Rogue Audio Sphinx integrated amplifier

Once, on a cold, dank, soundless day deep in the Eastern bloc, I watched a man spend over a million dollars on an audio system: a turntable, a fancy horn tweeter, a few wires, and some amplification for his modified Klipschorns. I asked him what he did for a living, and he told me he was a notary public.

Everyone there smirked and watched as he excitedly put the tonearm down on the first record, AC/DC's Back in Black. He laughed, he danced, he didn't sit down. He just skipped around the room, grinning and bouncing like a caffeinated child.

I thought, Does this man really need all this expensive gear to get that bouncy?

That notary public came to mind while I was removing my venerable Creek 4330 integrated amplifier and hooking up the new Rogue Audio Sphinx. As I connected the speaker cables, I could hear Music Hall's Roy Hall admonishing me, "You don't need no million-dollar hi-fis—just get you a little integrated and some good British two-way speakers."

The Sphinx costs almost 700 times less ($1295) than the amplification in that million-dollar system. It's a class-D (switching) amplifier, with a linear (not switching) power supply, that outputs 100Wpc into 8 ohms or 200Wpc into 4 ohms. It has a high-quality Avel Lindberg power transformer, a 12AU7 tubed line stage with three inputs, a phono stage with 40dB of gain, a fixed output (for a separate headphone amp or recording), and a variable buffered output (for driving a subwoofer or a second amp). It also has a balance control, an optional remote volume control ($100), and a discrete headphone amplifier with a front-panel jack. It's all contained in a solid-feeling but conventional-looking case that weighs 25 lbs. And, surprise surprise, this unassuming, solid, no-bling product is made in Brodheadsville, Pennsylvania, and is surely about 162 times more user-friendly and long-term purchase-wise than that boxes-full-of-Franklins stuff I mentioned at the start.

Just before the Sphinx arrived, I was lost in a mad and unusually deep exploration of solo-piano music and what I erroneously call High French Modernism. Mainly, I was playing records of compositions by Debussy, Ravel, and Satie, alternating with soulful cabaret music by Édith Piaf, Serge Gainsbourg, and Daft Punk.

I stream a lot of music, listening in the background as I do my workaholic thing. But this whole Paris groove had me retiring early, turning down the lights, lying on the couch, and dreaming my way into the music. I wasn't just listening and relaxing; I had an agenda: As I searched one record after another, I was trying to hear more of what these French composers were really about. Often, in the middle of a piece, I'd jump up and grab a book on music or go online to look up something. I was playing records to discover a time and a place that I could never visit. I wanted these records to take me to the cabarets and concert halls of Paris during La Belle époque. So it was natural that I feared this modestly priced integrated might throw some flat Moët and stale Gauloises into my nightly excursions to Montmartre.


Switching Moods
But before I begin telling you how the Sphinx played this music, I feel compelled (though not fully qualified) to discuss the "class-D amplifier" aspect of its design. My 1974 edition of Howard M. Tremaine's Audio Cyclopedia (Howard W. Sams & Co., New York) says that the term class-D was first proposed by the revered Norman Crowhurst, to classify a pulsed-type transistor audio amplifier that could be operated at something close to 100% efficiency by continually switching between the power supply rails at an ultrasonic frequency. My weirdo audio-designer buddies consider anything less than pure class-A (in which the audio signal current is never completely turned off) a cost-cutting compromise aimed at middle-level consumers, and definitely insufficient for perfectionist audio. While class-A amplifiers can easily sound beautiful—and glowing and colorful and textured—they are also very inefficient at converting 120V wall power into properly scaled current to drive loudspeakers. They require big power transformers and storage capacitors. They generate lots of heat and cost lots of dollars per watt to make and use. Class-D is pretty much the exact opposite.

I first heard about audiophile-quality class-D amps when I read Wes Phillips's enthusiastic review, in the August 2005 Stereophile, of Channel Islands Audio's class-D D-100 monoblock power amplifier. [Like the CIA D-100, the Sphinx uses class-D output modules from Hypex in the Netherlands.—Ed.] Wes raved on and on about the D-100's microdynamics and presence while driving three different loudspeakers. I was surprised, because weight, body, presence—and, especially, small-scale dynamics—are always at the top of my list of the things I most want an amp and speakers to do. But I still remember thinking, Class-D? What is the world of audio coming to? Well, judging by my experiences with the Sphinx, Rogue's owner and designer, Mark O'Brien, has taken this stigmatized, lower-class mode of operation to a new, more refined level.

