Rogue Audio Pharaoh II integrated amplifier

This morning, I received an email from John, my DIY friend in Europe, saying how happy he was. He had just finished building a new power amplifier using two UcD250LP class-D amplifier modules. He described the results as “quiet, clear, clean, effortless class-D power,” adding, “What more could I ask for?”

I am slow on the uptake, so I thought my friend’s question was sincere, not rhetorical. Moments later it hit me: This is a question I should try to answer in this review of the Rogue Audio Pharaoh II amplifier. Beyond the virtues John described, what more, indeed, could we ask for?

In closing, John mentioned, “Later, I might build a tube input buffer for it, but for now I am happy.”

My Euro friend’s letter reminded me that in last month’s Audio-GD DAC review, I speculated that most digital designers are probably trying to make their DACs sound like analog. (I mean, duh! What’s the alternative?) Then, this month, as I installed the Pharaoh II tube–class-D hybrid amplifier, I wondered: How many class-D amplifier designers are trying to make their small, light, cool-running amps sound like hot, heavy, high-power class-A amps? Or like glowing tubes?

That vein of thinking led to another question: What is it I relish in class-A amplifiers that I don’t get from class-D amplifiers? And what about triode tubes? Why is their effect so mesmerizing?

My answer to the class-A question is, first and foremost, that I always want amplifiers driving my speakers to deliver a natural, lifelike tone; anyone should be able to hear it. Instruments, voices, and recording studio effects should sound conspicuously like themselves. Natural tone is the trait I seek above all, in all audio gear, but it is not the first trait that comes to mind when I think of class-D, which I primarily associate with slam, deep bass, and paranormal clarity.

Along with natural tone, class-A amps specialize in recovering the microdetail and nanotextures that inhabit every recording at low signal levels but that other classes of amplification (B, AB, C, D) miss. The first time one experiences thick, rich, heavy class-A, its breathy atmospheric data might seem foggy or even distorted. Because of that, I think some audiophiles mistakenly associate “clean and empty” sound with “transparent and undistorted.” To those listeners, the stark clarity of class-D must be appealing. I am (pun intended) biased toward class-A, but I am also drawn to and impressed by class-D because I think it sounds clearer, better-sorted, and more appealing than steerage-class AB.

I once spent time with a class-D amplifier that didn’t sound class-D clear. Instead, it sounded dark, foggy, and atmospheric in a manner that suggested that its designer (another friend) was trying to spritz some class-A spice into those class-D voids. Maybe my DIY friend should be seeking the transmission of more information: more teeny, tiny notes and sparkling nano-energy to fill the spaces after class-D’s famously firm transient attack; more dense energy in the sustain and more touchable textures in the decay. That’s what I decided to seek in this review of the Rogue Pharaoh II amplifier.

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Description
For the Pharaoh II, Rogue’s founder and chief engineer, Mark O’Brien, opted to replace the original Pharaoh’s Hypex UcD400 module with Hypex’s slightly more powerful and, to my ears, cleaner and more relaxed-sounding NCore NC500 module. (The Sphinx V3 uses the UcD180.)

According to Mark, “The NCore modules are different than the UcD modules in terms of power supply requirements as well as needing an independent buffer stage, which is included in the UcD400 package. Since we generally design our own buffer stages, this allowed us to simplify some aspects of the original design and achieve a higher level of performance.

“The NCore modules require higher operating voltages for the B+ rails as well as an additional supply voltage for the driver stage of the module. Consequently, the power transformer in the Pharaoh II is 20% larger than in the old Pharaoh. We use strictly large, linear power supplies rather than switching supplies in our hybrid amplifiers. My experience has been that the sometimes-edgy sound of solid state and particularly class-D amplifiers may be a result of using switching power supplies in the design. While they allow for smaller amps and are less expensive, switching supplies just don’t seem to sound as good. I would point out to your readers that when they are listening to an amplifier, they are effectively listening to the power supply being modulated by the audio signal. I can’t overemphasize the importance of good power-supply design. “The power transformers—there are two—are both toroidal designs, for low noise. Stray noise is always a challenge in integrated amps because you are forced to locate electrically noisy components (eg, transformers) near noise-sensitive areas, such as a phono section.

