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