The Ultimate Headphone Amplifier

The flagship THX-888 headphone amplifier leverages the THX AAA™ system to reduce harmonic, intermodulation, and crossover distortion by 20 to 40 dB to guarantee a realistic and fatigue-free listening experience. It accomplishes this using a patented feed-forward topology to null conventional distortion and noise mechanisms, resulting in the world's most linear headphone amplifier. THX AAA™ allows the amplifier to reach its maximum output power and sound pressure level (SPL) without producing the distortion that normally accompanies increased output levels in traditional amplifiers.

The Ultimate Line Amplifier

The THX-888 amplifier is driven by a Benchmark line amplifier that features relay gain control, relay input selection, and relay muting. The line amplifier incorporates the finest gold-contact relays available. The gain control has 256 steps in 0.5 dB increments. It also features a balance control. Relay closures are precisely timed to deliver silky-smooth volume changes. No other relay gain control offers this level of precision and performance. The HPA4 includes 4 independent 256-step attenuators: two for the L&R headphone outputs, and two for the L&R line outputs. To make this all happen, the HPA4 includes a total of 64 precision relays.

100% Analog Signal Path

The HPA4 is 100% analog. It is designed to be driven from an external D/A converter or an external analog source. The HPA4 is designed to provide the ultimate analog signal path between inputs and outputs. The HPA4 eclipses the performance of typical high-end preamplifiers by achieving much lower noise and distortion.

High Voltage, High Current and High Power

The THX-888 amplifier can cleanly deliver high voltage into low-sensitivity high-impedance headphones and it can cleanly deliver high power and current into low-impedance headphones. The HPA4 delivers 11.9 Vrms into 300 Ohms and 6 Watts into 16 Ohms. Given these extreme capabilities, Benchmark has incorporated several protection systems to protect expensive headphones and the amplifier itself. These include DC detection, short-circuit detection, over-current protection, over-voltage protection, and thermal protection.

Speed and Precision

The bandwidth of the HPA4 extends from 0.01 Hz to over 500 kHz. This means that the HPA4 delivers very precise amplitude and phase accuracy over the entire audio bandwidth. Wave shapes are accurately reproduced, and the entire spectrum is delivered with precise timing. The HPA4 will deliver musical overtones with life-like accuracy. This means that musical instruments are rendered without changing their sonic character.

Balanced and Unbalanced I/O

The headphone output of the THX-888 amplifier features a 1/4" TRS and a 4-pin XLR. Both outputs deliver the full performance of the HPA4. However, we recommend the XLR4 due to its lower contact resistance. The HPA4 features two balanced stereo inputs and two unbalanced stereo inputs. The line amplifier provides one balanced stereo output, one balanced mono sum, and one unbalanced stereo output.

System Integration

The HPA4 includes IR remote control and can be operated using the optional Benchmark remote. The HPA4 is designed to work with the Benchmark DAC2 and DAC3 converters but may be driven from any high-end D/A converter. When paired with a Benchmark DAC, a single remote control will operate both units.

The HPA4 is the perfect complement to the Benchmark AHB2. It may be the only preamplifier or line amplifier that exceeds the signal to noise ratio of the ultra-quiet AHB2. This means that the HPA4 will extract the full performance of the AHB2. In contrast, other preamplifiers limit the system noise performance because they cannot match the SNR performance of the AHB2. The HPA4 is the only line amplifier/preamplifier that we recommend inserting between a DAC and the AHB2. The HPA4 can be inserted between a Benchmark DAC3 and AHB2 without degrading the system noise performance. With the HPA4 inserted, the DAC3's 32-bit digital gain control is replaced by the HPA4's more-resolving fully-analog relay gain control.

Two bidirectional 12V trigger ports can be used to link the HPA4 with external D/A converters and power amplifiers. The trigger signal controls the power-up and power-down sequencing of the entire audio system. The trigger ports are compatible with most industry-standard trigger input or output ports, but can communicate bidirectionally with other Benchmark products.

Touch Screen

The touch screen provides easy access to advanced features such as balance control, input level offsets, input names, screen dimming, remote control, and function locking. Help screens explain the special functions.

Rotary Encoder

The volume control knob features a high-quality optical encoder that is rated for heavy use. An acceleration feature makes it easy to move through the 256 volume steps while maintaining 0.5 dB/step resolution. A press of the control knob toggles between headphone volume, line out volume, or both.

Convenience Features

The HPA4 includes independent on-screen mute buttons for the headphone and line outputs. Both can also be muted with the volume knob or with the optional remote control.

The HPA4 includes an on-screen -20 dB dim button that instantly reduces the level by 20dB. This function provides a temporary volume reduction and an easy return to the previous listening level. This control makes it easy to transition between a normal listening level and a background level. The dim function is also accessible from the optional remote control.

Inputs may be renamed and unused inputs may be disabled. Input levels can be trimmed to provide input-to-input level matching.

Screen brightness is adjustable and timers can be set to dim or shut off the display. The screen can be locked to prevent access to advanced features.

Casework

The HPA4 is available with a black or silver faceplate and is designed to match the Benchmark AHB2 power amplifier. It occupies the same footprint as the Benchmark DAC1, DAC2 and DAC3 converters. The case features a milled faceplate and milled sides. Top, bottom, and rear panels are made from thick aluminum and feature a brushed texture. The HPA4 is built to last and will be a fine addition to your listening space.