A fine reputation isn't built in a fortnight. Just ask Sonic Frontiers' Chris Johnson. He'll tell you that over the period from 1991 to 1996, SF has released a steady stream of high-end products, many of which, I might add, set new benchmarks for sonic excellence at affordable prices. The SFL preamplification series is a case in point. Clearly, the SFL has sired the new LINE series of preamps, the intent being to improve significantly on the performance of the former without sacrificing its virtues and value.

The LINE series is all-tube and fully balanced. No hybrid circuitry here. All voltage gain is vacuum-tube derived. While the LINE 1 and 2 are derivatives of the SFL 2 circuit and use six 6922 low-noise triodes, the LINE 3 represents a quantum leap in circuit design. Most line stages feature on average a pair of dual triodes; the LINE 3 employs a dozen tubes (six per channel!): ten Sovtek 6922 dual triodes and two 6GH8A triode-pentodes. Of course, one of the reasons so many tubes are necessary is that in a balanced circuit both the positive and negative phases of the signal are amplified. The input/voltage gain stages use one 6922 and one 6GH8A per channel in a novel variation of a differential amplifier providing "active error" feedback. The remaining eight 6922s are wired in parallel, with a pair used per phase as a current-sourced cathode follower for low output impedance. To further lower the output impedance, Sonic Frontiers decided against using a large output coupling-cap, choosing, instead, to employ a servo controller that maintains the output stage at zero DC voltage.

In my experience, a great preamp has always been distinguished by its power supply. It is the foundation of sonic excellence. Looking under the "hood" at the size of this preamp's "engine. provides an accurate yardstick for gauging performance potential. Usually, the beefier and better regulated the supply, the more refined the preamp. Let me say that the LINE 3 sets a new standard in terms of power supply sophistication and voltage regulation. The guts of the supply are housed in a separate chassis. Parts quality is simply astounding. There are two toroidal power transformers-one per channel. Rectification is via fast, soft-recovery diodes, and Solen polypropylene caps are used in the filter network. Most of the development time was spent on perfecting the shunt-type voltage regulators for the plate voltages. An Audio Precision System Two analyzer was used to optimize the already extremely low source impedance of these type of regulators. The basic idea is to achieve a power reservoir that is instantly on tap over a wide frequency bandwidth. These shunt regulators approach the ideal, with an output impedance of about 0.05 ohms out to 200 kHz-quite superior to what is possible with series-type regulators of similar complexity. In addition to the eight shunt regulators, a total of eighteen 3-pin adjustable regulators are used throughout the circuit.

The purist audiophile camp-the simpler-is-better crowd-is going to have a fit over this preamp. This is no minimalist design. As a complete description of all the features would take too many pages, I'll just touch upon the highlights. For starters, there's a remote control handset-a cute puck-shaped device that's intuitive and easy to use. Volume, balance, and even signal polarity may be adjusted remotely. I found the ability to flip signal polarity back and forth right from my listening seat to be extremely useful. Within seconds, I could decide on the best setting for a particular album. (If you've never experimented with absolute polarity, you're in for a shock-certain albums sound so much better with reversed polarity [180-degree absolute phase reversal]. Also try polarity reversal for individual tracks, as it's possible for multitrack recordings that feature complex mixdowns to incorporate many polarity reversal screw-ups.)

Do you enjoy headphone listening? No problem with the LINE-3. When you plug a headphone into its front panel jack, the main out signal is routed to a high-quality, op-amp-based headphone amplifier. SF even licensed Headroom Corporation's cross-cancellation circuitry which provides a much wider and fuller spatial impression with standard stereo recordings. Without it, regular stereo through headphones appears rooted in the middle of your head. Even though it is a fully-balanced design, the LINE 3 can accommodate single-ended (RCA) inputs and also provides both single-ended and balanced (XLR) outputs. Let's turn, now, to the POWER 3 monoblock amplifier. Not since the heyday of Audio Research and conrad-johnson has anyone had the nerve to tackle and attempt to harness so many 6550 beam power tubes as you'll find in the POWER 3. The first thing you should do when you get within reach of the thing is pull the tube cage off and feast your eyes on an octet of Svetlana 6550Cs. Now I should confess that for quite some time I didn't regard the 6550 as highly as, say, the KT77 or the KT88. That opinion was changed for all time when I had a prime Harman-Kardon Citation II in for extended audition. (This relatively overlooked tube classic from H-K puts much contemporary high-end amplification to shame.) The moral of the story is that it's often not the tube type that matters most, but how it's used in a particular circuit, along with the quality of the associated output transformers and passive parts.

