PrimaLuna ProLogue Premium power amplifier - Stereophile 11/2016

Herb Reichert 
Stereophile 11/2016

Let us pretend . . . you have a pair of loudspeakers that have proven themselves to sound articulate and musically responsive in your room, without excess boom, bloom, or frail leanness. They mate with your décor and impress your friends. But maybe you're bored, and feel certain that your speakers would sound better with a better amplifier than the one you have now. Maybe you feel an urge to spend money? Perhaps a new amp will make your records sound the way you imagine they should sound?
I have had these thoughts many times.

The good news: It is much easier to find the right amp for your speakers than it is to find the right speakers for your amp.

The bad news: Finding the perfect amp for a beloved pair of speakers can still be difficult, because every amp you try will make your speakers sound different—better, or worse. Your perfect power amp is surely hidden in plain sight, somewhere on the Internet or at your local audio salon—but you don't know where to begin looking.

You might start by visiting your local dealer, and telling him about those speakers you love, and about your psychoacoustic eccentricities, and about your budget. Then listen—to him, to the advice of his salespeople, to his demonstrations—with relaxed ears and an open, trusting mind. I know this to be a good plan.

But before you begin that process, I recommend that you try what I do all the time: Ask a lot of questions that represent your concerns, and study a wide range of anecdotal accounts of amplifiers and speakers by interrogating your friends, audio-salon gurus, and random Facebook ideologues. Study your favorite reviewers, blogs, and audio forums. This is usually fun, and can be a mind-expanding way to make new friends. These conversations won't solve your problem, but they should make you less lonely, and may narrow the field to a manageable list of choices. If your loudspeaker model has been around a while and is reasonably popular, there will be scores of other owners willing to share their experiences with various amps—and for me, shared experiences are always the best place to start.

Then, armed with shared wisdoms, visit your dealer, tell him what you've learned anecdotally, and begin listening to music with greater confidence.

Recently, while reviewing Falcon Acoustics' LS3/5a speakers (footnote 1), I asked this question of an online forum devoted to the BBC's LS3/5a Type II minimonitor: "What are the best amps to drive these new Falcons?" I received dozens of suggestions, but there was little consensus. Most people mentioned old stuff: the Musical Fidelity A1, the Naim Nait, the Sugden A21, the Harman/Kardon Citation V, the Bedini 25/25, etc., etc. But one amplifier brand was mentioned more often than any other, and it was not a maker of classic, discontinued models now available only used and in need of expensive rebuilds: "Try a PrimaLuna!," many forum respondents said. Some suggested that I try the DiaLogue Premium HP integrated amplifier ($4399), reviewed two years ago by Stereophile's most charming audio sage, Robert Deutsch.

I knew little about PrimaLuna, so I called their US distributor, Kevin Deal of Upscale Audio, and told him that my peeps insisted I try a PrimaLuna amp with the Falcon LS3/5a's. He told me that PrimaLuna amplifiers are designed in the Netherlands, made in China, built like tanks, and work very well with the Falcons. He recommended their lowest-priced, basic stereo power amplifier, the ProLogue Premium ($2199).

Description

Long ago, I repaired vintage tube amps for a living. It was zero fun. I hated that lonely, underpaid drudgery. Worse, I didn't like the sounds of most of those amps—with two extremely memorable exceptions: the Western Electric 91A (single-ended, 300B tube) and the Marantz 8B (push-pull, EL34 tubes). The 91A looked industrial-hip and delivered the best midrange ever—but even long ago, it was rare as unobtainium. I serviced a lot of elegant-sounding Marantz 8Bs, and felt honored to be even touching this venerable Sid Smith design. For me, the 8B is the best-looking amp ever. It played my Rogers LS3/5a's with such satisfying musical charm that I wish I had one now—if only to put on a shelf for display.

Why wouldn't I put an 8B in my system? Because, while the ProLogue Premium can't match the museum-quality beauty of the 8B's classic case, the PrimaLuna has a 21st-century tube spirit that can reproduce recordings with levels of high-frequency purity, low-frequency force, and pulsing musicality that exceed the venerable Marantz in every way.

