Sonic Frontiers Power 2 power amplifier
"Hey, Bob Reina! I enjoyed your review of the Cary SLM-100 amplifier in the May 1996 Stereophile. So you're still looking for your dream amplifier under $5000? Well, here it is! The Sonic Frontiers Power 2. A review sample will be ready for you in two weeks. What's your shipping address?"
"Uh, well, actually, I have quite a full plate of review samples in-house, so I really wouldn't be able to get to your amp for quite some time. It looks like a very interesting design, but maybe you'd be better off having it reviewed by someone who could get to it a bit quicker."
Johnson's facial expression resembled that of the young executive who's just been told he's not getting the promotion he'd expected.
"But this is a direct trickle-down from our Power 3 200W monoblock! What we've done is make a 110W stereo version on one chassis. You've got to hear this thing!!"
"Well, let me discuss it with Wes Phillips."
Ultimately, I was able to squeeze the Sonic Frontiers into my review schedule. Aside from the fact that I enjoy reviewing four-6550/KT88-pentodes-per-side tube amplifiers because they tend to be very versatile and cost-effective, I was especially interested in the Power 2 because:
1) I have two well-heeled audiophile friends who constantly rave about their Power 3 amplifiers. Both of these guys are very picky and can afford anything on the market.
2) Sonic Frontiers' President, Chris Johnson, claims that the designs of the Power 2 and 3 amplifiers are so close that, if one owns speakers that require no more than 100W per side, he would not be able to tell the difference between the 2 and the 3. And my easy-to-drive Alón V Mk.IIs sing quite happily on 100Wpc, thank you very much.
The overall topology of this 110Wpc push-pull amplifier comprises an input cathode follower (6922) and two differential plate-loaded voltage amplifiers (6922s) in cascade, followed by a driver cathode follower (5687WB) direct-coupled to the output tubes (KT88).
The amplifier is fully balanced throughout, including the output transformer. The input voltage amplifier configuration allows balanced as well as single-ended inputs, and balanced feedback to be used. The second voltage amplifier is direct-coupled to the output of the first, and uses both positive and negative power-supply voltages. Next, the cathode followers are capacitor-coupled from the second voltage amplifier, and these are in turn direct-coupled to the output tubes. Balanced feedback from the secondary of the output transformer is returned to the first voltage amplifier, but the input signal is isolated throughout the input cathode follower. Sonic Frontiers claims this eliminates any influence the feedback has might have on the input signal and results in lower distortion than conventional feedback techniques. Finally, the amplifier uses an inner positive-feedback loop, which serves to lower the amp's output impedance and which, the company claims, further results in a higher damping factor and lower midband distortion.
Sonic Frontiers is fanatical about providing very high parts and construction quality for the money. The Power 2 is no exception, sporting parts from MIT MultiCap, Solen, Vishay, Roderstein, Cardas, and Kimber. Convenience features also abound: In addition to balanced, single-ended inverting and single-ended non-inverting inputs and individual power-tube biasing, the Power 2 has a standby function (to extend tube life) as well as a mute function (to enable interconnect changes while the amp is fully powered, as well as to facilitate tube biasing).
Setup & System
For $4495, the Power 2 purchaser will also receive a set of screwdrivers, a biasing tool, tube coolers with O-rings, an extra fuse, and a set of cotton gloves to keep from tainting tube glass with body oils during installation. The amp also comes with the most comprehensive owner's manual I've ever seen—an entire page is dedicated to the proper method of installing tubes.
Don't you hate manufacturers who list detailed unpacking instructions in their owner's manual—which, of course, you can't read until after you've unpacked the amp? What I hate even more is packing up the stuff—especially the heavy stuff—and shipping it back to the manufacturer. So my favorite Power 2 accessory is a sheet of paper accessible on the top of the box. This shows, step by illustrated step, the easiest way to pack and unpack this 110-lb monster (most of whose weight is, awkwardly, on the transformer side). Following Sonic Frontiers' instructions, it took me less time to pack this baby up than any product in my 13-year reviewing experience (and it was the second heaviest product I've ever reviewed).
For this review, I used a Goldmund Studio/Syrinx PU-3/Koetsu Urushi/Vendetta Research SP-2C and California Audio Labs Delta/Sigma II front-ends, Audible Illusions Modulus L1 line-stage, and Acarian Systems Alón V Mk.II speakers. Wires included MIT Digital Reference and MI-350 Twin CVTerminator interconnects, and Acarian Systems Black Orpheus tri-wired speaker cable.
What I've found most fascinating about banging around the reviewing community for as long as I have is how different reviewers can hear the same thing in a given component and not only differ in their reactions to it, but use the same descriptive vocabulary differently in verbalizing their opinions.
I had such an experience with the Power 2.
I liked the Power 2 very much—I would be quite happy using it as my reference power amplifier. But when I'd completed my listening for this review, I had trouble coming up with words that summarized what I liked best about it.