Multiply the tube total per channel by two-the POWER 3 is a monoblock amp-and you're looking at a grand total of sixteen 6550s! Yep, that's a lot of power tubes, but then this is a high-power amp, rated at 220 watts into 2, 4, and 8 ohm loads at less than 1% total harmonic distortion.

Rather than provide multiple taps on the back panel for various load impedances, SF has opted for internal load adjusters. The amp is set at the factory for a nominal impedance of 8 ohms. To change the load impedance requires removal of the bottom cover (to access a terminal block with the various transformer tap settings). It's easy enough to do, although, as I found out, there's a ton of screws to remove.

As with the LINE 3, the circuit topology of the POWER 3 is fully balanced from input to output, although SF does allow you the option of selecting balanced (XLR) or single-ended inputs (RCA) via a rotary switch on the back panel. The output stage is a conventional push-pull circuit operating in partial triode or ultralinear mode. The input stage is a current-sourced cathode follower which feeds a voltage gain stage. The gain stage is capacitor-coupled to a 5687 dual-triode-based cathode follower driver. This low-impedance driver stage is directly coupled to the output stage which improves the amp's recovery from clipping and overload.

Individual bias pots are provided for all of the output tubes. Unless you're color blind, biasing the output stage is a simple procedure. The color of the LED located next to each tube indicates bias condition: red means overbias, green means underbias, while no glow indicates proper bias. Before you adjust any pots engage the mute switch on the back panel, and always be careful with how you hold the screwdriver because this amp runs hot. (When you get this close to the tubes you may notice that all of the plates have an orange or reddish dull glow or hot spot. Not to worry, this is a normal operating characteristic of this tube.)

Passive parts quality, a Sonic Frontiers hallmark, includes an impressive assortment of high-caliber brand names that should be familiar to audiophiles: MIT MultiCap; Solen and WIMA caps; Vishay, Caddock, Mills, Roderstein resistors; Cardas binding posts; and Kimber Kable hookup wire.

Right out of the box, the POWER 3 sounded polite and veiled. Of course, MIT MultiCaps are notoriously slow to break in, requiring on the order of forty hours to mellow out. Whether it's these caps or some of the other parts as well, the Power 3 certainly needs a protracted break-in period to reach its full sonic potential. The Manual recommends a minimum of seventy hours of playback before critical listening. I suggest that you don't do any serious listening until a week of break-in has gone by.

The one sonic aspect that caught me by complete surprise with the POWER 3 was the exceptionally low-level of third and other odd-order harmonics. In my experience, just about all high-powered tube amps cast a glare over the upper mids and lower treble. The degree of textural brightening may range from just-noticeable to overbearing; but, because it is a dissonant effect, in the long run it is always tiresome. I was expecting some of that with the POWER 3 in the loop, but to my surprise musical overtones remained perfectly natural. I was fortunate to have this amp on hand during the final voicing phase of the Samadhi Acoustics Experience loudspeaker-my most recent speaker-design project. Voicing a speaker is a delicate business. It's so easy to tweak the sound to suit a particular amp or piece of music. Indeed, it's quite possible to max out the sound of a speaker with a given amp (I know, I've done it), only to find out that it then sounds horrible with another amp. That's why it only makes sense to consider the merits of power amps in the context of specific loads. The world's greatest amplifier? Just a myth in my opinion; always consider system context. That's why the issues of equipment compatibility and a systems approach to audio are so highly valued at Fi.

My strategy is to use a variety of amps and a range of music to judge the various tradeoffs. Pentodes, triodes, push-pull, single-ended, Eric Clapton or Mozart-they all ought to perform decently. My intent is not to create a speaker that masks or homogenizes amplifier differences. After all, pentodes and triodes do have distinct harmonic signatures, and each partnering amp's personality should be clearly audible. My design philosophy is that, power considerations aside, any amp should not be embarrassed by the speaker it is coupled with. Of course, favorites do emerge, but no amp should have to make apologies.

During this process, the POWER 3 made it possible for me to increase the presence region and lower treble balance of the Experiences 1-to-2 dB, with no objectionable side effects (whereas the Mesa Engineering Baron objected stridently to the same treble balance). As a result I'm pretty certain that the POWER 3 must have been voiced around a metal-domed tweeter. In any case, here's an amp that is ideally suited to dealing with the overly-assertive treble character of aluminum and most titanium dome tweeters.

The character of the POWER 3's midrange was every bit what you'd expect from a tube amp: suave and full-bodied. Symphonic music was catered to with exceptional authority and verve. Orchestral foundations were fully fleshed out, and various harmonic threads were clearly resolved. Clarity without brightness-now that's a novel musical concept.

