When faced with the choice between solid-state and vacuum tube amplification, I have traditionally chosen in favor of the transistor. I must confess, however, that factors other than sonics have played a part in the decision making process. Reliability, cost of maintenance, and operating temperature have also weighed heavily.

As both a reviewer and a consumer, product reliability is of paramount importance. When the power switch is flipped to the 'on' position, I expect, want and need to be greeted by the sound of music rather than a pyrotechnics display and a plume of black smoke. As for the cost of maintaining a moderately-powered, push-pull tube power amplifier, it can be prohibitive. Power tubes, such as the commonly used 6550C, are relatively expensive and often need to be purchased in matched pairs. Completely re-tubing a 6550-based power amplifier, perhaps as often as annually if the tubes are run hard, could set you back more than $500 depending on the circuit's tube count. Once past these issues, one must contend with the often prodigious amounts of heat generated by power tubes. Yes, we do have long, cold winters up here in Canada, but we inhabitants of the Great White North have come to rely on more traditional and cost-effective means of keeping our extremities from turning blue between the months of October and April.

After living with the Power 2 for many weeks, I'm happy to report that Sonic Frontiers has addressed at least two of my three major concerns with tube power amps. My concern over the reliability of tube amplifiers proved unfounded in the context of the Power 2. After two months of nearly continuous operation, amounting to over 1000 hours of use, the Power 2 never so much as uttered a hiccup, groan or wheeze (due to its high operating temperature, which I'll discuss below, Sonic Frontiers does not recommend continuous operation of the Power 2). Day in and day out, the Power 2 simply refused to let the music stop. While unfailing operation of a product over a two month period would not normally be cause for celebration, consider this: assuming one listens to music an average of ten hours per week, it would take nearly two years to run up the same 1000 hours of operation that was clocked on the Power 2 during the review period. From this I must conclude that long-term reliability of the Power 2 is a non-issue.

Sonic Frontiers has taken several steps to extend the lifetime of the Power 2's tube complement and reduce the frequency at which the amplifier must be re-tubed. The Power 2's two 5687s, used as high-voltage drivers, are operated at 1/3 their maximum power rating and are kept within a safe operating temperature by a supplied pair of Pearl tube coolers. Rather than requiring a full power-down when not in use, the Power 2 provides a standby mode (much like the one in the Line 1 preamplifier I recently reviewed) in which the tube filaments remain heated but plate voltage is reduced by ninety percent. This mode reduces warm-up time and avoids the cold starts that result in shortened tube life.

Incorrect biasing is another factor which contributes to the untimely demise of power tubes. Although an auto-biasing circuit, like that found in the Balanced Audio Technology VK-60, has not been provided in the Power 2, Sonic Frontiers has provided an intelligent, two-color LED biasing scheme which is ridiculously easy to carry out and doesn't require the use of a multimeter. The Power 2's biasing circuitry is activated when both rotary selector switches on its rear panel are switched to 'mute' and the amplifier is in 'operate' mode. Each power tube in the Power 2 has an associated LED mounted next to it on the amplifier's top plate which, during biasing, will either glow green, indicating under-bias, red, indicating over-bias, or not at all when the tube is correctly biased. To correctly bias an under- or over-biased tube, simply use the supplied biasing tool to turn the tube's biasing screw until its associated LED shuts off. Repeat for the rest of the tubes and c'est tout!

So, the Power 2 has the reliability for which I yearn and, if properly maintained, shouldn't require frequent re-tubing. What about the heat? Alas, the amount of heat generated by the Power 2's two 5687s, eight Svetlana 6550Cs and six 6922s was substantial. Closing the door to my relatively small (12' X 16') listening room caused the room's ambient temperature to rise sharply after only a brief period of time. Lengthy listening sessions usually required a T-shirt, shorts, a pitcher of piña coladas and a beach umbrella (the beach itself was provided by a leaky 50lb bag of silica sand used to fill the base of the Leadless balloon supporting my turntable). Don't get me wrong, the Power 2 is hardly the worst offender in terms of thermal by-product (the Audio Research VT-200 utilizes a fan to dissipate the heat generated by its sixteen 6550Cs!) but the level of heat it generates may overwhelm a small or poorly ventilated listening space. Although I found the heat generated by the Power 2 to be tolerable, several visitors to my listening room did not.

Look and Feel
Like other Sonic Frontiers products with which I am familiar, the Power 2 exudes quality. Its fit 'n finish are exemplary and its cosmetics are tastefully stylish. The Power 2's front panel sports a duet of stainless steel push buttons, one to turn the unit on and off and one to toggle it into or out of standby mode, and a pair of LEDs which indicate power-on status and whether the unit is in standby or operate mode. Interestingly, the Power 2's stainless steel push buttons felt a bit looser and less secure than those on Sonic Frontiers' Line series of preamplifiers, although they operated flawlessly throughout the review period. The rear panel sports three sets of inputs: single-ended non-inverting RCA, single-ended inverting RCA, and balanced XLR. The inverting RCA input should prove useful for users of preamplifiers, like the Audible Illusions Modulus 3a, which invert phase. All RCA connectors are by Kimber and the single pair of loudspeaker binding posts is by Cardas. A pair of rear-panel rotary selectors is used to choose the desired input for each channel, and to mute each channel's output in order to perform biasing or to switch speaker cables. Completing the rear panel are a detachable power cord, for those who like to experiment with such things, and a pair of ground posts, one per channel. A removable, black, powder-coated tube cage is supplied which, in this reviewer's opinion, somewhat diminishes the aesthetic appeal of the Power 2 but provides a buffer between the amplifier's hot tubes and curious pets or children.

