Sonic Frontiers Power 3 vacuum-tube
monoblock power amplifier

By Brian Damkroger

Sonic Frontiers Power 3 monoblock power amplifier

The internal battle between the head and the heart, between the analytical and romantic sides of our nature, is a difficult one. I’m an engineer, so it seems as if my cold, calculating side should have the upper hand. This is true in a lot of cases; most of my actions and decisions are based on straightforward, logical analyses. However, things like a house full of castaway dogs, or a garage full of quixoticc British cars and Italian motorcycles, suggest that my heart holds swayreasonably-perhaps distressingly-often.

This struggle is often in full force when I venture into the audio world. Inevitably, there’s a huge gap between a dispassionate accounting of a component’s pluses and minuses and my holistic, emotional response to the music it produces. Perhaps this reflects short comings in my analysis or comunication skills. Or it could be a contracdiction that’s inherent in trying to apply a fragmented, analytical picture to something as emotional and organic as my reaction to music.

Whatever the reason, it’s rare that an audio component excels across the board: frol-n the most analytical perspective to the most emotional. LPs, for example, have obvious flaws and don’t appeal to my logical side. Yet they manage to be more musically satisfying than CD’s “perfect sound forever.” Conversely, when the Melos SHA-Gold preamplifier of a few years back impressed me mightily, though I was hard pressed to come up with specific criticisms of its performance, it never seemed as musically satisfying as an analysis suggested it should be. The music never connected with me emotionally, never captured my heart.

Perhaps the best example in my recent history is a pair of integrated amps I auditioned a few years ago: one tube, one solid-state, both from the same manufacturer. The solid-state model was a technical marvel whose engineering and performance I truly admired, but when the lights went down and the music went on, I unfailingly found its tube sibling more satisfying.

This contradiction–or spectrum of response-is the backdrop against which the Sonic Frontiers Power 3 must be judged. SF has earned a reputation as a high-eiid heavy weight, and the Power 3 is their flagship amplifier. Its $9999/pair price tag isn’t exorbitant by today’s standards, but still, this isn’t a case of an amplifier being “good for the price” or “a reasonable compromise.” I expect a product like the Power 3 to do it all: to amaze and impress my analytical side, and to enchant and captivate my heart.

Drawing baffle lines
Starting from a purely analytical perspective, the Power 3’s spec sheet confirms that it’s a serious assault on the state of the art. It combines a tried-and-true tube circuit with modern, innovative engineering. The basic circuit uses four 6922 tubes as the input/driver stage, followed by a pair of 5687s for high-voltage drivers, and eight 6550C output tubes. The driver and output.

Description: Vacuum-tube monoblock amplifier. Tube complement (each monoblock): eight 6550C, four 6922, two 5687. Rated output power: 2OHz-2OkHz, <I% THD, 22OW into 8, 4, and 2 ohms (23.4, 20.4, and 17.4dBW, respectively). Frequency response: 5Hz-75kHz, ±0.5dB at I W; 15Hz-6okHz, ±0.5dB at 220W. Input sensitivity for full output power: 2.2V, balanced or single-ended inputs. Voltage gain: 25.6dB into 8 ohms, 22.6dB into 4 ohms, 19.6dB into 2 ohms. Input impedance: look ohms single-ended, 20ok ohms balanced. output impedance: 0.25 ohms at I kHz. Damping factor: >50 (using IHF method from RS-490). Power consumption: 375W at idle, 58OW at rated output.

Dimensions: 18” (46cm) W by 9” (23cm) H by 22” (56cm) D. Net weight:loo lbs (45kg) each.

Serial numbers of units reviewed:
106241,106242 (final pair).

Price: $9999/pair. Approximate
number of dealers: 100. Warranty: 5 years; tubes, I year, limited.

Manufacturer: Sonic Frontiers International, 3535 Laird Road, Unit #16, Mississauga, Ontario L5L 5Y7, Canada.
Tel: (905) 828-4575. Fax: (905) 828-4585. E-mail: SFisonicfrontiers.com. Web: www.sonidrontiers.com.

stages are direct- rattler than capacitor-coupled, to improve transient response and to avoid any signal blocking that might occur due to residual charge on the capacitors.

