Spiral Groove Centroid SG User Manual

Centroid SG Integrated Tonearm Manual

Thank you for your purchase of the Spiral Groove Centroid SG Integrated Tonearm. The Centroid
SG Integrated model is designed for use with with Spiral Groove turntables. As the name implies,
some functions, such as the arm lift, anti-skate support, and fluid damping, are integrated into the
Spiral Groove armboard. The Centroid Universal Integrated model is designed for use with all
other turntables and many of the arm mounting details are different in procedure than those
outlined in this manual. The discussion of the tonearm design below provides much useful
information for both model tonearms, but can be read before or after the installation and setup of
the tonearm. Those with some experience, and who are eager to get listening, may want to skip
directly to the setup procedures outlined on page 5, which will guide you easily to superior results.
Enjoy!

The Centroid unipivot tonearm

The Centroid tonearm design effort had two main goals. The first, and most obvious: to design a
tonearm that provides the best mechanical and electrical conditions for a phono cartridge to
transmit the signal from a record with the greatest fidelity and lowest noise. The second goal, and
one less frequently considered: to provide the simplest and most consistent means of setting up the
arm and cartridge in order to fully realize the performance capabilities designed in to the arm. As
a result, the Centroid is able to realize the greatest performance benefits in the greatest number of
turntable systems than any previous tonearm. The beauty of the design – its inherent elegance –
allows the basic elements to be understood in fairly simple terms.

A few words about the Centroid’s design...

The Centroid evolved from a holistic approach called Balanced Force Design™, which focuses on
preventing mechanically induced resonances from adversely affecting the music signal by
modulating the moments of inertia and in effect balancing the forces involved during playback.

Moment of inertia can be described as a body's resistance to angular acceleration. In the case of a
tonearm, the lower the resistance, or moment of inertia, the more effortlessly the cartridge is able
to respond to the normal record warps and the basic conditions of disc playback.

It might be easiest to think about the influence of these forces on the arm/cartridge system by
imagining holding a broom at the end of its handle, farthest away from the head or bristles. Your
ability to move the broom under precise control will be very difficult. The moment of inertia in
this case is high. The closer you move your hand to the head of the broom, the easier it is to
control, because the moment of inertia is being lowered. At a certain point, the broom will be
balanced at the center of the mass, or the centroid. At this point, the broom head is easiest to
control, because the moment of inertia is at its lowest.

The dynamic forces involved in controlling a broom during even the heaviest sweeping are not
nearly as complex as those found in the process of tracking of a microscopic record groove. In
order to achieve a similar level of control for a tonearm under those conditions, many unique,
even patent pending, features have been developed for the Centroid tonearm.

2

The tonearm uses a unipivot design. This means that the bearing assembly consists of a single pin
and cup. Taking advantage of this simple structure, the Centroid design puts the stylus tip and the
single pivot point of the unipivot bearing on exactly the same plane, contributing elementally to
the balance of the forces involved in the operation of the tonearm and drastically lowering the
moment of inertia.

Working in conjunction with this functional element, the patented counterweight takes further
advantage of the unipivot design by being able to wrap down and around the bearing in a way
that places the center of the arm mass, the centroid, at the optimal position in relation to the
bearing. With the optimal placement of the centroid, and the pivot point and stylus tip in the
groove being on the same plane, global moment of inertia becomes vanishingly low and the
stability of the system in all planes is very high.

The positioning of the mass relative to the pivot point is critical in a unipivot in order to take
advantage of its inherent virtues. Indeed if the mass is distributed incorrectly, it can destabilize the
tonearm as it reacts to any resonance or record warps. However, because of the strategic
distribution of counterweight’s effective mass, placing the centroid just below the pivot point, the
tonearm stabilizes extremely fast due to its inherently balanced nature, resulting in the extremely
linear dynamics of the tonearm. This is one of the reasons why the arm feels increasingly more
solid and stable as it is moved in to playing position, in that the balanced mass around the
unipivot bearing provides the essential mechanical loading and lateral stability the closer the stylus
gets to the plane of the bearing.

Additionally, the counterweight design allows for the most effective use of the widest range of
cartridge types: from low weight/high compliance to high weight/low compliance. Cartridges
weighing from 4 to 20 grams can be used without any additional counterweight. The micro­adjustable counterweight movement allows ultra-precise fine-tuning of tracking force. Similarly
precise in adjustment precision is the azimuth control, adjusted by using a stainless steel setscrew
on the side of the counterweight. This setscrew is set up high, near the pivot point, and buries
very deep into the weight. Like the counterweight itself, it requires very little movement to
accommodate any azimuth adjustment required, while its position further contributes to
maintaining system stability through its close relationship to the centroid of the arm and the plane
of the record.

The single bearing is composed of a complimentary set of Swiss sapphire jewel cup and bearing
pin matched for “Zero Tolerance” precision. This builds upon a unipivot’s inherent advantage in
providing a direct-coupled low impedance energy path from headshell to bearing for superior
control of resonances. The design of the Centroid’s VTA adjustment mechanism takes further
advantage of a single point bearing by allowing for the raising and lowering of the arm without
altering the relationship of the pivot point to the record plane. A setscrew on the top of the arm
that is easily accessed adjusts the VTA. However, the screw is quite stiff to turn, for performance
reasons, therefore does not allow for adjustment “on the fly.”

The patent pending anti-skate system is equally unique. It may not be well known that skating
force during playback is not constant. The design of the Centroid’s anti-skating force mechanism
addresses this fact, in that it applies the exact inverse force to the skating force in order to position
the stylus with uniformity in the groove regardless of its position on the record.

