Benchmark HPA4

NEW PRICE...Up for sale here is my Benchmark HPA4 Headphone / line-amp / pre-amp. A superlative device by any account, with reviews to back up that claim. I’ve owned and enjoyed this piece for about three years now and am sorry to see it go. 

From the excellent Benchmark web site regarding the HPA4:
THX AAA™ reduces 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 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.
Featuring the flagship THX-888 amplifier design, the revolutionary HPA4 headphone amplifier incorporates the same THX AAAtechnology that Benchmark uses in the AHB2 power amplifier. The HPA4 delivers sonic perfection. Hear the music without any contamination from electronic noise or distortion. The HPA4 delivers power, audio fidelity, speed and accuracy over an utterly silent background.
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.
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.

• THX-888 (AAA™) Headphone Amplifier
• Benchmark Low-Noise Line Amplifier
• 256-Step Fully-Balanced Relay Gain Control, 0.5 dB Steps
• Precision Timed Relay Closures
• Precision Metal Film Resistors
• Gold-Contact Relays
• Balanced and Unbalanced I/O
• 6 Watts into 16 Ohm Headphones
• 11.5 Vrms into 300 Ohm Headphones
• 0.01 Hz to 500 kHz
• SNR > 135 dB
• THD < 125 dB (0.00006%) under full load
• Short-Circuit Protection
• DC Protection
• Over-Voltage Protection
• Over-Current Protection
• Thermal Protection
• Touch Screen Control
• IR Remote Control (optional)
• 2 Balanced Stereo Line Inputs
• 2 Unbalanced Stereo Line Inputs
• 1 Balanced Stereo Line Output
• 1 Unbalanced Stereo Line Output
• 1 Balanced Mono Sum Output
• 2 Bidirectional 12V Trigger Ports