Rogue Audio has been designing and building tubed electronics in Brodheadsville, Pennsylvania, for over 20 years. In that time, the company has established a reputation for exceptional performance at reasonable prices. To achieve his performance goals, Rogue’s president and chief designer, Mark O’Brien, believes in applying solid engineering principles, careful parts selection, and attention to details and in manufacture. What O’Brien doesn’t believe in is showy marketing, smoke and mirrors, and coming out with new models just to keep his customers on the upgrade carousel. As such, when Rogue introduces a new edition of a model that has been in their portfolio for over a decade, it’s because he and his team think they’ve found a way to make improvements to something other than the nameplate.
Enter the subject of this review, the Atlas Magnum II stereo power amplifier ($2395 USD) -- a fully tubed design capable of delivering 100Wpc. This solid piece of equipment measures 18”W x 5.5”H x 17”D and weighs a hefty 50 pounds. Its case is mostly of stamped steel with a matte-black powder coat; the faceplate of machined, anodized aluminum is available in silver, or the handsome black of my review sample. The eight tubes, large power and output transformers, and power-supply capacitors stand proud of the amp’s top deck. Rogue offers an optional tube cage; the rest of us can enjoy an unobstructed view of the glowing glass.
The front panel sports only the pushbutton power switch -- an LED to its right glows blue when the amp is on -- and the names of the model and manufacturer. On the rear panel are gold-plated RCA jacks for the left- and right-channel inputs, and one pair of gold-plated speaker binding posts per channel. The Atlas Magnum II’s output transformers have taps for 4 and 8 ohms, but changing from one impedance to the other requires removing the top panel, and moving the wires connected to each positive speaker terminal to the appropriate terminal on each output transformer. Also on the rear panel are an IEC inlet for the removable power cord, and a fuse bay.
The Atlas Magnum II employs two 12AX7 and two 12AU7 tubes, as well as four KT120 output tubes in a push-pull configuration. The output tubes’ bias is adjusted manually and individually. On the positive side, this means that if one tube fails, you don’t have to buy an expensive matched set. And rather than making you fumble with a multimeter and test points on the circuit board, Rogue has thoughtfully provided an analog bias meter on the top deck, and tiny toggles to switch it in and out of each tube’s circuit. The manual also provides a detailed bias procedure that even someone new to tubes shouldn’t take more than 15 minutes to complete after the amp has warmed up.
Changes from the original Atlas Magnum include many discriminately selected parts, alterations of the circuit design -- including a new grounding scheme -- and a bigger power supply. The last was required to fully support the stock KT120 output tubes, which have increased the Magnum’s specified power output to 100Wpc into 8 or 4 ohms. Although the higher output is welcome, Mark O’Brien told me that the switch to KT120s was primarily due to sound quality. The Atlas Magnum II still supports KT77, EL34, 6550, KT88, and KT90 tubes, for those who want to experiment with other sound signatures.
I used the Atlas Magnum II to drive a pair of Esoteric MG-10 two-way minimonitors, at times with a REL R328 subwoofer connected via its high-level inputs to the Rogue’s speaker posts. As preamplifiers, I used both Rogue Audio’s own RH-5 and my Grace Design m902 headphone amplifier-preamplifiers. Sources were my Ayre Acoustics C-5xeMP universal BD player and the DAC in the Grace m902, the latter receiving signals via optical connection from a Google Chromecast Audio: music stored on my NAS or streamed from Spotify.
I encountered no operational quirks during the extended time I had the Atlas Magnum II in my system. It was exceptionally quiet, and not just for a tube amp. With no signal playing, I had to put my ear within inches of a loudspeaker to hear even a whisper of white noise. From my listening seat, the only way to tell that the amplifier was on was to glance at its power indicator or glowing tubes. Although every Rogue product is burned in at the factory, I let the Atlas Magnum II play for a couple hundred hours before taking any listening notes. I heard no substantial change in its sound over that time, although, as with most amps, I did find that it needed a few hours of warm-up each time I turned it on before the sound was fully fleshed out. If you audition the Atlas Magnum II, be sure the dealer knows you’re coming, and can give the amp time to hit its stride before you arrive.
For some people, the ideal power amplifier is one that imposes on the signal passed through it no character of its own -- all it does is increase that signal’s level. However, I think that most people who want a tubed power amp want one that adds something to the music passed through it. After trying the Atlas Magnum II with two preamplifiers that are also headphone amplifiers, I found that the Rogue did have some character of its own, but not so much as to obscure the differences between the preamps. Most of my listening notes refer to what I heard with the Atlas Magnum II connected to the more neutral preamp, the Grace Design m902, and thus better highlight what the Rogue did and didn’t bring to the music.
