Spiral Groove • Centroid Tonearm

A fresh approach to unipivot-tonearm design.

by Dennis Davis | July 26, 2013

electing a tonearm is treacherous business. First, you need to choose among 9", 10" and 12" 'arms and thereafter consider the availability, method and ease of adjustment for such things as VTA, tracking force and anti-skating, which vary radically from one design to another. With all of these choices comes almost certain user error and frustration. There are many ways to screw up tonearm alignment and optimization: initial spindle-to-pivot distance, tracking force, tracking angle and azimuth all seem to exist for no better reason than to act as barriers to extracting your money’s worth from a tonearm -- any tonearm. Manufacturers have come up with an ingenious number of ways to approach and solve each of these mysteries, and at an increasingly wide price spectrum. The median for today’s high-end tonearm market is the $6000 range. There are some very accomplished 'arms for half that amount or less, a few in the $15,000 range and even one new 'arm introduced at the stratospheric price of $35,000. In the middle are a handful of tonearms that set a very high bar. Among those fighting for attention is the Spiral Groove Centroid.

Allen Perkins, the designer of the Centroid, has been building turntables and tonearms for decades. He began his audio career with SOTA in the mid-1980s, and a few years later he designed the Immedia RPM 'table and 'arm. In 2005 Perkins formed a partnership with Lisa Thomas under the name Spiral Groove, which sells a range of audio products. But Perkins’ real passion is reserved for his two Spiral Groove turntables and the Centroid tonearm. The name Centroid sounds like it could be a character from a Star Wars sequel. This impression is heightened by the 'arm's unusual high-tech appearance. The less prosaic truth is that Centroid is a term from physics and geometry referring to the geometric center of an object’s shape, which nicely signals Perkins’ design goal.

The Centroid is clearly cut from a different bolt of cloth than most tonearms. It is petite compared to many, incredibly compact (concentrated might be a better word) and almost painfully minimalist, with none of the usual tower assemblies, adjustable knobs and heaps of massive counterweights. At first glance, the Centroid almost appears to lack some standard tonearm adjustments, but closer examination reveals that they are merely hidden from view. This unique appearance is fundamental to Perkins’ design brief, which he calls Balanced Force Design (BFD). This is a comprehensive philosophy for the design and manufacture of Spiral Groove products that takes into account both performance and usability. The Centroid is a unipivot design using a sapphire jewel cup and hardened steel pin, with the bearing interface situated in the same horizontal plane as the stylus resting in the record groove. The counterweight looks small compared to that of other tonearms because the design slings the mass lower, as close as possible to -- and even forward of -- the pivot point. This allows for a low moment of inertia that, according to Isaac Newton, should keep the stylus in the groove under the most complex musical passages.

The Centroid allows for vertical tracking adjustment, but not on the fly. Instead of the more familiar tower-and-knob arrangement, which accommodates adjustment while playing music, the Centroid offers a "set once" solution. A hex wrench is inserted into a hole recessed in the top of the bearing assembly. Turning a very stiff adjustment screw clockwise will raise the 'arm body or lower it if turned counterclockwise (an arrangement identical to the VPI JMW, where it is used to match the "height" of different armwands). The minimalist design and stiff adjustment are intentional -- the Centroid has the bearing fixed at record level as a major part of its design. Tower VTA adjustment moves the entire bearing to change VTA, thus defeating one of Perkins’ design elements. Perkins also prefers the least number of parts and the least number of connections. The stiff adjustment resulting from all this minimalism is said to add to the efficient transfer of energy starting at the headshell, through the tight bearing and down the bearing shaft.

There are two versions of the Centroid. The original uses a base that is made for installation on an almost camera-lens-like bayonet mount incorporated into the top-of-the-line Spiral Groove SG 1.1 turntable. This version also fits the SG 2, in which case it uses a spacer instead of the bayonet mount. The universal version of the 'arm, reviewed here, uses a slightly different base that works with almost any other 'table. With either base, the tonearm is simply lowered into place and a terminal block holding Eichmann RCA connectors (hardwired to the armwand) is attached to the back of the base. Each base also has a recessed trough for optional silicone damping fluid. The tonearm carries a screw that can be turned down to contact the fluid (or not). Each base also has an identical undamped cueing mechanism.

