"The HPA4 is Benchmark’s latest headphone amplifier. This amp is unusual in that it features a THX-888 Achromatic audio amplifier, which is claimed to reduce distortion by 20–40 dB through a patented feed-forward design, resulting in the world’s most linear amplifier. In addition to the THX amp circuitry, Benchmark has gone slightly nuts (in a good way) with the volume control, offering 256 levels in 0.5 dB steps via an array of relays. The idea is to limit noise and allow the user to dial-in volume precisely."
"The HPA4 is a high-voltage, high-current design to allow low-sensitivity headphones to work well. In addition, the damping factor is high (near zero ohms output impedance), with the aim of sounding the same with low-, medium-, and high-impedance headphones."
"I thought the HPA4 sounded as good as any headphone amp I’ve heard for dynamic headphones, and it might be the best of the lot depending on your circumstances."
"The HPA4 is exceptionally good at presenting a layered, dynamic, yet relaxed sound. You can hear these rich results on, for example, Eliza Gilkyson’s Hard Times in Babylon (Red House), where the instruments not only are clearly differentiated but also sound fully rendered, as live instruments do. You also can hear the overtones of each instrument as they decay, which makes them sound more real."
"... wish the review sample didn’t have to go back."
- Tom Martin, The Absolute Sound
"The AHB2 easily outperforms the DIY Hypex NC400 I had tested before which used to be the best amp I had tested."
"THD+N versus output level looks far cleaner than anything I have tested before."
"Intermodulation distortion versus power level shows the same story of clean power."
Signal to Noise Ratio:
(unweighted, 22.5 kHz BW)
Ch1: 130.286 dB
Ch2: 130.180 dB
-0.3 dB at 20 kHz
-3 dB down at 200 kHz!!
"Since this is not a switching amplifier, there is no filter there allowing the bandwidth to go to 200 kHz and beyond."
Stereo Power into 4 Ohms:
"We have 185 watts of power at incredibly low distortion of 0.00016%, besting the company specifications."
Bridged Mono Power into 4 Ohms:
"500 watts into 4 ohm! Stunning 0.00026% distortion at 500 watts!!"
"It goes without saying that the Benchmark AHB2 breaks new ground ... gets my strongest recommendation."
- Amir Majidimehr - AudioScienceReview.com
"The AHB2 power amps ... are fantastic."
"I use them as mono blocks due to my power hungry speakers."
"I hear clarity, precision and an openness in the treble that I haven't heard in my speakers before."
"The HPA4 line and headphone preamp and the power amps are made for each other..."
- Ulrike Schwarz, Anderson Audio NY
"The effortless and free-flowing nature of the Martin Logans paired up nicely with the transparent AHB2 amplifiers."
"The tonality and realism of the instruments were spectacular. An alto saxophone sounded as if it was in the room with me, and the pitch and timbre of both male and female vocals were absolutely spot-on. It was clear that nothing in this system was getting in the way of the music."
"Their room had a remarkable degree of transparency that made every listener feel closer to the music."
- Drew Gagliano, TheAudioBeatnik.com