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Benchmark HPA4 Headphone / Line Amplifier
The HPA4 features the Benchmark-exclusive THX-888 headphone amplifier. This is Benchmark's flagship headphone amplifier. It also marks the pinnacle of the THX headphone amplifier family. The THX-888 circuit board is manufactured by Benchmark.
Like our AHB2 power amplifier, the THX-888 features the patented THX-AAA feed-forward topology. The THX-888 keeps noise and distortion below the threshold of hearing, even when driving the most difficult headphones.
The award-winning HPA4 packs power, speed, and control into a package that includes all of the functions and features of our LA4 line-level preamplifier.
The headphone and line outputs are controlled by independent 256-step relay-switched attenuators. This is, without question, the best analog volume control system available.
- Much Faster than Feedback
- Eliminates Zero-Crossing Distortion
- Inherently Stable, Non-Recursive Correction
- Stable into Any Phase Angle
- Stable when Driving Very Low impedances
- No Rise in THD when Driving Low Impedance Headphones
- Flagship THX-888 Headphone Amplifier
- 30 to 40 dB reduction in THD
- Keeps THD+N Below 0 dB SPL at All Times
- No "Electronic Fingerprints" on the Music
- Accurate Impulse Response Into all Loads
- 135 dB SNR
- Ultra Wide 0.1 Hz to 500 kHz Response
- Bass is Delivered Without a Phase Shift
- Fast, Distortion-Free Transient Response
- Linear Phase Response
- Accurately Reproduces the Audio Waveshape
- Precise Rendering of Stereo Width and Depth
- Focused 3-D Stereo Image
- High Output Current - Drives Low Impedances with Ease
- High Output Voltage - Ample Headroom to Dive Inefficient Headphones
- 0-Ohm Output Impedance - Maintains Tight Control of Drivers
- Fault-Detection Circuit- Protected against Short Circuits and Overloads
- Dual Outputs - XLR4 and 1/4" TRS
- Independent Line and Headphone Balance Controls
- High-Precision Low-Impedance 256-Step Attenuator
- Low-Noise 16-Step Input Gain Stage
- Control Range is +15 dB to -127.5 dB in 0.5 dB Steps
- High Precision Laser-Trimmed Thin-Film Resistors
- 12 Relays per Output - 48 Total Including Line Outputs
- Precision Make-Before-Break Timing - Prevents Switching Noise
- The HPA4 Includes all LA4 Features
- 2 Pairs of Balanced Line Inputs
- Fully-Balanced Differential Input Amplifiers
- Fully-Balanced Relay-Controlled Gain Stage
- Fully-Balanced Relay-Controlled Attenuation Stage
- Fully-Balanced Output Line Drivers
- Left, Right and Mono - Balanced Line Outputs
According to independent tests, the Benchmark HPA4 delivers the lowest noise and lowest distortion available from a headphone amplifier or from a preamplifier.
The Benchmark-excusive THX-888 headphone amplifier board features the patented THX-AAA technology. This technology includes a feed-forward error correction system that reduces distortion by 30 to 40 dB. Distortion and noise are held below the 0-dB SPL threshold of hearing, even when driving the most demanding headphones.
The amplifier board is driven by a 256-step relay-controlled volume control. This system is engineered to deliver the lowest possible noise and distortion at each volume setting. A second, identical and fully-independent volume control drives the balanced and unbalanced line outputs.
The HPA4 has won many top awards and top recommendations from the press. It has received two "Product of the Year" awards, and is currently listed on Stereophile's short list of recommended components.
The Benchmark HPA4 delivers a clear, open, and uncluttered playback across the entire frequency range.
Instrumental overtones are rendered with exceptional precision and realism. Vocals are reproduced with outstanding accuracy and natural tones. Transients are fast and precise. Bass is deep and well controlled.
The ultra-linear phase response of the HPA4, allows it to create a precise three-dimensional rendering of the recorded space. This space is open and uncluttered because noise and distortion are held below the 0-dB SPL threshold of hearing at all playback levels.
This experience is not limited to the headphone outputs. The HPA4 includes all of the features and functions of the LA4 preamplifier, and this is perfect match for driving Benchmark's AHB2 power amplifier.
Headphone and line output volume are independently controlled.