The circuit is fully balanced, input to output - even including the output transformers. Although there is only one set of speaker binding posts, the amps can be configured for 8, 4, or 2 ohm loads by a simple operation of changing a set of internal connections. Mine were factory-set at 4 ohms to match the Thiel CS72s; I used the same setting to match the 5 ohm load of the Magnepan MG3.6/Rs.

A peck inside confirms that the boards and layout are neat and professional, and the assembly is beautifuly done. Similarly, the parts quality is extraordinary, even at this price. The tubes are sourced from Sovtek, Svetlana, and Philips (US JANS), and are exactingly graded and matched. Passive components include Solen and Wima capacitors and Vishay and Roderstein resistors. The heavy binding posts are rhodium-plated, solid-copper units from Cardas, and the input ‘acks and internal @ring are from Kimber.

A peek inside confirms that the boards and layout are neat and professional,
and the assembly is beautifully done. Similarly, the parts quality is extraordinary.

As I moved outward to the Power 3’s construction quality and user interface, my analytical perspective still dominated–but the less tangible, emotional response began to contribute. Sure, form follows ftinction, and I admire and respect simple, logical, functional controls. But less tangible factors like fit and finish, proportion, and feel also come into play.

The Power 3 scores 10s across the board here as well. Fit and finish are outstanding: The heavy, laser-cut, stain-less-steel chassis panels fit perfectly, and are securely assembled and thoroughly damped. The finish treatment combines smooth, brushed surfaces and black, textured, powder-coated ones. Corners are chambered exactly how and where they should be, and the overall proportions are “just so.” Imagine a top-level Mercedes or BMW sedan, and you’ll have the right idea.

The Power 3’s controls are logical and well executed. Front-panel buttons control power and select between Standby and Operate, each flanked by an LED that glows red or green to indicate operational status. Standby mode gets (or keeps) things warmed up for a listening session while drastically reducing the wear on the power tubes.

Red on the Power LED indicates that the amp is muted, which is one of the four positions on the rear-panel lnput Select switch. The Mute function not only permits cable swaps ‘ hout shutting down the amp, it also activates the Power 3’s simple, wonderfully user-friendly process of measuring and adjusting tube bias. The other three positions on the Input switch select between balanced (XLR), single-ended (RCA), and reversed-polarity single-ended. Cardas five-way binding posts and a removable power cord complete the package.

All this would be enough to put the Power 3 in good stead, but Sonic Frontiers tosses in a few more niceties that reflect their attention to detail. For example, 5687s run hot, so SF includes Pearl tube coolers. All Of the tools required to assemble, install, and maintain the amps are included, as are white cotton gloves to handle the tubes –to avoid getting fingerprints on the glass. Even the manual is simple and thorough. My favorite goody, however, is that only two screws must be loosened to remove the chassis’ top section (for biasing), and the screws are springloaded and captured.

Why can’t everything be built this well, and show the end user this level of consideration?

System and setup
I used two different pairs of Power 3's over a 12-month period, with a wide variety of systems and setups. Recent listening sessions, and most of my specific examples, refer to a system that paired the Power 3s with Magnepan 3.6/R loudspeakers and a VAC CPA1 MK.III preamplifier. Analog duties were performed by my VPI TNT IV/JMW Memorial 12” combo, fitted with a Grado Reference cartridge and suspended on a dedicated TNT stand and Bright Star TNT Air Mass/Big Rock combo. Wadia 830 and Ultech UCD100 CD players handled discs, and everything was wired up with JPS Superconductor 2 cables, single-ended upstream of the VAC and balanced from there on. To help triangulate the Power 3’s character, I used comparisons with pairs of VTL Ichibalis and Mark Levinson No.20.6s, and a VAC Renaissance 70/70 and a Krell KSA-250.

Use and listening
As I’ve noted above, the Power 3 was a delight to set up, install, and use. Mysamples were reliable, dead quiet (save for one amp that unfailingly emitted a couple of quick spits shortly after turn-on), and not much more than warm in operation. The amps’ biases drifted a bit in the first few days of operation (I ran them continuously for a week before doing serious listening), but were rock-solid after that. My experience with the Thiel CS72 suggest that the Power 3 has enough power and control to drive difficult loads with aplomb.

