"In the past decade, Benchmark consumer products, especially its digital-to-analogue converters, have achieved acclaim for ultra-low distortion and clean sound. While the company is very strongly engineering-oriented, it maintains that listening tests are critical to product development."
"The HPA4 is Benchmark’s latest headphone amplifier. This amp is unusual in that it features a THX-888 Achromatic Audio Amplifier, which is claimed to reduce distortion by 20–40 db through a patented feed-forward design resulting in the world’s most linear amplifier."
"In addition to the THX amp circuitry, Benchmark has gone slightly nuts (in a good way) with the volume control, offering 256 levels in 0.5 db steps via an array of relays."
"Benchmark doesn’t stop there. The HPA4 is a high voltage, high current design to allow low sensitivity headphones to work well."
"In addition, the damping factor is high (near zero ohms output impedance), with the aim of sounding the same with low, medium, and high impedance headphones."
"That’s all great, but many fancy-sounding circuits sound like dirt. Happily, that isn’t the case with this one."
"The HPA4 is exceptionally good at presenting a layered, dynamic yet relaxed sound."
"You can hear these rich results on, for example, Eliza Gilkyson’s Hard Times In Babylon [Red House], where the instruments not only are clearly differentiated but also sound fully rendered, as live instruments do."
"You also can hear the overtones of each instrument as they decay, which makes them sound more real."
"This adds up to a super-revealing amp that isn’t going to correct the mistakes of the rest of your system. I thought top-flight headphones sounded great as a result, but that doesn’t necessarily make it the amp for you. I, however, wish the review sample didn’t have to go back."
- Tom Martin, HI-FI+
After this review, Hi-Fi+ selected the HPA4 as one of the "Top 100 Products of the Past 20 years" (1999 to 2019).
"A real game-changer!"- HI-FI+
"This little unit will change the way you look and listen to amplifiers."
"My first taste of this remarkable new amplifier came earlier this year in April at Chicago's AXPONA where I discovered it driving a newly redesigned Studio Electric Pasadena loudspeaker, also bearing the Benchmark trademark. Now called the SMS1, the Pasadena's crossover had been reworked by Benchmark, upgraded with very low tolerance components, and the new look, more in line with the look of the rest of the Benchmark product line up, had been adopted."
"The subsequent sound in this room was one of the most musically engaging I encountered at this year's event, a remarkable result considering its modest overall system price of just over $7000, sans source."
- Greg Weaver, EnjoythMusic.com
Jim Austin wrote, "The DAC3 was all about depths, in several respects . . . I heard deeper into the music."
The concise conclusion to John Atkinson's Measurements sidebar: "All I can say is 'Wow!'"
In a Follow-Up, Jim Austin wrote of using the Benchmark processor with the same company's AHB2 power amp—a combination of high source output voltage and modest amplifier gain that he describes as "optimal for minimizing noise and distortion"—and reported hearing "richer and more interesting" reproduction of very subtle details.
- Stereophile Magazine
"Class A+" is Stereophile's highest award for Digital Processors
"Benchmark's LA4 is the widest-bandwidth, widest-dynamic-range, lowest-noise, lowest-distortion preamplifier I have encountered."
- John Atkinson, Stereophile
"The LA4 is probably the most transparent and revealing audio component I've ever used. It does not seem to leave any fingerprints on the sound."
- Kalman Rubinson, Stereophile
"Class A" is Stereophile's highest award for preamplifiers.