Integrated Amp Reviews

"Okay, all you high-rolling audiophile know-it-alls—what is the argument against amplifiers that operate in high-bias, class-A, single-ended mode, with the lowest possible parts count? Is there a better strategy for beauty, rhythm, color, texture, and easy-flowing musical verity? I think not. And please explain: Why has mainstream audio gone to such ridiculous and expensive lengths to avoid building and selling precisely these sorts of amps?"

It was I, your humble prattler, who in October 2016 posed that rhetorical question, in my review of the First Watt J2, a 25Wpc power amplifier designed by Nelson Pass.

Now I'm reporting on another class-A, single-ended amplifier, this one really low-powered. The 65V-1 integrated amplifier ($4000) uses EL34 or KT88 pentode tubes—at the time of purchase, the user specifies his or her preference—and is made by mainstream manufacturer Rogers High Fidelity, in Warwick, New York. Rogers's president and chief designer, Roger Gibboni, has obviously gone to extreme lengths to create a unique-looking integrated amplifier with an old-school finish of black crinkle paint, a tiny purple display, and an entirely new-school iOS control app for iPads that, among other things, uses Bluetooth connectivity to display the 65V-1's power output on a virtual VU meter on the iPad's screen.

That VU meter is an interesting feature. Rogers forgoes conventional power specifications (eg, by watts into 8 ohms) to specify the 65V-1's power output in an unusual way "THD less than 0.5% at 1 Watt, less than 3% at 10 Watt output, 25 Watts peak."

In the 65V-1's manual, Rogers emphasizes the importance of this iPad VU meter, which samples the power output of both channels, then displays the continuous average power. (It is calibrated in watts, from 0 to 25.) They advise the user to study its readings and learn to recognize the sound of amplifier clipping, beginning by "increasing the gain control until saturation is heard in the speakers. The first indication of this distortion is powerful low frequencies overpowering higher frequencies. Note the relative indication of this point on the meter and operate the amplifier approximately 20% below this level." I no longer own an iPad, but I easily accomplished this task without the meter: I turned down the volume whenever I heard smearing, hardening, squeezing, or congestion.

Stereophile defines clipping as the power in watts at 1% THD+noise. By that measure, and judging by the 26 pages of Audio Precision test results included with every 65V-1, my review sample clipped at 3W. But speaking anecdotally, I'd call it a 10Wpc Ultralinear amp and a 3Wpc triode amp—the user selects between these two modes of operation—that handles loud transients pretty well. In Ultralinear mode, the screen grid of a tetrode or pentode power tube is connected to a tap on the primary windings of the amp's output transformer—and so a portion of the signal that appears on the tube's plate also appears on that screen grid, providing a type of negative feedback. (In pure pentode operation, which the Rogers amp does not offer, there is DC voltage on the screen grid but no signal.) In the triode mode offered by the 65V-1 and some other contemporary amps that use pentode tubes, the screen grid is connected directly to the plate, so there is no feedback effect.

Description
The 65V-1 measures 17" wide by 7.5" high by 12" deep and weighs 24 lbs. It's available with a choice of Mullard EL34 or Gold Lion KT88 tubes. Rogers included sets of both tube types with the review sample, and I tried both. Each unit is burned in for 100 hours before shipping, and comes with a transferable lifetime warranty.

To the right of the front panel is a ¼" headphone jack. Roger Gibboni told me via e-mail that the 65V-1's headphone gain is identical to the speaker gain: 26dB. The 65V-1's input impedance is 100k ohms. According to Gibboni, "Because the 65V-1 is single-ended, it has a slightly higher output impedance: 9 ohms at 2kHz and 8.5 ohms at 10kHz, which yields a damping factor of approximately 1."

