Tip #31 (posted 11/25/01)
The Kuzma STABI Reference Turntable and the Graham 2.2 Tonearm
This is the third in a series of articles focusing on Components of Exceptional Merit, many of which figure prominently in my current reference system.
As I survey the past 40 years of analog audio, it is surprising to discover just how few turntables have withstood the test of time. Some were gorgeous looking, others captured our fancy by promoting a new technological wrinkle such as an air bearing, but in the final analysis it is clear that while many turntables talked the talk, only a few delivered the goodies. The problem was that only few designers had a clear vision of the engineering requirements for a good sounding turntable. Despite the commercial success of the British school of turntable design as exemplified by the Linn LP-12, it is still wrong to use a boxy base or plinth directly underneath the platter. Well, that covers about 99% of all the turntable ever sold. Fact: boxes produce resonances. Fact: resonances can be and often are transmitted to the stylus. Ideally, the phono cartridge stylus should only respond to the groove modulations. In reality, the stylus acts like a seismograph. It cannot distinguish between groove wall modulations and resonant energy from the arm, subchassis and motor vibrations, foot falls, or little junior banging on the wall. Looking at it from the stylus's vantage point, turntable design boils down to minimal vibration as in a high-quality motor and belt drive, stable platform as in minimal play bearings for the platter and speed uniformity, effective damping as in an acoustically inert platter, and effective isolation from external vibrational energy such as foot falls. Linn made a nice living off the LP-12's precision bearing, others excelled in one or more design aspects, but almost no one nailed all of these requirements once and for all.
The Kuzma Stabi Reference turntable joins my personal pantheon of the greatest turntables of all time. Kuzma Ltd. first started production in 1982, ironically right around the time the first CD players rolled off the production line. Its progenitor, Franc Kuzma, parlayed his interest in music, mechanical engineering education, and working experience with acoustic transducers, toward manufacturing a high-quality vinyl playback system. The Stabi Reference (SR), introduced in 1990, is based on solid engineering principles and an integrated vision of optimizing the essential mechanical and vibrational issues at the crux of good turntable performance. It is laid out in an open architecture and is built up entirely of a thick sandwich construction of two aluminum plates separated by acrylic, clamped together with pre-stressed, non-magnetic, stainless steel screws. And I mean everything: the base, subchassis platter, and even the arm board. This type of constrained layer damping is extremely effective in minimizing flexure and damping resonances. The overall thickness of the base and subchassis are an impressive 1.25 inch. After all, this is not a question of overkill. Keep in mind that typical groove modulations are minute, on the order of 0.00001 mm. It is therefore essential that the subchassis, carrying the platter bearing and tonearm base, be rigid and non-resonant. Any flexure here will change the position of the platter relative to the playback stylus.
The subchassis ( top plate) is suspended by four large springs submerged in silicone oil. The suspension is tuned to a resonant frequency of 2.2 Hz, which is within what is considered to be the optimum tuning range of 2 - 3 Hz. The reason for this is that suspension must resonate above the rotational speed of the turntable and below the tonearm/cartridge resonance. The former, even for a rotational speed of 45 rpm, represents a vibration less than 1 Hz, while the arm/cartridge resonance is typically in the range of 8 - 12 Hz. A tuning on the order of 2 Hz allows the table to resonate in a range that is not affected by the motor and feeds no energy into the arm resonance. It also proffers excellent immunity from structurally transmitted vibration, except of course for earthquakes and asteroid strikes. The spring compliance together with the mass provided by chassis, platter, tonearm etc., act as a low pass filter. This means, that the system filters out vibrations from reaching the chassis that are higher in frequency than the resonance of the system. However, vibrational energy in the range below the resonance of the system is allowed to pass. At resonance, vibrational motion is maximum so that damping must be provided to control movement. Hence, the silicone oil bath which dampens vibrations of the springs themselves.