The ProLogue Premium acknowledges its 8B influence with its steel-box–covered transformers, elegant tube deck, and hand-rubbed lacquer finish. Like the 8B, the ProLogue Premium uses solid-state rectifiers and push-pull EL34/6CA7 pentode tubes operating in class-AB to achieve 35Wpc. Inside, the PrimaLuna boasts hand-wired components of a high quality similar to that of the classic Marantz.

When I was done admiring the point-to-point wiring, choke-filtered B+ supply, and Nichicon capacitors, I noticed all the little green boards containing PrimaLuna's Adaptive AutoBias circuitry. This is neither an auto-bias with a cathode resistor nor an "intelligent" fixed-bias circuit, but a unique logic circuit that monitors the operating environment and condition of each output tube, and keeps each one locked to the flattest part of its plate characteristic. PrimaLuna claims that, with the Adaptive AutoBias and their soft-start circuits, "you never have to worry about biasing your amp ever again, and the need for matched tubes is eliminated." Kevin Deal says that these circuits also greatly extend tube life, and that "All PrimaLuna amps give you about 18W from each EL34, 20W from a KT88, 21W from a KT120, and 24W from a KT150." All this with no global negative feedback.

The ProLogue Premium has a 3/8"-thick brushed-aluminum front panel with a green LED power-on indicator recessed in its center. The on/off switch is at the front of the left side panel, and the switch for selecting between EL34 and KT88 tubes is in the matching position on the right. Voltage gain, phase splitting, and the driver stage are handled by two ECC82 or 12AU7 twin-triode tubes per channel.

Comparing the rear panels of the Marantz and PrimaLuna, it's obvious that fuse holders, AC power cords, speaker binding posts, and RCA sockets have improved a lot since the Golden Age of Marantz. So have output-transformer winding strategies and core materials: PrimaLuna winds their output transformers in-house, to their own wideband specifications. I suspect that most of the audible characteristics I'm about to describe are the results of the quality of PrimaLuna's output transformers and the design intelligence of PrimaLuna's founder, Herman van den Dungen.

Messe de la Septuagésima through Falcon Acoustics' LS3/5a speakers In the Christian calendar, Lent prepares believers for Holy Week, which concludes with Good Friday and Easter. Approximately 70 days before Easter, and just before the beginning of Lent, is Septuagesima (Latin for seventieth): a preparation for Lent and a stern foreshadowing that invades parishioner's consciousness as the liturgy suddenly darkens and grows serious. At this point, Christmas is officially over.

To that effect, the Gregorian chant Messe de la Septuagésime, sung by the Choeur des Moines de l'Abbaye Saint-Pierre de Solesmes under the direction of Dom J. Gajard (LP, French Decca 7505 A), sounds like a chilling, approaching darkness. The massed voices are closely but simply miked. They sound breathy and REAL and almost authentically scaled, with a minimum of added reverb or compression. Throughout this 1959 recording, the close miking made me feel emotionally connected to the choir and the mass. I like to sense the distance between the singers and the microphone, and the ProLogue Premium let the "breathy" Falcons do their accurately space-revealing thing. Pace and vocal tone were spot on, detail was pleasant enough; but with this recording, it was the explicit spatial descriptiveness that delivered the music's richest pleasures. The Falcon LS3/5a speakers and ProLogue Premium made a tight, glorious, extremely communicative partnership—exactly as the LS3/5a forum folk said it would.

Listening with KEF's LS50 speakers

You know those scenes in old movies: a gangster grabs a flunky by the shirt, shoves him up against a wall, and snarls, "Listen, punk—you're in for it now!" Well, that's exactly what the 35Wpc PrimaLuna ProLogue did to my KEF LS50s ($1499.99/pair)—and with Charlie Haden's early digital recording The Ballad of the Fallen (LP, ECM 1248), no less! In "Too Late," a duet with Carla Bley (who wrote the tune), the playing is all deep plucked double bass and left/right-hand piano contrasts. Through the KEF LS50s, Haden's bass was unabashedly bigger and stronger, and sounded distinctly more real, than I ever thought possible from these minimonitors. Unfortunately, Bley's right-hand notes were annoyingly hard and shiny. But this is a digital recording from 1982—what else should I expect? Despite the recording's slightly strident sound, the combo of Pass Labs HPA-1 preamplifier, ProLogue Premium, and KEF LS50s made this record worthy of repeated plays and showing off to friends.