Which brings me to Fi Magazine's classical sampler CD, titled The Originals. LAK handed me an advance copy at the Hi Fi '97 Show in San Francisco. It is a unique sampler, indeed, chock full of absolutely first-rate excerpts from Deutsche Grammophon's vast archive of musical masterpieces. Now that I've listened to it over and over again, I can tell you that it's absolutely delightful. Some of my favorites tracks are the Bach Concerto for Two violins, first movement, with David and Igor Oistrach, and the emotionally charged third movement from Bartók's Piano Concerto No. 2 with Geza Anda. But the piece I want to direct your attention to now is Wilhelm Kempff's interpretation of Beethoven's Sonata No. 8, Pathétique, recorded during the golden age of stereo back in 1965. This reissue destroys earlier releases as far as sense of presence, bass register authority, and feel for the Beethoven-Saal in Hanover are concerned. With the SF gear in the chain, the emotional salvo and sonorous timbres projected by this recording were so intense that I wouldn't have dreamed of leaving the listening room until the music subsided. In general, the POWER 3 and LINE 3 managed to reproduce the Fi/DG Sampler CD with full-bodied impact and liquid textures. If that's not how this CD sounds in your system, don't blame the messenger; it may be time for those system upgrades you've been putting off for awhile.

The LINE 3 preamp effectively complements the POWER 3 in terms of speed and transient control. Its ultra-wide bandwidth extends out to about 1 MHz and translates into a sense of transient speed that I've never before experienced from a vacuum tube preamp. The leading edge of each transient was defined with laser precision, while transient decay was elucidated without-and I mean without-any audible smearing or resonance right down to the noise floor of the recording.

This level of performance is on par with the best of solid-state land from the likes of Cello, Krell, and Mark Levinson, the one big difference, however, being how these two opposing breeds of preamplification portray harmonic colors and spatial outlines. The absolutely worst preamps of all time have got to be transistorized designs from the '60s and '70s. You know the type-plenty of bass and detail, but murky and thin as cardboard cutouts. Decent solid-state designs began to appear in the '80s and there are plenty of high-end solid-state designs to choose from in the '90s. Yet, as Audio Research so aptly proved in the '70s, tubes are hard to beat when it comes to palpability and vividness of harmonic colors. To my ears, solid-state preamps have yet to match tube performance in these areas. (Most annoying for me is their blandness or bleaching out of harmonic colors.) When you add to the picture solid-state's less sensitive ear for music's dynamic nuances , even the most expensive transistor offerings leave my soul unmoved. What's unique about the LINE 3 is its union of traditional solid-state strengths with considerable tube magic.

On top of this, the LINE 3 comes loaded with useful features that not only facilitate standard two-channel listening but also enable it to thrive in home theater and headphone listening environments. Even with the inexpensive Grado Labs SR80 headphones, I was able to enjoy headphones as never before. Over the years, I've listened to some of the world's finest headphones, including the best electrostatics around. I still own a pair of Stax, but I rarely use them. If there happened to be a larger selection of binaural recordings out there, the story might have been different. But I've always been a bit distracted and, well, freaked out by a standard stereo recording's placement of an entire orchestra between my ears. The Headroom circuit greatly improves the spread of instruments and the LINE 3's built-in headphone amp module is so clean that, as I gaze into my crystal ball, I see my headphone listening time on the rise. Another bonus is this preamp's low output impedance: you'll never have to worry about driving long, reactive interconnects with the LINE 3.

I do wish, however, that the LINE 3 were just a bit more tube-like in character. It lacks the last measure of spatial delineation and organic flow as exemplified by, say, the Air Tight ATC-2. There's also little of the latter's romantic halo. Neither is the LINE 3 the equal of the Jadis JP80MC in rhythmic flair and liquidity of harmonic textures. But when it comes to bass control and resolution of low-level detail it is without peer in its genre.

In the case of the POWER 3, I would also add to my wish list a bit more soundstage transparency and bass punch. As I've already mentioned, the amp is quite veiled right out of the box, but even after the prescribed break-in period a slight veil remained. At times, it took a little more mental focus than I wanted to expend in order to step into the recording's acoustic. With speakers that were polite to begin with, the Power 3 gave an even more laid-back impression. To paraphrase the trite saying about the three cornerstones of real estate, what matters most in audio is component matching, component matching, and component matching. Mated intelligently, the POWER 3 pleased me greatly, and I'm a hard guy to please. Bass extension is exceptional for a tube amp, though at no time was I fooled into mistaking the POWER 3's bass performance for that of a Krell. But then you don't buy a tube amp because of its killer bass. As with other high-power tube amps I've auditioned, the POWER 3 was also slightly reticent in extracting the music's microdynamics. I found myself cranking up the volume higher than I normally would to capture the music's boogie factor. It seems that such amps like to idle at several watts. With high efficiency speakers, this is a problem, as only a fraction of a watt is required for reasonable playback levels. So keep the POWER 3 away from 95+ dB efficient speakers.

