93%
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 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 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 an LA4 preamplifier, and this is perfect match for driving Benchmark's AHB2 power amplifier.
- 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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Benchmark HPA4 Headphone / Line Amplifier
The Benchmark HPA4 is a compact, reference-focused headphone and line amplifier built around THX-888 feed‑forward modules and a precision relay attenuator. Reviewers from Andrew Everard / HiFi News and Sandu Vitalie / Soundnews highlight its impact, openness and sheer control. Sonically it delivers reference-grade transparency: ultra-low noise, tight controlled bass, clear, layered mids and extended treble with an impressively cavernous soundstage.
Technically it offers high voltage/current drive for hard-to-drive headphones, four independent 256-step relay attenuators, balanced and single‑ended I/O and touchscreen control—features praised by The Ear. Ideal for listeners seeking forensic neutrality and for systems that pair a separate DAC. For audiophiles after uncompromising clarity and headroom the HPA4 remains a top reference option.
Pros
- Reference-level transparency and ultra-low noise that lets hearing chain detail rather than amplifier artifacts.
- Exceptional dynamics, headroom and current delivery (designed to drive low‑sensitivity planars and demanding loads without compression).
- High‑precision, relay‑based volume control and flexible I/O (256-step attenuators, balanced XLR/RCA preouts, mono sum) for tight system integration.
- Robust, compact build with thoughtful ergonomics (touchscreen, dual control of headphone and line levels) suitable as both headphone amp and line stage.
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Cons
- Premium price and positioning — performance justifies it for reference users, but cost will deter casual buyers.
- All‑analogue design with no built‑in DAC means most buyers will need a separate DAC to complete a digital chain.
- Extremely neutral, revealing presentation can read as slightly dry or less euphonic on some recordings or to listeners who prefer coloured sound.
Sound Quality
94/100
Reviewers repeatedly praise the HPA4's headroom, slam and transient speed—'lightning quick', 'slammed like thunder', 'prodigious capability'—and note it retains dynamics even at very high levels (Soundnews, The Absolute Sound, HiFi News). The high current/voltage design and THX-888 feed‑forward topology are cited as enabling excellent diaphragm control and punch across material. Overall it renders micro- and macro-dynamics with authority and musicality.
Noise Floor
94/100
Measurements and reviewers converge on an exceptionally low noise floor (specs: output noise <2.45 µV, SNR >131dB headphone; reviewers call it 'blackest background', 'the cleanest' and say the amp 'gets out of the way of your music') (Soundnews, The Ear). Several reviews quote measured microvolt-level noise and describe hearing the limits of their DACs/headphones rather than the amp, indicating near reference-level silence for almost all headphones. This performance makes the HPA4 very suitable for sensitive IEMs and revealing headphones.
Headphone Compatibility
93/100
Benchmark's near‑zero output impedance, 6 W into 16 Ω, 1.5 A current capability and reviewers' real-world testing with dynamics and planars lead to consensus that the HPA4 drives everything from sensitive IEMs to demanding low‑sensitivity cans with ease (The Ear, Soundnews, The Absolute Sound). Reviewers explicitly note it 'can drive pretty much anything' and that sound character is consistent across impedance ranges thanks to the low output impedance. The combination of high voltage and current plus balanced outputs makes it highly versatile for most headphone types.
Build Quality
92/100
Reviews describe the HPA4 as immaculately built: thick metal chassis for heat dissipation, CNC-milled front panel, high-quality relay-controlled 256-step volume attenuators and gold-plated contacts (Soundnews, HiFi News). The compact but robust industrial design and thoughtful ergonomics (touchscreen, input naming, volume offsets) support a premium feel and reliable long-term use. Benchmark's engineering-first approach yields an appliance-like, high‑precision build.
Features Connectivity
90/100
Starting from the 80 baseline, the HPA4 adds balanced XLR inputs (+2), a 4‑pin XLR balanced headphone output (+3), balanced XLR preamp outputs (+2), RCA preamp outputs (+1), multiple headphone outputs (+1) and an IEM‑friendly near‑zero output impedance (+1) for a feature score of 90. It also includes 256-step relay attenuators, touchscreen control, 12V triggers and tight integration with Benchmark DACs, though it intentionally lacks a built-in DAC. The connectivity set is very complete for an analogue-focused reference headphone amplifier.
Value for Money
88/100
Price sits in the ~$2,995–3,700 range depending on market; reviews call this a significant outlay but generally frame it as a justified premium for those seeking reference transparency and ultra-low noise (Soundnews notes the price as a drawback for some, while The Ear and others imply the performance justifies the cost for serious listeners). Several reviewers caution that most listeners may not need or hear the incremental gains, so the HPA4 represents excellent value for buyers prioritizing reference neutrality and technical excellence but is less compelling for buyers seeking coloration or a bargain.
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