As a line preamplifier, the HPA4 performed almost identically to Benchmark's superb-measuring LA4, which Kal Rubinson reviewed in January 2020, so I will refer you to that review. This report therefore focuses on the HPA4's behavior as a headphone amplifier."
"The headphone amplifier's frequency response was flat in the audio band and down by just 1 dB at 200 kHz. With the very low output impedance, the response into 300 ohms was identical to that into the high 100k ohms load, and there wasn't any audio band rolloff with impedances as low as 10 ohms."
"Both the response and the superb channel matching were identical at lower settings of the control and from the unbalanced headphone output."
"From balanced inputs to balanced headphone output, the Benchmark had extremely low noise, with the power supply–related spuriae in its output close to –130dB, even with the volume control set to +15dB. With the volume control set to unity gain, the noise floor was 12dB lower!"
"The THD+N percentage was extremely low throughout the audio band into both 100k ohms and 300 ohms."
"I concluded my report on Benchmark's LA4 preamplifier by saying it was the widest-bandwidth, widest-dynamic-range, lowest-noise, lowest-distortion preamplifier I had encountered at that time. To those virtues, the HPA4 adds equally superb headphone outputs."
"With DAC, preamplifier and power amplifier, Benchmark knows how to build a bridge between the professional sector and home hi-fi. Very beautiful."
HPA4 - "A Whopping Six Watts into 16 Ohms"
"If you value transparent, precise sound, but at the same time want a certain level of comfort and at least a little elegance, you are in good hands with the Americans."
AHB2 - "A High Degree of Precision"
"The DAC3, HPA4 and AHB2 are all characterized by their wonderfully transparent sound and their high degree of precision. At the same time, sufficient amenities are offered to offer adequate comfort. A successful mix."
"Here's a brand that's aptly named - its products providing a 'benchmark' technical performance. The HPA4 is no exception with its relay-switched stepwise volume attenuator calibrated in 0.5 dB steps over a 'useable' 105 dB range."
"Distortion and noise are vanishingly low."
"The frequency response is ruler flat (+/- 0.01 dB) from 1 Hz - 100 kHz."
"The [line output] source impedance is a sensible 30 Ohms and the maximum output a huge 22 V."
"Via the headphone amp, the maximum voltage is 11.2 V and ... the maximum power output is a substantial 4.4W/25ohm and 7.7W/8ohm."
High Power, Low Noise
"So, not only will the HPA4 drive the toughest headphone loads but its ... insignificant -102 dBV (8uV) residual noise also ensures exceptionally quiet backgrounds when listening with the most sensitive headphones/earbuds."
"Distortion is broadly unaffected by loading."
"The source impedance is a low <0.6 Ohms up to 10 kHz, increasing to 0.78 Ohms at 20 kHz."
"John Atkinson's measurements corroborated Benchmark's claim that the DAC3 is capable of "at least" 21-bit performance ..."
AHB2 - "135 dB A-Weighted Dynamic Range"
"Benchmark created an amplifier that more than matched the DAC3's dynamic range: the AHB2. Bridged to mono, the AHB2 has a claimed A-weighted dynamic range of 135dB ... it now sits in Class A of Stereophile's 'Recommended Components.'"
Benchmark System - "Richer and More Interesting"
"Through the Benchmark amps those quiet sounds were richer and more interesting. There seemed to be more going on in those quiet moments. It's harder to describe than it was to hear."
"Over the course of several days, I went back and forth between the Benchmark amplifiers and heard it every time. The difference didn't go away."
AHB2 - "Ideally Suited for Hard-to-Drive Speakers"
The Benchmark Media AHB2 showed the highest level of audioperformance in all metrics. Despite being a half-rack-sized compact product, it provided a constant voltage across a wide range of loads. In stereo mode, it performed well into a1Ω impedance load at phase angles of 0, ± 30, and even ± 60 degrees which is a very harsh operating environment. The amplifier is ideally suited forlow-impedance and phase-shifted loudspeakers, which are commonly referred to as "hard-to-drive speakers."
In SNR and THD measurements are very impressive,exceeding some of the measurement limits ofthe best measurement equipment available. The stereo-mode output of100 W into8Ω and 400 W into2Ω ismore than sufficientoutput under mostconditions. If you need more power, you can use the bridged-mono mode.
DAC3 DX - "Will Bring the Studio to Your Home Audio System"
"Benchmark’s DAC3 DX DAC is designed for recording and mastering studios, but it is a great product for consumer use as well."
"The Benchmark Media DAC3 DX is the successor to the DAC2 DX. The differences between the DAC3 DX and the DAC2 DX are (1) active 2nd harmonic compensation, (2) active 3rd harmonic compensation, (3) lower THD+N, (4) lower passband ripple, (5) improved frequency response, (6) faster PLL lock times, (7) faster switching between inputs, and (8) adjustable calibration."
"For the bench tests, I have moved to using much more sensitive measurements with the Audio Precision ... the distortion is so low, it is beyond the Audio Precision’s capability."
- John E. Johnson, Secrets of Home Theater and High Fidelity
"The Benchmark DAC3 offers extremely low levels of harmonic distortion from all its outputs. Intermodulation distortion was similarly vanishingly low."
"No power-supply–related spuriae can be seen, and the random noise floor lies below –160 dBFS!"
"When the DAC3 decoded dithered 16-bit and 24-bit data representing a 1 kHz tone at -60 dBFS, the increase in bit depth dropped the noise floor by more than 30 dB, indicating that the Benchmark’s resolution is at least 21 bits."
AHB2 - Driving PMC IB2S Passive Studio Monitors at AES 141
At the 141st AES conference we demonstrated two Benchmark AHB2 monoblock power amplifiers driving a pair of 4-Ohm PMC IB2S passive studio monitors (these monitor are also available in the PMC IB2SE hi-fi version).