One recording that revealed many aspects of the Atlas Magnum II’s sonic character was Ole Bull’s Concerto Fantastico, with solo violinist Annar Follesø and Ole Kristian Ruud conducting the Norwegian Radio Orchestra (SACD/CD, 2L 2L-067-SABD). The opening mezzo-piano notes in the trumpets had a controlled, covered brassiness, while the later forte passages exhibited greater brilliance. The entrance of the low strings was rich and full-bodied while maintaining adequate pitch definition. I’ve heard this recording through dozens of combinations of gear, and expect the sound of the solo violin to be more focused on the strings than on the instrument’s body -- and through the Grace-Rogue pairing, that’s what I heard. Lower notes had the distinct texture of bow hair scraping wound strings, and higher notes soared without ever turning steely. In fact, through the Atlas Magnum II, it was easy to hear the difference in violin sound between this 2L recording and one of Julia Fischer performing the Tchaikovsky Violin Concerto, with Yakov Kreizberg conducting the Russian National Orchestra (SACD/CD, PentaTone Classics 5186 095). The latter is a much warmer recording that emphasizes the sound of the violin’s wooden body and sweetens the sound of the strings. With both, I think the Atlas Magnum II added a touch of warmth to the Grace’s fundamentally neutral sound, but I felt it was all to the good. Substituting Rogue’s own RH-5 rendered all of the above a few shades warmer/darker. I enjoyed that sound too, though I think it was probably less faithful to what the microphones picked up in the recording sessions.
This recording of Concerto Fantastico has a wide dynamic range, and through the Atlas Magnum II, the orchestral tuttis and bass-drum strokes that follow from silence or a lone solo violin note were explosive. The Atlas Magnum II also conveyed enough low-frequency information for me to tell that this one was a properly large concert bass drum. That was in contrast with the kick drum in “Lose Yourself to Dance,” from Daft Punk’s Random Access Memories (24-bit/96kHz FLAC burned to DVD-A, Columbia), which is miked and mixed to have an extra dose of low-frequency energy, but lacks the sense of the symphonic instrument’s sheer size. On the other hand, the Rogue delivered punch from that kick drum that I could feel in my chest -- even with my subwoofer off. Yes, I’ve heard even punchier bass from some solid-state amplifiers, but it’s not a given that any particular solid-state amp would be able to deliver kick drums and the like with any more force than the Atlas Magnum II brought to bear.
For another perspective on the Atlas Magnum II’s sound, I cued up The Duane Allman Anthology (CD, PolyGram 831 444-2 Y2). The variety of tones that Allman coaxed from his Les Paul in “Going Down Slow” ranges from bluesy purr to searing. In “Rolling Stone,” with Johnny Jenkins, the Grace m902 and Atlas Magnum II crisply reproduced the buzzing, jangling upper harmonics of Allman’s slide acoustic guitar, sounding edgy enough but never too edgy. Swapping in Rogue’s RH-5 for the Grace m902 toned down the upper harmonics a bit and sweetened the sound. Again, that was probably less faithful to the recording, but I know that a great many listeners prefer a tonal palette that’s warmer than neutral, and with this recording I found the Rogue-Rogue pairing more to my liking. One of the advantages of using a power amplifier such as the Atlas Magnum II, which only slightly alters the signal it’s fed, is the ability to choose a preamp that will give you the tone that best fits your preferences.
I also heard notably different soundstage presentations from the Atlas Magnum II, depending on the preamplifier with which it was partnered. When used with the Grace m902, the Rogue could produce soundstages that were both wide and deep, with commendably precise and vivid positioning of aural images. With the Ole Bull recording, the orchestra was spread out beyond my speakers to left and right, and from a few feet behind the speaker plane to a few feet beyond my front wall. Separate sections of the orchestra occupied distinct areas of that soundscape in the width and depth dimensions, and there was an appreciable sense of the hall’s acoustic. I particularly noticed, in the third movement, some softer timpani notes coming from far back on the left side of the soundstage. Timpani are tuned by using a pedal to adjust the tension on the drum head, and when tuned low in the range of a particular drum, the slightly loose head has a characteristic sound. The Atlas Magnum II rendered that sound in the context of the venue’s acoustic with remarkable fidelity.
The sense of space I heard with the Ole Bull concerto is inherent to the recording, not an imposition on the signal by the Atlas Magnum II. By contrast, Duane Allman’s electric guitar in “Rolling Stone” emanated distinctly from my left speaker. Switching from the Grace m902 to the Rogue RH-5 pushed the front of the soundstage back a bit with all recordings I played through both pairings. But while the RH-5 maintained a good sense of soundstage width, there was somewhat less discrimination in depth. On the other hand, the soundstage felt fuller and denser with the RH-5. Just as with tonality, the fundamental neutrality of the Atlas Magnum II means that you can choose the preamp that gives you the specific nuances and sound you’re looking for.
