by John Richardson
Late last summer I was invited to a cookout at the home of an audio buddy of mine, Bill Magerman. I couldn’t refuse, as Bill is an excellent cook and a man of multiple talents and interests. Besides running his blueberry farm in the rural Pocano mountains of Pennsylvania, Bill also heads up Tribute Audio, whose primary business is restoring and rebuilding classic EPI speakers, which is how I first met him. You may also know Bill as a principal partner and chief designer (and builder) at Darwin Cables, a newer company that constructs minimalist high-end audio interconnects and speaker cables. If you own a pair of Darwin cables, they came directly from Mr. Magerman’s workshop. Oh, and if that’s not enough, Bill also is one of the guys who constructs circuit boards for one of the USA’s premier audio companies, Rogue Audio.
Back to the picnic. I arrived with the wife ready to dive into Bill’s cooking when I found that the gathering was a bit larger than I had expected; it seemed that there were around 30 or so folks packed into Bill’s barn. As it turned out, I had been invited to a company gathering for the good people who work at Rogue Audio. For a reviewer and gear hound like myself, this situation turned out to be a great opportunity to pick the brains of the folks who actually design and build these wonderful products. Not only were these people highly skilled technicians, but also music lovers and audiophiles. It was a pleasure to spend time with them, from company head Mark O’Brien down to the folks on the floor who stuff the chassis. And I wasn’t the only reviewer there; I was joined by analog guru Michael Fremer, with whom I had a nice chat about music, gear, and reviewing.
I must admit that I did feel a bit out of place and a tad uncomfortable. Why? Well, I had never before spent any real time with Rogue Audio gear, so I was unable to relate my own experiences regarding the stuff these folks were building. It was one of those classic “oh, crap” moments where this reviewer came up somewhat short and frankly seemed at a loss for words. Little did I know that soon thereafter I would have the opportunity to correct this shortcoming by getting comfy with one of Rogue Audio’s most popular products, the entry-level Sphinx Integrated amplifier. And what a pleasure this relationship has been!
First, let’s begin with some history. Rogue Audio was started up nearly 20 years ago in Broadheadsville, Pennsylvania, where the company still resides. It focuses primarily on the design and construction of quality vacuum tube amplification gear such as power amps, preamps, integrated amps, and phono stages. Over the years, Rogue Audio has earned a reputation for building some of the biggest bang-for-the-buck amplification products in high-end audio, with added value in my book since all of the gear is hand built right here in Pennsylvania (my state of residence as well). After meeting the talented and dedicated people who build it all, color me at that much more impressed. Rogue is also well-known for its high level of customer support, an added bonus that shouldn’t be underestimated these days. I feel like an audio idiot for somehow ignoring this company for so long, and if anyone says that Americans can’t manufacture anything anymore, I’ll just send them over to be educated by Mr. O’Brien, Mr. Magerman, and friends.
On then to the Sphinx. In ancient Greek and Egyptian cultures the sphinx was a wily beast with a lion’s body, wings, and a human head and face. The mythological Greek sphinx which guarded the city of Thebes had an infamous riddle, and if the passerby didn’t correctly answer it, he became dinner for said creature. If Rogue Audio’s Sphinx packs a riddle, it would have something to do with how so much versatility and sound quality can be packed into a box costing a tad less than $1300 (it’s $1295 to be exact). That’s right. A full function, high-end integrated amp for the typical cost of one month’s rent or mortgage. Well, maybe not.