A Rogue in the City of Light
The first record I played through the Rogue Sphinx was Aldo Ciccolini playing Erik Satie's Première Pensée et Sonneries de la Rose + Croix (LP, Angel S-36714). Ciccolini's firm notes approached me like staccato cat-paw steps. Dang! The left-hand register of the piano had more weight than I'd ever heard from the Totem Model One speakers. The piece's sad irony filled the room. I did not dance.

I just stood there. I forgot all about the Sphinx.

When the Sonneries finished and the nocturnes were kicking in, I thought, I could probably live with this amp for a long time. That thought came quickly because I believe that the primary purpose of high-fidelity equipment is not to distract the listener from the artistic intentions of the composer and musicians. The Sphinx accomplished this right out of the box. But . . . how?

I have never favored tubed over solid-state amplifiers. I always own and enjoy both. However, my experiences with a wide variety of amps have suggested that, as power ratings and damping factors increase, low-level detail, tonal color, subtlety, charm, and even soundstage dimensions seem to shrink. Surely there are grand exceptions to this rule, but to me, most amps of more than 30–60W output seem to summarize and reduce contrasts, especially through the midrange. When I installed the 100Wpc Rogue Sphinx, I had those expectations in mind.

At the start of my listening, I used the Sphinx with DeVore Fidelity's new Orangutan O/93 ($8400/pair) and Totem's Model One Signature ($2295/pair) speakers. Both models made it clear that this integrated amp could play lower, mid-, and upper bass—say, 40–120Hz—with unusual detail and authority. Bass attack, sustain, and decay with electric and acoustic instruments were clean, weighty, and articulated to the point of being almost distracting. Allusions to kick drum and the piano's left-hand register appear with multiple stars on every page of my listening notes.

Rogue Audio Inc.
PO Box 1076
Brodheadsville, PA 18322
(570) 992-9901

xsipower's picture

It’s nice to see that another manufacturer using Hypex’s OEM class-D amplifier modules perform so well. The last one Stereophile tested was the MBL Corona C15 monoblock power amplifier and it also performed very nicely (

Visually the 415 kHz ripple on the output appears incongruent to high quality audio, but apparently it doesn’t seem to impact the listening experience Mr. Reichert’s and Mr. Atkinson had. Makes you wonder if having a linear amplifier with radio frequency bandwidths (200khz and above) is really necessary or just a marketing ploy. The best tweeter rolls off sharply above 40 Khz and there is the question whether any audio information in any source goes beyond a few tens of kilohertz.

Hypex is demonstrating that Class-D has made it's place in the audiophile world when implemented properly.

Thank you for the review Stereophile.

BradleyP's picture

I'd love to hear a Sphynx! Class D has come of age. When I read reviews like these and see what kind of sound quality can be had for such do-able sums, I am convinced that these are the good old days of audio. A swell integrated that doubles power into four ohms--who ever heard of such at this price? As technology makes quality audio less and less expensive, it's possible in the future that an "audiophile" by today's standards will be anyone who owns a stereo. I just bought a $260 pair of new JBL studio monitors sporting four on-board class D amps for my desk, and they are almost a religious experience. (The good kind.)

BradleyP's picture

Oh, and thank you for the listening tip. The Guillaume De Machaut Motets are a real treat. Right up my alley. With the advent of Spotify, I devour every issue of Stereophile--I'm a paid subscriber--looking for music tips in the equipment reviews and always finding some keepers. Confession: on my desktop rig, which is no slouch, I am HARD pressed to tell the difference between 44.1/16 and a Spotify stream of the same material. I really ought to buy the stuff I like, but I like so much more than I can afford to buy. A trip to the online catalog (with audio samples!) which features the Zig Zag Territories and related labels is alike a trip to an art museum. Seriously do check it out:

remlab's picture

Nicely done. I'm really looking forward to your inteligent, thought provoking reviews. JA made a great move by bringing you in. It's just what the magazine needed.

commsysman's picture

The comment that the Sphinx is "all analog' is obviously incorrect, because any Class D output stage is a digital output stage.

Its output only becomes analog after the duty-cycle-modulated DIGITAL output of the switching stage is filtered back into an analog waveform by a filter.

deckeda's picture

That's a common misconception.

The modulated signal and filtering have constructs and methodology that superficially resemble digital signal sampling and filtering, and you could have an amplifier employ digital controls to the operation of the output devices but that's as far as it goes.

Transistors and MOSFETs are very much analog devices, and there's no ADC nor DAC at work here.

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