The universal Centroid includes a spindle-to-pivot jig that defines the appropriate place to drill the 27mm hole for insertion of an 'arm-mounting collet that will lock the post into the plinth. The spindle-to-pivot jig is then placed over the spindle at one end and the bearing post at the other, and the critical spindle-to-pivot distance is fixed by locking the collet assembly into place within the slightly oversized 27mm hole, an arrangement that eliminates any inaccuracy in drilling the large mounting hole. The next step is to lock in the height of the arm base so the bearing is exactly level with the LP playing surface. Next is cartridge alignment, which is relatively easy using the supplied mirrored alignment gauge. Perkins developed (and patented) a system for easier and quicker mounting of phono cartridges: a tool that fits into the included alignment gauge and connects, via a pin, to a hole in the headshell. This allows the user to situate the gauge in the perfect location in just a few seconds.

Perhaps the most difficult adjustment to make with the Centroid is setting the anti-skating force. This consists of a string with a weight on one end and a loop at the other. Various weights are supplied to match different cartridge weights. The loop at the end of the string slides up and down a vertical post and is held in position (at the record groove height) with tiny rubber grommets. The difficulty comes from squeezing fingers into such small spaces. A little patience and a pair of tweezers are all that's needed for an adjustment that must be made only once if done right. Other adjustments present less of a challenge. A thumb dial adjusts vertical tracking force, while azimuth is adjusted with a large horizontal setscrew on one side of the counterweight.

One of the first things you will notice about the Centroid is how small and delicate it appears to be. It’s a 10" tonearm, so it’s not the length that is responsible for leaving this impression. Because the design of the 'arm aims to place as much of the moving mass as close to the pivot point as possible, it follows that the overall length of the 'arm is likely to be shorter -- on both sides of the pivot. Most other unipivot 'arms place a chunk of metal over the pivot point to mass-load the bearing and then counterbalance that mass with another chunk of metal hanging off the back. With the Centroid, these two weights are replaced with a single movable weight, allowing a "composite" position as close to the pivot as possible. What makes this concentration of weight possible is the use of a lightweight carbon-wrapped aluminum armtube, looking much like that of the Graham but even more slender in appearance. The lower the mass of the armwand, the smaller the counterweight required. Compared to the man-of-war armtubes used for 'arms like the Kuzma 4Point or SME Series V, the Centroid is positively dainty. When you first work with the Centroid, its compact dimensions and delicacy can seem a bit daunting to the butterfingered.

Unlike that of many tonearms, the armtube of the Centroid has parallel sides along its entire length, making sighting easy. When someone tells you to set VTA by starting with the 'arm horizontal to the record surface, it’s handy to have a horizontal sight line to work with, and the Centroid is one of the few 'arms that supply it. This makes initial setup for VTA a snap, compared to tapered or stepped armtubes.

listened to the universal version of the Centroid installed on a VPI TNT-6 and then, after taking its measure, I moved it to a Spiral Groove SG 2. It performed brilliantly on both 'tables. I experimented with the damping and found that applying too much had a major detrimental effect on the sound, robbing it of much of its magic. The pace of the music became elongated and the dynamics collapsed. Allen Perkins prefers the sound of the 'arm undamped, but commented that others have preferred it with some damping. I found the 'arm to sound best when the screw head just barely broke the surface tension of the damping fluid.

Properly set up, the Centroid settled onto the vinyl with a sense of stability that is unusual in my experience for unipivot tonearms. Unless a unipivot 'arm is heavily damped or has some other trick going for it (like the multi-pivot of the Kuzma 4Point) you’ll almost always see a slight wobble as it contacts the record. The Centroid’s stable descent into the groove is assisted by the very effective cueing mechanism that drops the stylus with great precision. Then, when everything is dialed in perfectly, its low-slung design delivers amazingly quick, almost unnoticeable stabilization as the stylus settles into the groove.

That stability carried over into the 'arm’s sound. It was as though the stylus was locked in to the groove, the sonic effect of that intimate contact being immediately apparent. It only took a few bars of familiar music to appreciate this 'arm’s amazingly low background noise. When the musical backdrop was quiet to begin with, the Centroid played it back as inky black. Quiet backgrounds produce a dramatic increase in dynamic range, and with the Centroid the dynamics were immense and the slam palpable. Along the same lines, and as you might expect given the stability and superior dynamic range, the Centroid presented an extremely tightly focused image, devoid of the textural smear or grain so obvious with other tonearms.

