• SoundStage! Shorts - Devialet's Phantom Loudspeakers (August 2016)
  • SoundStage! InSight - McIntosh Home Theater and Streaming Audio (July 2016)
  • SoundStage! Shorts - McIntosh MC275 Stereo Amplifier (June 2016)
  • SoundStage! InSight - McIntosh History and Autoformer Technology (June 2016)
  • SoundStage! InSight - NAD Viso HP50 Headphones (May 2016)
  • SoundStage! Shorts - GoldenEar Technology's Anechoic Chamber (May 2016)
  • SoundStage! Shorts - PSB's M4U 4 Earphones (April 2016)
  • SoundStage! InSight - GoldenEar Technology's Triton Two+ and Three+ Loudspeakers (March 2016)
  • SoundStage! Shorts -- KEF's LS50 (February 2016)
  • SoundStage! InSight -- Monitor Audio's Platinum II Series (January 2016)
  • SoundStage! Shorts -- Pryma 0|1 Headphones (December 2015)
  • SoundStage! InSight -- KEF's Blade Two Loudspeaker (November 2015)
  • SoundStage! InSight -- KEF and the Uni-Q (October 2015)
  • SoundStage! InSight -- Monitor Audio Acoustics & Aesthetics (August 2015)
  • SoundStage! InSight -- PSB's Imagine T3 Loudspeaker (June 2015)
  • SoundStage! InSight -- Hegel's H160 Integrated Amplifier-DAC (April 2015)

Note: Measurements can be found through this link.

Reviewers' ChoiceAs Saul and the Israelites assembled in the Valley of Elah, preparing themselves for battle, a man from Gath strode out of the opposing camp of Philistines. He wore a bronze helmet and a massive coat of scale armor. Greaves adorned his legs, and a javelin was slung across his back. The man, grasping an iron-pointed spear of considerable size, proclaimed, “Why do you come out and line up for battle? Choose a man and have him come down to me. If he is able to fight and kill me, we will become your subjects.”

For 40 days and 40 nights, the man from Gath repeated this proclamation, only to be met by silence. Finally, a shepherd stepped forward. The youngest of eight sons, he was slight of build but filled with conviction. Saul exclaimed, “You are not able to go out against this Philistine and fight him; you are only a young man, and he has been a warrior from his youth.” Undeterred, the young man declined Saul’s armor and sword, collected five smooth stones, and, sling in hand, approached the mountainous Philistine from Gath. The warrior glowered as he noted the shepherd’s youth, and moved to attack. The young man then drew his sling, took aim, and hurled a stone into his opponent’s forehead. The warrior fell to the ground, dead. Seeing their hero vanquished, the Philistines turned and ran. David had defeated Goliath.

Benchmark Media Systems AHB2

While David is commonly viewed as the quintessential underdog -- an individual who overcame nearly insurmountable odds -- I tend to think that that characterization does the shepherd a disservice. He seems to have possessed a quiet confidence that he would prevail. The young man eschewed spear, sword, and the substantial metalwork that covered his muscled foe, relying instead on his unique if unheralded skills to emerge victorious. Where others see an underdog, I see cunning and cleverness at its maximum utility. A big stick, it turns out, will get you only so far.

AHB2, Son of Benchmark

You might look at Benchmark Media Systems’ AHB2 power amplifier ($2995 USD) and assume that it has been in production since 1991. At 11”W x 3.9”H x 9.3”D and 12.5 pounds, the AHB2’s appearance is not commanding. Its lines reflect a utilitarian aesthetic, with small-finned heatsinks lining each side, and a brushed-aluminum faceplate (in silver or black) with four mounting bolts, a Power button with LED, and a row of six LEDs: Mute, Temp, and Clip for each of the AHB2’s two channels. Etched into the right side of the faceplate is the Benchmark logo; the model name is inked in red on the left. The AHB2 is made in the US.

The rear panel is densely packed with connections. The two pairs of binding posts at the top accept spades only from below, and only small spades at that. The WBT spades on my Dynamique Audio Caparo speaker cables proved too wide -- I could use just one blade of each spade. Banana plugs or smaller spades are definitely recommended.

Benchmark Media Systems AHB2

With no choice of how to orient spade-equipped speaker cables, depending on your cables’ thickness, they may partially block the connections below. Those are pairs of 12V triggers and balanced (XLR) jacks -- the latter the only inputs the fully balanced AHB2 has. Users whose upstream gear has only unbalanced, single-ended (RCA) outputs will have to invest in adapters. Other ports include heavy-duty SpeakON connectors for commercial/professional use, a mono output for bridged operation, and a toggle switch to select between mono and stereo operation. There’s also a sensitivity selector with three positions: the top, 8.2dBu position is for use with unbalanced connections; the lower, 14.2 and 22dBu positions are for balanced ones. An AC input rounds out the rear panel.

