The Abis SA1 9.4″ Gimbal Tonearm

News:  You can find Art Dudley’s review of the updated SA1.2 here.

Dealers:  You can hear and purchase arms from these fine dealers/builders.

I am offering special pricing on Yamamoto Sound Craft headshells to existing and future Abis owners.  The Yamamoto HS3, weighing a little over 8 grams, is a perfect headshell for the SA1.2, especially for medium compliance cartridges, like the Grados.

The SA1.2 was added to Stereophile’s Class A list of recommended tonearms in the April 2016 issue.

The SA1 was revised, and replaced by the SA1.2.  The arm features improved bearings and geometry.  

The sound of the Abis SA1.2 tonearm is powerful and engaging.  Due to its substantial construction, cut from billet aluminum, and fastened together with great care, there is virtually none of the resonance associated with S-shaped arms.  In contrast to classic tonearms from the past, which suffered from resonance and irregular bearings, the SA1.2 provides the ideal mass for a cartridge like the Denon DL103 or Ortofon SPU (also, mono cartridges like the DL102, or even antique cartridges like the GE VR and Fairchild). 

The weakness of low mass tonearms is that they make poor matches for medium and low compliance cartridges.  The Abis SA1.2 gives you precise radial-bearing performance and low resonance, while providing the necessary mass for medium and low compliance cartridges.  

Key to the performance of the SA1.2 and SA1.2B is the use of very high grade ball bearings. Bearings used for horizontal movement are axial-loaded, angular-contact, thrust-bearings. These thrust bearings have zero play and are held in contact by gravity.  You can think of them as acting like a unipivot, but with more than one contact point.  Because they have two tapered seats, they will self-align in the presence of a load (gravity), have exceedingly low moving friction and are especially suited to angular and axial loads.  

The angular error needed to misalign these special bearings, commonly used in high precision machinery, are so severe that they fall well outside the operating conditions for a turntable (if you need an arm for playing in zero gravity, or turned at 90° to earth’s gravity, you will be forced to use a different style of tonearm).  Traditional deep-grooved ball-bearings are not specifically designed to take an axial load, being better suited for radial loads like a wheel bearing, and they suffer from much higher rolling resistance.  While the quality of the bearing materials are a key to success, the proper choice and loading of bearings is just as important.

Also key to the performance of all tonearms, and especially the SA1.2 and SA1.2B, is the resonance characteristics of the arm “tube”.  The SA1 design is built from four pieces of billet aluminum, milled to tight tolerances, finished, fitted by hand, and torqued to settings determined by experimental observations.  The torque values chosen introduces preload on the fasteners, and produces hysteresis stresses (basically, inner friction) in the crystalline structure of the metal.  These stresses damp vibration by forcing the crystalline structure to be more tightly bound, than when in a free state.  The elastic and anelastic properties of all four pieces are slightly different, preventing dominant acoustical nodes from developing.

When properly machined, fitted and torqued, a unit composed of several milled pieces will have lower maximum resonance, with several smaller resonance frequencies, compared to an armtube composed of one piece.  These statements are backed up by scientific study into weapons systems, rockets, engines, structural elements, etc..  Resonance is a key source of failure, and the research proves the point:  a single piece of billet material can have 1~3 dominant resonance frequencies, with one resonance frequency dominating the performance of the structural member. If you think about the bars that form the notes on a xylophone, you will have a practical understanding of the limitations of “one-piece” arm tubes.  In practice, a combination of surface finish, damping materials, shape, density, alloy, crystalline structure, fastening technique, and fastener preload, among others, will determine the relative distribution of acoustic energy in a tonearm.  Since extremely dense (heavy) materials, like depleted Uranium, don’t easily lend themselves for use in tonearms, a holistic approach is necessary.

For a more thorough, and scientifically correct overview, you should start with this paper from Los Alamos. 

The rectangular shape, the tight assembly by hand, and the nature of billet aluminum creates a low-resonance design that is essentially quiet.  The preference for 12″ arms has more to do with compliance match, than the theoretical advantages of a 12″ arm (which are nullified by the use of a spherical tip).  The SA1.2 and SA1.2B maximize the possible geometry at 9.4″, while excellent damping and high mass give it the tonal balance of 12″ arms.  With the SA1.2 and SA1.2B, the tracking error is very low, while the superior sonic signature of the billet aluminum arm parts, and the mass equivalent to most 12″ arms, gives 12″ arm sound in a compact form.  It is ideally suited for low to medium compliance cartridges, especially those that are particularly problematic when it comes to mistracking.  

Abis SA1-2 Geometry

One thing not always stated in tonearm literature is whether the tonearm in question uses the Stevenson, Baerwald or Lofgren geometries.  In many cases, older arms adhered to the Stevenson standard.  The theory behind the Stevenson alignment is that it lowers distortion on the inner grooves, which are often the most challenging when playing symphonies/operas/soundtracks etc..  Since then, there was a sea change.  Pop and rock outsell classical several hundred to one.  In light of current trends, the Baerwald geometry works better for many pop disks, which tend to have high levels of modulation in varying areas (at the discretion of the producer and group, the loudest track could be anywhere on a disk).  

Since there is no correct answer to this question of geometry, the Abis SA1-2 geometry was chosen to fall at a point between Stevenson and Baerwald (Lofgren A).  You can adjust the overhang to make the arm perform more like the Baerwald (Lofgren A) or Stevenson geometries, if you desire (see below).  Here are the results using the supplied protractor, assuming the spindle-to-pivot distance is correct:

Here are the actual projected distortion levels:

This shows that the SA1.2 is comparable to the standard curves.  It does, however, require the Arc Protractor to get the lowest possible distortion from the arm, and actually line up to the custom geometry chosen by Abis.

One other thing should be noted.  By slightly changing the overhang of the cartridge, the geometry can be made more like Stevenson or Baerwald (Lofgren A).  I experimented with minor changes in overhang and came up with some interesting results.  

[gview file=”https://mockingbirddistribution.com/wp-content/uploads/2015/09/SA1.2-Overhang.pdf”]

An important thing to remember is that unless your arm exactly matches the geometry of a given generic protractor, the generic protractor might cause noticeably higher distortion.  Generic protractors can use any popular alignment, or even use a custom alignment.  You should know if your arm is compatible.  If you go to Vinyl Engine and input your tonearm’s specifications, and they do not exactly match Stevenson or Baerwald, and you don’t have a factory supplied protractor, you should have a custom arc protractor made.  This is why I supply the Accutrak Protractor with Abis tonearms.

As a value added feature, and to accurately adjust your new tonearm, all Abis arms will come with an Accutrak arc protractor.  Click below to see the details.

[gview file=”https://mockingbirddistribution.com/wp-content/uploads/2015/09/Abis-Accutrak.pdf”]

Specifications

Custom made in Japan for SIBATECH, Inc., Tokyo, Japan