I’m not a member of the Everything Matters camp. I won’t list here all the things audiophiles do to alter the sound of their systems, but suffice it to say that I don’t spend hour after hour comparing footers or cable elevators in attempts to season the sound of my stereo to suit my palate. But most things, of course, do matter, and that’s where I focus my attention.
Case in point: power amplifiers. I vividly remember the first time, over 20 years ago, when I realized just how much the sound of a system could be changed by swapping in a different power amp. I had a pair of Bowers & Wilkins P4 floorstanding speakers in Rosenut finish. I owned a Classé Audio CA-100 power amp, and had bought a used Krell KSA-50S to compare to it. I don’t recall what I expected when I swapped in the Krell, but what I heard shocked me. The Krell sounded open, alive, and vivid -- by comparison, the Classé now sounded closed-in and dark. I switched back and forth between the Krell and Classé many times, marveling at the differences I heard. I’d known that the choice of power amp was important in terms of ensuring that it could drive my speakers properly and to sufficient sound-pressure levels. But from that day on I knew that even two power amps that met all of those requirements could still differ greatly in terms of something just as important: sound quality. Ever since, I’ve enjoyed comparing power amplifiers and listening for just these crucial differences.
That story of the Krell and the Classé instantly came to mind when I installed in my system the Plinius Reference A-150 power amplifier ($13,000 USD). I don’t exaggerate -- as you know, we audio reviewers never exaggerate -- when I say that it took me all of five seconds to hear a dramatic difference between the Plinius and my reference Boulder Amplifiers 2060 stereo power amp. But before I get into that . . .
The Reference A-150 is a medium-size (20”W x 8.75”H x 18”D and 83 pounds), solid-state, stereo/mono power amplifier manufactured in New Zealand. Plinius Audio Limited has been producing electronic components since 1980, so it’s probably safe to assume that they know a thing or two. In stereo, as I used it, the A-150 is specified to deliver 150Wpc into 8 ohms or 250Wpc into 4 ohms, and will produce current peaks of 50A per channel. As a monoblock, the A-150 will produce 450W into 8 ohms or 600W into 4 ohms. These considerable power outputs are made possible by transformers specified to supply over 1000VA into the output stages, supported by 14,700µF of capacitance per rail per channel, or 58,800µF per amplifier. There are four pairs of output devices per channel, totaling 16 output devices per amp. Hum and noise are specced as 100dB below rated output, 20Hz-20kHz, A-weighted, and total harmonic distortion (THD) as <0.03% at rated output power.
The Plinius A-150 has one fairly rare feature: selectable class-A or class-AB output. In class-A, it consumes 485W at idle; in class-AB, that drops to 92W. Plinius defines class-A circuit topology as “one in which the total current the amplifier is capable of delivering, is kept flowing in the circuit regardless of demand.” Since the current draw is constant, the power-supply modulation that Plinius says plagues class-AB designs is avoided. Of course, class-A generates a lot more heat, and the A-150 did run hot in that mode -- if you buy one, make sure it’s well ventilated. To prevent the A-150 from running in class-A when left powered up and unattended for long periods, Plinius has included a helpful feature they call Ecologic Control: After 15, 30, or 60 minutes (the user chooses) of sensing no input signal, the A-150 automatically switches from class-A to class-AB.
The front panel is pretty empty. There’s a small blue power LED dead center, and below that a pair of pushbuttons. On power up, Mute is the default mode -- press the Mute button to get sound. To the right of that is the Class A button, whose default position is class-AB (LED dark); press for class-A (LED on). Below these, at the bottom of the faceplate, a tasteful badge displays “RA-150.” Large, curved corner panels wrap around to meet the heatsinks that constitute the amp’s side panels.
On the A-150’s rear panel are four pairs of binding posts to permit biwiring, and balanced (XLR) and single-ended (RCA) input jacks. In the lower-left corner are a 15A IEC power inlet and the main power rocker. A knob at center, between the right and left inputs, switches the amp among four settings: RCA Stereo, XLR Stereo, RCA Bridged Mono, and XLR Balanced Mono. In the lower-right corner are a trigger input and a Chassis/Open Ground Lift switch. I didn’t need the latter, as my system presents no ground problems. The A-150’s four feet are individually adjustable for height, to ease leveling on an uneven surface.