When it comes to Miles Davis, I'm more a Bitches Brew than a Kind of Blue kind of person. Kind of Blue (1959) has this exquisitely formed but backward-looking (ie, modernist) modal structuring that makes me long for John Cage or Ornette Coleman. In contrast, Bitches Brew (2 LPs, Columbia PG26) gets me lost in the dark, druggy, openly questioning electric-piano funk of Chick Corea, Larry Young, and Joe Zawinul in early 1970. Miles and his producer, Attilio Joseph "Teo" Macero, introduced a new, forward-looking, emotionally penetrating jazz-pop format characterized by long, plaintive trumpet drones, Harvey Brooks's genre-bending Fender bass, John McLaughlin's surrealistic electric guitar, and Macero's wild looping and sampling innovations. On Bitches Brew, all of these diverse musical viewpoints converge to forge a new, multicultural, postmodern, dystopian angst that still seems relevant today.

Always . . .

What I always hope for from specialist hi-fi is that the structural and creative aspects of a musical performance will be brought forward so that I can notice and appreciate them. The PrimaLuna ProLogue Premium driving the KEF LS50 minimonitors did this with every record I played. This singular important quality—along with eight octaves of forceful, refined tone and the most impactful bass I have yet heard from the KEFs—makes this a distinctly recommendable combination of amp and speaker.

With DeVore Fidelity's Orangutan O/93 speakers

DeVore's Orangutan O/93s ($8400/pair) have been in and out of my system for almost three years now, and they're still my primary reference for highly revealing, properly balanced, "just right" reproduction. The ProLogue Premium enhanced each of those qualities—especially the highly revealing part. With the O/93s, I could hear what I felt certain is actually on that recording of Messe de la Septuagésime. I could better recognize the relationship between the close-miked voices and the sound of the hall. Decca's recording engineer (Kenneth Wilkinson?) really did create a satisfying balance, and the ProLogue Premium had no trouble showing it to me.

"My fellow Americans . . ."

The Electric Flag's first album opens with these words by then-president Lyndon B. Johnson: "I speak tonight for the dignity of man and the future of America. I urge every member of both parties . . ."

I've been a fan of drummer Buddy Miles since 1968, when I saw him play with Mike Bloomfield and the newly formed Electric Flag. I have played no recording more often than I have Electric Flag's "A Long Time Comin'" (LP, Columbia CS 9597), released in March of that year, which features an amazing cast of musicians, including Bloomfield on guitar, Harvey Brooks on bass, Barry Goldberg on keyboards, Nick Gravenites and Cass Elliot on vocals, and Richie Havens playing percussion and sitar. This disc, and Bob Dylan's Highway 61 Revisited (which also features Bloomfield and Brooks), anchored my transition from boy to man.

Unfortunately, nowadays, no matter what system I play it on, my 1A/1A pressing never sounded as good as I remember it sounding in 1968—until now. The ProLogue Premium and Orangutan O/93s got it more right than any system I can remember hearing it through in the last 40 years. The PrimaLuna-DeVore combo showed me clearly how poor the original stereo mix is, but I didn't care—it so well reconstituted the lyrical, free-flowing momentums and staccato horn section of the Flag's signature cover of Howlin' Wolf's "Killing Floor" that it made me feel it as if I were 16 again. "I should have quit you . . ."

It was difficult to stop all that Buddy-and-Harvey expressionism, but I felt a sudden urge to move on to something higher up the musical food chain—the Mahavishnu Orchestra's Birds of Fire, from 1973 (LP, Columbia KC 31996). Composer-guitarist John McLaughlin builds musical structures as if they were constructed of fiercely vibrating skyscraper beams, and the sensational Rick Laird (bass) and Billy Cobham (percussion) give McLaughlin's art a majestic architectural pulse. The PrimaLuna ProLogue Premium let each musical line display its own design. Micro- and macro-contrasts were expressed in a way that made the poignant, clashing rhythms of "Open Country Joy" feel like intersecting riptides. By side 2, I could fully perceive McLaughlin's post-and-beam construction—it was about 85% as solid as I know it to be, and as well sorted as I have ever experienced it. And the exceptional transparency of the ProLogue Premium made "One Word" sound extraordinarily deep, wide, and sensuous (footnote 2). Drum textures were sharp and definite. Bass was taut and clear.