For both the POWER 3 and LINE 3, the ruling passion is tonal neutrality. Neither unit is inclined to tilt the balance in a particular direction. Paradoxically, for some audiophiles the lack of euphonic colorations may in fact be a disadvantage. I've observed over the years that at times the more flawed the product, the more ardent its devotees. Well, I'm sorry but there are no presence region peaks or phasey highs to groove on here. These products approach the task of musical reproduction from a natural perspective. A premium is placed on timbral realism and tonal accuracy. Whether it be a simple melody or the most complex of harmonies, the Sonic Frontiers gear illuminates the music's tapestry, yet allows it to ebb and flow unimpeded. The LINE 3 and POWER 3 have joined that select group of products that I can confidently recommend to friends and family. Superbly engineered and superbly executed, this duo extends the Sonic Frontiers tradition of exceptional value. Bravo!

Technical Sidebar by Dick Olsher 1. THE POWER 3 MONO AMPLIFIER SF's POWER series of power amps was designed as a group and as a result shares many design features. Low-distortion at any power level was a paramount design goal. Reproduction of subtle detail was sought together with harmonic accuracy. Four feedback loops are used to reduce distortion and increase damping factors. Unlike many conventional tube amps and essentially all single-ended designs, the POWER series offers high damping factors. This minimizes speaker-amp interactions. Expect this amp to leave your speaker's frequency response intact. It will not roll off the highs or fatten out the bass. The circuit topology is fully balanced from input to output to minimize distortion. The voltage gain and driver stage is based on the exceptional "cross-coupled phase inverter" circuit. The output stage features an octet of the Svetlana 6550C beam power tube and is operated push-pull in partial triode mode for increased linearity. 2. SONIC FRONTIERS LINE-3 The LINE-3 is NOT a minimalist design. In fact, Sonic Frontiers believes that you can have a feature-rich product without compromising sound quality. The LINE-3 is proof that you can have your cake (i.e., features) and eat it too. The entire LINE series of preamps features an all-tube gain stage and symmetrically balanced topology. The main circuit board is decoupled from the chassis via an elastomer mount suspension to reduce microphonics. The output is direct coupled: there's no output coupling cap. A servo is used together with a backup safety circuit. As a result, output impedance is extremely low at 45 ohms. This preamp should be able to drive long cable runs with the greatest of ease. A total of twelve tubes is used (ten 6922 and two 6GH8A) in an innovative circuit of low-distortion and extremely wide bandwidth. The outboard power supply is dual mono and is exceptionally well regulated. The LINE-3 makes extensive use of Vishay and Caddock film resistors and top-grade MultiCap capacitors. Sonic Frontiers firmly believes that "God is in the details."

A Few Additional Thoughts About Life On (er... With) The Frontiers... Dick Olsher, we decided quickly enough, was the right reviewer for these products. A sophisticated engineer, he was able to appreciate and explain the advanced technology that went into the designs. I want to add a few comments from a perspective that may be relevant for a different type of consumer: 1. USER FRIENDLINESS From the preliminary instructions on how to unpack the amps to the comprehensive and comprehensible owner's manuals to the white gloves that are provided to avoid getting oil on the tubes to the biscuit-shaped remote control (so intuitive and easy that I was using it in complete darkness just an hour after set-up), these are the most user-friendly, ergonomically correct tube products I've come across-the ones to try if you've been hankering for tubes, but are afraid of tube hassles. 2. VALUE To be sure, these products are far from inexpensive. Nevertheless, I believe they deliver tremendous value to high-end consumers. Well designed and very well finished, they're not over-the-top glitzy. Instead, SF put its money where it counted most-in design, engineering, parts, and assembly that deliver great sonics. The result is components that compete even-up, no quarter asked and none given, with gear costing far more-in the case of the amps five or more times more! 3. SONICS I have no disagreement with DO's observations, but I may be even more enthusiastic than he. After the Sonic Frontiers had been broken in for better than 300 hours, the veiling Dick commented on completely disappeared in my system, leaving a sound that was extremely transparent and revealing of the textures of instruments. (A lot of my Thiel CS6 listening was done with these components; so, what I said about those speakers applies to the Sonic Frontiers electronics, too.) Great stuff! -Larry Alan Kay