Inside, the Power 2 is typical Sonic Frontiers fare; that is to say, a sophisticated circuit topology implemented with the highest quality passive parts such as MIT, Wima, and Solen capacitors, and Vishay, Roderstein, Mills and Caddock resistors. The Power 2 is a fully-balanced, 110 Watt design utilizing a direct-coupled output driver. Directly coupling the output driver to the output tube grids is said to prevent "signal blocking" and its resultant degradation of the input signal, which occurs under clipping conditions in capacitor-coupled designs. The Power 2's highly linear "partial triode" operation allows for the doubling of output power with the halving of load impedance. In practical terms, this means that the Power 2 should be able to drive virtually any real-world loudspeaker. Using internal jumpers, the Power 2's output taps may be tailored for 2, 4 or 8 Ohm operation depending on the nominal input load of the partnering loudspeakers. Although the procedure for modifying the Power 2's output configuration is outlined in the unusually well-written user's manual, Sonic Frontiers recommends that this procedure be carried out by an authorized service technician. Once again, I must commend Sonic Frontiers on its user's manual - clearly written and well illustrated, it sets the standard to which other manufacturers should aspire.

New Frontiers
In many ways, the core of my current reference system is a throwback to 1950s technology. I still make use of an analogue front end for LP playback, my preamplifier not only contains a phono stage but is based on vacuum tube technology, and my current loudspeaker is a traditional two-way dynamic system. Not much different from the sort of systems audiophiles were using forty or more years ago. Has high-end audio gear evolved at all in the past four decades? The current rebirth of the single-ended triode notwithstanding, the answer is a resounding "yes", even in the context of seemingly-obsolete technologies such as vacuum tube amplifiers and analogue playback gear. As proof, I need look no further than the Audible Illusions Modulus 3a, the Sonic Frontiers Line series, or the VPI Aries. These products simply could not have existed in the so-called golden age of audio. The same could be said of the Sonic Frontiers Power 2 amplifier. With its innovative circuit topology and truly modern design, the Power 2 shares little with its sometimes pleasing, but certainly more euphonic, predecessors, which rarely, if ever, achieved the same level of sonic neutrality or reliability.

At the risk of sounding cliché, the Power 2 had the ability to make me forget about the technology and just listen to the music. Although not completely neutral at the frequency extremes, the Power 2 did not exhibit many of the colorations traditionally associated with vacuum tube devices - bass was deep and powerful, the treble was fast, detailed, and smooth, the midrange was open and natural, and, when operated within its power limitations, dynamics were on par with the best I've heard from either tube or solid-state. In fact, in the Power 2, it appears as though Sonic Frontiers has managed to accentuate the positives of both solid-state and vacuum tube technologies whilst minimizing many of the negatives associated with each.

Some musical examples: My Baby Just Cares For Me from Holly Cole's Girl Talk (Alert Music Z1-81016, LP) is a wonderful duet featuring the plucked bass lines of David Piltch and a typically swinging Cole vocal. The attack and decay of each note of Piltch's extended solo were wonderfully rendered by the Power 2. The bass's woody resonance and the snapping of the strings against the fretboard were delivered with great fidelity to their live counterparts. Low bass notes had excellent weight and extension, providing further evidence that the Power 2 was not to be outdone by the best that solid-state had to offer in this area. Cole's voice had a presence, and what could best be described as a sense of "rightness", that I rarely hear from recorded music.

Kenny Burrell's Midnight Blue (Blue Note BST 84123, LP) proved to be another source of unusual delight. I urge anyone with even a passing interest in blues-influenced jazz guitar to seek out this superb example of the genre. While listening to this recording through the Power 2, I had the sense that I was experiencing all that Burrell and the Blue Note engineering team had to offer when they laid down the tracks comprising this terrific set. I knew I was in for a wonderful ride as I heard the uncannily realistic sound of the congas light up the room on Chittlins Con Carne. Clifford Jordan's sax floated in from stage right and was possessed of a delightfully full, rounded tone. Not to be outdone, the sound of Burrell's closely-miked guitar, placed stage left, had the appropriate amount of bite and sustain. The sound of Burrell's fingers pressing and releasing strings along the fretboard was clearly audible, and plucked guitar strings had great transient speed and clarity. The Power 2's highly involving presentation drew me deep into these performances and never let my attention wander from the music to the hardware - the sign of a highly musical device.