With Zu Audio's Soul Supreme speakers

As I ran AudioQuest's GO-4 cables between the Zu Soul Supremes ($4500/pair) and the 8-ohm taps of the PrimaLuna ProLogue Premium, I had a good feeling. Then, listening to Finbar Furey play Uilleann bagpipes as his brother Eddie accompanies him on acoustic guitar, on their Irish Pipe Music: Hornpipes, Airs & Reels (LP, Nonesuch Explorer H-72059), I immediately realized that this was a divine stereo recording, and that the Zu-PrimaLuna was a divinely lucid combination of speakers and amp.

The sensitive Soul Supremes presented every reel and air and hornpipe with a lively verity that I can describe only as fresh and invigorating. I'd just gotten this LP, and was deeply impressed by the literary, musical, and recording artistry behind every song. My favorite, though, is "The Fox Chase," which opens with Finbar speaking and giving us the gist of the musical narrative. During every minute of this zigzagging instrumental, the PrimaLuna-Zu combo delivered full-tilt, almost explosive excitement, a big spatial perspective, and genuine corporality. Tonal character—even through the highest highs—was exemplary.

Two weeks and countless recordings later, I'm still listening to "The Fox Chase" through this same system. I can say, without reservation, that the PrimaLuna ProLogue Premium driving the Zu Audio Soul Supremes comprises a system that sounds as if it should cost at least $21,000, not less than $7000.

21st-Century Tubes

The PrimaLuna ProLogue Premium is made in China and costs only $2199. Nonetheless, it showcased a neutral, clear-water transparency that was the equal of my reference amplifiers—including the twice-as-expensive Line Magnetic LM-518IA integrated amplifier ($4450). It let midrange tonalities shine through with something approaching true radiance. Stringed instruments, Uilleann pipes, and women's voices were reproduced in the purest

Technicolor. Maybe they didn't sound as textured, as radiant, or as shamelessly luminous as they do through the LM-518IA (which I've been using as a power amp), but still: they were radiant, in that special, clear way that tube fanatics crave. Nothing about the ProLogue Premium's sound seemed unnaturally warm. The ProLogue Premium delivered a well-managed, 21st-century tube transparency that seems to be unique to PrimaLuna products. It may be this amplifier's most obvious and compelling attribute.

Equally obvious was how clearly and powerfully the ProLogue Premium reproduced bass. Even through small speakers, bass scale—the ability of deep sounds to also be big sounds, when they're supposed to—was exceptional. High frequencies had a captivating purity. If the PrimaLuna lacked anything, it was the firm but gentle rhythmic authority of the more expensive First Watt J2, designed by Nelson Pass, which may be the world champion of "just right" loudspeaker control.

The ProLogue Premium also lacked the J2's meaty, superbly textured midrange and its sensational giddyup and dance élan. However, unlike the J2, which struggled with speakers with impedances of less than 8 ohms, the ProLogue Premium remained comfortable and musical driving speakers that presented loads as low as 4 ohms—but no lower.

PrimaLuna's ProLogue Premium has become my new reference for low-power, high-value amplification. Class A sound at a Class C price.

Specifications

Description: Push-pull, tubed stereo power amplifier. Tube complement: four 12AU7, four EL34 (KT88, KT120, or KT150 tubes optional). Output power into 8 ohms: 35Wpc (two EL34 tubes), 40Wpc (two KT88 tubes), 44Wpc (two KT120 tubes), 48Wpc (two KT150 tubes). Frequency response: 20Hz–85kHz, ±0.5dB. THD: <1% at full power. Signal/noise ratio: 89dB. Input sensitivity: 775mV. Input impedance: 100k ohms. Output speaker taps: 4 & 8 ohms. Power consumption: 210W.
Dimensions: 14.5" (370mm) W by 8" (200mm) H by 15.5" (390mm) D. Weight: 46.3 lbs (21kg).
Finish: Hand-rubbed, high-gloss blue lacquer.

