August 2013

Rogue Audio Sphinx Tube Hybrid Integrated Amplifier
A price versus performance bargain!
Review By Ron Nagle

  The Sphinx integrated amplifier has certainly raised a few east coast eyebrows. An audiophile friend of mine pointed it out to me at the Stereo Exchange in New York City. I jumped on an opportunity offered by my editor to audition the cause of this controversy. Subsequently Mark O'Brien, the Head Rogue guy kindly sent me a sample of the Sphinx to evaluate. The current Sphinx amplifier buzz is a basic no brainer. It is not very often you get a 100 wpc high-end, high fidelity integrated amplifier on the cheap. Rogue Audio company's top component line includes the Apollo dual mono tube amplifiers, with the unit having an MSRP of $10,995 for the pair. On the other hand, the Sphinx integrated amplifier will set you back a miserly $1295. If you add the $100 optional remote control the cost would rise to only $1395. This price is definably a bargain in the land of high-end, high fidelity two-channel audio. Additionally the Sphinx comes from a company with a reputation well known to most Audiophile types. The Rogue Audio people currently make nineteen separate kinds of tube and hybrid audio components. These components are designed and hand built in Brodheadsville, Pennsylvania U.S.A.

Design and Functionality
The first and most obvious question: Why is the Sphinx integrated amplifier called a hybrid? Well at the input there are two matched JJ/12AU6 triode tubes these comprise a mu follower preamplifier tube circuit. The mu follower design does a very good job rejecting power supply noise and provides very low output impedance. This is coupled to an OEM version of a pair of Hypex UCD180HG amplifier modules and an oversized 375VA Toroidal transformer supplying the amplifier power. The Netherlands based Hypex company tells us the modules are a Class D linear power supply". Class D amplifiers are hi speed switching devices. Using a Pulse Width Modulator as a comparator, it references the input signal against a (clocking) saw tooth generated wave form. The resulting output is binary and that signal is sent on too a MOSFET amplifier that switches on and off at a very high speed. Following that a low pass filter network filters out the high speed components.  The result is an amplified version of the preamplifiers input signal.

The speakers drive power is referred to by Rogue Audio as a: "Massive high storage linear supply". It is specified at 100 watts per channel into 8 Ohms. The Sphinx amplifiers physical dimensions are 15.5" wide by 17" front to back depth and it is 5" high. The unboxed amplifier weights 25 pounds. The top of the amplifier cover has openings on the right side to vent heat from the two JJ/12AU6 triodes. The front panel is a 0.25-inch thick-brushed aluminum rectangle also available in anodized black. Starting from left to right the front panel contains the following.  A circular opening for the remote control receiver, next to that is the power On/Off button. On either side of the power button, there are two LED's. On the left side, a Blue LED indicates power is on. Exactly opposite on the right is a yellow colored LED indicating the amplifier is in stand by mode. Just to the right of that is a socket for a 1/4" headphone jack.

At the rear panel, there is a rocker switch that applies mains/wall power to the amplifier. With the rear mains switch actuated the yellow "Standby" LED to the right side of the power button lights up. The headphone connection on the front panel is active even though the amplifier is in standby. Rogue Audio suggests that the Sphinx should be in the "Standby" state even with the audio system powered down. O.K. let us turn on the amplifier, after a short "soft start" interval the left side Blue LED comes on, then depress the power button and you're ready to listen.

Hardware
In pro audio, anything that plugs something into something is called a "Jack". However, in stereo hi-fi land this most often engenders a gender of male or female RCA plugs or XLR's. (Then shouldn't that be a Jack into a Jill?)

The front panel sports three control knobs. First is the source select with the following four positions: Phono, Line 1, Line 2, and Line 3. Next is a kinda retro channel balance knob (I like them) and lastly there is the high quality Alps motor driven volume control knob. Moving around back to the rear panel. We take a look the business end of things; of course this is the component interface. There are six pairs of RCA plugs, with two pairs used as output connections. There are two pairs of plastic left and right channel five way speaker-binding posts. Next there is a round Phillips head screw labeled Phono Ground. In addition, there is the main power off/on switch and the IEC line cord socket. On the left are the five pairs of RCA receptacles that represent the  source/input connections.