It’s what’s inside the AHB2’s unassuming case that should pique an audiophile’s curiosity. Benchmark’s roots are in professional audio, and their modus operandi is hardcore engineering. They made waves in the mid-2000s with their DAC1 digital-to-analog converter, a version of which I owned and loved for some years. The DAC1 was, in many respects, the first affordably excellent 21st-century DAC embraced by audiophiles. Benchmark’s excellent sequel, the DAC2, which I reviewed two years ago, improved almost every aspect of the original’s performance. Benchmark’s manuals and literature for these products are bereft of the marketing garbage that so many audiophile companies peddle these days. Rather, they’re chock-full of graphs and measurements that quantitatively demonstrate the product’s value.

Benchmark Media Systems AHB2

Lifting the lid on the AHB2 reveals circuitry that is class-AB-ish. As its model name hints, the AHB2 is nominally a class-H amp, which means that when power demands are low, it functions as would a traditional class-AB design. But as the listener asks for more power, extra voltage rails are activated that deliver more power with higher efficiency than can class-AB (hence the AHB2’s small size), but not as efficiently as class-D (hence the prominent heatsinks). While Benchmark is not the first to tackle this topology -- Arcam’s recent efforts using the very similar class-G topology are very good -- Benchmark has come up with its own unique implementation.

In the mid-2000s, the folks at THX Ltd. set out to design an amplifier with class-A performance but minimal generation of heat. Their patented approach, named the Achromatic Audio Amplifier (AAA), is a complex circuit that relies on local and global feedback as well as feedforward. This unorthodox setup provides several advantages. The low-power, error-corrected AAA runs in parallel with the high-power main amplifier, allegedly keeping it free of the crossover distortion inherent to class-AB circuits. Another deviation from the traditional class-H formula is the use in the AHB2 of a switching (vs. linear) power supply, which made possible the amp’s small size with, Benchmark claims, no electrical or sonic tradeoffs.

The result of all this, on the specification front, is damn near biblical. The AHB2 generates 100Wpc into 8 ohms or 190Wpc into 4 ohms, is stable down to 2 ohms, and manages 380W when configured for bridged mono. It delivers up to 18A of current, and has a damping factor that tops out at 350. Its total harmonic distortion plus noise is a claimed <0.0003% at 1kHz. The signal/noise ratio is an absurd 132dB in stereo, 135dB in bridged mono. The AHB2’s crosstalk is better than -115dB at 1kHz, and its frequency response exceeds 0.1Hz-200kHz, +0/-3dB.

In a vacuum, of course, such measurements mean nothing. It’s when they’re compared with the measurements of the competition that things get interesting. My excellent reference amp, Hegel Music Systems’ H300 ($5500), produces 0.005% distortion, and has a claimed S/N ratio of “more than” 100dB. In other words, the Benchmark’s distortion levels are more than an order of magnitude lower, and the AHB2 is a ridiculous 30+dB quieter. Even the vaunted Devialet 120 -- which I adored and reviewed last summer, and which, by a wide margin, is the best electronic component I’ve ever heard -- produces about three times as much distortion as the AHB2 and is 2dB noisier. Holy crap.

Benchmark Media Systems AHB2

I hooked up the AHB2 to Benchmark’s own DAC2 DX, a variation of the DAC2 HGC (I’m very familiar with both, having reviewed the DAC2 HGC in 2013). I used Benchmark’s Studio&Stage StarQuad balanced interconnects ($38/pair), which they supplied for this review. Speakers were KEF’s LS50 and Definitive Technology’s Mythos ST-L, though the latter saw greater use as I tried to push the little Benchmark to its limits. My trusty 2009 Apple MacBook Pro, connected to the DAC2 DX via a DH Labs Supersonic USB cable, provided the music. The AHB2 powered up within a few seconds of my pressing its front Power button, and I set to work.

Sound

The AHB2 was, almost without qualification, astonishingly good. Spotting sonic differences among the ocean of class-AB amps offered for less than $10,000 can be challenging because those differences can be so subtle. But with the Benchmark, it was immediately apparent that I was listening to something special. Only one other amp has come close to matching the AHB2’s utter lack of noise and grain. I recall putting my ear practically on my speaker’s tweeter to hear only the faintest white noise from the Devialet 120, and I had much the same experience with the AHB2. There was just nothing there. Reading this on your screen, it might be difficult to imagine so total an absence of grain or noise floor in the sound of your own system. But let me tell you, the effect was profound.

The AHB2 was incredibly transparent. It just tore down the cloud of ambiguity that burdens the sounds of, well, just about everything else I’ve heard.

Benchmark Media Systems AHB2

I threw on “The District Sleeps Alone Tonight,” from the Postal Service’s Give Up (16-bit/44.1kHz ALAC, Sub Pop), and was floored by the AHB2’s powers of resolution. Ben Gibbard’s voice emerged from my speakers with great precision and articulation. I could easily pick out the contours of his voice from the foreground of the soundstage, the drums and backing voices recessed and to either side of him. The stereo imaging was superlative. The entire recording was laid bare before me, bereft of artifice, totally clear. It was the kind of outright clarity, quickness, and tight-fisted control I’d expect from a pair of massive monoblocks. The transients in the opening of “Sleeping In” only reinforced this impression, with outrageous delicacy and effortlessness.