Associated Equipment

Analog Sources: Technics SL-1200GAE turntable with Hana EL cartridge; Roksan Radius 7 turntable with Corus Silver, Dynavector 20X2L cartridges.
Digital Sources: Schiit Audio Yggdrasil DAC, Integra DPPS-7.2 DVD-A player.
Preamplification: Dynavector SUP-200, Bob's Devices CineMag 1131 step-up transformers; Lounge Audio Copla active step-up device; Dynavector P75 Mk.3, Lounge Audio LCR Mk.III, Parasound Halo JC 3+ phono preamplifiers; Pass Labs HPA-1, Rogue Audio RP-1, Simaudio Moon Neo 350P preamplifiers.
Power Amplifiers: First Watt J2, Simaudio Moon Neo 330A.
Integrated Amplifier: Line Magnetic LM518 IA.
Loudspeakers: DeVore Fidelity Orangutan O/93, Dynaudio Excite X14 & Excite X18, Falcon Acoustics LS3/5a, KEF LS50, Technics SB C700, Zu Audio Soul Supreme.
Cables: Digital: Kimber Kable D60 Data Flex Studio (coaxial). Interconnect: AudioQuest Red River (balanced) & Cinnamon, Auditorium 23, Kimber Kable Silver Streak. Speaker: AudioQuest GO-4, Auditorium 23. AC: AudioQuest NRG-2.
Accessories: AudioQuest Niagara 1000 Low-Z power conditioner, PS Audio PerfectWave PowerBase, Dr. Feickert Analogue Protractor NG & Adjust+ software, Acoustical Systems SmarTractor cartridge-alignment protractor, Musical Surroundings Fozgometer, Parastat Mk.IIA disc brush, RTOM Moongel stylus cleaner

Measurements

I performed a full set of measurements on the PrimaLuna ProLogue Premium power amplifier, using both my Audio Precision SYS2722 system (see the January 2008 "As We See It") and my vintage Audio Precision System One. As I did so, I got a strong feeling of déjà vu: the amplifier's behavior was similar in many respects to that of the ProLogue Premium integrated amplifier, which Robert Deutsch reviewed in June 2012.

As the review sample of the ProLogue Premium was fitted with EL34 output tubes, I set the bias switch on the amplifier's right side panel to the appropriate bias position. The voltage gain into 8 ohms was 28.65dB from the 8 ohm output-transformer tap and 28.15dB from the 4 ohm tap, and the ProLogue Premium preserved absolute polarity from both taps. The input impedance was a usefully high 92k ohms at 20Hz, dropping inconsequentially to 78k ohms in the midrange and treble.

The output impedance from both output taps was significantly higher than that of the ProLogue Premium integrated amplifier. From the 8 ohm tap, I measured 9.2 ohms at 20Hz, 8.75 ohms at 1kHz, and 8.45 ohms at 20kHz; from the 4 ohm tap, the respective impedances were 4.7, 4.5, and 4.35 ohms. As result, the variations in frequency response with our standard simulated loudspeaker were extreme, reaching ±3.1dB from the 8 ohm tap (fig.1, gray trace), and with a large drop in level each time the load impedance was halved (cyan, magenta, and green traces). As expected, these variations were smaller from the 4 ohm tap (fig.2), but the matching between channels was excellent from both taps.

Like our 2012 sample of the integrated amplifier, the power amplifier's frequency response featured a small, damped peak between 70 and 80kHz that grew more pronounced into low impedances, and a peak of much higher Q an octave higher. This latter peak gave rise to overshoot and ringing with a 10kHz squarewave (fig.3).

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Fig.1 PrimaLuna ProLogue Premium, 8 ohm tap, frequency response at 2.83V into: simulated loudspeaker load (gray), 8 ohms (left channel blue, right red), 4 ohms (left cyan, right magenta), 2 ohms (green) (1dB/vertical div.).

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Fig.2 PrimaLuna ProLogue Premium, 4 ohm tap, frequency response at 2.83V into: simulated loudspeaker load (gray), 8 ohms (left channel blue, right red), 4 ohms (left cyan, right magenta), 2 ohms (green) (1dB/vertical div.).

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Fig.3 PrimaLuna ProLogue Premium, 8 ohm tap, small-signal, 10kHz squarewave into 8 ohms.