I compared the Atlas Magnum II to my longtime reference integrated amplifier, a GRAAF GM 50 ($7500 when last available). The GM 50 is a fully balanced, all-tube design specified to deliver 50Wpc from four KT88 power tubes (I use KT90s, which have marginally higher output-power specs). Output levels were matched at the listening position using an SPL meter.
The GM 50 is not a particularly tubey-sounding amp, but its tonal balance fell between those of the Atlas Magnum II as driven by the Grace Design m902 and as driven by Rogue’s RH-5 -- there was equal high-frequency extension and slightly more warmth in the midrange as with the m902, but a touch more HF energy and not as much saturation in the upper bass and midrange than with the RH-5. As the tonal palette of the Atlas Magnum II can be altered to a substantial degree by selection of partnering preamp, further comparison of these two amplifiers’ tonal characteristics would mostly be unhelpful. The one exception is in bass response.
The GM 50’s bass sounded more open, and seemed to reach deeper than the Atlas Magnum II’s, whether I was comparing them with or without the REL subwoofer connected. (REL claims that using the high-level inputs carries forward the sound of your amplifier, but as my system employs no high-pass filter, the difference with the sub could still be due, in whole or in part, to the differences in how each amplifier drove the main speakers.) For some specific examples, while the concert bass drum in the Bull violin concerto sounded big with the Atlas Magnum II, its fundamental pitch was more obviously lower in frequency with the GM 50. Likewise, it was easier to hear the fundamental pitch of the concert harp in the final movement of Mahler’s Symphony No.4, as performed by the Royal Concertgebouw Orchestra under Bernard Haitink, with soprano Christine Schäfer (SACD/CD, RCO Live RCO 07003). For a nonclassical example, Alan Anton’s bass in the Cowboy Junkies’ The Trinity Session (16/44.1 FLAC, RCA) sounded a bit tubbier with the Atlas Magnum II, a bit more linear with the GM 50. On the other hand, the kick drums in both The Trinity Session and Random Access Memories had noticeably more punch with the Atlas Magnum II -- I felt as well as heard them.
Low-bass extension is closely tied to the perception of acoustic space. Perhaps that’s why the GRAAF GM 50 repeatedly gave the impression of larger recording venues than did the Atlas Magnum II. With The Trinity Session, any good system should convey a sense of the ambient envelope surrounding the musicians. The Grace m902 and Atlas Magnum II certainly did that, but the GM 50 reached farther back toward the edges of the recording venue, Toronto’s Church of the Holy Trinity. However, though the GM 50 accurately positioned the sound of each instrument and Margo Timmins’s voice, the Grace-Rogue system drew the outline of each sound source more starkly against the surrounding ambience. Ideally, I’d like to have that larger sense of space and the well-defined outlines, but the only amplifier I’ve ever had in my system that could simultaneously do both was the Devialet 120.
Rogue Audio’s Atlas Magnum II is everything a modern vacuum-tube amplifier should be: solidly built, easy to set up and maintain, reasonably powerful with very little self-noise, and having a sound that shows a bit of tube warmth without smearing over the details in good recordings. Depending on which preamplifier I used with the Atlas Magnum II, I found I could tailor both its tonal balance and the way it reproduced soundstages. These things make the Atlas Magnum II an excellent choice of amplifier on which to start building a system. The Rogue is hand-built in the US from components sourced as locally as possible. In an industry that may be best known for its ever-higher-spiraling prices, that all of the above can be had for $2395 is nothing short of astounding.
Rogue’s Atlas Magnum II is not only a great amplifier, it’s a great value -- very highly recommended.
. . . S. Andrea Sundaram
- Preamplifiers -- Grace Design m902, Rogue Audio RH-5
- Amplifier -- GRAAF GM 50
- Sources -- Ayre Acoustics C-5xeMP, Google Chromecast Audio
- Speakers -- Esoteric MG-10
- Subwoofer -- REL R328
- Interconnects -- DH Labs Revelation, QED Silver Spiral
- Speaker cables -- AudioQuest GBC
- Power conditioner -- Equi=tech Son of Q
Rogue Audio Atlas Magnum II Stereo Amplifier
Price: $2395 USD.
Warranty: Three years parts and labor; six months, tubes.
PO Box 1076
Brodheadsville, PA 18322
Phone: (570) 992-9901