Recommended Components

Editor's Note: Because of the disparity between typical tube and solid-state "sounds," we have split Class A for separate power amplifiers into two subclasses. Nevertheless, even within each subclass, Class A amplifiers differ sufficiently in character that each will shine in an appropriate system. Careful auditioning with your own loudspeakers is therefore essential. Except where stated, output powers are not the specified powers but rather those we measured into an 8 ohm resistive load. All amplifiers are stereo models, except where designated.

A (Solid-State)

ATC P1: $3999
No strangers to the making of solid-state amplifiers—ATC has, for decades, specialized in building self-powered speakers for the pro and domestic markets—the British firm now sells a 150Wpc standalone power amplifier. The P1 is said to offer wide bandwidth (2Hz–400kHz) and a high damping factor (400), plus true balanced inputs alongside its unbalanced RCA jacks. (ATC recommends the former for best performance.) After spending a number of weeks with the P1, JM concluded that "the P1 did not editorialize on the music; it just delivered it." Indeed, his time with the ATC P1 led JM to wonder if perhaps another recommendable amp was, by comparison, adding a bit of "zip" to the sound, "and that perhaps the ATC P1 was telling the story straight." JM concluded: "I am unaware of any other amplifier built from discrete components with this level of build quality, and from a firm with a record of accomplishment similar to ATC's, that offers so much excellent wattage at such a comparatively low price." (Vol.37 No.10 WWW)

Classé CA-M600 monoblock: $14,000/pair
Classé CT-M600 monoblock: $13,000/pair ✩
In a mundane-looking black box with a detachable rack-mount front panel that matches the styling of Classé's CT-SSP preamplifier-processor, the CT-M600 is rated to deliver 600W (700W at actual clipping) into 8 ohms. It employs Classé's Intelligent Cooling Tunnel, in which internal heatsinks are mated to a microcontroller to actively ensure a thermally stable environment. All the audio circuitry, including the 36 output devices, is carried on two six-layer boards, allowing signal paths to be very short and keeping the amplifier's noise floor very low. The CT-M600 was the "consummate chameleon," drawing the best from a wide variety of loudspeakers, providing enormous dynamic range, deathly quiet backgrounds, and intensely saturated colors. "They are the best-sounding amplifiers I have auditioned in my system [as of 2013]," said JA. Compared to the massive Musical Fidelity AMS100, the CT-M600 offered better upper-bass definition and slightly more upper-frequency energy, but lacked the AMS100's sweet, forgiving treble, said JA. The CA-M600 is essentially the same amplifier, housed in Classé's traditional Delta-series enclosure, with its brushed-aluminum front panel curved around to form the side panels. (Vol.34 Nos.3 & 9 WWW)

Constellation Centaur monoblock: $54,000/pair
The 103-lb Performance Centaur Mono is rated to deliver 500W into 8 ohms, features minimalist industrial design by Alex Rasmussen, and offers conventional balanced and unbalanced inputs as well as a Direct XLR input for use with Constellation preamps. Utilizing Constellation's proprietary Balanced Bridge topology, each Centaur Mono includes a pair of carefully matched amplifiers, both using only N-channel MOSFETs. Though they lacked ultimate bass depth and definition, the Centaurs produced a fast, open, transparent sound that was ruthlessly revealing, but never unnaturally harsh or edgy, said MF. For best results, the Centaurs' open sound will require careful matching of associated gear, and especially careful choice of cables, he cautioned. "Constellation Audio's Performance Centaur Mono is a powerhouse of an amplifier capable of delivering very high power with very low distortion into 4 and 8 ohms," JA concluded. (Vol.36 No.11 WWW)

Dan D'Agostino Momentum monoblock: $55,000/pair
Dan D'Agostino's statement product, the 300W (450W at actual clipping into 8 ohms) Momentum has a compact chassis (12.5" W by 5" H by 21" D) machined from a single aluminum billet. A large, round power meter dominates the front panel, while thick copper side panels act as heatsinks. The low-feedback, fully complementary, balanced design uses 1% metal-film resistors and two dozen 69MHz output transistors in a direct-coupled, discrete, bipolar output circuit with a claimed frequency response of 20Hz–20kHz, ±0.1dB. The Momentums produced a seamless overall sound, with slightly reserved highs, a tube-like midrange, and an authoritative bottom end, said MF. "With the darTZeel NHB-458, it's one of the two most satisfying power amplifiers I've ever heard," he concluded. "This is an amplifier that is as well engineered as it is beautiful to behold," said JA. Add $5000 for black finish. (Vol.36 No.2 WWW)

darTZeel NHB-458 monoblock: 151,000 CHF/pair
Made in Geneva, Switzerland, the 450W (530W at actual clipping) NHB-458 measures 18" H by 11" W by 20" D, weighs 154 lbs, and has a deep-gold, brushed front panel and retro-industrial, red-anodized case. Tinted glass side panels allow magnetic fields to escape the chassis and reveal the amp's enormous cylindrical transformer. The large rear-panel heatsink has a cutout for connections that include RCA and XLR inputs, as well as a Zeel BNC 50 ohm input, for use with darTZeel's NHB-18NS preamplifier and Playback Designs' SACD player and DAC. It combined outstanding speed, precise high-frequency transients, and unlimited dynamic range with powerful bass and unsurpassed transparency, said MF. "The darTZeel NHB-458 is easily the finest power amplifier I have ever heard in my listening room," he concluded. At a price! (Vol.35 No.8 WWW)