Starting with the basics, our modern-day Sphinx is a class D switching amplifier with an active vacuum tube preamplifier section. It puts out 100 watts per channel into eight ohms and is said to double its output power into four ohm loads. The preamplifier section is based around a pair of matched 12AU7 tubes which can be viewed through ventilation holes in the top panel of the unit. The circuit boards are well constructed and cleanly assembled (thank you, Mr. Magerman and friends), but what really jumps out from under the hood is the large toroidal transformer which serves as the basis of a linear supply powering the unit. Output jacks are gold-plated and are board mounted while the speaker binding posts are the cheaper plastic units seen on a lot of gear in the lower end of the high-end of audio. I don’t have any problem with this, as cost considerations have to come into play somewhere on an amplifier at this price point, and they worked just fine with the spade lugs on my speaker cables. The listener also gets a front-panel mounted balance control and a custom Alps volume potentiometer, which is accessed from either the front panel or from an optional ($100 extra) remote control. This all metal remote is good for volume change only and is heavy enough to probably inflict a knockout blow to the rear of the head of the unfortunate victim at whom it is wielded. Of course, I can’t verify this assumption first-hand.
What really gets me is the plethora of useful features that Rogue Audio offers on this budget unit. The Sphinx really has about everything someone dipping their toes into the world of high-end audio could want. We have three sets of line level inputs and two sets of preamp outputs (all single ended), a phono stage offering 40 dB of gain with a fixed loading of 47 kohm (appropriate for most high output mm or mc cartridges), and even an on-board headphone amplifier. Run a subwoofer from the variable outputs or use them as a separate tube-based preamp in a pinch. The options seem endless; all you need to get started are a source component or two, a pair of speakers, some cables, and you still have plenty of room to expand outward from there. I will say that I am glad that Rogue Audio wasn’t tempted to build an on-board DAC into the unit. While such things are seen as a typical convenience in this age of computer audio, I feel that digital technology is changing fast enough that the DAC will become obsolete way faster than the amplifier will.
The main amplifier section is built around an OEM version of the popular Hypex switching module driving MOSFET output devices. As an aside, the Hypex switching units are often found on much more expensive class D amplifiers, including my reference Merrill Thor monoblocks, which clock in at $4800 retail. This amplification circuitry is well supported by the beefy power supply circuitry I mentioned earlier, leading to a robust output into a range of speaker sensitivities and impedances (more about this later). You’ve heard that class D amps are hard sounding and unforgiving in a musical sense, right? Well, these modern class D amplifiers aren’t your older brother’s switching amps, as a bit of critical listening will most surely demonstrate. I too used to be a nonbeliever, but as is nearly always the case, circumstances change as technology marches forward.
As I see it, the Rogue Sphinx is a hybrid design which melds the best virtues of vacuum tubes and solid state amplification into a single device. The mixing of switching amplifier and tube technologies is somewhat unusual, but not unique. Down in my living room I use a Virtue Audio Sensation M451 integrated amp which employs Tripath (e.g., class T) amplification with a Dodd Audio tube buffer preamp section, all to very pleasing sonic effect.
Using the Sphinx is quite simple. The mains power is controlled by a rocker switch on the rear panel. When turned on, the unit goes into a standby mode in which the main amplifier section is warmed, but no power goes to the tubed preamp section. Incidentally, the headphone amplifier section is powered and activated in the standby mode and is controlled by either the main volume knob or optional remote. Quite efficient. The standby mode is exited by pressing a button on the front panel, which puts the amp into full listening mode after about a 20 second warmup period for the tubes. At the end of a day of listening, I always put the Sphinx into standby and then gave it a half-hour or so of warm-up in full-on mode before doing any serious listening the next day.
The Rogue Sphinx was enjoyed using a range of speakers: Shahinian Compasses, Spendor SP1s, Tekton Pendragons, and ATC SCM 19 (version 2) monitors. Other components in the system remained constant. The digital front end consisted of Channel D’s Pure Music engine installed on a 2012 Mac Mini running bits to an Antelope Audio Zodiac DAC via a Sound Devices USBPre interface serving as a USB to S/PDIF converter. Both the Zodiac and the USBPre were powered by custom linear power supplies from Your Final System (YFS). To keep things local, interconnects and power cable to the Sphinx were sourced from Tel Wire, which produces its wares just down the road from Rogue Audio in Allentown, Pennsylvania. Fantasy speaker cables from Harmonic Technology were also used while the DAC and amp were both plugged in to a Spiritual Audio VX-9 power conditioner. As an aside, the Tel Wire HC power cord I used costs $1100, which isn’t much less than the Rogue Sphinx itself! Even so, I fully believe that a component of high quality such as the Sphinx deserves and reaps the benefits of a good power cord. Perhaps my choice was a bit of overkill, but I was more than pleased by the sonic benefits of the pairing.