A reviewer from another magazine gave me an idea. Said journalist was visiting my summer place for the weekend, and we were hanging out listening to obscure alternative music. Of course, I am bound by the Stereophile Prime Directive not to reveal to anyone my views of equipment under review. (JA installs this little chip under the scalp when you join up. It doesn't really hurt, and, hell, Uncle Larry pays for the surgical procedure.) But my friend was free to say what he pleased; he wasn't reviewing the amplifier.
My friend was not impressed. "Yeah, it sounds like a Sonic Frontiers amp. It's boring!"
That's the word I was searching for. I love the Power 2 because it's...boring!
Okay, I'll explain. As far as listening biases are concerned, I have two primary drives. First, I am a flaw-minimizing audiophile, not a strength-maximizing audiophile. I'm not the kind of guy who will settle for an egregious coloration in order to achieve sonic nirvana elsewhere in the spectrum. If a component's got a big zit somewhere, it gets knocked out of the box pronto. The Power 2 had remarkably few flaws, and those it had were minor—and, I suspect, would be easily dismissed by most listeners.
Second, I have a high regard for products that present a balanced sound—products whose strengths are uniform across the timbral and dynamic spectra, as opposed to products that excel at one frequency extreme at the expense of another, or whose dynamic performance is uneven at different frequencies or volume levels. In this respect, the Sonic Frontiers Power 2 had many, many strengths that were uniform across the sonic spectrum. But none of them particularly called attention to themselves.
So the Power 2 is boring—because its few flaws are not very noticeable, and its strengths are many and balanced across the frequency and dynamic spectra. The strengths of the Power 2 that most impressed me were: 1) exemplary dynamics, micro and micro; 2) superb resolution of inner detail; and 3) realistic soundstage presentation. Images were placed with holographic precision on a wide and deep stage, with a bit of a laid-back spatial presentation (mid to rear of hall; say, Row L).
With such performance characteristics, one would expect the Power 2 to excel in reproducing well-recorded classical music, and it did. On Classic Records' reissue of Pulse (New World/Classic NW 319), John Cage's Third Construction was reproduced with layers of depth, and the low-level dynamic nuances of the percussion instruments came through as "live." Interestingly, the transient reproduction of this amplifier was extremely fast, but without a hint of sharpness or edge.
The definition of individual instruments on Kohjiba's The Transmigration of the Soul, from Stereophile's Festival CD (STPH007-2), was captivating. The woodblocks resonated in real space after they were hit, and the slaps of bows against strings were sharply defined. The pitch definition on the timpani was extraordinary—for the first time it became clear to me that, in the middle section of the piece, the timpani were actually playing a contrapuntal melody against the female vocal line. On the Previn performance of Messiaen's Turangalîla Symphony (EMI SLS 5117, LP), the piano reproduction was natural and airy; gongs shimmered realistically, and the bass drum was powerful and deep. I clearly heard the trombones resonate in the recording space against the back wall of the deep stage.
Though the Power 2 was very revealing, I wouldn't call its presentation "analytical." Its natural perspective was very easy to listen to: relaxed but not slow, laid-back but not rolled-off. And it sounded much more powerful than any 110W amp I've ever heard.
The Power 2 did have two colorations that deviated from complete neutrality: Its overall silky and liquid presentation was combined with a forward midrange. This added an emphasis to certain woodwind instruments at the expense of instruments whose predominant energy profile is in the lower-midrange/upper-bass or high frequencies. Also, the midbass was a bit fat and forward, but was obtrusive only on recordings with prominently mixed electric bass guitar—like Mighty Sam McClain's Give It Up to Love (AudioQuest AQ-1015).
These colorations did not interfere with well-recorded strings—the solo violin on Boult's interpretation of Rachmaninoff's Symphony 3 (EMI ASD 2185, LP) was arresting—nor were vocals or brass particularly affected; the layered vocals and French horns along the back wall on Cantate Domino (Proprius 7762) were as lifelike as I've ever heard them.
The Power 2's colorations are best described as "sunny and warm." The opening track of the Ginger Baker Trio's Going Back Home (Atlantic 26522-2) has a happy Caribbean lilt. With the Power 2, Bill Frisell's guitar was a little forward and Charlie Haden's bass was a bit thick, but who cared? I was sitting in the hot sun on some Caribbean island, swaying gently in the hammock, Pi;tna Colada in hand.
When compared with my reference, the long-discontinued Audio Research Classic 60, the Sonic Frontiers Power 2 presented an interesting tradeoff of strengths and weaknesses. The Classic 60 had the more neutral midrange and midbass presentation, but the Power 2's high frequencies were much more convincing. The ARC did not, however, approach either the low-level or high-level dynamic capabilities of the Power 2. And, although one of the Classic 60's strengths is its resolution of inner detail, the Power 2 exceeded the 60's performance in this area by a great margin. All in all, although the Classic 60's character is more in tune with my own listening biases, I felt that the Power 2's performance was a significant step higher.
Chris Johnson, designer Mike Kerster, and the Sonic Frontiers team should be congratulated for their high-quality, user-friendly, and superb-sounding Power 2 amplifier. Although its character may not be to everyone's taste, anyone considering spending close to $5000 on a power amplifier would be a fool not to audition the Power 2. It's one of the finest-sounding amplifiers I've ever had in my home.