Tube Preamp Reviews

At the left of its rear panel, the RH-5 had an optional RCA phono input. In contrast, the RP-7 has line-level inputs only. At the left of its rear panel are eight black XLR jacks: two pairs of balanced (MOSFET-buffered) outputs and two pairs of balanced inputs. These dark XLRs are followed by a regiment of bright gold RCA jacks: two unbalanced outputs, a unity gain input, a processor loop, a fixed output, and three line-level inputs. Happily, this arrangement gives me up to five line-level sources. Very nice. Stacked at far right are the main power rocker, a fuse bay, and a three-pronged IEC power-cord inlet.

The RP-7 includes a 30-second soft start with auto mute, to go easy on the tubes and suppress turn-on transients.

Listening with the First Watt amps
The HoloAudio Spring DAC driving the Rogue RP-7 driving the First Watt SIT-3 power amp driving the 93dB-sensitive DeVore Fidelity Orangutan O/93 speakers created a superbly balanced and invigorating—nay, intoxicating—system that didn't sound like tubes or solid-state. But it did reproduce, with extraordinary weight and saturated tones, my latest favorite piano album: Alexander Melnikov performing Debussy's Préludes, Book 2, then joined by Olga Pashchenko in Debussy's own four-hands arrangement of La Mer, all performed on an 1885 Érard piano like the one Debussy used when composing the Préludes (24-bit/96kHz FLAC, Harmonia Mundi/Qobuz). This exotic album is all about the sound of a vintage piano. Its purpose is to show the listener how richly toned and expressive these old, less tightly strung instruments can sound. The playing of Melnikov and Pashchenko isn't lacking in feeling or poetic insight, but the intent of this recording is to present what Debussy must have heard while working on these compositions. Through the RP-7, note attacks were arousing. Note decays were extended. Pedaling was psychedelic. Tone was full-spectrum and saturated.

After my experiences with the First Watt SIT-3, which has only single-ended inputs (RCA), I felt a need to try the RP-7's balanced XLR outputs. I connected another First Watt amp, the J2 (25Wpc into 8 ohms, $4000), which accepts balanced inputs and is a pure made-in-heaven match for Harbeth's Monitor 30.2 speakers ($6495/pair).

When John Atkinson measured the M30.2s for my review of them in the April 2018 issue, he estimated their sensitivity at 87.3dB(B)/2.83V/m—which, he said, "is usefully higher than the specified 85dB." The M30.2's impedance remains above 6 ohms throughout the audioband. As a result, the Harbeths sound rich, lively, and articulate with the First Watt J2. Most important, the Rogue RP-7 kept a cool, steady hand on the J2. This combo of preamp, amp, and speakers made beautiful sounds: saturated tone, never too hard or too soft, never too warm, never stressed or compressed. My only dilemma was which music I should listen to next. Pleasurable.

Now the sound of Melnikov and Pashchenko playing Debussy reminded me of aged French brandy: It had a sensuous, mood-enhancing flavor that lingered, inspiring reverie. Suave and sophisticated.

The bass frequencies on Pat Metheny and Charlie Haden's Beyond the Missouri Sky (Short Stories) (24/96 FLAC, Verve/Qobuz) sounded slightly digital-artificial, but the RP-7 plus J2 made the Harbeth M30.2s sound deeper and fuller in the lower octaves than I'd thought possible. Haden's bass work was just-right tight, and his instrument was almost full height. The added reverb surrounding Metheny's guitar fashioned a dreamy, intoxicating mix with pulsing illusions of a vast dark space. This combination of gear and recording generated the kind of pure beauty of sound that, for me, makes being an audiophile a rewarding enterprise.

In fact, this combo of tubed preamp and solid-state amp sounded so enjoyably sophisticated that I'm compelled to include one more supreme listening experience. Anyone who thinks digital is more truthful or lifelike than analog has never owned a Koetsu Rosewood Signature Platinum moving-coil cartridge, and has definitely never experienced the vivid analog reality of the Purcell Consort, under the direction of Grayston Burgess, in Now Make We Merthe: Medieval Carols (LP, Argo ZRG 526). I know this 1967 LP intimately; it showcases stunning three-dimensional sound in the service of great but humble human art and seasonal merriment. I've heard it through countless systems, some with preamps costing six times the RP-7's price, but none has put me in closer, more intimate touch with these ancient Christmas songs sung by the Boys of All Saints, Margaret Street. With the Tavish Design Adagio phono preamp added to the system, I played this record on a wet, cold December night, my apartment lit only by beeswax candles. I wish you could have been there to sense the purity of space and tone. This delightful mix of Rogue tubes, Koetsu magic, and First Watt silicon put my mind near a Christmas choir singing in a stone church.