Live recordings seemed perfect fodder for the AHB2, so on went “Little Lion Man,” from Mumford & Sons’ The Road to Red Rocks (16/44.1 ALAC, Island). Again the Benchmark illuminated a track I’ve heard dozens and dozens of times in the last couple years. Lead singer Marcus Mumford’s voice was completely unencumbered, unfettered, unburdened by previously unrecognized shackles. The sound was cleaner and clearer than my Hegel H300 ever could manage with this track, while just as smooth and easy to listen to. And the Benchmark’s squeaky-clean sound was still somehow unapologetically neutral. Coloration of any kind was wholly absent. Those wishing for a euphonic midrange should temper their expectations.

The AHB2’s appeal was precisely in its ability to simultaneously speak the languages of unswerving accuracy and of heart and soul while, for better or worse, revealing every nook and cranny of every recording. Lead singer Till Lindemann’s opening lines in “Spieluhr,” from Rammstein’s  third studio album, the excellent Mutter (16/44.1 AIFF, Island), practically dripped with his heavy, foreboding enunciation. In terms of linearity, the Benchmark was ruler flat across the audioband. The attack of Christoph Schneider’s drums was reproduced with real impact, but not overcooked in terms of slam. Despite its cacophonous nature, “Spieluhr” never sounded harsh or abrasive in the highs, never approached the tetchy, brittle treble I occasionally hear from some other amps.

Wanting to hear how the AHB2 would handle richer, denser music, I cued up the high-resolution version of “Get Lucky,” from Daft Punk’s Random Access Memories (24/88.2 FLAC, Columbia). My concern about this monster single sounding in any way threadbare was misplaced. Pharrell Williams’s velvety chorus was supple and substantive, while the foundational bass guitar and kick drum were as solid as I could hope to hear them. The higher the fidelity of recording I threw at the Benchmark, the more rewarding my listening experience became.

Considerations

For all of the Benchmark AHB2’s phenomenal talents, and my unabashed affection for what it did, it may not warm the cockles of every listener’s heart. There’s a certain three-dimensionality and magic to class-A circuits, such as those found in Devialet’s 120 and Luxman’s L-550AX, that I didn’t quite hear from the Benchmark. But these competing designs aren’t necessarily better, they’re merely different. That’s an important distinction to make, because I can’t overstate just how accomplished this little amplifier is.

Some audio aficionados are willing to spend tens of thousands of dollars on power amps alone. There’s no question that many high-priced amps offer current, wattage, and an ability to drive brutal impedance swings that the Benchmark may not be able to match. The lavish, artisan-level casework that accompanies such designs can also be quite impressive. But the expectation is that, by virtue of their intimidatingly beautiful physical appearance, and through an astronomical asking price, the buyer will get better sound than anything else out there. Benchmark’s AHB2 smashes this notion to bits. It’s every bit as good as the revolutionary Devialet 120, and with the right partnering electronics, may provide even better sound than that svelte French amp.

Conclusion

Benchmark Media Systems’ modest-looking little AHB2 power amp may be hi-fi’s biggest bargain. It is one of the -- if not the -- quietest, most resolving amps I’ve heard. Time and again, without ever having intended to, I wound up hours deep in listening to the fringes of my music collection, thanks to the AHB2’s reference-level transparency and obscene athleticism. If ever there were a giant-killer of an amp, this is it.

. . . Hans Wetzel
hansw@soundstagenetwork.com

Associated Equipment

  • Speakers -- Definitive Technology Mythos ST-L, KEF LS50
  • Earphones and headphones -- NAD Viso HP50, Shure SE535LTD-J
  • Integrated amplifiers -- Hegel Music Systems H300, Luxman L-550AX
  • Digital-to-analog converters -- Arcam irDAC, Benchmark Media Systems DAC2 DX
  • Sources -- Apple MacBook Pro running iTunes  
  • Speaker cables -- DH Labs Q-10 Signature, Dynamique Audio Caparo
  • Analog interconnects -- Benchmark Media Systems Studio&Stage StarQuad (XLR), Dynamique Audio Shadow (RCA), Nordost Blue Heaven LS (XLR)
  • USB cables -- DH Labs Silversonic, Nordost Blue Heaven

Benchmark Media Systems AHB2 Stereo/Mono Amplifier
Price: $2995 USD.
Warranties: One year, parts and labor; with registration, extendable to five years (US and Canada) or two years (elsewhere).

Benchmark Media Systems
203 E. Hampton Place, Suite 2
Syracuse, NY 13206
Phone: (315) 437-6300
Fax: (315) 437-8119

Website: www.benchmarkmedia.com