to learn more about it.

From what I read, it's a unipivot design with a unique counterweight and bearing housing that concentrate most of the mass at the center pivot point, hence the name Centroid. I am also curious about how it deals with azimuth rocking in a unipivot design. Does it have a secondary ball bearing to stabilize torsional behavior like the Graham Phantom, Basis Vector, and Continuum Coppperhead, or the slightly different Nottingham and Simon Yorke? Or is it a pure unipivot with a spike and dimple? In unipivot designs, it is how the designer handles the azimuth rocking that truly shows the creativity. I'm surprised this tonearm has garnered much talk among the forum lurkers. If you know more about it, please contribute and discuss. Thanks!

Some pictures.
hiho
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.
Thanks for the posts here. And I agree no one is being promotional and I appreciate the all the info. What't the best websight for some more detailed pics?
Hi jfrech,
We have scheduled a photo shoot for the Centroid, but it has yet to take place. No photos yet. Sorry. They will be posted on www.spiral-groove.com when ready. Thanks for asking.

Stirling Trayle
Immedia

Judging from Stereophile's brief review, the Centroid's design features apparently have been rewarded in sonic terms; two distinct positive characteristics are low noise floor and accurate deep bass. Here's what Brian Damkroger has to say in the review in June 2010 issue.

"As I listened more, the characteristics that made the Centroid sound so different became obvious. First and foremost, it had no noise floor - not a dramatically reduced noise floor, but NO noise floor.... A second distinct and obvious characteristic of the Centroid's performance, and one new to me, was how accurately it reproduced the tonal and dynamic elements of deep bass notes."

Unipivot arms tend to sound quiet to me so I am not surprised, especially since the Centroid opted for a classic unipivot design with no secondary bearings (the chance of bearing chatter). And quality deep bass is something new in the unipivot genre as it traditionally have a less impactful bass due to the azimuth instability so I have to guess the centroid concept overcomes that. Very promising indeed.

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