HPA4 - "The best sounding headphone amp I've heard"
- tmallin, Moderator of Tom's Corner at What's Best Forum
"While you may think that any amp whose quiescent residual noise you cannot hear from your usual listening position is quiet enough, that has not been my subjective experience. This is one reason I'm now a big fan of the Benchmark equipment, including the AHB2 amp. I've been using a pair of them in bridged mono, as well as the Benchmark DAC3 HGC to drive my Harbeth M40.2s for awhile now."
"With this combination of electronics, for the first time in my audio life I can pin my ear to each speaker driver and hear absolutely no sound coming from the speakers in a quiet room with the system volume control at any position from minimum to maximum with no source material playing. Most amps produce quiescent noise under such conditions loud enough to be clearly heard at least a foot from a speaker driver, often more like several feet."
"I find that lowering the background noise paints the music on as black a canvas as possible and thus seems to bring out realistic low-level detail in recordings. While I may not actually hear residual amp noise as hiss/hum/rumble/roar, I more clearly hear the environmental ambient noise captured on the recording if the amp noise is lowered and this increases my perception of hearing the music in its recording venue, as well as my perception that the music is being made by real humans producing little noises like forceful breathing in rhythm, sub-vocalizations, lips parting, risers and chairs creaking, etc."
"For best headphone sound, use the four-pin XLR connector on the front panel of the HPA4, rather than the 1/4" TRS jack on the HPA4 ... the four-pin XLR connector has no chance of producing measurable distortion."
"Expect to hear quite-audible-from-the-listening-seat rapid clicking/chattering when adjusting the volume up or down with either the remote or front-panel volume controls. That's the sound of the HPA4 relays. If your SPL is already moderate or higher, the sound of the music may well cover up the sound of the relays. Just to be clear, this noise is purely mechanical and comes from the HPA4 chassis. There is no electronic clicking noise audible at all through speakers or headphones when the volume is adjusted."
"My reference headphones are the Audeze LCD-4 fitted with an aftermarket "balanced" Moon Audio Silver Dragon cable with a 4-pin XLR connector at the amp end."
"The whole presentation sounds more "solid" with the HPA4 than it did with the 430HA, giving the impression that the amp has a more solid grip on the drivers. The presentation gains a more "out front" aspect, with the presentation seeming significantly more in front of my head than it was before, while having equally wide spread. This is especially true of the NAD Viso HP50 headphones, probably because the subjective frequency response of those phones lacks any depression of the presence range and lower highs whatsoever and especially because of the "RoomFeel" response technology built into those phones."
"The Benchmark HPA4 is the best sounding line amplifier I've yet heard. It's innovative approach to controlling system volume/SPL results in what for me is a uniquely transparent-to-source experience. It is also the best sounding headphone amp I've heard, both for very-insensitive, hard-to-drive phones and those sensitive enough to easily be used directly from a smart phone. The HPA4 truly stands apart in terms of measured and subjectively low background noise and distortion when driving either loudspeakers or headphones."
Note: Above quotes are from a very lengthy and well-written review of the HPA4 by tmallin (Tom) at What's Best Forum. We recommend following the links below and reading Tom's complete review.
"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
"John Atkinson's measurements corroborated Benchmark's claim that the DAC3 is capable of "at least" 21-bit performance ..."
"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."
"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."
"The comparison system consisted of PS Audio DirectStream DAC and BHK Signature preamp and, variously, PS Audio BHK 300 and Pass Laboratories XA60.8 monoblocks."
"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."
- Jim Austin, Stereophile