Moving from the left the first RCA pair is the left and right channel phono cartridge inputs. The next three pairs of RCA inputs are labeled, Line 1, 2, 3. Farther to the right side of the back panel are two additional pairs of RCA connectors, these provide a fixed output and a second set with a variable output. The variable output can be used for a second amplifier, possibly for a subwoofer. The fixed output connections can be used for a recording device, A/D processor, et al.

Economy
To keep the Sphinx price within reasonable limits there are some cost considerations. The speaker binding posts are not expensive like the German WBT style but a very common plastic type with 3/4" spacing. The RCA female connections at the back of the enclosure are cost saving board mounted and not individual sockets mounted on the back panel. The Phono amplifier ground connection is just a Phillips head screw. There are two protective fuses, a 5 Ampere main fuse and a 6 Ampere power supply fuse both located inside the amplifier. In addition, all of the graphics are simply silkscreen printed on the case work.

Features
Offsetting some of the economy is the addition of these very nice and well thought out features. Ranked at the very top is the inclusion of a passive RIAA Phono amplifier. This is a definite value added inclusion. It is a MM or Hi-output MC Phono stage that provides 40 dB gain and is a very unexpected feature at this $1295 price. Additionally a discrete headphone amplifier is included. In the standby mode the stereo speakers are silent but the head phone amp is active and the volume is adjusted with the front panel control knob. With the cover removed there is a two-ounce copper plated mother board, (that's a very good place to put your money). A motor driven Alps remote volume control, "made for Rouge Audio in Japan". My sample came with a very nice carved out of solid aluminum remote volume control. However the remote only does two things, up and down volume. And last but not least the Sphinx is all handmade in Pennsylvania, U.S. A.

The Sound Of CD
To describe the sound of individual compact discs or for that matter vinyl records really serves little purpose. After all a writer should realize you do not have the same system or the exact same recordings that I have. It therefore only makes sense to find the underlying voice or we could refer to it as the thread woven into the sound of the many compact disc's reproduced by the Sphinx. My very first listening sessions lead to a question. How do you describe almost nothing at all?

You could gloss over the sonic side of the voicing and keep mumbling the word, neutral. The word neutral will work if every body had the exact same concept of what was considered neutral. Unfortunately, reviewers don't get off that easily. However, if a grizzly bear chased me up a tree and I had to make a quick decision I would say the sound was a bit, dry No not transistor dry, and no not cool sounding. This is one way of saying the Sphinx exhibits the very same broad spectrum frequency response. Along with that it implies that the Sphinx has the same intonation and timbral structure over the reproduced music range. At the same time there is only a vanishing digital grain riding on the musical fundamentals. The tube section seems to remove a lot of the digital rough edges. This is made all the more obvious because everything is overlaid on an extremely quiet noise floor. Understand you won't hear a little extra twinkle when brushed cymbals sing out, or a little extra bass fiddle woodiness coloring the sound.

The Sphinx presentation doesn't add any information, it starts and stops very quickly and there is no hint of overhang. Imbued with speed, a low noise floor and even frequency response this is what I call a "dry neutrality". Back in November of 2010 I reviewed the Virtue Audio Sensation M451, another hybrid tube integrated amplifier for Enjoy the Music.com. That amplifier company as an afterthought installed a Dodd Audio 12AX7 tube in the M451 as a buffer stage. This was an addition made only after the Virtue completed its first production run. The tube buffer circuit was available as a $300 optional retrofit for the original units. The Buffer was configured so that it could be quickly switched in and out of the amplifiers circuit. The knowledge I gained in the process was invaluable. At one point I swapped out the stock buffer tube with many others ending up with a very old Mullard 12AU7. That tube successfully tamed most of the digital artifacts.

Understand I do like the trembling resonant sound a bow makes as it is drawn across strings. And there could be just a little added touch of Tinker Bell style treble glissandi thrown in; it wouldn't bother me at all.

