"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
"Going into this test, based on measuring previous Benchmark products, I expected excellent performance. The benchmark HPA4 shattered even that high bar. It brings such a high performance to the table that leaves no doubt whatsoever about its transparency. No stone has been left unturned to optimize audio performance of this device. Even obscure measurements like ultrasonic interchannel phase shift is nailed."
"And then we have tons of power without messing with balanced cables and such. Plug in any headphone and you are in heaven."
"The preamp performance is even higher still, breaking and shattering any expectation one would have in a lab instrument let alone a consumer hi-fi."
"It goes without saying that the Benchmark HPA4 garners my strongest recommendation for a headphone amplifier and preamplifier. It doesn't get better than this folks."
- Amir Majidimehr, Audio Science Review
"I ended up visiting this room more than any other room at the show. I couldn’t help myself; I had to keep coming back for more!"
- Drew Gagliano, TheAudioBeatnik.com
"It’s ... been a while since I have been this excited about an audio product."
"Audeze LCD-2C, Quad Era-1, Brainwavz Alara, Sennheiser HD650 ..."
"It’s the first time when I have heard the headphones mentioned above to their full potential. In the first minute my jaw dropped ..."
"From my perspective this is the best headphone amplifier I have ever heard. It’s no competition really."
"It’s not cheap, I can give you that. Is it worth it? That is up to each and every one of you, but if you really want the best amplifier out there, an end game amplifier…this is it."
- Dan-Alexandru Gheorghe, HeadMania.org