Tube Power Amp Reviews

There's a wonderful, unjustly obscure 1981 Chico Freeman album, The Outside Within (LP, India Navigation 1042). The first track on side 2, "The Search," begins with a very slow, bluesy duet between Freeman's bass clarinet and Cecil McBee's bowed bass, the two playing in perfect unison. A good test of midbass clarity is whether the two players sound clearly distinct up and down the scale, tonally, spatially, and harmonically—ie, whether you can pinpoint where each is standing on the soundstage and which player is bowing, which blowing. The Atlas passed the test, but not with aces; I had to listen really closely, and it helped that I'd heard the track often before.

Back to Górecki and another stereotypical deficiency of inexpensive tube amps: When the violins started playing higher and louder, they did sound a bit pinched—I suspect because the Atlas was rolling off the uppermost overtones. The suspicion was reinforced 12 minutes into the first movement, when much of the orchestra sits out, leaving the playing to a chamber-sized ensemble. Through some (usually more expensive) amps, I suddenly get a vivid picture of the hall—I hear empty space, the reverberation of fewer musicians in a space that had been saturated with sound in the more full-blown passages. With the Atlas, I could tell that fewer players were playing, but the music merely sounded quieter; I didn't get that sense of altered spaciousness.

There were similar shortfalls of ambience on a number of albums recorded in large spaces. On Miles Davis' Live Around the World (LP, Warner Bros. 9362 46032-1), a terrific compilation of his concert performances from the late 1980s and early '90s, with excellent sound on CD (and better still on this European two-LP set), listen particularly to Miles' take on Cyndi Lauper's "Time After Time." Through some amps—for instance, the Krell FPB-400 that I had on loan until recently—it sounds as if the hall's ambience extends all the way to my ceiling. With the Atlas, it went about halfway up. I was in the hall, but not completely.

But back to the Górecki again—and on to good news: About 13 minutes into the first movement, soprano Dawn Upshaw begins to sing in front of the orchestra, and I melted: such a gorgeous voice, such full-bodied 3D presence. To the extent that the rest of my system captured Upshaw's subtle shifts of inflection, her slight dynamic contrasts, her crisp, subtly rolled r's, the Atlas let it all flow through without obstruction. Several minutes before that, at around 5:10, when the violins enter, they sounded so warm and silky—that magical tube midrange—and I could hear individual instruments.

On that Miles Davis album, too, his trumpet sounded so golden, and I could hear the subtle variations of his breath on the mouthpiece. All the players appeared palpably on the stage—not as Etch-a-Sketch approximations but as fully rounded musicians, blowing, strumming, or pounding their instruments. And speaking of pounding, the drums were way back there.

When it came to imaging in general—left to right as well as front to back—the Atlas was a champ. Listen to Omer Avital's Asking No Permission (CD, Smalls Records 011), a rousing jazz-sextet session—bass, drums, one alto sax, and four tenor saxes—recorded live at Smalls, a (yes) small club in Greenwich Village, with superb balance and minimal miking. Especially on the final track, "The Field," I could identify the positions and the distinct tone of each horn player. One of them (Mark Turner, I think) stands just inches behind and to the left of the right speaker. Sometimes, with some equipment, some recordings, and enough concentration, you can mentally force a right-center sonic image into the right-channel speaker. I tried very hard to squeeze Turner back into the speaker box and couldn't. That is a testament to the skills of Luke Kaven, Smalls' engineer-proprietor, but no less to those of the Rogue Audio Atlas.

Nor did the Atlas confine images to the space between the speakers. On Miles Davis' Kind of Blue (LP, Columbia CS 8163 or any of Classic Records' many vinyl reissues), John Coltrane's tenor bellowed, as it should, from way to the left of the left speaker. Ditto for the bass drum on "Jonah," from Paul Simon's underrated "middle period," on disc 2 of his three-CD boxed set, 1964/1993 (Warner Bros.). In other words, at least by this measure, the Atlas didn't seem to suffer any severe phase problems.

