Spiral Groove Centroid tonearm

Thank you so much for the write up, Mr. Trayle. No apologies needed. That's the kind of info I was looking for and it couldn't be better. You managed to talk about all the design features without lapsing into even one sentence of pornographic sonic description. Bravo! You have no idea how sick I am reading reviews about how "neutral" or "musical" a device is without any analysis of its function and mechanics. Just for that, I applaud you.

The said alignment arrangement is a great idea and I wish more manufacturers can adopt that in the future and, hopefully, it can be standardized among cartridge and tonearm makers. ANYTHING getting the alignment close to the ballpark is better than nothing. All it takes is two tiny holes, one on the headshell and one on cartridge body. Hey, why not!

Thanks for the explanation on the centroid concept applying to the arm pivot. Does the arm still retain the design feature in the Immedia arm like adjusting VTA WITHOUT moving the pivot point? Judging by the picture, the set screw in the middle of the bearing housing appears like such mechanism. I always find that a very unique feature in the Immedia arm, even though the VTA obsessives might complain about the lack of on the fly adjustment - not surprisingly they are usually unipivot users because, I believe, typical (not all) unipivot arms inherently require mass below center of gravity to be stabilized and its pendulum effect can affect VTF, hence sensitive to VTA adjustment. The Centroid concept probably helps in that department. Does it have VTA on the fly adjustment, then? No big deal to me, I rather be listening to records than constantly fuzzing over VTA. Speaking adjustment, how is azimuth adjustment achieved? Another question is damping. Does it have fluid damping like the Immedia or any damping at all?

Don't worry about being promotional. I am sure prospective buyers are more than happy to find out all the design features than not. Your write up is professional, informative and, to me, educational. Thank you for your time.

I am tickled by the story that a bunch talented designers from competing manufacturers sitting around "chatting about things analog" and coming up with ideas that can benefit audiophiles "in the spirit of furthering the art and not market competition." It is this spirit I wish to see more in the forum world.

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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