"John Atkinson's measurements corroborated Benchmark's claim that the DAC3 is capable of "at least" 21-bit performance ... and corresponds to a dynamic range—the ratio of the highest achievable digital-domain volume to the DAC's internal noise—of 128dB. That's well above the dynamic range that most power amplifiers can achieve. A good-measuring high-end solid-state amplifier is likely to have a dynamic range—the highest attainable ratio of signal to noise—of about 100dB ref. its maximum power."
"Benchmark created an amplifier that more than matched the DAC3's dynamic range: the AHB2. Bridged to mono, the AHB2 has a claimed A-weighted dynamic range of 135dB ... it now sits in Class A of Stereophile's 'Recommended Components.'"
"With the DAC3 HGC and the AHB2, Benchmark seems to have achieved the lowest-noise, lowest-distortion system of source and amplification on the planet. The signals this combo sends to loudspeakers should be cleaner—truer to the source—than any other audio components can achieve. Wanting to know what that means musically, I asked Benchmark to send me a pair of AHB2 amplifiers to complement the DAC3 HGC already in my possession."
"This article is unusual in that my goal was not to take the measure of a particular component but to determine whether Benchmark's entire low-noise system could resolve musical detail that a more typical audiophile system, with noise and distortion levels that are low but not as low, could not. More broadly, I wanted to determine whether the two systems sounded meaningfully different."
"If you follow John Atkinson's measurements sidebars, you know that just because a digital audio format is 24-bit doesn't mean you get 24 bits of audiophile goodness in your listening room. The analog side can't match what digital is doing—AC line noise is especially pernicious."
"It was the "Lullaby" from Mussorgsky's song cycle Songs and Dances of Death (Pesni i Pljaski Smerti) that was more revealing. "Lullaby" has many quiet, breathy moments with quiet, subtle sibilants and fricatives. Those sounds sounded different through the Benchmark system, with more roughness, texture, and complexity. Through my reference system there wasn't really anything to miss—the same moments and sounds were suitably quiet, breathy, and fricative—but through the Benchmark amps those quiet sounds were richer and more interesting. There seemed to be more going on in those quiet moments. It's harder to describe than it was to hear."
"Over the course of several days, I went back and forth between the Benchmark amplifiers and heard it every time. The difference didn't go away."
"My PS Audio BHK 300 monoblocks are capable of great delicacy, but their character is clean and authoritative, and they have lots of power for speakers that present difficult loads. The Pass Laboratories XA60.8 monoblocks, which I also have on hand, emphasize sweetness, richness, and delicacy without sacrificing authority. The less-expensive AHB2s can play in this league and offer a different, and in some ways better, listening experience. It's a fine situation we find ourselves in."
- Jim Austin, Stereophile, October 2, 2018
"Benchmark describes its product as a 'reference Stereo Headphone Amplifier and Reference Line Amplifier with Relay Gain and Input Control', which should give you some idea of what's going on here, but only hints at the fact that this is actually two completely separate products packed into one relatively compact unit."
"The headphone section is powered by a power amp from THX, employing the same AAA (Achromatic Audio Amplifier) technology first used by the company in its AHB2."
"Benchmark's line amplifier uses relays for input selection, gain control and muting while four independent 256-step attenuators ... feed the the headphone ... and preamp outputs."
"As PM notes in his Lab Report, this design gives the HPA4 not only outstanding performance, but also rather impressive - to say the least - signal delivery."
"All of a track or two should do the trick, as whether with revealing headphones ... or used as a preamp, the HPA4 simply drops jaws with the sheer impact, openness and vivacity of the way it plays music."
"It was one of those real 'performer in the room' experiences and I was instantly transported back to the time I spent monitoring the recording as it was being made ..."
- Andrew Everard, Hi-Fi News, November 2018
AHB2 - Class A Recommended Component - Fall 2018 - Power Amps
'Class A' is Stereophile's highest classification for recommended components. Very few components receive this elite classification. Stereophile defines 'Class A' as follows:
"Best attainable sound for a component of its kind, almost without practical considerations; "the least musical compromise." A Class A system is one for which you don't have to make a leap of faith to believe that you're hearing the real thing."