Lamm Industries M1.2 Reference monoblock: $27,190/pair ✩
The 110W M1.2 with tube front end and MOSFET output stage, comprehensive short-circuit protection, and high/low impedance settings, offered "unflinching honesty in conveying the true nature of the music that passed through it," said PB. "Utterly continuous and coherent from top to bottom," the M1.2 combined resolution and transparency with harmonic completeness, timbral richness, and glow. JA concurs. Compared to the Classé CT-M600 and MBL 9007, the Lamm had a more robust, less delicate sound, but nevertheless impressed JA with its three-dimensional soundstaging and midrange richness. "This is a great amplifier," JA decided. "Highly recommended." (Vol.28 No.2, Vol.35 No.4, Vol.37 No.6 WWW)

mbl 9011 Reference monoblock: $106,000/pair ✩
The 440W (540W at actual clipping into 8 ohms) 9011 measures 19" W by 13" H by 34" D, weighs 223 lbs, is available in several high-gloss finishes with accents in chrome or gold plate, and can be used as a stereo amp or bridged monoblock. Though it lacked some speed and bass punch in absolute terms, the MBL produced a rich midrange and excelled in scale, atmosphere, ease of presentation, and sheer power, said MF. When used as a bridged monoblock, the 9011 must be driven by a balanced signal, cautioned JA, who noted superb measured performance. (Vol.35 No.3 WWW)

mbl 9007 Noble Line monoblock: $42,800/pair ✩
The 440W Reference 9007 can be used as either a balanced monoblock or a single-ended stereo amplifier and has provisions for biwiring and biamping. It uses mbl's Direct Push/Pull circuitry design and Isolated Gain Cell technology, and its gleaming black exterior is decorated by a large, gold mbl logo. Sacrificing bloom and suppleness for crystalline transparency and offering tightly focused imaging, shimmering highs, and well-damped bass, the 9007 was one of the most exciting and engaging amplifiers in MF's experience. His recommendation only concerns the 9007 used as monoblock pairs, however. JA was thrilled by the mbl's superb measured performance. Compared to the humongous Musical Fidelity AMS100, the mbl monoblocks were a little more forward in the low treble and offered more ultimate slam, but lacked the AMS100's sweet, forgiving treble, said JA. (Vol.29 No.9; Vol.34 No.9, Vol.37 No.6 WWW)

mbl Corona C15: $25,000/pair
Although it employs a custom-specified version of the popular Hypex class-D amplifier module, the Corona C15 monoblock, which offers 280W into 8 ohms, 520W into 4 ohms, is, according to its designer, a "Linear Analog Switching Amplifier," the overall design concept of which entails the use of a linear rather than switch-mode power supply—itself built around a toroidal transformer with generous mu-metal shielding. (The latter is presumed to contribute to the amp's 48.5-lb weight.) Indeed, in his measurements, JA confirmed that "the C15's transfer function appears to remain relatively consistent with both frequency and output current"; also unusual for a class-D amp was the C15's admirable output-impedance behavior: JA discovered that its low-pass function into loads of 4 and 2 ohms was "very similar to its 8 ohm behavior." In his listening tests, JA found that the C15's "intrinsic character was all about control, especially the tight control of low frequencies"—a quality that served well the amp's pairing with the somewhat rich-sounding woofer alignment of the Vivid Giya G3 speaker, but less so the Joseph Audio Perspective, with which the MBL sounded clean but lean. Especially when combined with the classic Rogers LS3/5a, JA observed "superb imaging definition and stability" with the good-looking MBL amps. (Vol.37 No.6 WWW)

Musical Fidelity M6PRX: $3495 $$$
This dual-mono, class-A/B design is rated to deliver 260Wpc into 8 ohms from four pairs of bipolar output transistors per channel, using circuitry based on Musical Fidelity's flagship Titan. Much more modest in size and appearance than the massive Titan, the M6PRX measures 17.5" W by 5" H by 15.5" D, offers balanced and single-ended inputs, has choke-regulated power supplies, and comes in a choice of silver or black faceplate. "This is one of the sweetest-sounding, most fatigue-free solid-state amplifiers I have met up with," said Sam. His solid-state reference. (Vol.35 No.6)