Further evidence of the Power 2's innate musicality was its lovely reproduction of all sounds throughout the vital midrange. The sound of strings, woodwinds and well-recorded vocals oozed the sweetness, smoothness and utter beauty that have traditionally been the hallmark of high-quality tube amplifiers - on this basis alone, the Power 2 has earned its place among the latter group of components.

But while tubes have traditionally been victorious in conquering the vital midrange, they have in turn traditionally lost the signal-to-noise battle to their quieter, solid-state cousins. Aside from some audible transformer hum, however, the Power 2 was extremely quiet, allowing the most minute sonic detail to make its way to the listener. The unraveling of low level details, such as audience noises captured at live recordings, musicians turning the pages of their scores, and vocalists breathing, contributed to the illusion of a live musical event unfolding in the listening room.

In the rhythm and pace department, I found that the Power 2 shone brightly. Now, I wouldn't consider myself a "Linnie" per se (although a Linn LP-12 did grace my listening room for several years), but I do place a high value on rhythmic ability in an audio component, and the Power 2 didn't disappoint. On Yellow Fellow, from Ahmad Jamal's Rossiter Road (Atlantic 81645-1, LP), the masterful rhythm section of Manola Badrena, percussion, Herlin Riley, drums, and James Cammack, bass, was so well rendered that my toe was permanently locked on automatic pilot. Impressive.

Unlike many other amplifiers of relatively modest power, the 110 Watt Power 2 reproduced orchestral fortes with superb authority and absence of strain, in no way diminishing their impact. Power music spectaculars, such as Camille Saint-Saëns' Third Symphony (RCA 09026-61500-2), and Rachmaninoff's Symphonic Dances (Athena ALSW-10001), were presented in all their splendor. In fact, the Power 2 delivered music with a weight and authority unequaled by the other 100 Watt amplifiers I've had in my reference system, leading me to conclude that this amplifier's output capability exceeds its specified rating. Having said that, I did encounter some practical limitations on the amount of power the Power 2 was capable of delivering. Mobile Fidelity's superb reissue of Muddy Waters' Folk Singer (MFSL 1-201) features some extremely wide dynamic swings, some of which resulted in gentle, but audible, clipping of the Power 2 at realistic playback levels. I initially thought that I was hearing some form of overload of the electronics used at the original recording sessions, but a quick switch to the 175 Watt Celeste Moon W-5 convinced me otherwise.

As adept as the Power 2 was at flexing its sonic muscle in service of large-scale symphonic music, it also displayed a gentler, more softly-spoken side when appropriate. Intimate jazz, solo instrumentals, and other small-scale works were handled with the delicacy and finesse normally the domain of lesser powered amplifiers.

While I clearly found much to like in the Power 2's musical presentation, I did uncover a few weaknesses which couldn't be completely overlooked at its price point. Firstly, the Power 2's upper treble, while sweet and very pleasing, did exhibit some degree of roll-off, leading to a slightly dull picture of high-frequency, percussive instruments. The triangle, cymbals and snare drum heard in Prokofieff's Lt. Kije Suite (Chesky Records RC-10), for example, lost some of their respective sparkle and sizzle through the Power 2, lending this classic performance a somewhat less lively, open feel. Secondly, while it managed to reproduce deep bass notes with all of their weight intact, the Power 2 was not as tight or articulate in this region as the best solid-state amplifiers. Apples to oranges you say? I think not. The search for the absolute sound must transcend technological boundaries, and I therefore feel fully justified in comparing the Power 2 to similarly priced solid-state competition. Finally, the aural image elicited by the Power 2 was slightly smeared and somewhat more opaque than that produced by the Celeste Moon W-5. On Finger Fillibuster, from Clark Terry's Portraits (Chesky Records JR-2), for example, the sound of Terry's patented scatting, and the accompanying drums, bass and piano, had a tendency to blend into a slightly diffuse image, resulting in a blurring of distinct instrumental lines.

To put these criticisms into perspective, let me emphasize that none of the weaknesses identified above seriously detracted from my enjoyment of music as rendered by the Power 2. On the contrary, I found the Sonic Frontiers Power 2 to be a highly involving and enjoyable device, whose few sonic shortcomings were heavily outweighed by its overall musicality. Still, shortcomings in an amplifier with the Power 2's not-insignificant asking price are certainly more noteworthy than they are at lower price points, and I feel compelled to point them out, however minor.

Conclusions
The Sonic Frontiers Power 2 power amplifier is a highly musical, and eminently enjoyable piece of gear with which I spent many pleasant hours. The Power 2 embodies many of the assets of both solid-state and tube amplification while, at the same time, overcoming many of the liabilities of each. In fact, throughout much of my listening, I was blissfully unaware of the technologies at play, and completely immersed in the music. My enthusiasm was tempered somewhat by the Power 2's inability to portray the last ounce of top end air and extension, its relative lack of low-end articulation, and its slightly murky rendering of instrumental outlines. These minor shortcomings aside, the Power 2 communicated the core of the musical message with great authority and conviction, and is certainly worthy of serious consideration by anyone contemplating a power amplifier, tube or solid-state, at its price point.