Vinyl Evocation
Is there a Sphinx sound of a different color? Yes, it emanates from a separate 40 dB RIAA phono amplifier circuit contained within the Sphinx. It provides the necessary passive RIAA compensation and resistive and capacitive cartridge loading. Note: The Sphinx cartridge loading is fixed at 47 kOhms.

Question: With thousands of cartridge variants available what Phono Cartridge would make a meaningful reference source?

I chose the Shure V15 V-MR Cartridge, of the seven cartridges I own this is easily the most ubiquitous. Additionally the Shure is a moving magnet (MM) design that will interface perfectly with the 47 kOhm resistive load built into the Sphinx phono section. The first vinyl recording I cued up, had to turn up the gain past the one o'clock position on the dial. In a phone conversation the head Rogue. Mark O'Brien informed me that approximately two units went out with the wrong value of padding resistors connected to the volume control. My sample was not one of them.

Not by accident, I have the Basia Trzetrzelewska album Time And Tide on [CD EK40767] and on Vinyl [Epic, FE 40767-1]. The contrast in the sound reproduction when switching between these different formats perfectly describes the differences between the Sphinx Phono section and the line stage amplifier. The phono cartridge voicing of the first track "Promises", elicits far more subtle details than the same track contained on the CD copy. And in addition there is an overall warmer quality to the vinyl performance along with an expanded sound stage. What is made clear is that you can hear back to the cartridge and the contribution that it makes, and that is a good thing. On the other hand the CD performance is far more dynamic. The speed of the hi-level line amplifier section offers a contrasting shift of sound levels which injects a greater sense of excitement. By comparison to the line source a common thread of the vinyl presentation is that  seems to exhibit some dynamic compression especially at the frequency extremes.

CODA
You might prefer an all tube phono stage over the Sphinx especially if you listen to classical music or operatic works. As things stand now you have a presentation that inhabits the near middle ground sound of digital and hollow state performance. The Sphinx at $1295 is a price versus performance bargain. I will go even farther and say that it is a rare high-end amplifier that could hold onto sixty or even seventy percent of its value in the used aftermarket.

Semper Hi-Fi

Associated Equipment
Speakers: Onix Rocket Strata Mini 4 way speakers and Aurum Cantus Leisure 2 SE two-way monitors on 24-inch stands, Mark and Daniel Omni Harmonizers using Heil Tweeters.
Reference Amplifiers: Audio Research CL60, Prima Luna Prologue 2, Roger Sanders ESL Power Amplifier, Audio Research SP9 MK III Preamplifier.
Analog: SOTA Sapphire Turntable, SOTA flywheel power supply, Grado Signature tone arm. Shure V15 V-MR Cartridge 
Digital: Marantz CD player DV8400, Music Hall DAC 24.3 D/A Converter, Sangean HDT-1 AM FM Digital tuner. 
Speaker Cable: Kimber 12 TC
Interconnect Cables
Monster Reference 2 pairs, 1 meter and 1.5 meters
Nordost Red Dawn, 1 meter
Audio Research Litzlink 2 pairs, 1 1/2 meter
Chord Silver Siren, 1 meter
Audiobhan 0.5-meter digital

Specifications
Type: Stereo vacuum tube integrated amplifier
Power Output: 100 wpc @ 8 Ohms
THD: <0.1% typical,  <1% at rated power
Frequency Response: 20 Hz to 20 kHz
Phono Section: 40 dB
Pure tube mu-follower preamplifier
Slow start turn on sequencing
Damping factor > 1000
Discrete headphone amplifier
MM/MC phono section for high output cartridges
Matched 12AU7 preamplifier tubes 
Gold plated RCA inputs and speaker binding posts
Inputs: Four (phono, line 1,2,3)
Outputs: Active outputs for subwoofer or bi-amping 
Metal remote volume control (optional)
Detachable IEC power cord
Dimensions: 15.5" W x 17" D x 5" H
Weight: 25 lbs
Entirely designed and hand built in the USA 
Warranty: Three year limited warranty (6 months on tubes) 
Price: $1295 standard, add $100 for remote control

Company Information
Rogue Audio, Inc.
3 Marion Lane
Brodheadsville, PA 18322 

Voice: (570) 992-9901
Website: www.RogueAudio.com