The base (bottom plate is supported by three aluminum and stainless steel spikes. The top plate is easily leveled using four knobs, one for each spring tower. When this plate is lifted (for transport), the silicone suspension reservoirs are automatically sealed.
The drive system is based on the classic belt drive principle, but uses two motors in a diamond configuration for increased torque and drive stability. The heavy platter (8 kg) rides on top of a subplatter. Ideally, the drive bearing should possess zero friction, be noise free, and totally stiff so as to only allow rotational movement without any wobble. In practice, how closely these ideal performance characteristics are met depends on maintaining close tolerances in the manufacturing process, Remember: loose or cheap bearings are guaranteed to doom turntable stability. The SR bearing is of the inverted type and uses a ruby ball and an oil bath for low friction. The power supply is housed in an external enclosure and incorporates precision quartz-locked speed control, and two 20 watt power amps for drive signal amplification. Drive speeds (33 and 45) are selectable from the front panel of the power supply.
The platter is covered with a mat of the correct hardness to provide a proper acoustical impedance termination for the vinyl record. Vibrational energy punched into the vinyl by the stylus is transmitted to the mat and is dissipated resistively. A well thought out record clamp is included, which ensures that the vinyl is tightly coupled to the mat. Since almost no record is perfectly flat, it is bound to rattle during playback – unless a hold-down system is provided.
The Graham Model 2.2 Tonearm
To understand what the model 2.2 is all about one has to start with the model 1.5, which first crossed my path many years ago. To quote from my original review of the 1.5 in Stereophile Magazine: "To fully understand what the Model 1.5 arm is all about, one has to start at the very beginning, at the genesis of the concept, with the sparkle of inspiration in Bob Graham's mind. It is next to impossible not to like Bob. His friendly demeanor puts one at ease, and his care and love for the art bubble forth. His design is fully accessible to open discussion. There is no mysticism or classified industrial secrets to get in the way. The 1.5 is first and foremost a distillation of the best design ideas the art has produced over years -- executed with care and engineering precision. Of course, there are some new wrinkles here, covered by no less than two US patents, but the foundation is sound engineering practice aimed at providing the most perfect operating platform for a phono cartridge achievable at the current state of the art. The basic design was refined over a period of several years to yield what is presently in my estimation the finest tonearm money can buy." With the hindsight of about a decade, it gives me great pleasure to extend this assessment to the model 2.2 tonearm.
To appreciate the role of the tonearm in phono playback, it is useful to consider matters form the perspective of the cartridge. Seen from the cartridge, the arm is essentially a "monkey on the back." While the stylus is attempting to negotiate delicate groove modulations, the cartridge has to literally drag this monkey kicking and screaming down the groove spiral. Bearing friction at the arm pivot, sufficient to impede the motion of the cartridge gives rise to distortion because frictional forces along the groove wall increase as a result. Thus, low bearing friction is an automatic prerequisite for a good arm. Another essential element is bearing tightness to minimize chatter. As the arm rattles, its motion directly impacts phono signal amplitude and frequency. Unfortunately, for conventional bearings of the gimbal or ball-race design, the requirements of low friction and tightness (no chatter) are contradictory and some compromise must be struck between the two. In other words, the tighter the bearings, the greater the friction, and vice versa. This is where a well-damped unipivot design, as featured in the Graham tonearm, really shines.
The new Graham 2.2 improves the dynamical performance of the 2.0 by introducing a re-engineered and refined pivoting system. The good news is that owners of Graham 1.5t and 2.0 models can easily upgrade to the new bearing system. The procedure is simple. Unscrew the cap of the old bearing assembly and replace it with the new 2.2 brass bearing cap. The cost of the upgrade is $300. The mechanical effect of the new pivot system is to raise the center of gravity of the arm even further above the pivot point. On some arms the pivot is located below the arm's center of gravity in what is known as a "stable static balance." The analogy suggested by Bob Graham is that of a high-wire artist balancing himself with the use of a large pole which bends at the ends to well below the plane of the wire. The pole confers stability by lowering the center of gravity below the "pivot point," which in this case are the artist's feet. Any tonearm so balanced, has a more difficult time navigating record warps. That's because once the arm is knocked out of balance by the warp, the arm attempts to steer back to stable balance irrespective of what the dynamical situation demands. And vinyl is definitely a warp magnet. A perfectly flat record only exists in audio legend. The 2.2, offers superior real-world performance, as it is able to stay in the groove, in the proper alignment, under greater g-force accelerations.