The Power 3’s most obvious charactenstic – one that appealed greatly to my analytical side – was its flat tonal balance and incredible consistency from top to bottom. I cued up one of my favorite LPs, the Munch/Boston reading of Debussy’s La Mer (RCA LSC-2111), and kicked back. The double basses and bass drum were deep and articulate, with superb precision and pitch definition. Moving up through the cellos, woodwinds, and violins, it was a continuous flow, with no change in the amp’s character. Instruments retained their harmonic balance and texture across their ranges, and the overall mix -instruments, sections, soundstage, and ambience -was continuous as well.
Measurement:

A full set of measurements was made on the Sonic Frontiers Power 3 in its balanced mode, with selected measurements repeated in unbalanced (single-ended) mode. Unless noted otherwise, all measurements are for balanced configuration.

Following its one-hour warmup, the Power 3 was typically hot for a tube amplifier. Its input impedance measured a high 198k ohms (99.3k ohms unbalanced), its output impedance a maximum of 0.17 ohm at 20Hz and 1khz, increasing to a maximum of 0.22 ohm at 20kHz. These are very low and very good–
values for a tube amplifier, and indicate that the Power 3’s performance should be less affected by
real-world loudspeaker loads than most of the breed.

The Power 3’s voltage gain measured 22.9dB (22.8dB unbalanced) with the output transformer set for
4 ohm operation. This is lower than that of most amplifiers; you should ensure that the preamplifier you Intend to use wiII provide adequate overall gain in your system.

DC offset was unmeasurable. Pin 2 of the balanced input is positive, and the Power 3 is noninverting from its unbalanced SE+ input. The signal-to-noise ratio measured 84.5dB from 22Hz to 22kHz, 83.ldB from 10Hz to 500kHz, and 96.3dB A-weighted. The unbalanced results were within 1dB of these figures.

Fig.1 shows the Power 3’s frequency response at 1W into 8 ohms. Note how small the deviations are into our simulated load. The 10khz squarewave is shown in fig.2. There is a small overshoot, and some ringing at about 110kHz. The latter is also visible on the 1khz squarewave (not shown), but should have no audible consequences.

The Power 3’s THD+nolse vs frcquency performance is plotted in fig.3–a good result for a tube amplifier, though the inevitable reduction in linearity above the audioband makes its presence known in this graph.



The waveform of the distortion at 2W into 4 ohms (at 1khz) is shown in fig.4. The result is heavily second-liamionic, plus noise.

Fig.5 shows the spectrum of the Power 3’s output in response to a 5OHz input, taken at a 147W output into a 4 ohm load. The second harmonic (100Hz) is -54.2dB (about 0.2%), the dird (150Hz) is -63.6dB (0.07%). Fig.6 shows a



similar spectral analysis, using a combined 19+20kHz input signal at an output of 96W into 4 ohms. (The amplifier will clip above this power with this input signal.) The largest artifact, at 1kHz, is -56.3dB (0.15%). The results of figs.5 and 6 are respectable for a tube amplifier, but not really exceptional.



The THD+noise vs continuous output power measurements are plotted in fig.7; the discrete clipping levels are shown in Table 1. (it didn’t prove possible to carry out pulse testing using the Miller Audio Research Amphfier Profiler.) The Power 3’s test-bench results are good for a high-powered tube amplifier. The single exception is that it fell short of its specified power into 8 ohms, even at the 3% THD+noise level. This is presumably is due, to the fact that, as supplied for review, the amplifier was configured for 4 ohm operation.



– Thomas J. Norton

The SF’s clean, controlled presentation extended up into the top end. There was no change in character whatsoever as violins or pianos, for example, moved to the very top of their range. Cymbals were open airy, and even piccolos were obviously the same instruments playing in the same space, from the bottom to the very top of their range. Occasionally, a touch of edginess crept into massed violins during crescendos near the top of their range. The majority of the time, however, the Power 3’s top end was smooth as well as clear, clean, and open.

In comparison, all of the other amps I used had slight but noticeable aberrations in frequency response. Comparison with the Power 3 made it obvious that the Mark Levinson No.26, for instance, had a dark, sivery sound slightly bloomy upper bass, sweet, prominent upper midrange and lower treble, and closed-in top end.