The Reference A-150 seems to be a solidly built product that should last a very long time. It’s not audio jewelry -- its brushed-aluminum finish is pretty old school -- but I like this classic look. No one will mistake the A-150 for a mass-market component.
The Reference A-150 replaced the Boulder 2060 in my system. I connected it to my Vimberg Tonda speakers with Siltech Explorer speaker cables, and plugged its power cord directly into the wall. A Hegel Music Systems HD30 digital-to-analog converter with integral volume control fed signals directly to the A-150. My source device was an Apple MacBook Pro laptop computer loaded with Roon software and streaming Qobuz. The Hegel was powered by a Shunyata Research Hydra Alpha A12 power conditioner connected to the wall with a Shunyata Venom NR-V10 power cord. Other than the Plinius, all electronics sat on an SGR Audio Model III Symphony equipment rack.
Back to that Krell-Classé shoot-out.
When I put the Krell KSA-50S in the system, I immediately preferred it to the Classé CA-100 -- it kicked the sound quality of my smallish B&W speakers up a notch. The sound wasn’t merely different, it was better, and I heard it right away. Shortly thereafter I sold the Classé, and never missed it.
With the Plinius Reference A-150 in my system, I also immediately heard a difference. But before I tell you what that difference was, it might help to know where I’m coming from in terms of power amps.
After years of having reference systems that included the very best solid-state power amplifiers in the world, I chose as my long-term reference stereo amp the Boulder 2060, for several reasons: First, it’s tonally dead neutral, which makes it possible for me to review audio gear knowing that any colorations I hear in the sound are not being produced by my power amp. Second, the Boulder is free of any kind of noise, which results in a transparent, holographic sound that lets through any and every microscopic detail. Third and last, the 2060 delivers a specified 600Wpc into 8 ohms and can produce 2400Wpc into 2 ohms -- I can review any speakers I want without worrying about running out of power. The 2060 retailed for $44,000; its replacement in the Boulder line, the 2160, costs more than 50 grand.
The Plinius Reference A-150 doesn’t do everything the Boulder does. Its 150Wpc output into 8 ohms is only one-fourth the Boulder’s; it’s not as quiet -- details aren’t quite as fully exposed; and tonally, the A-150 is not quite dead neutral. But it’s that last item that might have you actually preferring the Plinius over the Boulder. One other thing the Plinius won’t do is put you in the poorhouse: it costs just over a fourth of the Boulder’s price when the latter was still available.
Literally from the first notes it reproduced through my Vimberg speakers, I really liked the A-150’s sound -- through it, I was struck by a new expressiveness of tonal colors. It sounded as if soundstages were being sketched in my room as usual, but that someone had used brightly colored markers to fill in all the spaces. Sounds such as those produced by pianos popped off the page -- I felt I could almost bite into the notes, so tangible were they. I listened to Benoît Delbecq and François Houle’s Because She Hoped (16-bit/44.1kHz FLAC, Songlines/Qobuz), an album that reviewers have described as “exploratory” -- the various sounds on this album tickle the ears in multifaceted ways. In “Ando,” Benoît’s piano and Houle’s clarinet wove a remarkable soundscape that was displayed as lush sound in my room, a dense, thick jungle of tangled notes and tones. The sounds had texture and beauty, the antithesis of dry or antiseptic.
Next I went all old-school audiophile -- I had a feeling the Plinius would have a field day. I loaded up “Only Time,” from The Very Best of Enya (16/44.1 FLAC, Reprise/Qobuz), and raised the volume on the Hegel until the SPL meter on my phone measured 85dB at the listening position. The sound was fully enveloping, the Plinius melding with the Vimbergs to produce dense images on a vast soundstage. The bass was strong but more round than square, and the feathery highs were miles from harsh. “Caribbean Blue” was next, from Enya’s Shepherd Moons (16/44.1 FLAC, Reprise/Qobuz), and the sound was just right. Her lead and overdubbed backing vocals were clear and just a touch upfront, but the characteristic that set the A-150 apart from most other solid-state amps I’ve heard was the density of tonal color. This amp gave me the gestalt of what music should be -- full, rich, dense -- without primarily focusing on detail retrieval and transparency.