Channel separation was okay, at 75dB in both directions at 1kHz, but decreased at the frequency extremes, reaching 68dB at 100Hz, and 52dB L–R and 56dB R–L at 20kHz. The wideband, unweighted signal/noise ratio from the 8 ohm tap, ref. 1W into 8 ohms and measured with the input shorted to ground, was a modest 66.3dB in both channels. (With the 4 ohm tap's lower gain, the S/N ratio from that tap was slightly better, at 67.1dB.) With an A-weighting filter, the ratio improved to 88.3dB left and 91.0dB right. Spectral analysis of the amplifier's low-frequency noise floor (fig.4) reveals that the primary source of noise was a component at 60Hz, presumably due to magnetic interference from the AC power transformer.

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Fig.4 PrimaLuna ProLogue Premium, 8 ohm tap, spectrum of 1kHz sinewave, DC–1kHz, at 1W into 8 ohms (linear frequency scale)

The ProLogue Premium's maximum output power with EL34s is specified as 35W; our sample clipped at 35Wpc into 4 ohms from the 4 ohm tap (12.43dBW), and 38Wpc into 8 ohms from the 8 ohm tap (15.8dBW). But as shown in the plots of the percentage of THD+noise against power from the 8 ohm tap (fig.5) and 4 ohm tap (fig.6), less power is available when the load impedance is both higher and lower than the nominal tap impedance (as you'd expect from a design with such a high source impedance, footnote 1), and the distortion at lower powers is relatively high

 

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Fig.5 PrimaLuna ProLogue Premium, 8 ohm tap, both channels driven, distortion (%) vs 1kHz continuous output power into (bottom to top at 1W): 8, 4 ohms.

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Fig.6 PrimaLuna ProLogue Premium, 4 ohm tap, both channels driven, distortion (%) vs 1kHz continuous output power into (bottom to top at 1W): 8, 4, 2 ohms.

The distortion increases into lower impedances and at low frequencies, as shown in fig.7, which was taken from the 4 ohm tap at 2.83V, equivalent to a power of 1W into 8 ohms, 2W into 4 ohms, and 4W into 2 ohms. Even into 8 ohms (blue and red traces), the THD+N remains above 0.1% at all frequencies, and was a little higher from the 8 ohm tap at the same voltage (fig.8). Fortunately, the main distortion component was the second harmonic (fig.9), which tends to be subjectively benign. However, even at 1Wpc into 8 ohms, a regular series of lower-level, higher-order harmonics can be seen (fig.10), though intermodulation distortion at the same output power was relatively low (fig.11), the difference component at 1kHz lying at –63dB (0.07%) ref. the test signal's peak level. But at a higher level from the 8 ohm tap, the intermodulation distortion had risen to a level that should be audible (fig.12).

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Fig.7 PrimaLuna ProLogue Premium, 4 ohm tap, THD+N (%) vs frequency at 2.83V into: 8 ohms (left channel blue, right red), 4 ohms (left cyan, right magenta).

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Fig.8 PrimaLuna ProLogue Premium, 8 ohm tap, THD+N (%) vs frequency at 2.83V into: 8 ohms (left channel blue, right red), 4 ohms (left cyan, right magenta).

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Fig.9 PrimaLuna ProLogue Premium, 8 ohm tap, 1kHz waveform at 1W into 8 ohms, 0.2% THD+N (blue); distortion and noise waveform with fundamental notched out (red, not to scale)

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Fig.10 PrimaLuna ProLogue Premium, 4 ohm tap, spectrum of 1kHz sinewave, DC–10kHz, at 1W into 8 ohms (linear frequency scale).

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Fig.11 PrimaLuna ProLogue Premium, 4 ohm tap, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 1W peak into 8 ohms (linear frequency scale).

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Fig.12 PrimaLuna ProLogue Premium, 8 ohm tap, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 10W peak into 8 ohms (linear frequency scale).

As I wrote of PrimaLuna's ProLogue Premium integrated amplifier, the ProLogue Premium power amplifier measures about as well as can be expected from a classic tube design that uses a push-pull pair of EL34 output tubes. But its sonic signature will be far from neutral, especially with lower-impedance speakers.—John Atkinson

Żródło: Stereophlile 11/2016