As for dynamics, the Atlas wasn't ideally suited for big, loud music, whether Mahler or metal. Back to the Górecki one last time: Toward the end of the first movement, at around 16:00, as the orchestra builds to a crescendo and the music gets higher, louder, and finally hits full throttle, it didn't break up through the Atlas—I still heard all the parts, all the instruments—but it did get harsh. Maybe 55Wpc go only so far.

But the Atlas was extremely agile at handling dynamic contrasts; the subtle shifts of emphasis—the release of a piano pedal, a singer's accent on a syllable, a slightly harder or softer guitar strum—as long as the decibel levels weren't very high overall. In other words, it was excellent at capturing the differences between f and ff or pp and ppp, less so at distinguishing ff from fff. On the late Lorraine Hunt Lieberson's ravishing disc of Bach's Cantatas 82 and 199 (CD, Nonesuch 79692-2), the Atlas flawlessly conveyed her voice's slightest shifts, the baroque oboe's quivering vibrato, the organ's pulsating reeds and pipes. Or check out Don Pullen's final album, Sacred Common Ground (CD, Blue Note 8 32800 2), especially its penultimate track, the bittersweet ballad "Resting on the Road." Pullen was a blazingly precise jazz pianist—sort of Cecil Taylor in his right hand, gospel blues in his left—and this was the last tune he recorded before dying of cancer at age 51. He injected more poignant pauses than usual into this solo, extending rubato to just short of the breaking point. When I hear this solo on a system that's great at dynamic contrasts, I can't help but tear up. The Atlas aced this test.

Just as the Atlas was best at getting the dynamic details at mid-level decibels, it was best at getting the textural details at midrange frequencies. On that same Don Pullen track, off to the right of the soundstage, someone softly plays drum skins with his palms. The Atlas captured the tonal color and texture of bare hands on drum skins. When Santi Debriano plays his bass's middle and upper strings, I heard the details of his plucking and the resonance of the wood; when he plays the lowest string, I didn't so much. The same was true with Wendell Marshall's bass on Duke Ellington's wondrous Masterpieces by Ellington (CD, Columbia 87043), an album recorded in 1950 that, except for the mono, sounds as you-are-there real as almost any modern audiophile disc: plucky and woody the higher Marshall played, more like a soft test tone the lower he went.

One thing needs emphasizing, about not just the Atlas but tube amps in general: the importance of matching the amp's impedance to that of the speakers. Initially, I listened with the Atlas's impedance set to its default mode of 8 ohms. The bass was soft to the point of flabby. On the Górecki, there was no sense of bowing on the double basses or the cellos—no sense of anyone playing the instruments. The midrange was warm, but the music lacked vitality. Looking into matters more closely, I realized that the speakers I'd been using for a while, the magnificent Verity Audio Parsifal Ovations, have drivers with different impedances: the two-way satellite, with tweeter and midrange, is 8 ohms; the woofer is 4 ohms. (I'd previously been using a Krell solid-state amp, which handles any impedance down to well below 4 ohms, so this wasn't much of an issue, and I paid no attention to it.) When I switched the Atlas to 4 ohms, thus matching it to the woofer, the bass didn't go from night to day, but it did take on some life. The bowing was suddenly palpable, at least as far down as the cellos.

Switching the impedance had little effect on the treble and practically none on the midrange. In some particularly high and loud passages of symphonic strings or screaming guitars, the sound sometimes got a bit steely at the 8 ohm setting, and less so, but a bit more rolled off, at 4 ohms. The difference was very slight in any either case, much less marked than the difference in the bass. For the purposes of this review, I listened to the same music, carefully, on both settings. All my comments here apply to the 4 ohm setting, except for my comments about high-frequency rolloff, which are taken from my notes on the 8 ohm setting. In other words, even at 8 ohms, the Atlas truncated the extreme highs—just not quite as much as at 4 ohms.

Conclusion
I have tried to weigh the Atlas' merits and flaws irrespective of its pricetag. But in conclusion, I'll get real: we're talking about a $1395 amplifier. By that measure, the Rogue Audio Atlas is a spectacular success—lively, enjoyable, an ideal entry to the High End for someone on a budget. I'll go further: I could live with it.