The Sphinx performed admirably with all of the speakers I tested it with, allowing the strengths (and sometimes the warts) of each pair to shine through. Most of these speakers are relatively easy loads with sensitivities around 90 dB or above with the exception of the ATC SCM 19s, which, while a benign load with regard to reactance and phase, are only around 83 dB efficient. Right now, I’m listening to Lyle Mays’ album Street Dreams through my vintage Spendor SP1s, and I’m glued to my chair. A good portion of the wonderful classic midrange beauty and bloom of the Spendors shine through, coupled with articulate and well controlled synthesizer bass offering plenty of slam, but without any excessive overhang or sloppiness. I’m sensing that the class D strength of bass control without loss of extension is a match made in heaven with the old school polypropylene woofers on the Spendors. No matter what I queued up, be it Buddy Rich or Bill Frisell, I got plenty of punch and drive along with loads of fun and musical enjoyment. Folks who are interested in vintage speakers should really enjoy this matchup; that is, if you are lucky enough to find a pair of SP1s on the market. They match well price-wise with the Sphinx also, as they can be found in the $400-$900 range when they do come up for sale.
Most of the critical listening and evaluation I did with the Rogue Sphinx utilized the ATC SCM 19 monitors. Of the speakers in permanent or revolving residence in my household, the ATCs are probably the most resolving and transparent to any changes made elsewhere in my system while remaining eminently listenable. I also find them to be plenty neutral, such that they don’t add colorations of their own to the overall sound of the system. In contrast, I love my Shahinian Compasses in part because they couple well to almost any amplifier and sound remarkably homogeneous in a good and musically satisfying way. This sort of audio homogenization is an ideal property for a music-loving consumer’s speaker, but it’s not always the best choice for reviewing. I need to hear what is going on when I make a change elsewhere in the system, but without sacrificing long term musicality, and that’s exactly what the ATC monitors give me.
The ATCs are a sealed box design, which in turn means that they need some power to really get up and go. I’d say 100 watts per channel is about the minimal requirement for most applications, which is exactly what the Rogue Sphinx delivers. I had some initial concerns about the Sphinx being able to handle the low efficiency of the ATCs, but I needn’t have worried. The amp did just fine. It never got more than warm to the touch, and it didn’t seem to run out of gas, even when played at moderate to high volume. The speakers also did exactly what they are supposed to do by getting out of the way and letting the Sphinx strut its stuff.
My overall impression of the Rogue Sphinx playing through the ATC SCM 19s is that it is an exceptionally capable amplifier, and not only for an amp requiring a relatively small monetary outlay. I’m getting power, finesse, dimensionality, and excellent neutrality though the entirety of the audible waveband. Keying up Bill Frisell’s album Blues Dream (CD), I found it hard to get up and do my chores for the day. I was hoping that the down-home country feel of the music would put me in “chore mood”, but alas, it was not to be. The listening experience was just too enjoyable to allow me to get up and work. Arrayed around and in front of me were blaring horns, twangy guitars, vivid percussion, and God knows what else. Nothing was hidden under the bushel barrel, and everything was enchanting. I could close my eyes and almost feel like I was at the recording session. Depth and width of soundstage were excellent and exactly what I know the ATCs capable of delivering with the right amplification. I think those vacuum tubes in the front end of the amplifier play a big part in making it all happen. Even so, with the tubes in there, I never felt that there was any excessive warmth of tone; everything seemed just right, or maybe with some recordings, just to the cool side of neutral. Of course, bass control and extension were exceptional down to a reasonable frequency, say 45 Hz or so, as would be expected when mating a class D amplifier to a smaller sealed box monitor design. What was there was so good that I didn’t really care about what I was missing in the “feel it but don’t so much hear it” lowest frequency domain. Let me reiterate that these ATC speakers cost $4300 nowadays, so you are looking at nearly five grand to get up and running with an appropriately good pair of stands. I think they are worth every penny of that asking price, but more importantly, Rogue Audio’s $1300 full-function integrated amp more than stands up to the task of driving these exceptional monitors.