Parasound Halo JC 1 monoblock: $9000/pair $$$ ✩
MF heard exactly what this high-power—400Wpc specified, 586W at clipping!—John Curl-designed amp's specs showed: "ultra-wide bandwidth, high-current capability, low, low noise, a high S/N ratio, and a fast slew rate, among many other indicators of outstanding amplifier performance....There was an honesty to the overall tonal and harmonic presentation that transcended technological stereotypes." MF found the overall sound to be powerful, refined, smooth, organized, dynamic, transparent, and rhythmically supple, if a little on the subtly warm and rich side of the sonic spectrum, but decided that this not at the expense of transient speed and resolution of detail. "Perhaps some listeners will find the JC 1 too refined and perhaps a tad polite, but I didn't." "Rocks for sure," says ST, adding that with the amp driving the Triangle Magellans, he found the "bass firmed up, the sound wasn't strained in any way, and there was an overall sense of ease. Dynamic ease. Listening ease. Just ease. Compared to the Halcros, the Parasound JC 1s brought the soundstage forward. Tonally, the Parasounds were magnificent...with no trace of solid-state hardness. And the amps weren't even broken in." "The Parasound JC 1 is one of the finest high-powered solid-state amps I've heard," said ST. "Think of it as a 25W class-A amp that does 400W class-A/B when pushed." Matched with the JC 2 preamp, the JC 1s presented even greater holographic detail and transparency. The Parasound Halo JC 1 traded the Moscode 402Au's snappy, vivid tonality and larger soundstage for "quiet precision," clarity, and focus, said WP. The Halo JC 1 traded the Aesthetix Atlas's creamy midrange for greater bottom-end heft and top-end extension, said WP. Compared to the Bryston 7B SST², the Parasound had deeper bass, tighter images, faster transients, and greater low-level resolution and microdynamic delicacy, said MF. A favorite of JA's, who was equally impressed by how the JC 1 performed on the test bench: "This is excellent measured performance. The Halo JC 1 is not only the best amplifier to come from Parasound, it ranks up there with the best high-end heavyweights," though WP felt that while the Halo JC 1 exhibited grace and delicacy compared with the much more expensive Luxman B-1000f, it lacked some impact, drive, resolution, and detail. Stereophile's—and Sam Tellig's—"Joint Amplification Component" for 2003. (Vol.26 Nos.2, 6, & 12, Vol.30 No.12, Vol.31 No.3, Vol.32 No.9, Vol.33 No.1, Vol.34 No.2 WWW)

Pass Labs XA60.5 monoblock: $11,000/pair
Designed by Nelson Pass, the XA60.5 is rated to deliver 60W into 8 ohms (130W into 8 ohms at clipping) and uses Pass Labs' balanced, single-ended, class-A Supersymmetry circuit topology. Housed in the same case as the XA30.5 stereo amplifier, it has a gray-anodized aluminum front panel with a large, blue-illuminated meter that indicates the output stage's current draw. The interior is dominated by a large Plitron toroidal power transformer flanked by two circuit boards, each carrying 10 pairs of complementary power MOSFETs. Though it lacked some bottom-end authority, the XA60.5 produced a natural, transparent overall sound, with especially beautiful mids and highs, said JA. "It is the best-sounding amplifier I have ever used," he concluded. (Vol.37 No.1 WWW)

Pass Labs XA30.5: $5500 ✩
This solid-state stereo power amplifier from renowned engineer Nelson Pass is rated to deliver 30Wpc into 8 ohms, but actually delivered clipping-free peaks 6dB higher in power. Its strong yet elegant physical appearance is matched by a simple, symmetric internal design using Pass's Universal Gain Stage and 10 pairs of power MOSFETS along each side of the rugged chassis. Though it lacked the snap and energy of some larger, more powerful amplifiers, the XA30.5's "lifelike smoothness" and "effortless purity" brought forth the subtle microdynamic nuances of more intimate material. BD: "The XA30.5 is a superb-sounding amplifier. Absolutely, positively, and enthusiastically recommended!" Compared to his reference Pass Labs Aleph 3, the XA30.5 had a leaner midrange but provided a wider soundstage, greater resolution, and better dynamics, EL concluded. Compared to the tubed Rogue M-180 monoblock, the XA30.5 offered a slightly more forward sound that was "rounder, richer, less controlled but more sumptuous" overall, said EL. The XA30.5 traded the Pass INT-150's bass control and wide dynamics for greater purity and texture in the midrange, said EL. (Vol.32 Nos.5 & 8, Vol.33 No.1, Vol.34 No.1 WWW)

Siltech SAGA: $75,000
With their unabashedly expensive Structural Amplifier Gain Architecture (SAGA), cable specialists Siltech took a new approach to the two-box power amp: This is neither a pair of monoblocks nor a split between an amplifier and its power supply, but rather a split between a voltage amplifier and a current amplifier. The former, called V1, is a battery-powered tube amp that's switchable between triode and pentode modes, while the latter, P1, is a mains-powered solid-state amp. More unusual is the P1's Apollo Light Drive technology, in which bias current for the output transistors is produced by training high-intensity LEDs on a solar panel: Take that, orthodoxy! According to MF, in comparison with other top amps of his recent experience, "the SAGA sounded as if it had tightened the turnbuckles of tonality, space, and, especially, rhythm 'n' pace—the sound was positively exhilarating." But tightened turnbuckles have their price: "Soundstage depth was somewhat foreshortened, with images between the speakers that normally appear well behind the speaker plane presenting themselves closer to a line drawn between them." Still and all, MF concluded, "As soon as I pulled [the SAGA] from my system, I began to miss it." JA's measurements, spread over two sample sets, revealed "idiosyncratic" performance, prompting the recommendation that "this expensive amplifier must be auditioned with the prospective owner's own speakers. Stated price is for the V1 (voltage amp) plus P1 (current amp). C1 (preamp) costs $37,500. Entire system costs $112,500. (Vol.37 No.10 WWW)