Sonic Frontiers Power 3

The Power 3 didn’t sound perfectly neutral, however. Its overall character was slightly cool, dry, and distant–exactly the opposite of the VTI’s slightly warm, liquid, immediate personality. On the vinyl version of the Ray Brown Trio’s Soular Energy (Concord jazz LELP 111, Bellaphon 180gin half-speed-mas-tered version), Brown’s bass sounded a little more prominent with the VTL, but more consistent across its range with the Power 3. Similarly, the VTL had a bit more midrange and upper-midrange bloom than the SF, so Emily Remler’s guitar and Red Hofloway’s sax were tonally richer and more vivid. Recent visits to concert halls and jazz clubs suggest that reality-and true neutrality–fall some where between the two.

Another immediately obvious component of the Power 3’s sound, and one that contributed strongly to its character, was a reduction in the size of dynamic gradients. Compared to the Levinson, VAC, or VTL, the Power 3’s deltas the differences between loud and soft simply weren’t as big. The transients were clean and fast, and the dynamic swings were very well controlled, but just not as big. Rim shots had a crisp, clean initial impact. The character was correct, the sound was detailed, and the leading and trailing edges were sharp but they just didn’t have the snap-your head-around sort of impact that the other amps did, and that makes the sound seem a bit more alive.

I wrestled with this a bit, playing with different preamp gain settings,carefully matching levels, and wondering if what I was really hearing was the Power 3’s superior control of the speaker. That may be part of it, but I’m convinced that it’s not the whole story. At any volume level and with any speaker I threw at it, the Sonic Frontiers’ dynamics were genuinely smaller across the board, from micro- to-miacro dynamics.

The second movement of La Mer runs the gamut from delicate woodwind passages with barely perceptible microdynamic shadings to all-out crescendos. With the Power 3, the crescendos didn’t have as much power as with the VTL. At the bottom end, a lot of the subtle microdynamic information was noticeably reduced, and in some cases gone altogether.

Backing up a step, however, there is no doubt that the Power 3s did do an excellent job of controlling the speakers. I’ve mentioned the speed and precision of the dynamic transients. Images were tightly focused as well, with excellent edge definition and a very clear sense of the space between them. The soundstage was very wide, extending well out beyond the Maggies’ outer edges, and the space between the images gave it an open, airy feel.

The Power 3s’ soudstage didn’t have quite the depth of the other amps’, but the depth it did have was more consistent from side to side. The other amps’ soundstages were deeper, but their shapes were slightly trapezoidal, perhaps even concave on the rear edge, with more depth in the center than at the edges. With the Power 3s, the rear cortiers were pushed further back and a bit better illuminated. There was a better sense of the orchestra’s back row - the percussion on La Mer, for example-and of the stage walls behind and beside them.

The Power 3s’ image specificity was excellent, and their reproduction of the images’ boundaries was very natural. Instruments transitioned smoothly into the surrounding space, maintaining distinct edges but flowing continuously into the background ambience. That ambience itself was clearly reproduced, but not as lushly as by the VTLs or Levinsons. Similarly, the Power 3s’ images themselves were a little less dense than with the other amps. On La Mer and Soular Energy, the SFs sounded a bit bleached in comparision -not as rich, and with a slightly pale, less complex harmonic structure. In contrast, Diana Krall’s luscious when I Look In Your Eyes (Impulse!/Verve IMPD-304) was better served by the Power 3s; this disc sounded a bit syrupy on the VTLs and Levinsons.

Images through the Power 3s were smaller than they should have been. With some source material -say, the Ray Brown album -there isn’t a real reference Point, so “small” means “smaller than I’ve heard with other equipment.” With orchestral recordings,on the other hand, the spatial relationships between instruments, sections, hall boundaries, and listener form a refcrence into which the apparent image size needs to fit. The Sonic Frontiers’ image sizes suggested a listener-to-orchestra distance inconsistent with other cues.

Images were also less dimensional with the SFs than with the other amplifiers. And although the Power 3 did a great job of resolving low-level detail–the background whispers and noises on Dave Bailey’s One Foot in the Gutter (Epic/Classic BA 17008) is a great example -they seemed to have slightly less inner detail than with the VTL, VAC, or Levinson amps, as with Emily Remler’s guitar on Soular Energy. Intellectually speaking, the subtle interplay of vibrations that occurs as the string sound transitions to the body resonance were there with the Power 3, but were more obvious with the other amps. Emotionally, it’s simpler: With the other amps, the guitar was a bit more vivacious and had more texture-it was a bit more alive.

