"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
SMS1 - "Voices sounded genuinely lifelike, with a blessed absence of sibilance"
"There was no compromising of the vocals’ clarity, no clouding of the space."
"The SMS1 has a high crossover point, so the larger driver is acting as a true mid/bass unit. Suffice it to say, voices sounded genuinely lifelike, with a blessed absence of sibilance."
"What made it so involving was the way the harmonies meshed, the resolving power of the tweeter ensuring that each singer could not only be heard clearly, but defined in their own space."
"This classy monitor has a distinct character, leaning toward the rich at the bottom and the analytical at the top, rather than the totally neutral ‘studio’ sound I might have anticipated. If the balance suits your taste, you'll find it sounds bigger than a small two-way, it’s easy to drive and the perceived value suggests a price of at least a grand more."
- Ken Kessler, Hi-Fi News
AHB2 - "I was struck by just how much focus and clarity was on offer"
"This is an amplifier with very serious slam, and – even better for those with less sensitive speakers, big rooms or just a hankering for ‘just in front of the PA stack’ listening levels – it keeps it all together however loud you decide to play things."
"If that doesn't make you smile every time you listen, I don't know what will."
- Andrew Everard, Hi-Fi News
"... the widest A-wtd S/N ratio of any amplifier I've measured in some 30 years."
- Paul Miller, Hi-Fi News