The anti-skate force is applied using a weight hanging from a string and connected to the arm
body through a precisely positioned guide system. Sapphire ring jewels, inset at contact points in

3

the mechanism, allow for frictionless system function. The point at which the thread connects to
the arm body is variable in height; so, no matter where the VTA is set, the point at which the anti­skate applies force on the arm is centered within the mechanism.

The point where the string and guide mechanism are centered is also the precise height of both the
platter and the bearing, thereby applying the anti-skate force on the same plane and in balance
with the major elements of the tonearm; this can easily be seen by laying a ruler on the platter and
gauging the height of the string. The result is that the anti-skating mechanism will not misalign the
azimuth setting and further contributes to the stable dynamics of the arm.

Additional design elements that contribute to controlling system resonance include a carbon­wrapped aluminum arm tube, yielding the ultimate in lightweight, rigidity, and damping
characteristics. An adjustable silicone fluid damping system helps further to control system
resonance.

Even the cueing mechanism is designed for superior control, in that its undamped, direct,
mechanically controlled action combines with stable horizontal positioning for greater precision
when placing the stylus in the groove.

The same level of attention to the mechanical elements of the tonearm has been applied to the
electrical elements. A custom wire harness of ultra-low-mass GrooveLine wire connects directly
to Eichmann RCA connectors, for maximum signal transfer and low noise. The wire itself is
composed of 68 individually insulated 50-gauge wires. The reasons for using a wire of this
configuration, known as “Litz”, and size are two-fold. The first is that the Litz configuration
reduces electrical resistance due to the increased overall surface area relative to diameter. The
second is that mechanical resistance is reduced due to the wire bundle’s extremely low mass and
inherent flexibility.

A few words about Centroid installation…
Unless properly installed, aligned, and adjusted, the features outlined above for the Centroid

tonearm would never realize their potential for providing superlative performance. To make the
setup of the tonearm both easy and effective, a patented alignment system provides precise fine
adjustment of overhang, VTA, azimuth, and zenith.

The use of this system will result in a setup that provides a better alignment of the tonearm than
most people are capable of, unless they have extensive experience in turntable setup. This, in
effect, gets the setup in the bull’s-eye. However, getting the setup to the very center of that bull’s­eye – those final fine adjustments necessary to wring the absolute best from any system – must still
be done by ear. There is no substitute for this final step.

The alignment system tools consist of an etched mirror alignment protractor, a guide base, and a
locating pin. Additionally, there is a patented locator pinhole in the headshell that is precisely
above the point where the stylus will be positioned. These simple elements form the tool used to
set up all major alignment parameters.

The advantage of a mirrored protractor is that it has depth, or is three-dimensional, which provides
alignment precision impossible with any two-dimensional tool. Etches on the glass face of the
mirror correspond to reflections on the silvered surface under the glass. Similarly, the cantilever
corresponds to its image in the mirror. Aligning the cantilever not only with the etched lines but
also with their reflections assures that you are able to find the precise viewing point from which to
gauge alignment accurately.

4

Put another way, two-dimensional protractors can actually allow for misalignment, while a three­dimensional protractor allows us to use parallax view to see any error in viewing position – first
the image of the etch mark has to be aligned so there is one line, not two – one at the surface and
one below the surface; then when these two elements are correctly aligned, the cantilever must
cover both the combined etches and its reflection in the mirror. These four elements need to be
aligned – the two etched images and the cantilever and its image in the mirror – in order to
achieve proper alignment of the cartridge.

The patent pending stylus to pivot point locator pinhole on the headshell deserves further
discussion. It works in a few ways to aid alignment. First, to determine cartridge height, the guide
base and locator screw is inserted into the protractor, and the protractor is placed on the spindle of
the platter. The cartridge is then put on its back next to the guide, and the locator screw is then
raised or lowered so that the screw’s shoulder is at the same height as the stylus tip. From here,
the locator pin serves to locate the protractor in the correct position to adjust the overhang of the
cartridge. This is accomplished by rotating the protractor from the spindle so that the locator pin
can be inserted in to the headshell pinhole. Once the pin of the guide is in the pinhole, the
tonearm can be leveled, based on the predetermined cartridge height, by raising or lowering the
back of the arm, using the VTA adjustment screw, until the tonearm tube is level.

At this point, the cartridge is installed, with overhang and zenith adjustments being made using the
protractor. Adjustment of overhang involves positioning the stylus tip on the appropriate spot on
the protractor.

Note: When using the new generation Lyra Delos or Kleos cartridges, overhang is even simpler to
achieve, in that these cartridges have pinholes in the top of their bodies directly above the stylus.
So, overhang adjustment is simply a matter of removing the locating pin from the base and
inserting the pin through the pinhole from the top of the headshell. Then the pin is inserted into
the pinhole of the Delos or Kleos to determine overhang. The cartridge is then rotated around the
pin to adjust for zenith.

Whether using a Lyra or other cartridge correct zenith is achieved when the cantilever is aligned
with the etched line on the protractor that runs under the tonearm. When adjusting for zenith with
other cartridges, care must be taken to maintain the overhang previously determined using the
protractor.

It must be noted that while there is a patent on the arm’s stylus point locator hole system, the
patent is really only to maintain a standard. All cartridge and tonearm manufacturers are invited to
use this system in an effort to standardize and make all tonearm setup easier. Credit must be given
to both Jonathan Carr of Lyra and Allen Perkins of Spiral Groove for their conceiving and
executing this system. It is done in the spirit of furthering the art and not market competition.

A few final words about the resulting application of these design elements…

When both the design elements and the setup tools are brought fully into play, the result is a noise
floor lower than that achieved in any other tonearm, allowing for inner details to be revealed in a
coherent way as of yet unheard. This means that virtually any cartridge can be used in such a way
that its fullest potential is realized and that the system, and a record played on it, performs at a
level that provides greater involvement and enjoyment.