Terse setup instructions are provided for the SR. Although the table is easy to assemble and adjust, the addition of a few photos in the instruction manual would have made the whole assembly process go more quickly. As is the case in any architectural project, providing the proper foundation is also critical for a phono system. The base plate should be sited on a stable, non-resonant platform. I used an old Arcici Lead Balloon isolation stand, with the lead on the bottom, and a Bright Star Audio (http://brightstaraudio.com/) sand-filled isolation platform positioned on top. Next, level the base plate on the stand. After the platter is placed in position on top of the subplatter, it should be leveled using the adjustment knobs on top of the suspension towers. Clockwise rotation causes the subchassis to descend. The idea is to align the bottom edge with the 7-mm marks on all the towers.
I ran into a problem in adjusting the height of the Graham 2.2 arm to match that of the platter. Various turntable manufacturers follow their own design logic in this regard. There really isn't a standard for arm installation/height dimensions. As a result, I had to shim up the arm board by a few millimeters using metal washers. I was able to elevate the arm sufficiently for its VTA adjustment to work correctly. Of course, this is in the nature of a temporary fix, and what is required is a shim for the arm base, about 6 mm thick. Bob Graham has promised to machine just such a shim for me. This situation is very similar to the installation problem I experienced while reviewing theOracle Delphi Mark V Turntable.
The rest of the phono system consisted of my long-time reference, the Symphonic Line RG-8 Gold phono cartridge, the Audio Note An-S3 step-up transformer, and the Air Tight ATE-2 phono preamp. Acrotec 8N copper interconnects completed the front end.
As Captain James T. Kirk of the Star Ship U.S.S Enterprise has proclaimed ad nauseum, through countless re-runs of Star Trek, space IS the final frontier. And even in today's digitally dominated world, analog goes boldly forward in recreating a convincing spatial illusion - well beyond the capability of a standard CD player. The most startling spatial reproduction aspect of the Kuzma SR and Graham 2.2 combo was a sense of rock-solid stability. The depth and width perspectives of the soundstage were absolutely unwavering during the music's dynamic modulations. This was the first instance in a lifetime of analog auditions when I did not experience some spatial pumping action, with shrinking and expansion of the soundstage. As a result, the illusion of a real acoustic space was more believable than ever before. This is one of those perceptual attributes of good sound that is difficult to quantify measurement wise. There is nothing in the standard engineering measurements of vinyl-bound playback systems that would lead a rational meter head to deduce that analog's spatial performance should exceed that of the standard CD. Yet, this Zen-like aspect of vinyl is undeniable. The illusion of being there starts with a portrait of the original acoustic. No one in his right mind is going to be totally fooled. I don't expect to transform my listening room into a symphony hall; the limitations of two-channel audio do not allow that. But I do expect to experience a flavor of the original acoustic. The great joy of music reproduction in the home lies in its ability to occasionally transcend the hard physical boundaries of a typical living room. The Kuzma SR and Graham 2.2 tonearm were able to consistently transport me to another place and time.