After attaching the Bluetooth antenna, power cord, speaker cables, and the interconnects from line-level sources to their respective connectors, flip up the Power toggle at far left on the front panel. Observe the red light at the toggle's tip. Wait 30 seconds, then flip up the Standby toggle to its immediate right. The 65V-1's front-panel controls are a snap to use. Spring-loaded toggles allow the amplifier to be switched between Standby and Operate, between triode and Ultralinear modes, between headphone and speaker outputs, and to select one of the four line-level inputs—three on the rear panel and one on the front panel. Both these switches and the amplifier's front-panel display are duplicated on the iPad app, which is the 65V-1's only form of remote control, and will be found essential by the visually impaired. In my bunker listening room, the amplifier's tiny (2.75" by 1.625"), violet-and-yellow display functioned mainly as a nightlight—it's almost impossible to read, even close up.

But that was okay.

Listening with Falcon Acoustics LS3/5as
I asked my Facebook friends: "What are the virtues and liabilities of single-ended tube amps?" Their Timeline replies rang true to my own experience: wholeness and continuity; a lit-from-within quality; they "breathe" naturally; hyper-three-dimensional; fully developed harmonics; organic, ear-friendly, coherent, stimulating, musically involving; they produce the finest nuances, incomparable midrange texture, amazing microdynamics, and eerie, preternatural tonality; an intimacy with music like no other; the intentions in the music are more discernible.

One friend wrote, "Virtues: inconvenient, antisocial, unconventional. Liabilities: inconvenient, antisocial, unconventional."

Along with weak bass, the most universally cited liability of single-ended amps was the difficulty of finding loudspeakers sensitive enough to match their low power outputs. Therefore, I thought I'd begin my study of the Rogers 65V-1 by connecting it to a revealing but low-sensitivity (83dB/2.83V/m), two-way, acoustic-suspension loudspeaker, albeit one with a tube-friendly high impedance (15 ohms).

A lifetime of owning Dynaco Stereo 70 amplifiers has created a storehouse of good feelings about EL34 tubes connected in Ultralinear driving various versions of the BBC's classic minimonitor design, the LS3/5a. So I had no choice but to connect the EL34-equipped 65V-1 to Falcon Acoustics' LS3/5a variant, which I reviewed in the August 2015 issue. I played a variety of roots, reggae, and British ska, and right away remembered: I've never experienced an EL34 amp I didn't like.

In my small room, the insensitive Falcons made some big, enjoyable sounds—but only at low volumes. With "Carbine," the final track of Black Uhuru's Red (LP, Mango MLPS 9625A), obvious dynamic compression set in at distinctly un-reggae-like levels (82dB/2m average). Triode mode was too low-powered to be usable.

All was not lost. At lower average volumes of around 76dB/2m, Cheng Gong-liang's Guqin (CD, Wind Music TCD 1027), "A UNESCO Masterpiece of the Oral and Intangible Heritage of Humanity" engineered by Kavichandran Alexander, of Water Lily Acoustics, was a sublime experience. The guqin, a 3000-year-old Chinese instrument similar to a zither, generates a complex palette of saturated tones that permit a range of expression that may exceed that of the Western violin. Long known as the "ancient qin," the guqin was the instrument of choice for Chinese poet-scholars. Through the Rogers-Falcon duo, this spectacularly beautiful recording showcased guqin master Cheng Gong-liang's Taoist spirit and creative fingerings. The sounds entering my chamber were exceedingly rich and exceptionally tactile. They reminded me for a moment of Jet Li's martial-arts sword fight in the Chess Courtyard, in the film Hero: Cheng Gong-liang's notes felt like the quintessence of pure, pulsing, fluxing energy. The Falcon-Rogers pairing's reproductions of this music were small and precise—it couldn't deliver realistic sound-pressure levels—but the transients of the guqin's plucked strings and the supersaturated colors of its harmonics were mesmerizing pleasures.

Listening with DeVore Fidelity Orangutan O/93s
With triode-connected EL34s, the Rogers 65V-1 played the DeVore Fidelity Orangutan O/93s (10 ohms, 93dB/W/m) loudly and dynamically enough to provide genuinely satisfying sound.