Simaudio Moon Evolution 880M monoblock: $45,000/pair
Rated to deliver 800W (1050W at actual clipping), the flagship of Simaudio's Evolution line is a DC-coupled, fully balanced differential design. Its massive power supply is built on two 1.3kVA toroidal transformers and two banks of large capacitors. With a chassis of black-anodized aluminum and a front panel comprising elegantly curved extrusions of brushed aluminum, the 880M measures 18.75" W by 7.5" H by 16.5" D and weighs 92 lbs. Though it wasn't as tonally rich as the VTL S-400 Reference, the Simaudio was extremely well balanced, exhibiting an effortless precision and iron-fisted control that extended from top to bottom, said BD. "The 880M is an excellent design superbly executed, with a professionalism and attention to detail that promise consistently outstanding performance and long, trouble-free life," he concluded. Must be auditioned fully warmed-up, notes JA. (Vol.36 No.6 WWW)

Soulution 710: $50,000 ✩
The 130Wpc Soulution is a dual-mono, dual-differential design housed in a large (21" W by 10.9" H by 18.7" D), clean, matte-gray case. Two massive 1000VA toroidal transformers, solid copper bars carrying rectifiers and capacitors, and a thick, heat-dissipating aluminum baseplate contribute to the amp's 176 lbs. The Soulution offered unparalleled transparency, startling transient clarity, and impressive soundstaging, but lacked some harmonic richness and bass impact. "A technical and sonic achievement not to be denied," said Mikey. With impressive dynamic range and exceedingly low levels of noise, the Soulution proved one of the best-measuring amplifiers in JA's experience. (Vol.34 No.8 WWW)

Theta Digital Prometheus monoblock: $12,000/pair
Joining the growing ranks of class-D amplifiers with perfectionist aspirations, the Theta Prometheus combines the Hypex Ncore NC1200 module developed by noted class-D specialist Bruno Putzeys with a linear power supply designed by Theta's own David Reich. (The latter—or at least its enormous toroidal transformer—accounts for the amps' 54.5-lb weight.) Specs include 500Wpc, less than 0.001% THD+N at 1W, and an output impedance said to be extremely low. According to LG, "The most striking things about the Prometheus's sound were its huge dynamic range and bass impact." He also noted that "The Prometheuses projected a broad, detailed, involving, three-dimensional soundstage," and "the midrange response blossomed when my [Quad ESL-989] speakers were driven by the Thetas." LG's conclusion: "My last impression of the Prometheus was the same as my first: It's one of the best-sounding amplifiers I've heard in my listening room." Following the Theta's time on his test bench, JA wrote, "The measured performance of Theta Digital's Prometheus is superb, even for an amplifier with a class-D output stage." (Vol.38 No.3 WWW)

Ypsilon Aelius monoblock: $36,000/pair
Made in Athens, Greece, the 200W Aelius monoblock power amp measures 16.6" W by 9" H by 16.6" D and weighs 99 lbs. Its audio circuit has only two gain stages and almost no passive components in the signal path. Its single-ended class-A input stage uses either a Siemens C3g or an Electro-Harmonix 6C45PiEH tube. With the C3g tubes in place, the Aeliuses produced a punchy, direct, and insistent sound with "hair-raising" transparency and three-dimensional imaging; with the 6C45PiEH tubes, the Aeliuses had a much warmer, darker, softer overall sound, said MF. On the test bench, the Aelius exhibited measured performance that was in many ways typical of a classic tube design, but with the ability to drive low impedances usually associated with solid-state designs. "Its sound quality will very much depend on the input tube fitted," said JA. (Vol.36 No.4 WWW)

A (Tube)

Air Tight ATM-1S: $9500
Among the audio world's artisanal power amplifiers, only a few have more impressed AD than the Air Tight ATM-1S, the earliest version of which was made by Japan's A&M Limited way back in 1987. Today's ATM-1S uses two EL34 pentode tubes (configured as triodes) per side, for 36Wpc into 8 ohms. It also features solid-state rectification, dual-channel input-level controls, Hashimoto output transformers, a distinctly easy-to-use tube-biasing system, and a high level of build quality (including point-to-point wiring). AD found the ATM-1S to sound enjoyably warm and lush in his low-powered-amp–friendly system, yet with "an appropriate sense of [musical] momentum and drive." He praised the Air Tight for sounding "forceful and present when listened to at lower volumes," while noting that it remained "poised and free from gross colorations" when pushed. In his measurements, JA noted excellent squarewave response with short risetimes—but, on the downside, "drastically higher levels of second and higher harmonics in the left channel," a problem that may have been caused by a bad tube or damage in shipping. AD summed up: "The Air Tight ATM-1S is among the few power amps I'd care to live with." (Vol.37 No.11 WWW)