The Sphinx/ATC combination was every bit as impressive when playing back orchestral and chamber music. I often fall back on the Lyrita catalog when evaluating gear because it represents a perfect mix of excellent performances and superb recording technique, mostly captured by top Decca engineers during the 1970s in exquisite analog glory. I suspect that Lyrita owner and producer Richard Itter was something of a perfectionist given the technical strength and consistency of the label. The only downside is that the label exclusively dealt with 20th century English chamber and orchestral works, which may not be to every music lover’s tastes.
A good, but somewhat obscure example of the Lyrita catalog is David Morgan’s Violin Concerto and Contrasts (LP, Lyrita SRCS 97, digitally archived) which was recorded in 1978, right at the apex of analog recording technology. The music is decidedly modern but melodic and accessible. The whole thing is beautifully recorded, with the violin shining through but perfectly balanced against the orchestra as its sound wafts slightly above and in front of the rest of the ensemble, as perfectly captured by the Rogue Sphinx/ATC combo. Recorded string tone is a real thing about these recordings, and the Sphinx rendered it with appropriate edge, immediacy, and shimmer, along with a touch of lushness when called for. Again, dimensionality, depth, and width of soundstage were consistently good, which kept me totally engaged in the realism of the performance. Overall orchestral dynamics were also good, but maybe not the best I’ve heard; perhaps this is the one area where maybe the ATCs could have used a bit more oomph. I did mention that these speakers like power, right?
Moving on to another Lyrita selection which showcases several of Gustav Holst’s lesser known works (LP, Lyrita SRCS 56, digitally archived) allows me to comment further on the strengths of the Rogue Sphinx. This disc features “A Somerset Rhapsody”, a tone poem for orchestra which showcases Holst’s musical expressions toward the bucolic English countryside. Here may be found lovely string and woodwind tones counterpointed against percussion and brass lines of an almost martial feeling, all of which were expertly rendered mood-wise by the Sphinx. I found the oboe especially convincing in tone, with all of its complex harmonics reproduced as in a real instrument played in real-time and space.
I had on hand two amplifiers I wanted to compare with the Rogue Sphinx, both of which are considerably more expensive. The first was my REDGUM RGi60 ENR integrated, which is a highly musical design putting out just over 100 watts per channel, class AB, into eight ohms. The REDGUM amp retails for $2850. The other comparison I wanted to make was with another class D amplifier, in this case the Merrill Audio Thor monoblocks, which sell for $4800 and put out 200 watts per channel into eight ohms.
First up was the REDGUM, driving the ATC SCM 19 monitors. I could immediately hear distinct differences between the REDGUM and the Rogue amplifiers. Compared to the Sphinx, the REDGUM RGi60 ENR sounded softer and much more tube-like in the traditional sense. Bass was pleasingly plump and full, but nowhere near as taut and controlled as through the Sphinx. I’d almost call it wooly, but not quite. Just really nice and warm, and even perhaps a bit emphasized. Likewise, the midrange via the REDGUM was luminous, warm, and big, providing lots of space between and around instruments. Individual notes were rounder with a more legato quality, without quite the sense of incisiveness or attack I heard when listening through the Rogue amp. Not that the REDGUM seemed slow, but maybe just in less of a hurry rhythmically. Treble notes were clean and nicely rounded as well, giving a hint of almost excessive harmonic texture at the cost of ultimate extension. I’d suggest that listeners who prefer warmth and harmonic texture would come down on the side of the REDGUM amp while those who prefer a faster, more rhythmically paced amp may well prefer the Sphinx. The REDGUM comes with a few caveats as well. First, it lacks a few of the amenities of the Sphinx, such as a built-in phono stage and headphone amplifier. Secondly, I have found that the REDGUM experienced occasional thermal shutdowns when driving the inefficient ATC speakers, mainly during warmer weather. While I never got to run the Rogue Sphinx in excessively hot weather, I just don’t anticipate it ever struggling to drive any speaker, primarily due to the efficiency of its class D design. I thoroughly enjoyed both amplifiers mated with the ATC speakers, but for obviously different reasons.