In bridged mono, the AHB2 can deliver over 518 watts into each of these 4-Ohm speakers. This is a perfect match to PMC's 500 watt recommendation. The AHB2 easily provides the power, the output current, and the damping required by these low-impedance speakers.
"I am very impressed with the clarity and accuracy of these outstanding professional monitors. The Benchmark AHB2 and PMC IB2S are an absolutely killer combination!"
AHB2 - "Stable and Load-Independent, Capable of Driving Difficult Loads"
"AHB2's output power ... easily confirmed the specs given by the company itself."
"Based on this performance, the amplifier seems more than capable of driving difficult loads."
"Damping factor was estimated above 200, therefore, no system frequency response discrepancies, due to loudspeaker's impedance variability, should be expected."
"In distortion measurements, AHB2's behavior was impressive ..."
"The amplifier's spectral behavior does not seem to change significantly with a 4-Ohm load at its outputs."
"This stable and load-independent behavior of the output stage is something not often encountered."
"This performance clearly shows that the Benchmark/THX design approach works ... the result is a power stage with very low distortion, indeed."
"The noise performance of the amplifier was, also, top-class ... there is an apparent absence of noise components from the power supply ... this is a remarkable behavior, especially with the output stage under load conditions ..."
DAC2 HGC - "Very High Level of Performance, Very Low Distortion"
"The noise spectrum shows that the DAC2 HGC is indeed a very quiet device without problems of interference or hum."
"Frequency response is flat across the entire range of measurement without a visible cut-off towards the lower frequencies, and with a rather mild roll-off at very high frequencies close to 80kHz. The differences between the two channels are small, in the range of 0.2dB."
"The THD+N Vs Frequency graph does not hide any unpleasant surprises. The curves (for an output level of 1Vrms) are below 0.003% with an apparent increasing trend from the 10kHz upwards but with minimal level-depended variation, an indication for a good analog stage design."
DAC2 DX - "Had Some of the Lowest Distortion of any DAC We Have Ever Tested"
"Listening to my music collection via USB was a pleasure with this DAC. It had a very musical sound, reminding me of a Class A triode tube amplifier. When you check out the bench tests, you will see why."
"For my money, the Benchmark DAC2 DX represents one of the best values in high end audio today."
- John E. Johnson, Jr., Secrets of Home Theater and High Fidelity
AHB2 -"An Extraordinary Amplifier ... at the Limits of What is Possible for Me to Reliably Test"
"Conventionally, it is assumed that the measurement system used to test a product is much better than the device under test."
"However, the Benchmark amplifier's specifications are close to those of my Audio Precision system ... correctly characterizing the AHB2's measured performance would therefore present a challenge. The second and third harmonics lie close to the residual distortion in the Audio Precision's signal generator."
"The Benchmark amplifier has a claimed S/N ratio "approaching 130dB," which, at 6.02dB per bit, is equivalent to more than 21-bit resolution. It is truly a high-resolution amplifier."
"Benchmark Media Systems' AHB2 is an extraordinary amplifier."
DAC2, AHB2, SMS1 - "I Was Impressed with the Sense of Space"
"I was admittedly quite cruel with my initial choice of listening material ... Vladimir Homyakov playing Bach organ works on the Eule organ at St. Alexander Church in Cheylyabinsk. Yes, we're going to try playing organ music on a modestly-sized pair of bookshelf speakers! And my jaw dropped. Unexpected depth there is, and natural it sounds too. I was also impressed with the sense of space the system created; it felt uncannily as if I was in the church"
"Benchmark ... has managed an impressive feat. If you want a large-scale yet musical sound but don't have the space for big boxes, they're well worth checking out."
DAC2 HGC - "Better Performance than DACs Ten Times its Price"
"I have analysed the test results of a half-a-dozen of the world's best DACs, most of which sell for more than ten times the price of the DAC2, and across almost all parameters tested the performance of the Benchmark DAC2 HGC equals or exceeds that of every single one of those DACs."
"Superb: I have used that word a number of times to describe the results returned by the Benchmark DAC2 HGC, and there is really no better word to describe its overall performance as well."
"This is digital audio engineering at its very best."
AHB2 -"Less distortion and noise than any other power amp I’ve measured over the years"
"All amplifier measurements are performed independently by BHK Labs."
"The AHB2 is Benchmark’s attempt to produce a very-low-distortion, low-noise power amplifier using THX’s AAA Technology, which linearizes the amp’s class-AB output stage without using large amounts of overall negative feedback. I must say that they’ve succeeded; I measured less distortion and noise in the AHB2 than in any other of the many power amps I’ve measured over the years."
"High-frequency THD+N is admirably low, and in stereo and mono modes, the AHB2’s level of distortion throughout most of the power range is amazingly low."
"... the signal harmonics -- consisting of the third and fifth harmonics in stereo mode -- are extremely low in amplitude."
SMS1 - "Voices Sounded Genuinely Lifelike, with a Blessed Absence of Sibilance"
"There was no compromising of the vocals’ clarity, no clouding of the space."
"The SMS1 has a high crossover point, so the larger driver is acting as a true mid/bass unit. Suffice it to say, voices sounded genuinely lifelike, with a blessed absence of sibilance."
"What made it so involving was the way the harmonies meshed, the resolving power of the tweeter ensuring that each singer could not only be heard clearly, but defined in their own space."
"This classy monitor has a distinct character, leaning toward the rich at the bottom and the analytical at the top, rather than the totally neutral ‘studio’ sound I might have anticipated. If the balance suits your taste, you'll find it sounds bigger than a small two-way, it’s easy to drive and the perceived value suggests a price of at least a grand more."