In fact, the Plinius got something right that I’ve heard for years from good class-A amplifiers. In the past I’ve called this a “golden glow,” (I may have gotten that from someone else, though) and I heard it with the A-150. The sound had a slightly burnished quality that painted notes more vividly than do most other amplifiers. The bass was all there, and the highs weren’t attenuated -- but music’s life is in the midrange, and that’s where the Plinius glowed . . . golden.
I cued up one of my favorite tracks of recent years: Hannah Reid and her London Grammar bandmates singing “Rooting for You,” from Truth Is a Beautiful Thing (16/44.1 FLAC, Ministry of Sound/Qobuz). Reid’s voice was big and beautiful, just as it should be, its sound developing fully in my room, with shape and power and majesty. I loved what I heard from the A-150, and never felt it lacked in power or headroom or, well, anything. In the last few seconds of the track there’s an intense low-frequency energy that locked on to my room and energized the walls, the floors, my listening seat. The Plinius pushed my Vimbergs to their full potential of bass reproduction. It was satisfying indeed.
The Plinius A-150 is no poor man’s anything. I say that because it competes at a pretty high level. If you want class-A from, say, Gryphon Audio, but can’t make that deep a financial plunge, the Plinius offers a fine alternative to those fantastic products. There is some difference in sound quality, mainly because the Plinius doesn’t produce bass in the same way. All of the Gryphon amps I’ve heard have been bass monsters, moving the earth and pushing speakers for all they’re worth in the low frequencies. The Plinius was plenty centered and solid in the lows, but slightly less likely to make me think that someone had snuck a subwoofer into a corner of my listening room. In some ways, the A-150 reminded me of my vintage Coda Model 11, which produces 100Wpc of class-A sound. I’ve often thought that you just can’t buy an amp like the Coda any more: a real class-A amp of medium power that has all the glory of class-A biasing, but that doesn’t require a second mortgage and/or a significant sacrifice of output power. Well, friends, the Plinius has proven me wrong. It’s just such an amp.
As for comparing the A-150 with the Boulder 2060, they’re different beasts. The Boulder’s sound is more neutral, more resolving, more holographic, and, yes, more powerful. But it doesn’t sound bigger than the Plinius or Coda, and it doesn’t produce those amps’ golden glow. That was my point earlier, when I wrote about someone preferring the Plinius to the Boulder or other amps of its ilk. The qualities of the Plinius’s sound -- feathery highs, strong but round bass, a midband of tonal density to die for -- might be exactly what you and your speakers need. It’s a beautiful sound. And beautiful sound is the point of all this audiophile stuff.
I’m tempted to say that the Plinius Reference A-150 harks back to the days when, for ten to 15 grand, you could buy a first-class amplifier that operated in class-A and produced enough power to drive almost any speaker -- the days before Boulder and Soulution and CH Precision came along and raised the prices of the very best solid-state beyond what most people can afford.
I could leave it at that and do no disservice to Plinius or their Reference A-150. But here’s the thing:
Those amplifiers that preceded the Plinius -- remember the KSA-50S, from back when Krell made real amps? -- aren’t available any longer. I’m no engineer, but I suspect that the Reference A-150’s innards comprise modern parts made with modern manufacturing techniques superior in many ways to those used in the amps of yesteryear. What this means to me is that the Reference A-150 sounds so good that, 25 years from now, it may have proven to be one of those amps that someone is still proud to own and still enjoys listening to. This is the type of sound that never goes out of style -- the type of sound that stands by you on your audiophile journey, no matter how long that journey is.
. . . Jeff Fritz
- Amplifier -- Boulder Amplifiers 2060
- Preamplifier-DAC -- Hegel Music Systems HD30
- Speakers -- Vimberg Tonda
- Source -- Apple MacBook Pro computer running Mojave 10.14.5, Roon, Qobuz
- Cables -- Siltech Explorer interconnects, speaker cables, power cords; Shunyata Research Venom NR-V10 power cord
- Power conditioner -- Shunyata Research Hydra Alpha A12
- Rack -- SGR Audio Model III Symphony
Plinius Reference A-150 Stereo/Mono Amplifier
Price: $13,000 USD.
Warranty: Three years parts and labor.
Plinius Audio Limited
1 Tanner Street
PO Box 19531
Phone: +64 3-982-4766
Fax: +64 3-982-4764