Audio Research Reference 150: $13,000
The 150Wpc Reference 150 measures 19" W by 8.75" H by 19.5" D, weighs 75 lbs, offers output taps for 16, 8, and 4 ohm loads, and is available in silver or black. It uses eight matched pairs of KT120 output tubes and four 6H30 driver tubes; the output-stage coupling is a combination of the familiar ultralinear configuration and ARC's patented "partially cathode-coupled" topology. EL: "With its open soundstage, neutral tonal balance, finely textured musical presentation, wide dynamics, and supremely musical feel, the ARC Reference 150 connected me with my music better than almost every other amplifier I've heard." Compared to the Octave RE 290, the Ref 150 lacked some bass control but sounded significantly bigger, clearer, more colorful, and more natural, said EL. A JA favorite. (Vol.35 No.7 WWW; Vol.36 No.1)

Audio Research Reference 75: $9000
A half-power version of ARC's Reference 150, the 75Wpc Reference 75 uses four KT120 and two 6H30 tubes. Two front-panel VU meters double as adjustment meters for biasing each of the four KT120s. A relatively simple, straightforward circuit design enables short signal paths; high-quality output transformers offer 4 and 8 ohm taps, with a common ground. BJR noted lightning-fast transient articulation, superb detail resolution, and exceptional bass slam and authority. He bought the review sample. JA noted good measured performance, but advised against using the amp with speakers whose impedance drops significantly below the nominal value of the output-transformer tap. Also see JA's Nola review in Vol.37 No.10. (Vol.36 No.5 WWW)

Conrad-Johnson Classic 60 SE: $5000 ✩
The Classic 60SE uses four Tung-Sol KT120 tubes to deliver 60Wpc into 4 or 8 ohms. Upgrades over the standard Classic 60 include Teflon capacitors in the power supply and main reservoir, Vishay resistors at key points, and Cardas binding posts. With its handsome tube cage in place, the Classic 60SE measures 17.4" W by 6.6" H by 13.4" D and weighs 41 lbs. It combined exceptional dimensionality, pinpoint imaging, and excellent low-level resolution for an overall sound that was "the antithesis of mechanical or contrived," said ST. (Vol.35 No.4)

Fi 421A: $4575 ✩
Designed and built by Don Garber in Brooklyn, New York, the Fi 421A is a single-ended, capacitor-coupled, 4Wpc stereo amplifier with a single 421A power tube. It measures just 10" W by 8" H by 10.5" D, weighs 20 lbs, and uses high-quality parts throughout. The Fi sounded "open, clear, compelling, and lovely," and had a knack for reproducing the human voice with outstanding presence and texture, said AD. Class A in special systems only, he cautions. Price increase since review due to new output transformers. One of AD's long-term references. (Vol.35 No.1 WWW)

Lamm ML2.2 monoblock: $37,290/pair
Like its predecessor, the ML2.1, the 18W ML2.2 is a single-ended-triode monoblock power amplifier with a 6C33C indirectly heated power tube. Other tubes include two 6N6P, one 6AK5, one 5651, and one 12AX7. Refinements over the ML2.1 include a new input circuit, new power transformer, five power-supply filter chokes instead of two, revised printed-circuit boards, and upgrades of various parts. Measuring 16" W by 8.25" H by 20.375" D, weighing 81 lbs, and with 14 tubes total (all of which must be installed and adjusted by the user), the ML2.2s require careful setup. Though it lacked the Shindo Haut-Brion's knack for expressing musical force, the Lamm combined superb spatial and temporal performance with rich texture and tone color, said AD. "An extraordinary product," he concluded. (Vol.36 No.4 WWW)

Lamm ML-3 monoblock: $139,490/pair
Rated to deliver 32W, Lamm's flagship design is a zero-global-feedback, class-A monoblock with a single-ended-triode output stage and an outboard power supply. It uses one 12AX7, four 6N30P-DRs, and one direct-heated GM70 triode transmitter tube, and its assortment of premium internal components include: military-grade Dale metal-film resistors, Caddock power-film resistors, Cornell-Dubilier and United Chemi-Con electrolytic capacitors, and Electrotube, Elcon, and Roederstein film caps. While the ML3 sounded "lusher and bloomier than life," it produced natural attacks and generous sustain, and had an airy, extended top end, said MF. "Cost and value for money aside, the Lamm Industries ML3 Signature is among a handful of the most pleasurable-sounding amplifiers I've ever heard," he concluded. JA noted good measured performance for an amplifier with a single-ended output stage. (Vol.36 No.9 WWW)

Luxman MQ-88: $8000 ✩
The massively built, 40Wpc MQ-88 is a classic push-pull tetrode design based on the KT88 power tube. The amp is hand-wired, point-to-point, and all internal circuit components are suspended from its 15mm-thick top plate. While the MQ-88 lacked some bass control, it sounded much more powerful than the typical 40Wpc amplifier, producing surprising "oomph factor," said JM. Compared to Ayre's AX-7e, the Luxman lacked resolving power, bass extension, and soundstage clarity, but offered a "delectable midrange." (Vol.35 No.4 WWW)

McIntosh MC275: $5500 $$$ ✩
The revived 75Wpc MC275, preserves the look of the original while adding modern innovations. Chimneys are used to cool the tubes by convection, and three circuit boards have been replaced by a single board on which are mounted all components, tube sockets, and power-supply parts. ST: "I heard all the dynamic quality, all that aliveness of the original, plus a level of transparency that brings the MC275 definitely into the 21st century." Sam bought the review sample. The fifth incarnation of the 75Wpc MC275, originally introduced in 1961, retains the first incarnation's classic appearance and its use of four KT88 power-output tubes, three 12AX7 input tubes, and four 12AT7 driver tubes. New are a stainless-steel chassis, balanced inputs, and gold-plated, five-way binding posts. While the MC275's two hefty transformers utilize the same "unity-coupled circuit" invented by McIntosh in 1947, the copper wiring is now insulated in a more durable synthetic material. Though dynamic expression was restricted and bass notes were "a bit muddy" in dense musical passages, the MC275 produced "stunning" soundstage depth and "spooky" intertransient silences, said FK. Meanwhile, the MC275's superb signal/noise ratios led JA to conclude that "Good audio engineering is timeless." Compared to its predecessor, the Limited Edition version of McIntosh's MC275 ($6500) has beefier binding posts, a more conveniently positioned power switch, and a gold-plated rather than stainless-steel chassis. In addition, a new output-transformer winding process has resulted in wider bandwidth, increased damping factor, and improved linearity. RD noted an ideal top-to-bottom tonal balance and an impressive sense of rhythmic drive, concluding, "The MC275LE is simply a wonderful-sounding amplifier, able to bring out the best from a wide range of loudspeakers." He bought the review sample. (Vol.27 No.7, Vol.33 No.10, Vol.35 No.10 WWW)

Miyajima Labs Model 2010 OTL: $9950
Built into "some of the loveliest steel casework" AD has ever seen, the Model 2010 from Miyajima Laboratory is a stereo OTL amplifier that uses a total of eight 6080WC dual-triode tubes to produce 7Wpc. The fixed-bias 2010 also uses two 12AX7 dual-triodes, two 12AU7 dual-triodes, solid-state rectifiers, and a host of vintage and vintage-style parts, including 18 NOS Black Cat capacitors. Used as a stereo amp, the 2010 impressed AD by sounding "distinctly open and transparent" while lacking "nothing in the way of color or texture." Driving AD's DeVore Orangutan O/96 speakers, the 2010 surpassed the similarly priced and powered Shindo Cortese in top-end sparkle while giving up nothing in terms of "superb touch and force." Adding a second 2010 and strapping the amps for mono—resulting in 16Wpc—delivered what AD described as some of the best sound he has had in his home: "The monoblock experience seems to be the way the Miyajima 2010 was meant to be heard—and I loved it." Full Class A status refers to the use of two 2010s. AD suggests that, even at nearly $20,000 for a stereo pair, the Miyajima represents very good value. (Vol.37 No.7 WWW)

Music Reference RM-200 Mk.II: $5500 ✩
Made in the US, the 100Wpc RM-200 Mk.II has the same basic physical and electrical architecture as the original, but uses better output transformers, adds a capacitor-forming function to extend tube life, and has a revised power supply. The fully balanced design features a high-power, bipolar, solid-state input stage and tubed driver and output stages. It uses two matched pairs of KT88 (standard) or 6550 (optional) output tubes, and a pair of 6BQ7 drivers. Though it lacked the slam and bass authority of more powerful solid-state amps, the RM-200 Mk.II produced airy highs, well-defined bass, and a lush midrange. "When the RM-200 Mk.II was in my system, I wanted for nothing," said MF. JA noted "superb measured performance for a tubed design." Hand-wound output transformers, add $1000; tube bias balance control, add $800. (Vol.34 No.12 WWW)

Octave Audio RE 290: $10,000
Made in Germany, the beautifully built, 75Wpc RE 290 is a push-pull design with class-A/B output stage and adjustable bias for each tube. It uses KT88 or KT120 power tubes, provides a single set of binding posts optimized for a 4 ohm load, and has a switch-activated power-saving mode. The RE 290's well-balanced sound was marked by tight bass, clean mids and highs, and excellent dynamic range, said EL. JA noted impressive measured performance. Compared to the Audio Research Ref 150, the Octave had better-controlled bass but lacked soundstage size, transparency, and tonal color, said EL. The optional Black Box ($1200) and Super Black Box ($3500) hook up to the RE 290 via an umbilical cord and respectively increase the capacitance four- or tenfold. (Vol.36 No.1 WWW)

PrimaLuna DiaLogue Premium: $3199
Rated to deliver 25Wpc in Triode mode or 42Wpc in Ultralinear, the extremely versatile DiaLogue Premium is a push-pull design that uses six 12AU7 and four EL34, KT88, or KT120 power tubes. Like other PrimaLuna models, it offers: an LED-based Bad Tube Indicator system for the output tubes; a Power Transformer Protection circuit; an Output Transformer Protection circuit; an AC Offset Killer circuit intended to eliminate hum; and an Adaptive Autobias circuit. With every recording AD played, the DiaLogue Premium exhibited an open, clear, and dramatic overall sound, with good tonal balance, realistically weighty bass, and remarkable spatial depth. "A very strongly recommended amplifier and a hell of a good value," AD concluded. Due to the amp's high output impedance and its rising distortion when the load impedance drops below the nominal value of the output-transformer tap, careful matching with the user's loudspeakers is mandatory, cautioned JA. (Vol.37 No.2 WWW)

Rogue Audio M-180 monoblock: $5995/pair ✩
Built in the US, the rugged Rogue M-180 delivers 180W in ultralinear mode, and uses four Electro-Harmonix KT90 output tubes. Upgrades over the earlier M-150 include: increased power-supply storage; PRP resistors; Cardas binding posts, input wiring, and RCA jacks; improved input circuitry; HexFred high-speed diodes for the bias supply; and upgraded small-signal tubes. EL was most impressed by the Rogue's ability to maintain articulation and propulsion while providing bass extension and weight. Compared to the Pass Labs XA30.5, the Rogue offered greater low-bass control and had a drier tonal balance. "A great value," sums up EL. See also EL's Rogue Atlas Magnum review in Vol.35 No.4. (Vol.33 No.1 WWW)

Shindo D'Yquem monoblock: $24,995/pair
Shindo's newest mono amp produces up to 18W from a parallel pair of Russian-made Genelex 300B directly heated triode tubes, operated in single-ended, pure class-A mode. Like all Shindo designs, the D'Yquem is made from a careful mix of modern and vintage parts and has beautiful steel casework finished on all surfaces in the company's trademark shade of green. While the D'Yquem shared with other Shindo models an excellent ability to portray music's natural color, texture, impact, and momentum, it added an especially clean and colorful low end, said Art. (Vol.37 No.2 WWW)

Shindo Cortese: $10,995 ✩
Like a sax player who can't make himself perform the same solo twice, Ken Shindo brings a certain artistic restlessness to the design of his hand-made tube amplifiers; the 10 Wpc Shindo Cortese—the least expensive of his single-ended amplifiers and the only one built on a stereo chassis—has now been recast, offering the same essence but with slightly different phrasing. The Cortese's input circuit now uses two 6AW8A pentode/triode tubes per channel instead of one, its bias-supply circuit is laid-out somewhat differently, and the Sprague Black Beauty coupling caps have given way to Orange Drops; Allen-Bradley carbon-comp resistors, Siemens F2a indirectly heated output tetrodes, a ginormous Denki power transformer, and Shindo-designed Lundahl output transformers, the single secondaries of which are tailored to high-impedance loads, remain. The sound is punchy and very vivid, with exceptional drive and a bit less gooshiness than its immediate predecessor, says AD, who found it a particularly good match with the DeVore O/96 loudspeaker. (Vol.30 No.7 WWW)

Shindo Haut-Brion: $10,995 ✩
Like earlier models, the latest Haut-Brion uses two matched pairs of the rare 6L6GAY pentode tube to deliver 25Wpc. The output section is a fixed-bias design, with a regulated bias supply and individual adjustment pots for each of the four output tubes, while the output transformer is a C-core Lundahl model made exclusively for Shindo. Unlike earlier models, the new Haut-Brion has three 6AW8A triode/pentode tubes per channel, uses a pair of Alps 250k ohm potentiometers, and forgoes global feedback. Though it lacked some low-frequency tightness, the new Haut-Brion created an enormous soundstage and showed impressive force. "The amp was the pizzicato king," said AD. (Vol.35 No.2 WWW)

Thöress 300B monoblock $12,995/pair
Provisional rating. See AD's review in this issue.

VTL Siegfried Series II Reference: $65,000/pair
VTL's Siegfried Series II Reference weighs an abdominal-wall-challenging 200 lbs and uses a dozen 6550 beam tetrode tubes to produce 330W in triode mode or 650W in tetrode mode. High-tech touches abound: A microprocessor delays and ramps up the output section's B+ rail on power-up and enables (reasonably) fast switching between triode and tetrode modes. And rather than use an output transformer with multiple secondaries—an approach that designer Luke Manley considers a sound-sapping compromise—the Siegfried Series II Reference has a trannie optimized for a 5-ohm load, plus a four-setting feedback control to adjust the damping factor as needed. In MF's system, where tetrode was the preferred mode (with damping factor set to Medium, and with occasional forays into triode), the VTL sounded three-dimensional, with "slam not in spades, but in dump trucks full!" MF reveled in the VTLs' midrange creaminess, while acknowledging the slightly greater transparency of the darTZeel NHB-458 monoblocks—and noted that the Siegfried II Reference was "as neutral and uncolored as any tube amp I've listened to." (Vol.37 No.5 WWW)

VTL MB-450 Series III Signature monoblock: $20,000/pair ✩
Rated to deliver 425W (tetrode) or 225W (triode) into a 5 ohm load, the MB-450 III uses eight 6550 output tubes, a 12AT7 input tube, and a 12BH7 driver. Revisions to the Series II include a redesigned, fully balanced differential input stage, a lower-impedance output stage, premium Mundorf capacitors, and a shorter, faster, fully balanced negative-feedback loop. While the VTL sounded soft and "tubey" in triode mode, its tetrode performance was marked by an expansive top end, unusually fast attacks, clean decays, and well-controlled bass. "A significant evolutionary advance" over its predecessor, said MF. Because it provides lower distortion into higher impedances, the MB-450 III will sound best with higher-impedance speakers, JA advised. (Vol.34 No.4 WWW)

B

Allnic A-5000 DHT monoblock: $19,900/pair
Designed and made in South Korea by Kang Su Park, the Allnic A-5000 DHT, a 10Wpc single-ended monoblock, has three gain stages and an unusual combination of tubes: one Marconi CV1673, one 3A/110B, an Electro-Harmonix 300B, and a 5U4G full-wave rectifier. Construction quality was first-rate, with exceptionally clean solder joints and a solid, attractive case of aluminum alloy. Compared to AD's Shindo Corton-Charlemagne monoblocks, the Allnics had a slightly dark timbral balance with soft highs and short decays, but offered superb scale, drama, and impact. "Distinctive sounding and consistently musical," sums up AD. Along with the second-order distortion typical of single-ended designs, JA's measurements found an impressively wide frequency response, excellent squarewave reproduction, and low output impedances. Almost Class A in some respects. (Vol.35 No.6 WWW)

Anthem Statement M1 monoblock: $6998/pair
Despite its relatively slim proportions (19.25" W by 2.25" H by 18.75" D; 20 lbs), the class-D Statement M1 is rated to deliver a whopping 1000W into 8 ohms. An internal heat-pipe cooling system allows multiple M1s to be stacked without the need for cooling fans or heatsink fins. The tidy rear panel holds balanced and single-ended inputs, a balanced-output gain switch, various trigger options, and a single pair of output terminals. The M1's detailed, extended highs were offset by its gritty, congested bass, which unnaturally colored almost every recording KR played. While the Anthem is extraordinarily powerful for its size, JA was very suspicious of the high level of ultrasonic noise in its output. "This will make the Anthem Statement M1's sound quality very system dependent," he cautioned. Be sure to audition with your own components and cables. (Vol.35 No.12 WWW)

Lindell AMPX: $1595 $$$
Made in Sweden, the 20Wpc AMPX is a single-ended, dual-mono, class-A power amplifier with balanced XLR inputs. Designed primarily for pro-audio applications, the AMPX measures 18.8" W by 3.5" H by 17.4" D, and its faceplate, machined for rack mounting, is dominated by two large, blue power meters, calibrated to show watts into 8 ohms. Driving Opera's Callas loudspeakers, the AMPX was lively, detailed, and "unfailingly musical, sounding both powerful and revealing," said JM. "A great amp and an amazing bargain," he concluded. As long as it isn't used to drive loudspeakers with impedances that drop significantly below 4 ohms, the Lindell should perform well, concluded JA. (Vol.36 No.12, Vol.37 No.1 WWW)

Rogue Atlas Magnum: $1995 ✩
Magnum upgrades over the basic Atlas (reviewed by Fred Kaplan in March 2007), include larger, quieter power supplies; polypropylene bypass capacitors; Dale-Vishay resistors in critical spots; sturdier binding posts; gold tube sockets; and the option of KT90 or KT120 output tubes, to increase the specified power rating to 90 or 120Wpc, respectively. EL preferred the fuller, more extended sound of the KT120 output tubes, and appreciated the Atlas Magnum's well-balanced character: "This amplifier had enough dynamic power, enough timbral accuracy, enough soundstage illusion, enough resolution, and enough musicality to turn off the analytical part of my brain and let me simply listen to music." JA was disappointed with the Rogue's lack of high-frequency linearity. Stock Atlas models can be upgraded to Magnum status for $650. (Original, Vol.30 No.3 WWW; Magnum, Vol.35 No.4 WWW)

Sophia Electric 91-01 300B monoblock: $4999/pair
The 9W (3W at 1% THD) Sophia Electric 91-01 300B is a single-ended power amplifier designed around the 300B directly heated triode tube, operated without negative feedback. The input stage is capacitor-coupled to the signal grid of one of Sophia's own Princess Mesh Plate 300B tubes, and both the mains and output transformers are designed and made in-house. Inside, the Sophia exhibited haphazardly routed point-to-point wiring, some sloppy solder joins, and under-insulated capacitor leads. Though its overall sound was slightly dark and lacked some top-end sparkle and mid-treble openness, the Sophia provided decent color, very good texture, and acceptable senses of touch and force, said AD. JA was concerned about some idiosyncratic aspects of the design. (Vol.36 No.12, Vol.37 No.1 WWW)

Editor's Note: There are no amplifiers listed in Class C and D.

K

Ayre Acoustics MX-R Twenty, Bricasti M28, Benchmark AHB-2, Luxman M600; Pass Labs XA60.8, Shindo Corton-Charlemagne, Simaudio Moon Evolution 860A.