Country of Origin
Reviewer: Srajan Ebaen
Financial interests: click here
Sources: Soundaware D100Pro SD card transport, Jay's Audio DAC-2 Signature Edition [on loan]
Preamplifier: Nagra Classic
Headphones: Raal Requisite SR1a
Cables: Zu Event MkII XLR interconnects x 2, Crystal Cable power cords
Review component retail: $2'995
Benchmark Media. Today that name has extra relevance. That's because Aleksandar Radisavljevic, chief weaver at Serbia's Raal Ribbon, used this American amplifier as his reference during R&D of the Raal Requisite SR1a earfield monitors™. This assignment thus does no more or less than retrace his footsteps to test his assertion that of all the amplifiers he's tried (those included Bryston, Pass, Krell, McIntosh, Classé and more), to him and on his own recordings, the AHB2 still sounds the most like live music. With Product of the Year 2014-2017 awards from various high-profile publications, our Benchmark amplifier has been comprehensively covered many many moons ago – on standard loudspeakers. But nobody yet thought to review it on headphones. And why would you?
Because to remain wearable without two pounds of transformers yet not present a virtual dead short, these have their 0.0018Ω impedance boosted by an interface box. Together with the supplied cable, that presents the amp with a purely resistive 6Ω. Dream boat load. On purpose, it also converts about 95% of the amplifier's power into heat since the ribbons don't need more than about ½ watt.
This scheme obliterates any damping factor the amplifier would normally express. But it still transfers its current. And current—the Benchmark is capable of 18 amperes—is what these ribbons thirst for on challenging bass transients of which they're stunningly capable down to about 30Hz. For the math to add up as intended, a 100/200wpc into 8/4Ω amp is recommended. The interface box also builds in a passive de-emphasis circuit to compensate the line source's rising response so no external EQ is needed.
As a true ribbon which floats on an open carbon-fibre baffle before your ears similar to an old AKG K-1000, the SR1a suffer neither in-the-way magnetics nor ear cups of any kind. This removes common compression, reflection and turbulence effects of air that gets trapped between driver and ear. I think of their sum as ear-muff syndrome. With a very low resonant frequency and in extreme proximity to your ears, these ribbons sport exceptionally clean impulse response from zero energy storage. That acts very fast, ultra resolved and wickedly dynamic. As true statement transducers, they also scale willingly as the quality of associated components increases.
In 100wpc/8Ω stereo mode (it bridges to near four times that), here the class A/B Benchmark Media amplifier with class H rails, a switching power supply and sophisticated feed-forward error correction system based on a THX patent checks in with true 22-bit resolution, i.e. signal to noise of a whopping 132dB. Bandwidth -3dB is 0.1Hz to 200kHz. Prior reviews and the firm's own materials explain how these extraordinary specs came about. For our purposes, it's sufficient to think of this amp as on par with the dynamic range of the very best modern DACs. By contrast, most amplifiers give up 20-30dB along the way. Certain SET barely hit 14-bit dynamic range.
As a flagship transducer liberated from all room effects and the limitations of common headphone drivers, the SR1a really are most desirous of a matching benchmark amplifier. Would the AHB2 be that one? Benchmark's own Rory Rall must have been curious himself to accommodate this unusual loaner request. Because if you want to learn what their amp sounds like on regular loudspeakers, you've come to the wrong review. Alex too was curious. "Though, I must admit, now I'm a bit concerned over what you're going to say. You've tried many amps that I haven't/couldn't. Now I fear that the AHB2 won't be as unique as I think it is though I've been quite vocal about it with my ribbon earspeakers. So I can't wait to see what you'll think of it!"
… to be continued…