Free your mind, and your heart will show you truth
Taking the retional, calculating approch, the power 3’s sonic attributes added up to a pretty solid scorecard. it got all the big things night: it was essentially neutral, sounding flat and very low in coloration, and imposing very little character of its own oil the music. Bass,midrange, top end–all excellent, and all obviously cut from the same sonic cloth. Transients were fast, clean, and precise, and the amps’ reproduction of images and soundstage were first-rate.

The Sonic Frontiers Power 3 is an ambitious assault on the state of the art, and in
most ways succeeds spectacularly, reflecting a sound, intelligent approach.

In comparison, the Power 3’s shortcomings-reduced dynamic gradients, smallish images, slight lack of inner detail and dimensionality, and a tonal balance a bit on the light, dry side of neutral - seemed pretty minor when viewed analytically. But when I would switch out of reviewer mode and let my heart take over – when I would Just sit back and listen to music – my overall experience just wasn’t as engaging as with the VAC, VTL, or Levinson amps.

Some of my dissatisfaction with the Power 3 was mine and mine alone, and may not apply to another listener. Two of the areas in which it fell short dimensionality and inner detaiI – contribute heavily to how engaging I find any given component. Similarly. the Power 3’s tonal balance erred slightly on the light, dry, analytical side of neutral, whereas I’m more tolerant of errors to the warm, liquid side – where the VTLs and Levinsons reside.

The biggest drawback was the Power 3’s smaller-than-average dynamic gradients. Intellectually, this is only one factor on the checklist, and was a relatively minor deficiency. On the emotional side, however, the effect was more significant. Although dynamic gradients can be extracted and analyzed, they’re woven inextricably into the fabric of the music, and contribute subtly to a whole host of factors that bring it to life. In fact, the “Holiday Inn Effect” – knowing, from hearing it from your room at the end of the hall, that the music from the hotel bar is a live band -is all about dynamic gradients.

On “Authority Song,” from John Mellencamp’s Uh-Huh (Riva RVL 7504), there’s a wonderful guitar line with a rich, complex mix of textures and dynamic shadings that makes it seem as if you can hear deep into and around the guitar’s strings. With the VTLS, it bounces and careens around the instrument’s lower strings, positively screaming “Let’s party!” – a grin-inducing, toe-tapping, suck-you-in air-guitar riff if ever there was one.

With the Power 3, the tiff was still there: absolutely, positively there, each detail and aspect of the instrument’s character cleanly reproduccd – from the analytical point of view. But a few of those parameters dimensionality, harmonic complexity and richness, dynamic gradients – were slightly diminished. So, from the emotional, musical-conncction point of view, something tanble had been lost. I put down my air guitar and stopped bouncing in lily seat. Words like “measured” and “controlled” popped into my head, but Bonnie put it more succinctly as she got up to leave: “These amps don’t rock.”

Conclusion
 The Sonic Frontiers Power 3 is an ambitious assault on the state of the art, and in most ways succeeds spectacularly, reflecting a sound, intelligent approach that combines well thought-out design and superb execution. It’s incredibly well built, lavislay appointed, and reflects an attention to detail that’s at the absolute top of the audio – or any other – craft.

It succeeds in many sonic criteria as well. Things like speed, precision, and clarity are excellent, and the Power 3 will effortlessly control virtually any speaker. Its low coloration, flat tonal balance, and superb performance at the frequency extremes are at the top of its class. In some respects, the Power 3 is one of the best tube amps I’ve heard, and among the best amps I’ve heard of any type.

For some listeners, the Power 3 may be just the ticket; I suggest that anyone shopping for a high-performance amplifier give it a listen. As successful as it is, however, and as much respect as I have for its design, execution, and performance, it wouldn’t be my choice. I can analyze the Power 3’s performance and explain my reactions in terms of its specific shortcomings and my listening preferences, but the simpler, truer explanation is that, as much as my head liked the Power 3, my heart Just wouldn’t sign up.