Perhaps an even more interesting comparison exists between the Rogue Sphinx and the Merrill Audio Thor, only because both are class D designs built around Hypex switching modules. Although the amps differ in price point and execution, they do have a fair bit in common with one another. The Thor has no preamplifier section, so I ended up controlling its output level using the volume potentiometer built into the Antelope DAC. Also, because the Thor has only balanced inputs, I used a pair of XLR-terminated Darwin Audio Truth interconnects between the DAC and amplifier units (another nod to Mr. Magerman here).
Some folks might be tempted to trumpet the Rogue Sphinx as a slayer of the overpriced giants of high-end audio. It may well be, but I tend to be a bit more reserved in my judgment. Direct comparison with the nearly four-times-as-expensive Merrill Audio monoblocks explains why. While the Merrill Thor lacks all of the features and conveniences of the two integrated amps, it strode decisively ahead of both, performance-wise. Put against the Sphinx, the Thor demonstrated marked improvement in all of the following areas: decreased noise floor, detail retrieval, overall dynamics, and soundstage width and depth. It also imbued the music with just the right touch of warmth that I sometimes found missing with the Rogue Sphinx. I’m sure that some of these improvements had to do with the doubling of power output, but we can’t escape the fact that the Merrill Thor is just a much more refined amp. And it should be, given the price differential.
In the end, I came away mightily impressed with Rogue Audio’s Sphinx integrated amplifier. It was enjoyable enough that if I hadn’t had two much more expensive amplifiers on hand to compare it with, I probably would have been happy as a pig rolling in mud listening to the Sphinx indefinitely. Keep in mind that I offer such praise based on its sonic qualities alone; recalling all of the built-in features offered brings the amp value-wise to a whole new level.
The one aspect of the Sphinx’s performance that I was unable to evaluate was its phono stage. I didn’t have a turntable on hand fitted with a high-output cartridge (nor do I even have such a cartridge), so that option was out. I hear that it is quite good for what it is, and given the level of quality of the rest of the amp, I wouldn’t be surprised. I did spend some time with the headphone output, and I found it to be as good as anything else I had on hand when listening through my Audio Technica ‘phones. Again, I’m not surprised.
The Rogue Sphinx probably won’t satisfy the needs of the most demanding audiophile, but that’s OK. Rogue Audio has higher-level offerings to fill that niche. I see that Sphinx appealing most to someone on a budget who is looking for a very high level of performance accompanied by lots of functionality. As I said before, this amp would be perfect for the budding audiophile looking for a centerpiece component to build a system around that he or she could be proud of and enjoy for many years to come.
Well done, Rogue Audio, and I’m glad I finally had the opportunity to make your acquaintance.
About the Author
John Richardson has been interested in music and audio since his early teen years, or stated another way, as long as he can remember. He has been involved in the audio community in one way or another for around 20 years and for the last five has been a regular contributor to the on-line magazine Stereomojo. There, he has been the resident computer audio guy and “value conscious audiophile” (aka “cheap bastard”).
John is also a professor of analytical chemistry and forensic chemistry consultant in his spare time when he isn’t listening to music or evaluating gear. He tries to fit in plenty of time to hang out with his two teenage kids, his lovely wife, and the family cat, though only the cat also seems to harbor audiophile tendencies. John also enjoys running, cycling, golfing, hiking, or just about any other activity that sucks up time and money.
Financial Interests: Writing for Part-Time Audiophile is his sole intersection with audio’s high-end.