I know this system is not inexpensive, but to my taste, it played up there with the very best I've heard.

Listening with the Bel Canto Design monoblocks
Connecting the RP-7 to Bel Canto's e.One REF600Ms showed me how low in so-called tube coloration this Rogue actually was.

The REF600M's input impedance is 200k ohms in balanced mode, 100k ohms in single-ended. Therefore, it mated comfortably with the RP-7's MOSFET-buffered output impedance of 50 ohms, balanced.

When I used the RP-7 and REF600Ms to play the Debussy piano recording, I was surprised at how dark and nontransparent it sounded—not thick or slow, just slightly dark-gray opaque. I doubt this was caused by the Rogue, which all along had sounded cool-air crisp and water-clear with every other amp in the house. I was expecting the Bel Cantos to produce more light and air, more of a sense of openness—but I got less. To its credit and my pleasure, the Rogue–Bel Canto pairing did an excellent job of reproducing the weight and impact of acoustic pianos and pipe organs.

Listening with the Rogue Stereo 100
But Rogue's best preamp didn't need to pass those other tests. It needed only to do a perfect job of driving Rogue's own 100Wpc power amplifier, the Stereo 100. Which it did.

The first song I played, via the Harbeth M30.2s, was "I'm So Glad," from Skip James's well-recorded (ca 1964) comeback album, Blues from the Delta (16/44.1 FLAC, Vanguard/Qobuz). It sounded so good that it jumped out and smacked me down, and made me feel a little bad for praising those other amps as much as I had. That first track with the Stereo 100 was an instant wow moment. This preamp-amp-speaker ensemble sounded so startlingly present, so absolutely clear, so completely undistorted, that I sat there laughing and shaking my head. What's that corny old audiophile line? "Veils were lifted!" In this case, it felt like all the veils were gone. James's ethereal voice, his guitar and piano, were laid bare, blatantly there.

You say you want a revolution
Well, you know
We all want to change the world

Next I played The Beatles (aka the White Album), and remembered what had led me to this Rogue combo in the first place. While reviewing Harbeth's Monitor 30.2, I'd realized that this medium-size stand-mounted model would make a perfect, neutrally balanced reference speaker. But I needed just the right amp—one with more horsepower than my Line Magnetic, PrimaLuna, First Watt, or Pass Labs could provide. Now, while listening through the RP-7 to Giles Martin's remix of The Beatles in this 50th Anniversary Edition (2 LPs, Apple B0028831-01), I felt completely validated in my decision to choose Rogue's Stereo 100. The sound was transparent, insightful, and extraordinarily alive. I had almost no criticisms of it.

Take this brother
may it serve you well

Listening through headphones If you came of age with the Beatles, as I did, I humbly suggest that you listen to "Revolution 9," from The Beatles, from start to finish, through audiophile-quality headphones—say, Sony's overachieving MDR-Z1Rs, Audeze's lively LCD-Xes, HiFiMan's state-of-the-art, planar-magnetic Susvaras, or JPS Labs' revelatory Abyss AB-1266 Phis. Any of those revealing transducers will show you everything your big speakers don't.

The RP-7's headphone amp and Giles Martin's remix showed me gobs of what I'd never known this incomparable classic contained—but the Rogue's headphone output also tainted "Revolution 9" with rolled-off high frequencies that made it sound dull, and with more noise than I find acceptable. The noise seemed like a 120Hz ground-plane problem. It was worst with the 103dB-sensitive LCD-Xes, least noticeable with the 83dB-insensitive HiFiMan Susvaras.

Conclusions
Rogue Audio's RP-7 line preamplifier is definitely a Herb Product—how could it not be? It's built like a farm tractor, and looks unpretentious and timeless. It sounded remarkably uncolored—to its great credit, the RP-7 walked the narrow path between tube sound and transistor sound. It was dynamic. It delivered exceptional transparency along with extraordinary weight and body. It played with a relaxed, organic tone enhanced by only the slightest touch of burnished tube glow. Alert and water clear are the most apt descriptors. My new reference.