Benchmark HPA4 Headphone Amplifier

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General:
The Benchmark HPA4 Headphone amplifier is a very capable piece for the most demanding headphones and critical listening. 

This particular unit is in great condition and functioned perfectly in testing.

From Benchmark:
Benchmark Media Systems, Inc. and THX, Ltd. have partnered to introduce the Benchmark HPA4 headphone/line amplifier featuring THX Achromatic Audio Amplifier (AAA™) technology.
Featuring the flagship THX-888 amplifier design, the revolutionary HPA4 headphone amplifier incorporates the same patented THX technology 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 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 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.

SkyFi Cosmetic Notes:
Some light scratches on the unit, Overall very good.

SkyFi Technical Notes:
No remote is included with this unit.

Brand Background:
The founder of Benchmark, Allen H. Burdick, began by building very high-performance audio equipment to meet the specialized needs of television broadcast facilities. The company quickly grew and was incorporated as Benchmark Media Systems on March 5, 1985. Benchmark expanded into additional audio markets and relocated to Allen's hometown, Syracuse, NY. To this day, all Benchmark products are designed, assembled, and tested in their Syracuse facility.

Ownership:
Single Owner

Connections:
RCA,XLR, IEC Power, 12v Trigger

Cosmetic Condition:
8/10 = Very Good. Excellent front faceplate, one minor flaw on chassis side or top. See our detailed rating description here.

Working Condition:
Working perfectly and tested in our lab and listening room.

Included:
Unit and Manual

Packing:
Will be packed using our highly developed in-house process and custom packing materials.Original MSRP:
$3,499.00

Specs:
### THX-888™ Headphone Output:
- THD < -125 dB (0.00006%)
- SNR > 131 dB, unweighted, 20-20 kHz
- SNR > 135 dB, A-weighted
- Frequency Response - 0.003 dB at 10 Hz, -0.001 dB at 20 kHz
- - 3 dB Bandwidth exceeds 0.1 Hz to 500 kHz
- Output Impedance, near 0 Ohms
- Output Noise < 2.45 uV at Unity Gain, 20-20 kHz
- Maximum Output Power, 6 Watts into 16 Ohms
- Maximum Output Current, 1.5 A
- Maximum Output Voltage, 11.5 Vrms into 300 Ohms
- Crosstalk < -133 dB @ 1 kHz, -115 dB @ 10 kHz (XLR4)
Balanced Line Outputs:
- THD < -125 dB (0.00006%)
- SNR > 135 dB, unweighted, 20-20 kHz
- SNR > 137 dB, A-weighted
- Frequency Response - 0.003 dB at 10 Hz, -0.001 dB at 20 kHz
- - 3 dB Bandwidth exceeds 0.1 Hz to 500 kHz
- Output Impedance 60 Ohms
- Output Noise < 1.9 uV at Unity Gain, 20-20 kHz
- Maximum Input and Output Voltage, 20 Vrms (+28 dBu)
- Crosstalk < -133 dB @ 1 kHz, -116 dB @ 10 kHz

Dimensions:
8.65" W x 3.88" H x 8.33" D - Including Feet

8.65" W x 3.47" H x 8.33" D - Excluding Feet

Weight:
12 lbs.

Link to Manual:
Click Here

Recommended Cables:
Kimber Kable - RCA Interconnects - Better

Kimber Kable - RCA Interconnects - Best

Kimber Kable - Phono Interconnects

Kimber Kable - BALANCED XLR Connectors - Better

Kimber Kable - BALANCED XLR Connectors - Best

Kimber Kable - Speaker Cables - Better

Kimber Kable - Power Cords - Better

Kimber Kable - Power Cords - Best

Kimber Kable - Select Series Reference USB Cable

Testing Process:
We start with a visual inspection of all internal components to make sure that there are no signs of heat stress or damage. Capacitors are checked for telltale signs of predictive failure including bulging, shrunken wrappers, or physical leakage. We also inspect the PCBs for discoloration from resistors or transistors that may have been running hot. On vintage units we often spot check select capacitors for value and ESR.

If the device has the ability to decouple the preamplifier from the power amplifier, we remove the jumpers and independently test each section. If the device cannot be decoupled, we assess the electronic condition of the piece by analyzing the speaker level output only.

We start by connecting the "Pre-Out" jacks of the integrated to a Sencore PA81 Power Analyzer which simulates real world loading conditions and gives us an oscilloscope interface. The first order of business is checking that the volume control works smoothly throughout its entire range with acceptable channel balance. This is accomplished by feeding a 1 KHz sine wave into one of the preamp’s line level inputs while monitoring the preamp’s output on an oscilloscope.

We then switch to a 1 KHz square wave to test the tone controls, loudness function, and filters where applicable. During this step we are watching for equal alteration of the test signal by both channels. This also helps us identify dirty controls that will need treatment.

Once the basic line stage functions are verified, we test each input individually. This is especially important for devices that use relays to select their sources.

If the preamp section is equipped with a phono stage we test that as well. We use an inverse RIAA filter which allows us to feed a reference test signal into the phono input with the proper RIAA equalization and level. A square wave or sine sweep is used to verify that the device’s phono stage is faithfully reproducing the RIAA curve.

Next we test the power amplifier section by connecting the integrated amplifier speaker outputs to a Sencore PA81 Power Analyzer which acts as a dummy load, DC offset monitor, and oscilloscope interface. We start with a low level 1 KHz test signal at the "Main In” jacks and slowly increase its amplitude while monitoring the output on an oscilloscope for signs of noise, clipping, distortion, or improper channel balance. We continue increasing the signal level until the amplifier reaches clipping.

At this point we take an output power measurement and compare it to the spec sheet of the amplifier to verify proper performance. We finish off the bench evaluation with a 1 KHz square wave check and a 20 Hz to 20 KHz sine sweep to assess the amplifier’s frequency response characteristics.

This battery of tests will usually reveal if the amplifier has any issues that need further attention.

If the preamp and power amp both pass these tests, we reconnect the sections and verify that the preamp section can drive the power amp to rated power with a 1KHz tone on one of the line level inputs.

Before the device leaves the bench, we perform a listening test with actual music using a variety of preferred test tracks. Our benches are outfitted with familiar monitor speakers which help us identify inconsistencies that will not always show up on our test gear. The main things that we are listening for are hum or noise with no signal present, proper center image, clicks, pops, or any other obvious undesirable audio characteristics.

If the unit passes all of these tests it moves to our long term testing rig where we simulate real word operating conditions for 6-8 hours minimum. This allows us to monitor the unit for signs of thermal runaway or intermittent issues that only crop up when the unit has fully come up to temperature.