- On/Off Momentary Switch
- IR Remote Sensor
- Color Touch-Screen Display
- Attenuation Shown in dB
- Many Programmable Features
- 1/4" TRS Jack - Professional Grade Connector
- XLR4 Jack - Provides the Best Output Connection
- Long-Life Heavy-Duty Optical Encoder
- 0.5 dB per Step, 256 Steps
- Push to Toggle Between Line and Headphone
- Allows Independent or Simultaneous Control of Line and Headphones
- Input 1 - XLR (L,R)
- Input 2 - XLR (L,R)
- Input 3 - RCA (L,R)
- Input 4 - RCA (L,R)
- Left Out - XLR
- Right Out - XLR
- Mono Sum Out - XLR
- Left Out - RCA
- Right Out - RCA
- Bidirectional Operation
- Work with all Single and Dual Direction Trigger Ports
- Time Delays Allow Noise-Free System Startup and Shutdown
- Standard 3-Pin IEC Connector
- Fuse Drawer with Two Fuses
- Auto-Ranging
- 50-60 Hz
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Professional Reviews 91/100
Deliciously Crispy
Sound Quality
95/100
Build Quality
93/100
Features Usability
92/100
Value for Money
78/100
The ultra-low-noise Benchmark HPA4 delivers a reference-grade window onto recordings, with reviewers from HiFi News, The Absolute Sound, and The Ear praising its openness, precise imaging, and effortless drive. Its flexible preamp features and black background make it a serious choice for listeners chasing maximum transparency.
What Reviewers Are Saying
Pros
Exceptionally transparent, revealing layered detail and precise imaging without obvious coloration.
Very low noise floor with a silent, black background that suits sensitive IEMs and demanding headphones.
Strong drive and headroom, with reviewers noting effortless control across low- and high-impedance loads.
Feature-rich analogue design with balanced and single-ended inputs/outputs, relay volume control, and touchscreen usability.
&
Cons
Its highly revealing tuning can sound a little dry or less tonally rich than more euphonic amplifiers.
The price is a significant hurdle, especially once regional pricing and the optional remote are factored in.
SOUND QUALITY PERFORMANCE 95/100
Reviewers are consistently struck by the HPA4’s clarity, openness, and lack of coloration. They describe it as highly transparent and revealing, with a very low noise floor, strong drive, and an unusually expansive, precisely layered presentation.
Transparency Resolution
97/100
Multiple reviewers call it super-revealing, transparent, and a window onto the recording rather than a tonal overlay. They praise the way it exposes detail, layering, and spatial cues with a very high level of clarity.
Tonal Balance Musicality
88/100
The amp is repeatedly described as neutral, clean, and truthful, but several reviewers also note a slight dryness or reduced tonal density compared with more euphonic designs. Even so, they still present it as an engaging, natural-sounding component rather than a sterile one.
Dynamics
97/100
Reviewers highlight impressive headroom, strong impact, and a sense of effortless control, with comments about heads nodding, feet tapping, and loud playback without the sound changing. It is repeatedly described as fast, authoritative, and able to slam while staying composed.
Noise Floor
96/100
The HPA4 is praised for a black background and ultra-low audible noise, with reviewers explicitly noting its very low output noise and absence of hiss or distortion. The commentary consistently frames it as effectively silent in normal use.
Headphone Compatibility
95/100
Reviewers report excellent behavior across low- and high-impedance headphones, with strong voltage and current delivery, near-zero output impedance, and ample headroom left in use. It is presented as unusually unconcerned by load, while still being a very capable match for demanding dynamics and planars.
Assessments of Build Quality, Usability, and Overall Propositions.
Build Quality
93/100
Reviewers praise the HPA4’s solid, no-nonsense construction, thick metal chassis, quiet power supply implementation, and smooth relay-based volume control. There is little criticism of workmanship, though the commentary stays focused more on functionality and execution than on luxury flourishes.
Features Usability
92/100
This is unusually well equipped for an analogue headphone amp, with balanced and single-ended headphone outputs, balanced and RCA inputs, preamp outputs, relay volume control, remote support, trigger connections, and a touchscreen interface. Reviewers also note useful input naming, output-level settings, and integration with Benchmark’s DACs, making it very flexible in daily use.
Value for Money
78/100
The reviews are respectful of its performance but clearly flag the price as a drawback, with one calling out the $2,995 starting price and another noting the added cost in Europe. The consensus is that it is a serious, high-end component rather than an easy value buy, even if some reviewers feel the performance is justified.
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Authorized dealers for Benchmark HPA4 Headphone / Line Amplifier
- The Music Room — online and in-store — Erie, Colorado, United States (website)
- 110Hz — online and in-store — Kielce, Województwo świętokrzyskie, Poland (website)
- Acton Gate Audio — online and in-store — Cymru, United Kingdom (website)
- Alto Music — online and in-store — Middletown, New York, United States (website)
- Atlas Pro Audio, Inc. — in-store — Sun City Center, Florida, United States (website)
- Audio Advisor — in-store — Michigan, United States (website)
- Audio Extreme — in-store — Kowloon, China (website)
- Audiolab Stereo & Video — online and in-store — Morrisville, Pennsylvania, United States (website)
- AUDIOPHONICS — in-store — Bordeaux, Nouvelle-Aquitaine, France (website)
- B&H Photo — online and in-store — New York, New York, United States (website)
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