These attributes applied across the board, with every record I played, but they were more pronounced with certain types of music. The pitfall of high resolution is that when something is not just right under normal conditions magnification of the problem makes the defect less bearable. One case in point: early stereo recordings where some of the instruments are panned hard right and some hard left, with little in the middle. With tonearms that deliver lower resolution, the hard edges of this artificial and exaggerated placement may not be quite as evident, the presentation more forgiving than the Centroid’s stark view of reality. One early jazz classic that exhibits this failing is John Coltrane’s My Favorite Things [Atlantic 1361], a recording that always sounds dreadful in stereo but comes to life in mono. A recent stereo reissue by ORG Music [ORG Music ORGM-1080] made for instructive listening with the Centroid. While the audiophile, 45rpm, Bernie Grundman-remastered pressing cleaned up the tonal anomalies of the original stereo pressing, it did nothing to fix the left/right/center image locked within the stereo master tape. With the modest amount of image smear introduced by many tonearms, the stereo image of this LP is almost bearable. Introducing the Centroid into the equation, however, not only locked in image stability, but also locked the listener into the straightjacket of miniaturized instruments stuck in a single speaker. So if you are looking for a more benign tonearm to smooth over the imperfections of less-than-perfect recordings, one that will smooth over the rough spots, this may not be the one for you.

On the other hand, the Centroid excelled at pulling out hitherto unknown detail in good to excellent recordings, detail that was lost to the average cartridge/tonearm/turntable combination. While I found this applied to virtually any recording, it was most recognizable with either large-scale orchestral pieces or rock music with amplified guitar and drummers on steroids. As I am addicted to both of these, I found myself surfing through a whole swath of LPs, accumulated over decades of collecting, that no previous tonearm/cartridge combination had been able to unveil successfully. Over and again I found myself remarking on lyrics hitherto misunderstood or hearing orchestral detail previously lost in the mix.

But the most remarkable demonstration of the Centroid’s abilities showed up with several small-group acoustic recordings. While this 'arm delivers lightning-fast dynamic response, deep bass, a black background and spot-on tonal reproduction, it was these small acoustical groups that revealed perhaps the most important strength of the Centroid: the ability to deliver notes on time and with such precision that the recordings were put into focus, delivering the size, shape and spatial relationships of closely spaced instruments from an effortlessly natural dynamic and stereo perspective.

I have listened to Pete Townshend and Ronnie Lane’s Rough Mix [UK Polydor 2442 147] more times than I can remember since the late 1970s, and it sounds pretty amazing on any optimized front-end, even those with modestly priced components, so much so that with each improvement in my analog rig I’ve become increasingly certain that Rough Mix can’t really get any better. The first time I listened to it with the Lyra Atlas was just such a moment. Yet the Centroid edged the bar up a couple more notches.

But the epiphany came as I cued up one of my favorite test records -- one with only two instruments. I was not prepared for what I heard with This One’s For Blanton with Duke Ellington and Ray Brown [Pablo 2310-721]. With only piano and bass to capture, you might think this recording presents a system with a fairly simple acoustic to get right. I mean, how hard can it be to reproduce something this clear? Over the decades, I’ve owned the Pablo original, along with a 33rpm reissue from Analogue Productions, and a 45rpm reissue also from Analogue Productions released some years back and now sold out. Again, this is a record that sounds pretty good in any pressing -- as long as you are playing it on a well-tweaked system. TOFB is super-critical when it comes to both system setup and component quality (thanks to analog swami Roy Gregory for alerting me to this). As things improve, the relationship between the instruments on both the temporal and spatial planes improves. Every cartridge, turntable and tonearm I have heard this record through presents a different version of the relationship and shape of the two instruments. But when I listened to the LP with the Atlas mounted on the Centroid, the music completely shed all audiophile credentials or markers for the first time. Instead it simply sounded like two great musicians playing real instruments right there in my room.

hen I first heard the Lyra Atlas I thought that it marked such a huge, such a fundamental advance in record replay that I’d be safe from upgraditis for years. Sure, I knew that I could eke out a few incremental improvements with some super-expensive and imposing turntables and exotic 'arms, but at what price? Having heard the Centroid mounted on VPI and Spiral Groove 'tables, I can answer that question precisely: You get way more than incremental improvements. What the Centroid demonstrates is that a reference-quality tonearm (it is among the very best of these) is essential if you are to extract everything that a topflight cartridge has to offer. I’d never appreciated just how musical my LP collection was until now, and I won’t be letting go of this tonearm anytime soon. In fact, I’m pretty sure that someone has put Loctite into the threads of the mounting bolts and headshell screws. No, really!

The Centroid may not offer all the creature comforts of some 'arms, such as easy VTA adjustment or interchangeable armwands (the bayonet mount on the SG 1.1 takes care of that -- at the price of a second 'arm), but what it does right is so compelling that I don’t notice the lack. Let me just ponder the meaning of that while I play another record.