The second aspect of the Zen of good HiFi is the illusion of real instruments performing live in your listening room. Of course, for that to come off correctly, the loudspeaker and its acoustic radiation pattern play a major role. The soundfield at the listening seat is greatly influenced by room reflections. Some audiophile have worked long and hard to deaden their listening environments, believing that any reflected energy is tantamount to sonic poison, The end result for stereo listening, is an artificial, unnatural experience. Imagine all of the music, both direct and all of the reverberant energy of the recording, originating from a plane right in front of you. That is not my idea of a concert hall experience. I believe that dipole radiators, such as planar speakers, are a step in the right direction toward a natural spatial presentation. Selective room diffusion methods, rather than absorption, often works wonders with dipole speakers in creating a believable spatial experience in the home. With my BassZilla, which incorporates a full-range driver on an open baffle as a dipole radiator, image outlines were palpably focused. The spatial coordinates of each individual instrument in a mix stayed firmly rooted in space. The antithesis of this is a swimming presentation, where outlines dance around a particular position within the soundstage. Does the concept, chiseled in stone, mean anything to you? That was exactly the sort of precise spatial impression generated by this combo.
One of the most often cited bits of feedback regarding the Graham family of tonearms is the perception of a lean bass tonal balance. I happen to disagree completely with such a finding. It typically originates from users who are conditioned to a hyped up low-end response. In my experience, many conventional arms (read: non unipivot types) such as the SME V, exaggerate or beef up bass lines. The effect works synergistically with a host of anemic British mini-monitors much in need of a steroid injection. Now if you really seek a ripe bass response, a mating of the Linn LP-12 with the SME-V will put you squarely in bass heaven. However, if it is neutrality that you seek, then the Graham arm delivers the goods. In the context of the Kuzma SR, its bass range was precise and uncolored.
Pitch precision extended through the midrange and treble. Another hallmark of a superb analog front end lies in its ability to track through high-velocity dynamic passages without compression or loss of detail. Macrodynamics were given full scope of expression. Subtle dynamic shadings, in which much of music's emotional expression resides, were allowed to sparkle. Musical lines were unraveled with little effort. The nuances buried in complex passages were clearly elucidated. The treble range was well-extended and always in control. Although the midrange was not objectively over emphasized, I had a difficult time keeping my ears off it. Old favorite recordings were reproduced with an amazing level of clarity. By analogy with a fan, the better the bearing, the less noise it generates. Low-level vibrational energy is coupled back via the table and arm to the cartridge. In the process, micro detail and clarity are lost, as this extraneous energy smears the attack and decay of transients, making the reproduced sound less distinct. Resolving power is, therefore, a direct consequence of an ultra "quiet" bearing and a non-resonant arm. The stylus was simply allowed to perform its job of tracking groove modulations with almost no external interference. There can be no higher praise for a turntable or tonearm.
Having installed the Model 1.5t on the SR, prior to making the switch to the 2.2, and having auditioned the older 2.0 version extensively on the Oracle Delphi Mark V, I can now safely report that latest version of the Graham arm pushes the performance envelope even further. The differences have to do with more stable image focus, enhanced pitch precision, and better dynamics. The 2.2 now clearly qualifies as the 2.0's older brother, being more sure of itself and slightly more eloquent in expression.
My search for a definitive analog front end and a personal reference is over. The winner in the turntable category is the Kuzma Stabi Reference. While it isn't the most expensive, exotic, or prestigious table out there, it is extremely well-built, reliable, and does exactly what a turntable should do. An extremely quiet bearing, coupled with an excellent drive system, and effective suspension and isolation give the Kuzma a real-world edge over other turntables I've lived with. The record clamp may not appear as sophisticated as a vacuum hold-down system, but it works well enough to satisfy my requirements.
The winner in the tonearm category, and this should come as no surprise to those readers who have followed my analog adventures during the past decade, is the Graham Engineering Model 2.2. The upgraded pivot system gives better bass precision versus the Model 2.0 and nudges the spatial and detail resolution capabilities of this design to its full potential. The upgrade for owners of 1.5t and 2.0 arms is highly recommended.
Don't be mislead by fancy advertising: there are no better facilitators of analog magic out there than this mating of the Kuzma SR and Graham 2.2 tonearm. A five star recommendation for these two maestros of the analog world!
2. Graham Engineering, Inc.
Kuzma Stabi Reference: $5,500
Graham 2.2 tonearm: $3,200
Kuzma Stabi Reference: