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)

Accustic Arts AMP V: $50,000
The 176lb Accustic Arts AMP V (pronounced Amp Five) was the heaviest, tallest, most powerful—specified power is 900Wpc into 8 ohms, 1360Wpc into 4 ohms, and 1500Wpc into 2 ohms—and most expensive stereo amplifier JVS has auditioned in his system. It requires two 15A power cables, one for each channel. The AMP V is a fully balanced class-AB design with 40 output MOSFETs heavily biased into class-A. The amplifier offers switchable "damping factor linearization," which, when turned on, linearizes its output impedance over a wide frequency range. JVS found that the highs were softer with damping factor linearization active. The AMP V sounded most transparent without it, he concluded. Listening to Patricia Barber's Clique, JVS commented that what immediately stood out "was the pristine silence between the notes. The AMP V is one of the quietest amps I've ever heard. … Equally notable was the impressive color saturation, with primary hues and infinite shades of pastel vying for attention with midrange warmth." The AMP V was not just a powerhouse; "it's a musical instrument that produces bright colors, huge images, and seat-shaking bass. Nor does it skimp on detail." JA found that measuring such a powerful stereo amplifier was problematic, as it blew 15A circuit breakers at high powers into low impedances. When he plugged it into a 20A circuit, the breaker didn't blow, but the droop in his AC supply voltage meant that the amplifier clipped at 665Wpc into 8 ohms and 890Wpc into 4 ohms. Distortion was extremely low and primarily consisted of low-order harmonics, he found. (Vol.45 No.1 WWW)

Bel Canto E1X: $6000
Trickled down from Bel Canto's premium Black line, this slimline, lightweight amplifier uses the well-regarded Ncore class-D modules and a low-noise switch-mode power supply. TG commented positively on the e1X's image specificity, low-frequency control, and extremely low background noise. "I didn't expect to be so completely gobsmacked by the level of clarity and musicality I'm hearing now from the e1X," he concluded. JA's measurements revealed that the Bel Canto easily exceeded its rated output powers of 250Wpc into 8 ohms and 500Wpc into 4 ohms, clipping at 340Wpc into 8 ohms and at 530Wpc into 4 ohms. Noise, harmonic distortion, and intermodulation distortion were all impressively low in level. (Vol.43 No.6 WWW)

Benchmark AHB2: $2999 $$$ ★
Named for the late Allen H. Burdick, the engineer whose work formed the basis for its design, Benchmark's AHB2 makes use of THX Corporation's Achromatic Audio Amplifier (AAA) technology, in which a low-power feed-forward amplifier drives a low-bias class-AB output section. In his listening tests KR discovered "much more apparent low-level detail in already-familiar recordings"—a characteristic he credited to the Benchmark's evident noiselessness—and a tonal balance that "sounded more 'right' than any of [the other amps on hand]." In measuring the AHB2 and attempting to confirm its specified (very) high signal/noise ratio, JA observed nonlinearities in his testing equipment that "haven't affected the measured performance of other amplifiers I've tested, but they were detectable with the AHB2's very low intrinsic distortion and noise." His conclusion: "an extraordinary amplifier." In his Follow-Up report JCA described comparing the AHB2 to his reference amp: "Although I preferred the AHB2's denser presentation of certain details, it's not clear to me which is truer to the source." (Vol.38 No.11, Vol.41 No.10 WWW)

CH Precision M1.1 Reference Power Amplifier: $104,000/pair
The Swiss-made CH Precision M1.1 is a modular solid state amp—the user can configure the amp for stereo or mono use, as well as for a choice of output-power-delivery modes—with a JFET front end and a class-AB output stage. A robust power supply built around a massive 2200VA transformer helps account for the M1.1's extraordinary (165lb) weight. MF, who found the amp's timbral balance to be very slightly on the warm side of neutral, was taken with a pair of M1.1s configured for mono, noting that their richness did not come with the penalty of softened transients and praising the amps' combination of bass depth and bass kick. In measuring the M1.1, JA observed that its performance on the bench was dependent upon the amount of global negative feedback dialed in (MF preferred the sound at 20%) and noted the amp's preference for loads higher than 2 ohms. (Vol.42 No.7 WWW)

Classé Delta Mono monoblock: $21,998/pair
The first fruits of the Canadian company's acquisition by Sound United, the Delta series products were in development for several years. Designed in Canada but made in SU's Japanese factory, where the high-end Denon and Marantz products are manufactured, the Delta Mono impressed JA not only with its sound quality but also with its impeccable construction. The front panel features an accurately calibrated VU meter. With its lateral-MOSFET output devices heavily biased into class-A, the Delta Mono's waste heat is expelled from its rear with a quiet-running, microprocessor-controlled fan. "The midrange transparency of the Classé amplifiers was impressive," wrote JA, adding that "the high frequencies were impressively clean and smooth" and that the Delta Mono exhibited tight low-frequency control and articulation. Compared with the Parasound Halo JC 1+s, the Delta Monos had a touch less bloom through the lower midrange. The Delta Mono exceeded its specified output power of 300W into 8 ohms and 600W into 4 ohms, clipping at 380W into 8 ohms and 610W into 4 ohms. Price includes high-quality DR Acoustics AC cables. (Vol.43 No.7 WWW)

Constellation Centaur II 500 Stereo: $70,000
For five times the price of their Inspiration Stereo 1.0 amplifier (see elsewhere in "Recommended Components"), Constellation Audio offers the Performance Centaur II 500 stereo amp, with 2.5 times the power (500Wpc into 8 ohms) and nearly three times the weight (150lb). As with a relative few of audio history's most distinguished solid state amps, the Centaur uses all N-channel transistors; here, they're built into single-ended modules, themselves combined into what Constellation calls their Balanced Bridged topology. Both balanced (XLR) and unbalanced (RCA) inputs are provided, as is a switch allowing the user to bypass the amp's input-voltage gain stage, for systems in which the Performance Centaur II 500 is preceded by a Constellation preamp. Used to play a recording of Rachmaninoff's Symphony 1 through a review pair of Wilson Alexia Series 2 speakers, the Constellation provided JA with "a transparent window on the acoustic of the Amsterdam hall where the recording was made," with stable and appropriately scaled imaging of solo instruments. And with Tidal's mighty Akira speakers, the Constellation offered "superb" dynamics: "The timpani blows … rocked me back in my chair." Reporting from his test bench, JA noted the amp's significantly-lower-than-specified input impedance but also its slightly-higher-than-specified (550Wpc) power into 8 ohms. Quoth the editor: "a powerhouse of an amplifier." (Vol.41 No.10 WWW)

Dan D'Agostino Progression M550 monoblock: $44,950/pair
This massive monoblock has balanced inputs only and requires a power cord fitted with a 20A IEC connector. JVS was impressed: "In addition to their far blacker space between notes, greater resolution of small details, and natural-sounding illumination, the Progression M550s consistently wowed me with their dynamic mastery." The latter is what one should expect from such a powerful amplifier: The M550 is specified as offering maximum powers of 550W into 8 ohms, 1100W into 4 ohms, and 2200W into 2 ohms. JA found that the amplifier met its specified power into 8 ohms, though the inevitable droop in his AC wall voltage meant that the M550 offered less power than promised into the lower impedances. JA was concerned by higher levels of distortion than he was expecting at moderate powers, which he ascribed to underbiasing of the 48 output-stage devices in the sample he was sent. Nevertheless, JVS concluded of his samples, which had had their output stage bias currents checked, that "For anyone who values colorful and glowing amplification that brings natural timbre and the subtlest of details and dynamic shifts to the fore while supplying a breathtakingly full measure of big-picture dynamics, slam, and top-to-bottom frequency response, the Progression M550s must be heard." (Vol.44 No.11 WWW)

darTZeel NHB-108 model two: $53,000
This dual-mono, solid state power amplifier offers balanced and single-ended inputs plus the Swiss manufacturer's impedance-matched Zeel inputs. Nominal output power is 150Wpc into 8 ohms and 225Wpc into 4 ohms, which was confirmed by JA's measurements. No global negative feedback means that the distortion level is a little high, at 0.1%, but not only is the distortion signature predominantly the subjectively innocuous second harmonic, notably the level of the distortion doesn't change with frequency or power (up to actual waveform clipping). "Detail was remarkable," noted JVS, remarking, "Welcome to the rare amp that manages to reveal the smallest details without sounding etched, hyperdetailed, or unnatural. Ever." He felt that the only thing lacking was stronger and tighter bass compared to his reference D'Agostino monoblocks. Still, JVS wrote, the darTZeel was among the most satisfyingly musical amplifiers ever to sing in his system, concluding, "There is an inherently nonmechanical, organic flow to the NHB-108 model two's golden sound that will keep enticing many a music lover back for more." (Vol.45 No.3 WWW)

darTZeel NHB-468 monoblocks: $195,000/pair
The darTZeel NHB-468 monoblock, which looks outwardly similar to its predecessor, the NHB-458, is claimed to be rather different on the inside, said changes including a technology called Constant Power to Current, or CP2C: a circuit that, according to darTZeel, "mimics a current source with the output impedance of a voltage source." The new amp retains the same massive power supply as the old, down to its enormous, spring-suspended mains transformer, yet most power specs are lower for the 468 than the 458 (eg, 475W into 8 ohms instead of 530W). The NHB-468 impressed NHB-458 owner MF with sound that was "more supple, more liquid, and noticeably more 'wraparound' three-dimensional, without turning soft." MF's verdict: "This amp does what the NHB-458 does—just better." Technical Editor JA noted that the new amp did not meet its power spec—he observed 398W into 8 ohms—but praised the fact that it does not exhibit increased distortion with rising frequency, saying the newest darTZeel is "an intriguing design." (Vol.42 No.11)

First Watt F8: $4000
Designer Nelson Pass describes the F8 as "a stereo, two-stage, single-ended class-A amplifier using the [new-old-stock] Toshiba 2SJ74 P-channel JFETs and SemiSouth R100 SiC power JFETs for signal gain, plus IRFP240 MOSFET mu-follower current sources, for a total of only three devices per channel." Specified voltage gain is a low 20dB, and specified power is 25Wpc into 8 ohms and "maybe" 13Wpc into 4 ohms. HR found the F8's midrange as densely detailed as the First Watt J2's "but clearer and more brightly lit." He described the F8's production of recorded piano's left-hand octaves as "firmer and better defined." However, he preferred the slightly more expensive but similarly power-rated Pass Labs XA25's well-focused lower octaves and what he described as "its inherent hyper-transparency." Nevertheless, with the F8 driving his fave Falcon LS3/5a minimonitors, HR wrote that this pairing revealed more of each recording's sonic and poetic essence than—possibly—any other system he'd used in his Bed-Stuy bunker. (Vol.43 No.12 WWW)

Gryphon Essence Mono monoblock: $44,400/pair
This massive solid state amplifier from Denmark has an output stage that can be operated in class-A or class-AB. JVS very much preferred the sound in class-A, writing that with the Lorraine Hunt Lieberson Wigmore Hall recital album, "Words cannot describe the alchemical transformation wrought by the Gryphon Essences on this remarkably air-filled recording." Even so, he did use words to sum up his time with the Gryphon Monos: "Although fully capable of conveying the entire frequency range, even through speakers that bring some modestly powered amplifiers to their knees, they cannot convey the huge dynamic swings and minute details that some more powerful beasts command. But on music that touches the heart, they can transport to a realm where few components know to go." Specified maximum power is 55W into 8 ohms, 110W into 4 ohms, and 220W into 2 ohms. JA found a small shortfall in clipping power, but the Essence Mono's distortion was very low at typical output powers. (Vol.43 No.12 WWW)

Lamm Industries M1.2 Reference monoblock: $34,990/pair ★
The 110W M1.2, with tubed front end, 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," he decided. "Highly recommended." In his Follow-Up, JCA observed that "the Lamms didn't bring out every tiny nuance … but, boy, are they musical! In that way, they deviate from the stereotype of a big-boy amp." (Vol.28 No.2, Vol.35 No.4, Vol.37 No.6, Vol.39 No.12, Vol.41 No.10, Vol.43 Nos.6 & 7 WWW)

LKV Research Veros PWR+: $10,000
This surprisingly massive, American-made amplifier powers its Purifi class-D output stage modules with a hefty linear power supply utilizing a hefty 1kVA toroidal transformer and two smaller transformers. Front-end and driver circuitry is based on paralleled discrete devices biased into class-A. HR wrote that "the class-D LKV amp played equally rich and atmosphere-soaked through the entire audio band. It did atmospheric dreamy like class-A does atmospheric dreamy." He found that every recording he played with the Veros PWR+ sounded "richer and wetter (atmospherically) than class-D is supposed to." In the test lab, the LKV amplifier exceeded its specified power of 200W into 8 ohms, clipping at 221Wpc with both channels driven, while it delivered the specified 400Wpc into 4 ohms. With one channel driven, the clipping power into 2 ohms was 505W. Noise and distortion levels were both very low, and the distortion signature was almost pure third-harmonic in nature. (Vol.43 No.9 WWW)

McIntosh MC462: $9000
As of this writing the most powerful stereo amplifier in the McIntosh line, the solid state MC462 is rated at 450Wpc into 2, 4, or 8 ohms, and weighs a floorbending 115lb. The output section is class-AB, designed so that each individual phase of the signal waveform is amplified by a complete push-pull output section; there are two complete push-pull amps in each channel, their outputs combined—using autoformers—in what McIntosh refers to as a Quad Balanced architecture. SM praised the Mac for delivering, without strain, a piano sound faithful to the original, for portraying brass instruments, drums, and other instruments with appropriate force, impact, and, when called for, swing. As for value, SM opined that "$9000 is more than fair for the excellence delivered." Reporting from his lab, JA declared that the MC462 is "an extraordinarily well-engineered, exceptionally powerful amplifier." (Vol.42 No.5 WWW)

NAD C 298: $2199 $$$
An affordably priced, powerful—185Wpc into 8 ohms. 340Wpc into 4 ohms—utilitarian-looking, class-D stereo amplifier based on the Purifi-Eigentakt output modules used in NAD's more expensive M33 and M28. The C 298 features balanced and single-ended inputs, variable gain, and can also be operated in bridged-mono mode. KR found that a pair of bridged-mono NADs offered explosive dynamics without breaking a sweat—JA measured the clipping power into 8 ohms in this mode as 980W! "The NAD C 298 is a transparent, uncolored, powerful stereo power amplifier," concluded KR, adding that even in stereo mode it can easily drive most speakers "to levels that exceed domestic tranquility." Measuring man JA commented that the C 298 continues NAD's tradition for conservative and competent engineering but "sets a new standard for combining very high power with supremely low distortion." (Vol.44 No.6 WWW)

Parasound A 21+: $3499
The successor to the Parasound A 21, the new A 21+ offers 300Wpc into 8 ohms, compared with its predecessor's 250Wpc—and the new model, which operates in class-AB, can be bridged to serve as a 1000W monoblock. Other refinements include a gruntier power transformer, brawnier speaker connectors, an increase in power-supply filter capacitance, and other niceties. Balanced (XLR) and unbalanced (RCA) inputs are both provided, as are dual-mono level controls. According to KR, "listening to the A 21+ was eminently delightful and satisfying from the first note," and he pointed to the new amp's "transparency without highlighting or emphasis" and the manner in which it handled dynamic challenges in orchestral music "without stress." Technical Editor JA found that the A 21+ exceeded its power specs, delivering a full 400Wpc into 8 ohms, and noted that the amp "isn't fazed by impedances as low as 2 ohms." (Vol.43 No.3 WWW)

Parasound Halo JC 1+ monoblock: $17,998/per pair
A replacement for the long-term "Recommended Components" resident, the original Halo JC 1, the 1+ represents designer John Curl's further thoughts on this powerful solid state monster. While more expensive in real terms than its predecessor, the Halo JC 1+ is 30% heavier, still heavily biased into class-A, and offers slightly more power than the original amplifier: 450W into 8 ohms, 850W into 4 ohms, and 1300W into 2 ohms. Bass guitar and kickdrum were reproduced with appropriate force and definition, felt JA, exclaiming, "Low-frequency power and delicacy!" JA was also impressed by the pair of monoblocks' ability to differentiate soundstage depth and described the Parasound's high frequencies as sounding "more like what I experience from a good tube amplifier." "This is a superb-sounding amplifier that will get the best from every loudspeaker with which it is partnered," JA concluded, adding "Well done, Mr. Curl." On the test bench, the Halo JC 1+ exceeded its specified power into 8 ohms, clipping at 500W. It didn't quite meet its specified power into lower impedances, clipping at 830W into 4 ohms and at 1200W into 2 ohms, though JA did note that the slight shortfall was due to him not holding the AC wall voltage constant in the testing. Commendably, the JC 1+'s distortion was predominantly the subjectively innocuous second harmonic, though at a very low level. (Vol.43 Nos.6 & 7 WWW)

Pass Laboratories XA25: $7600
The lowest-priced amplifier in Pass Laboratories' XA series, the XA25 strips away all inessentials—front-panel meters, balanced inputs, excessive output power—and provides the listener with a three-stage amplifier in which output power is generated by a single pair of transistors per channel, operating in push-pull class-A. Output is specified as 25Wpc into 8 ohms or 50Wpc into 4 ohms. HR tried the Pass with a great variety of speakers, starting with a rebuilt pair of original Quad ESL electrostatics: "Through the Quads, the XA25 radically improved the tactile presence of music and musicians, their voices and instruments," he wrote. "It made the Quad's legendary midrange more solid, dynamic, and well defined than I'd ever thought possible." Another, very different panel speaker came next: "Driven by the Pass Labs XA25, the Magnepan .7s did real-life natural with ease and élan." Additionally, HR found, "bass weight and organ power were well reproduced by a speaker not famous for these traits." But even that pales in comparison to Herb's adventures using the Pass amp to drive his DeVore Orangutan O/93s: "I began to realize that the XA25 is the most transparent amplifier I've ever heard." His verdict: "reasonably priced, strong beyond its power rating, and positively revelatory." Writing from his laboratory, JA noted that the Pass far exceeded its rated power output, concluding that "the XA25 performed well on the test bench, as I've come to expect from Pass Labs." (Vol.41 No.2 WWW)

Pass Laboratories XA60.8 monoblock: $14,250/pair ★
In reviewing Pass Laboratories' solid state XA60.8 monoblock amplifier, JCA echoed JA's earlier published response to the amp's predecessor, the XA.60.5: "the best amplifier I've heard." Each 88lb XA60.8 operates in pure class-A, made possible in part by the amp's massive aluminum heatsinks and no-less-massive steel mains transformers. (Indeed, the most obvious change from XA60.5 to XA60.8 is a weight increase of 22lb—per channel.) Output is specified as 60W into 8 ohms, doubling to 120W into 4 ohms. JCA thought the Passes sounded "sweeter, warmer, more delicate" than the more expensive monoblocks that preceded them in his system, but reserved his greatest praise for their spatial prowess: "I'd never heard an amplifier make such an obvious difference … . To walk into this room while a good recording was playing was to enter an immersive aural space." JA, now acting as measurer rather than reviewer, wrote from his test bench that the "well-engineered" XA60.8 "considerably exceeded" its rated output power, delivering 150W into 8 ohms at 1% THD, and he praised its A-weighted signal/noise ratio of 93.6dB: "This is a quiet amplifier." JCA's conclusion: "I am smitten." (Vol.40 No.12 WWW)

Primare A35.2: $3995
This hefty Danish amplifier uses what Primare calls their "proprietary UFPD2 analogue class-D amplification technology" to deliver 200Wpc into 8 ohms. According to the manufacturer, UFPD2 integrates the class-D output stage and the necessary low-pass filter, "making control with feedback much more immediate and accurate." HR found that with his Magnepan .7 speakers, the A35.2 sounded very similar to the slightly more expensive Bel Canto Ref600M class-D monoblocks. He wrote that the A35.2 "gripped the Magnepans' diaphragms with greater control and force than either the class-A Pass Labs XA25 ($4900) or the $3495 all-tube, class-AB Rogue Stereo 100 (in Ultralinear mode). This control delivered a tauter, more rhythmic bass." With Harbeth M30.2 speakers, HR found that the Primare's high frequencies were "crisp and super-clear—but not luxuriant and engaging." On the test bench, the Primare exceeded its specified powers, clipping at 225Wpc into 8 ohms and at 460Wpc into 4 ohms. (Vol.43 No.5 WWW)

PS Audio BHK Signature 300 monoblock: $16,498/pair ★
Named for its designer, Bascom H. King, the BHK Signature 300 is a hybrid monoblock with a tubed input stage and a MOSFET power stage, and is specified to deliver 300W into 8 ohms. In a departure from the usual practice, all of those output transistors are N-channel devices, implementation of which requires cunning—and, according to King, a bit of global feedback. Both single-ended (RCA) and balanced (XLR) inputs are provided on the rear panel, where one also finds a removable panel for access to the amp's two dual-triode tubes. In MF's words, "the BHK Signature 300 is a powerful, nimble-sounding amplifier that immediately drew me in with fast, punchy, tight bass; rich, liquid mids; and delicate, transparent highs—all effectively well integrated into a coherent whole." On JA's test bench, one of the BHK Signature 300 monoblocks became unstable, and while it didn't fall and break its hip, it stopped working. JA carried on with the other monoblock, describing it as "a well-designed, well-engineered powerhouse of an amplifier, though it will perform at its best with speakers having an impedance of 4 ohms and above." In 2017, JCA embarked on an interesting pairing—PS Audio's "big brute" amps with the sensitive, easy-to-drive DeVore Fidelity Orangutan O/96 speakers—and discovered that while the DeVores didn't necessarily benefit from such a surplus of power, he "slightly preferred the BHKs' weight" to the "airier, spacier" sound heard with his Leben tubed integrated amp. (Vol.39 No.2, Vol.40 No.8 WWW)

PS Audio Stellar M1200 monoblock: $6598/pair
This slim, powerful amplifier—specified power is 600W into 8 ohms, 1200W into 4 ohms—combines a gain stage that uses a single Psvane 12AU7-TII tube with an output stage based on a class-D output module from ICEpower. MF was impressed by what he heard, writing, "It's no surprise that this superquiet class-D amplifier excels on bottom. Bass is what class-D was originally built for. … The M1200's ability to couple with, control, and drive the woofers of my Wilson Alexx loudspeakers matched that of any amplifier I've had here." The M1200 was as fast, precise, and clean from the mids on up as it was in the bottom octaves, he decided, adding that this "helps ensure a bottom-to-top rhythmic coherence and transparency that lets you 'see' into the farthest reaches of the soundstage." Compared with his cost-no-object reference darTZeel amplifiers, he noted a lack of microdynamic delicacy, and timbral verisimilitude was dependent on the recording being played. Summing up, MF wrote: "Maybe the M1200s were just too fast for their own good. After the superclean attack, they went right for the too-fast decay and missed the sustain. While that often leads to 'skeletal' sound, the M1200s never delivered bones, because the transients were never edgy or nasty. They were natural and just right." On the test bench, the M1200 offered low levels of primarily third-harmonic distortion and met its specified output power. (Vol.44 No.1 WWW)

Rotel Michi M8: $7499.99/pair
The massive Michi M8 monoblock weighs 130.3lb. "I should have known that a class-AB amplifier said to deliver 1080W into 8 ohms and 1800W into 4 ohms would be heavy," wrote MF. Designed by an engineering team with members based both in Japan and in the UK, the superbly well-made M8 is manufactured in China. Mikey didn't just like it, Mikey loved it: "The M8 doesn't sacrifice transparency or well-articulated transients to achieve a sweet disposition." On the test bench, the M8 offered excellent measured performance, though both its balanced and unbalanced inputs inverted absolute polarity. Oh, and that enormous rated power? JA measured clipping powers of 1020W into 8 ohms and 1500W into 4 ohms, which should be more than enough for even the lowest-sensitivity speakers. (Vol.44 No.7 WWW)

Schiit Audio Aegir: $799 $$$
The solid state Aegir amplifier uses a proprietary class of operation called Continuity, which gets around certain limitations of class-AB operation—particularly transconductance droop beyond the class-A power envelope—by means of a current-feedback topology. It's specified at 20Wpc into 8 ohms and 40Wpc into 4 ohms and runs a bit hot—but not as hot as one might expect from a pure class-A amp of the same output. HR described the "titillating physical pleasures" of the made-in-California Aegir driving Wharfedale Linton loudspeakers as something he could "live [with], satisfied, forever," and praised the pairing of Schiit Aegir and Harbeth P3ESRs as offering "80% of the … detail-rich humanity" he hears from his $4000 reference amplifier. In measuring the Aegir, JA found higher than specified output power—28Wpc into 8 ohms, 43Wpc into 4 ohms—and described the Schiit as "a well-engineered amplifier at an affordable price." Herb's conclusion: "a design that will withstand and even rejoice in the scrutiny of time." (Vol.42 No.10)

Vandersteen Audio M5 High Pass Amplifier M5-HPA: $16,800/pair
Class A rating applies to use with Vandersteen speakers or minimonitors. (Vol.42 No.11 WWW)

Verity Audio Monsalvat Amp-60: $58,000
The Monsalvat Amp-60 differs from other premium-priced solid state amps in a key way: Verity Audio set out to create not an ultra-high-power amp—something the Amp-60's designers regard as involving "compromises that hinder the quality of the sound"—but rather to make a more modestly powered amplifier. Thus the Amp-60 delivers 60Wpc into 8 ohms and 120Wpc into 4 ohms. Driving JVS's Wilson Alexia 2s, the Verity amp "began weaving a web of seduction" from the first track he played, with a "velvet smooth" midrange in which individual sonic texture maintained their characters—although, on a recording of a Mahler symphony, "the sound lacked oomph" and the work's "big bass poundings shook the room less" than he wished. In measuring the Monsalvat Amp-60, JA discovered that, counterintuitively, the amp's balanced inputs yielded lower S/N ratios than its single-ended inputs. Also, although he found higher-than-specified output power (95Wpc) into 8 ohms, JA observed that the Amp-60 clipped at just 50Wpc into 2 ohms. (Vol.42 No.5 WWW)

A (Tube)

Air Tight ATM-300R: $19,500 with Electroharmonix 300B tubes ★
AD, who was on record as having "never heard a single-ended 300B amp that I disliked," was especially smitten by this compact yet remarkably heavy (54lb) stereo amplifier: a three-stage design in which 12AU7 and 12BH7 dual-triodes are used as voltage-gain stages and drivers, respectively. The output tubes are a single 300B per channel, specified to output 9W each. Distinctively, the ATM 300R uses global feedback, but tapped from the primary rather than secondary side of each channel's output transformer. AD heard from the Air Tight amp "startling … details of musical nuance," "lusciously textured and colorful" strings and woodwinds, "realistic force" in its reproduction of timpani, and the ability to sound surprisingly big. He also made special mention of the ATM 300R's way with orchestral double-basses, noting their "depth and power, and far greater clarity of pitch than I've heard through any other 300B amplifier, bar none." Re-auditioning the amp in his newly modified listening room, through vintage Altec Flamenco loudspeakers, confirmed those positive impressions, and then some. Writing from his test bench, JA described the Air Tight as "well engineered," praising in particular its apparently "excellent output-transformer design." (Vol.41 No.2, Vol.42 No.11)

Audio Research Reference 160 M monoblock: $34,000/pair
The Reference 160 M wrings 140W from a push-pull quartet of KT150 pentode tubes, operated in class-AB, with phase inversion and voltage gain provided by a pair of 6H30 dual-triode tubes. It also offers switch-selectable balanced and single-ended inputs—during testing, JA was surprised to see the latter mode of operation offered considerably more gain—and employs a modern auto-bias system. The Ref 160M also allows the user to choose between Ultralinear and triode modes at the flip of a switch (in triode mode, the amp outputs 75W). With a pair of Ref 160Ms driving his Wilson Alexia 2 floorstanders, JVS reported sound that was impressively "natural, full-range, and beautiful," including an ability to convey "hard-to-distinguish details and sonorities … with clarity." Writing from his test bench, JA reported evidence of only "a modest amount" of global feedback, and commendably higher-than-specified output power when operating in Ultralinear mode and speaking to the world through its 8 ohm outputs. (Vol.41 No.10 WWW)

Audio Research Reference 160 S: $22,000
Essentially a stereo version of ARC's Reference 160 M monoblock, the Reference 160 S uses four KT150 output tubes per channel to deliver 70Wpc into 8 ohms in triode mode or 140Wpc in Ultralinear, the two being switch-selectable. The user can also select between balanced (XLR) and unbalanced (RCA) inputs, the latter a first for an ARC Reference-series amp, and speaker outputs are provided for 4, 8, and 16 ohms. JCA enjoyed his time with the Ref 160 S, particularly when assessing the differences between triode and Ultralinear: "In triode mode there was a fine velvet, burnished beauty. In Ultralinear … the music was more explicit—but the sound was just as lovely." Jim remarked, before the ARC amp left his home: "I didn't know that so much of the music in my collection possessed so much tonal beauty." JA felt the amp's very low feedback should compel users to exercise careful load matching. (Vol.43 No.2 WWW)

Doshi Audio EVO Monoblock: $43,995/pair
The EVO (for "Evolution") replaces Doshi's Monoblock V3.0 that JVS reviewed in Vol.41 No.11 and that had been in production for seven years. The amplifier still employs a pair of Tung-Sol KT150 output tubes for each channel, but changes include a machined-aluminum, constrained-layer top panel, a stiffer chassis, passive power correction, improved capacitor and resistor quality, and "slight" circuit changes to increase the amplifier's small-signal bandwidth. With a violin recording and at 170mV bias, the EVO monos driving Wilson Alexia 2 loudspeakers "beautifully conveyed the violin's intermingling of horsehair, resin, and steel," but the recommended bias of 190mV "rendered the sound too warm and pleasant." The class-AB EVO is specified as outputting up to 160Wpc into 4 ohms, the first 120Wpc in class-A. At the amplifier's recommended bias setting of 190mV, JA measured 107W into 8 ohms and 127W into 4 ohms from the single output transformer tap at 1% THD+N, though relaxing the clipping criterion to 3% THD+N increased the maximum power into 4 ohms to 153W. The output impedance was commendably low for a tube design—0.54 ohm at low and middle frequencies and still 0.67 ohm at the top of the audioband. "The Evolution Monoblock power amplifier's measured performance indicates conservative audio engineering, a superb output transformer, and the ability to deliver high powers into relatively low impedances," JA concluded. An NOS Tube Upgrade package, which JVS recommends, adds $500 to the price. (Vol.44 No.5 WWW)

Feliks Audio Arioso: $6499
When HR replaced his reference solid state amplifier, the high-power Parasound Halo A 21+, with the Feliks Arioso, which offers 8Wpc with its Electro-Harmonix EH Gold 300B output tubes, he shook his head in disbelief at how radically different a track from old-time country blues singer Turner Junior Johnson sounded. What really got him, with the Arioso's 8 ohm taps driving Falcon's 15 ohm "Gold Badge" LS3/5as, was how Turner appeared to be directly there in front of him "with a definite tangible humanness" that he had not noticed with the Parasound. "The Arioso appeared to recover some extra amount of low-level information," he felt, though he added that the Feliks did not sound warmer, fuzzier, blurrier, more distorted, or more euphonic than the Parasound. "It did not emphasize the midrange or roll off the frequency extremes. It was simply more transparent," he decided. With the 10 ohm DeVore Fidelity Orangutan O/93s driven by the Arioso's 8 ohm output taps, he felt that the sound was not as rich of timbre or as bitingly textured as he thought it should sound. But when he connected the DeVores to the Arioso's 4 ohm taps, "the sound displayed a more grain-free clarity. Colors became more saturated. The sound felt more correct." HR summed up this experience: "The lesson here is: If you have a tube amp that offers multiple output taps, never assume 8 ohms to be 8 ohms, or 4 ohms to be 4 ohms. Try them all and choose the one that pleases you most." Replacing the stock Electro-Harmonix 300Bs with the new Western Electric 300Bs, the Feliks Arioso's 50Hz–1kHz octaves were more brilliantly lit and refraction-free than with the stock tubes, and the bass with the WEs was more tightly damped than with other 300Bs. (Vol.44 No.8 WWW)

Luxman MQ-88uSE: $5995 $$$
Luxman's limited-edition MQ-88uSE—only 100 have been made—is that rarity in contemporary high-end audio: a modestly powered tube amplifier unburdened by microprocessor-fueled gimmicks or a ghastly, massive, machined-aluminum case. The fixed-bias, push-pull, class-AB Luxman uses two KT88 pentode tubes per channel, operated as triodes, producing 25Wpc; ECC802 and ECC803 dual-triode tubes supply input gain and phase inversion. Power-supply rectification is solid state, and output transformers, mains transformer, and power-supply choke are all designed and made by Luxman. The chassis is old-school minimalist, and a tube cage is supplied. The amp is mostly hardwired, and the build quality is first-rate. With the MQ-88uSE driving his DeVore Orangutan O/93 speakers, AD reported superb musicality—excellent musical momentum, flow, and pacing—and a sense of touch by which "every [harp] arpeggio was a tactile delight." AD's conclusion: "brilliantly musical and unmistakably high value; … grab one while you can." In his Follow-Up, JA described the full set of measurements he made of the Luxman; his observations included higher-than-specified power (30Wpc into 8 ohms) and excellent squarewave reproduction ("a tribute to the high quality of its output transformers"). His conclusion: "an excellent example of a classic push-pull tubed design." (Vol.41 Nos.9 & 11 WWW)

Music Reference RM-200 Mk.II: $7000 ★
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." Now comes with handwound output transformers; tube bias balance control, add $800. (Vol.34 No.12 WWW)

Rogue Audio Stereo 100: $3695
If you like tube amps and you also harbor a fondness for audio-frequency transformers, you may well love the Rogue Stereo 100, which greets the input signal with a Jensen line-level transformer—this as much to buffer unbalanced signals as to couple balanced signals that enter via the Rogue's XLR jacks—then hands off to dual-triode–based input and driver stages with a pair of KT120 output tubes per channel, operating in class-AB push-pull, with the user's choice of switch-selectable Ultralinear and Triode modes. The fixed-bias, solid state–rectified Stereo 100 outputs 100Wpc in Ultralinear, 60Wpc in Triode; in either mode, the Rogue kept HR's Harbeth M30.2 speakers "obviously well-tempered and well-nourished, power-wise. Both modes delivered detailed sound that was neither warm nor cool, just well balanced. The bass was tight and clean, maybe slightly lean, with no overhang or fuzzy harmonic additives." In measuring the Stereo 100, JA noted "superbly square" squarewaves in both modes of operation, and quite respectable signal/noise ratios, though power output was a bit lower than specified in both modes. Herb's conclusion: "the Stereo 100 is everything … that we could hope for in a 21st-century tube amp." (Vol.41 No.11 WWW)

Shindo Cortese: $13,500 w/F2a output tubes
The current version of Shindo Laboratory's only stereo single-ended amplifier—there are at least four different earlier versions, possibly more—uses a single Telefunken ECL82 pentode-triode tube per channel to drive a single F2a tetrode per channel in an autobias circuit. (A 300B version, priced at $12,995, is also available but remains unauditioned.) Distinguishing characteristics include the use of a rectifier tube (5U4GB) instead of a solid state full-wave rectifier and the addition of an NOS Micromold Radio oil cap to the power supply's smoothing circuit—both of which have, at times, characterized earlier Corteses. Output power is specified as 10Wpc. AD noted generous gain—the Cortese is a three-stage amplifier—and, in general, the amp's ability to make music sound physically present, not to mention physically large, with sufficient bass extension and power that an orchestral bass drum on one recording "sent shivers down my spine." (Vol.43 No.2 WWW)

Shindo Montille 391: $7995 $$$
A somewhat more expensive variant of the company's entry-level amp, the Montille—which AD wrote about in the July 2007 Stereophile—the Montille CV 391 is a push-pull amp that coaxes 20Wpc from stereo pairs of the British CV 391 beam power tetrode. A true three-stage amp, thus blessed with generous gain, the Montille CV 301 uses 6AW8A triode-pentode tubes and 12AT7 dual-triodes as input tubes, as well as NOS Sprague coupling capacitors and Hammond output transformers. Shindo's second-least-expensive amp has a voice different from that of the company's more expensive offerings, but is no less musical—and in fact distinguished itself as one of the most vivid Shindos AD has heard, not to mention the one that is most comfortable driving 8 ohm rather than 16 ohm loads. (It sounded extraordinary through Art's DeVore O/93s.) Other Shindos may have more sophisticated or nuanced voices, but the Montille 391 is no less effective: Not only does this amp deserve Class A status, it offers conspicuously high value. (Vol.42 No.8 WWW)

VAC Statement 452 IQ: $75,000 stereo; $150,000/pair as monoblocks
Reviewed as a pair of monoblocks, MF marveled at "the relaxed and fully immersive presentation" from this massive, high-powered, cool-running amplifier, which uses banks of horizontally situated output tubes operated in class-AB using VAC's patented iQ Intelligent Continuous Automatic Bias System. Though he sometimes felt that these amps produced a picture that was too large for his room, the soundstage produced by a pair of these amplifiers on the Wilson Alexxes "was wider, taller, and especially deeper than anything I've ever experienced." MF also commented that "On the right recordings, the illusion of 'there' produced by this amp, thanks in part to the sensation of shimmering soundstage air, is extraordinary." Summing up, he wrote that the sound "was at all times coloration-free, exhibiting no frequency lumps or bumps and sounding refreshingly timbrally neutral, particularly from the midbass through the lower midrange, where I was expecting warmth and bloom. The bottom never sounded or felt sluggish or insufficiently extended, even on electrified rock, though its overall character was somewhat polite. The upper frequencies were addictively clean and pure, with faultless transient speed and clarity." The Statement 452 IQ is specified as delivering 225Wpc in two-channel mode or 450W in single-channel mode, both into 4 ohms. When he measured the amplifier as a monoblock, JA found that the VAC clipped at 235W into 8 ohms, but at 183W into 4 ohms unless he relaxed the definition of "clipping" from 1% THD+N to 10%, when the amplifier delivered 410W into 4 ohms. Fortunately, the VAC's distortion in the midrange and above was predominantly the subjectively innocuous second harmonic. Though he was bothered by what appeared to be modulation by the audio signal of the amplifier's noisefloor, JA noted the amplifier's very low distortion in the treble at low-to-moderate powers into high impedances. (Vol.43 No.5 WWW)

B

Akitika GT-102: $534 (assembled); $349 (kit) ★ $$$
As HR mused in his review of the solid state AkitikA GT-102, "Jeez, Louise—should I even bother to drive a $7700 pair of [Joseph Audio Pulsar] speakers with a $488 amp?" That question is made more poignant by the fact that the GT-102 is available in kit form for only $314—far less than many of you would dream of spending on an interconnect or even a cable riser. To ensure that ours was an exemplary sample, for the sake of measurements if nothing else, HR tried a factory-built sample and found the 60Wpc GT-102, which is based on the same power op-amp as the well-regarded 47 Laboratory Gaincard integrated amp, had a "warmer, darker" sound than that of his Pass Laboratories XA25. The AkitikA didn't make much headway with the difficult-to-drive Magnepan .7 planar-magnetic speakers, but it partnered well with Falcon Acoustics' LS3/5a minimonitors, Herb being especially impressed by "how attractively it rendered the complex harmonic structures of … saxophone, harmonica, violin, and marimba." His conclusion: "Super-highly recommended." Writing from his lab, JA noted that the AkitikA "is happier driving higher impedances, though this drawback must be considered in the context of its very affordable price." (Vol.41 No.7 WWW)

Balanced Audio Technology VK-56SE: $8000
This three-stage, push-pull, fully-balanced amplifier uses one pair per channel of the Russian 6C33C triode to produce 55Wpc into 8 ohms—110W when bridged for mono—all in class-AB mode. As the company name might lead one to expect, inputs are balanced (XLR) only—adapters are available, from BAT and elsewhere, for users with single-ended-only preamps—and output connectors are provided for low-, medium-, and high-impedance loads. The 52lb BAT won HR over with "a force-filled liquid vividosity that presents itself with the scale, detail, and color saturation of 70mm film" and described its characteristic sound as "liquid and clear, effervescent, and richly toned," although he said the amp lacked a bit of "boogie" with the Magnepan .7 (a notoriously current-hungry load). At the test bench, JA was bothered by what he described as the amp's "high output impedance." (Vol.42 No.6 WWW)

Cary Audio CAD-805RS monoblock: $15,995/pair
On the cover of the January 1994 Stereophile, the original Cary CAD-805 monoblock—a single-ended triode amp that offered 27Wpc—posed next to a 300Wpc Krell amplifier; above them, a headline fairly taunted: "If either of these amplifiers is RIGHT … the other must be WRONG." A quarter-century later, that Cary monoblock endures as the CAD-805RS. Now as then, the user can select between a single 845 or 211 output tube: both are supplied, and both deliver 27W in class-A, which is how this amp operates under most conditions. But when more power is required the Cary slips into class-A2, and there the output tubes differ, the 845 delivering up to 50W for short durations, the 211 up to 70W. The CAD-805 offers adjustable global feedback (0–10dB), apparently high voltage gain, and separate output taps for 4, 8, and 16 ohm loads. In his listening observations, AD expressed a preference for the 845 tubes, but noted from both tube types a bass range that was slightly too generous but nonetheless sublime, giving impact and taut tone to timpani and rewarding him with electric-bass lines that were always engaging and never sluggish. Consistent qualities were believably rich timbral colors and textures and spatial performance in which "centrally positioned voices and solo instruments popped forward from the mix … [with] pure, not-unexpected single-ended magic." Reporting from his test bench, JA noted output impedance that was "relatively low for a single-ended triode amplifier," yet also confirmed that load-impedance–related modulation of the amp's frequency response resulted in a low-bass boost. (Vol.42 No.1 WWW)

ELAC Alchemy DPA-2: $1749.98
A skinny, 14lb device from the Americas division of ELAC Germany, the DPA-2 was designed by veteran engineer Peter Madnick. Its output stage uses Hypex UCD class-D modules, which Madnick prefers to the more recent Purifi-Eigentakt modules. Balanced and single-ended inputs are available, and the gain can be increased by 6dB. Although the Alchemy DPA-2 is a stereo amplifier, JVS auditioned it as a pair of bridged monoblocks, commenting that in this mode they were "the finest low-priced power amplifiers I've encountered." "What caught me off guard, and pleasantly, was the wide range of color I heard from these inherently musical amps," he added, concluding that "Peter Madnick has exceeded his goal 'to provide the kind of real-life transparency and clarity that you would not expect at this price point.'" Maximum power is specified as 325Wpc into 4 ohms in stereo mode—JA measured 339W into 4 ohms and 202W into 8 ohms at 1% THD+N. As a bridged monoblock, the "powerhouse" DPA-2 delivered 590W into 8 ohms and 550W into 4 ohms. (Vol.44 No.6 WWW)

EleKit Tu-8600RS: $1980 as reviewed ($1285 basic version)
As the name suggests, the EleKit TU-8600R is a build-it-yourself power amp, a single-ended design that uses one 300B directly heated output tube per side for a specified output of 9.2Wpc at 10% THD. (A pre-assembled version is available at extra cost.) Prices start at $1185 without tubes and top out at a $2985 version that includes Lundahl output transformers and deluxe German-made Elrog 300B tubes. Herb Reichert tried a variety of 300Bs in his Lundahl-equipped review sample and praised the EleKit for sounding not warm and soft but "fast and vigorous, as transparent as any amplifier, and extremely captivating," with a sonic character that's "clean, neutral, and precise." HR's conclusion: "This is what I call value for money." Other kits are available, but availability is sporadic. In his May and August 2021 Gramophone Dreams, HR used the Elekit TU-8600S as a platform for comparing different 12AX7s and 300Bs. (Vol.42 No.4, Vol.44 Nos.5 & 8 WWW)

First Watt SIT-3: $4000 ★
Designer Nelson Pass commissioned a now-defunct maker of semiconductors to produce for him an exclusive run of static induction transistors (SITs), and the limited-edition (250 units) SIT-3 may prove to be the last amplifier created to use them. The SIT-3 is a single-ended amp in which the input signal has its voltage gain boosted only by an onboard step-up transformer; the amp's single active stage provides only current gain. The product of all this simplicity is a decent enough 18Wpc, but with less gain (11.5dB) than most other amplifiers. HR tried the SIT-3 with a variety of loudspeakers and declared it "a modestly priced masterpiece" and "one of the two or three finest-sounding amplifiers I've heard anywhere, at any price." JA's measurements did nothing to dispel that notion: "Although [its] relatively high level of second harmonic distortion, which is a deliberate design choice, is controversial, the First Watt SIT-3 is a well-engineered amplifier." (Vol.42 No.2)

Mytek Brooklyn AMP+: $2495
A complete change in the facility that manufactures Mytek products led to the company's entire component lineup being revised. The Brooklyn AMP+ is the first of the new-generation products to be reviewed, replacing the AMP that KM reviewed in Vol.41 No.9. Compared with the original amplifier, the AMP+'s clarity "facilitated better microdynamics, those small dynamic shifts that make reproduced sound more lively and more live," noted KM, adding that the AMP+ dispenses with the AMP's overt midrange lushness. "The AMP+'s upper midrange and treble were decidedly cleaner while maintaining just a touch of richness." Compared with the Parasound Hint 6 Halo, the Parasound presented an even deeper and more layered soundstage than the Mytek. On the other hand, the AMP+ sounded more sensuous with more low-end force. The AMP+'s class-D output stage is based on modules from Danish company Pascal and offers specified maximum powers of 250Wpc into 8 ohms, 300Wpc into 4 ohms, and 400Wpc into 2 ohms. JA found that the clipping power with both channels driven was 265W into 8 ohms. However, the Mytek went into protection mode when he tried to measure the maximum power into lower impedances. Nevertheless, he concluded that, like its predecessor, "Mytek's Brooklyn AMP+ is indeed a tiny powerhouse." (Vol.44 No.5 WWW)

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

Deletions
MBL Corona C15, replaced by newer model not yet reviewed. Border Patrol P21 EXD, Bricasti Design M15 Stereo, Constellation Inspiration Stereo 1.0, Margules Audio U280-SC Black, Mark Levinson No534, McIntosh MC275, Moon by Simaudio 888 Monoblock, Pass Laboratories XA200.8 monoblock, Ypsilon Hyperion monoblock, not auditioned in a long time.