“The power supply for the mu-follower preamp is quite straightforward and consists of a string of RC Pi filters that are large enough to swamp any AC ripple as well as decouple the two channels from each other. The 12AU7 preamp tubes are run at a very low current, so they don’t require much in the way of storage capacity. There are also separate regulated supplies for the heater filaments in each tube. Isolating heater supplies may contribute to lower noise and greater channel separation.

“The new Pharaoh was designed on a CAD system that we installed not long after the first Pharaoh came out back in 2015. This new platform allows us to create more complex designs with better grounding and tighter traces. This gives us cleaner circuit layouts, which in turn result in a lower noise floor and better performance. We also completely redesigned the headphone circuit and updated the phono section.

“The phono section uses three Texas Instruments OPA2134 dual op-amps. These new op-amps pretty well outperform discrete devices and have extremely low noise figures. They use a JFET input and are designed specifically for use in high-end audio.

“I pretty much always use passive RIAA equalization in our phono sections, as is the case in the Pharaoh.

“The signal for the headphone circuit is taken directly from the tubes and then fed into a pair of MOSFET buffers to lower the output impedance to close to nothing. It puts out about 1.5Wpc and will drive most headphones.”

Unlike ancient Egypt’s, Rogue’s Pharaoh is larger than its Sphinx. According to the owner’s manual and Rogue’s website, the Pharaoh II is built entirely in the USA. It measures 18.3″ wide, 6.5″ high, and 18″ deep and weighs 39lb. Rogue rates the Pharaoh II at 250Wpc into 8 ohms and 400Wpc into 4 ohms. Its input sensitivity is 1.0V RMS (for full power), and it draws 10W from the wall on standby, 1065W at full power. Its damping factor is said to be >1000.

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The Pharaoh II’s back panel includes three single-ended (RCA) line-level inputs, a unity gain input (RCA), and a balanced input featuring Neutrik XLR sockets. On the far left is an RCA phono input with internally adjustable gain (40dB or 63dB) and MC cartridge loading of 20, 75, 100, 230, 300, 1k, and 47k ohms. There are two preamp-level outputs on RCA—one fixed, one variable—and a tape loop for the 21st century: processor in and processor out. Finally, there’s the usual loudspeaker binding posts and IEC socket.

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The Pharaoh’s front panel may be ordered in black or silver brushed aluminum. With either choice, the knobs and buttons are silver and arranged in a bilateral symmetry, with a big power button on the far left mirrored by a headphone button of equal size on the far right. Inside Rogue’s signature recessed oval are a medium-sized input-selector knob followed by a small processor-loop button, then the large, centered volume control, then a small unity-gain button, and a medium-sized balance knob. The sensor for the remote control on the far left is mirrored by a similar-looking hole for a 6.3mm headphone jack on the far right.

The top of the Pharaoh II’s chassis features a 3.25″ × 5.5″ perforated vent that lets users see the two long-plated JJ ECC802S/12AU7 twin-triode tubes. These tubes, a tube-roller friend told me, are “not an unworthy successor” to the legendary Mullard and Telefunken long plates. What users can’t see (without removing the cover) are the large (400VA) Antek toroidal transformer and the smaller Avel Lindberg toroid, the premium Nippon Chemi-Con electrolytic power-supply capacitors, and the German-made Mundorf aluminum and oil-coupling capacitors. All premium bits.

Listening
Rogue Audio’s Pharaoh II entered my system on a Sunday morning. For the whole day, through both phono and line inputs, it sounded like a guitar string stretched too tight, ie, overdamped and out of tune. It showed not even a vague family resemblance to the Sphinx V3 I had been using for the two previous days. I chalked up the Pharaoh’s tightly wound demeanor to its needing more time for its fancy transformers and capacitors to form.

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