Solid State Power Amp Reviews

One of the finest chamber music performances I have ever attended took place this past August under far from ideal circumstances. The venue was one-month-old Field Hall in Port Angeles, Washington, a city of fewer than 20,000 people known more for its port and proximity to the Olympic National Forest than for its rich culture. Perhaps that reputation will soon change, because the performers in the concluding concert of the Music on the Strait chamber music festival (footnote 1) included its two local founders, violinist James Garlick of the Minnesota Orchestra and violist Richard O'Neill, the newest member of the Takács String Quartet. These excellent musicians, who have been friends since high school, were joined by the superb pianist Jeremy Denk and cellist Ani Aznavoorian (footnote 2). These are world-class musicians who attract eager audiences to New York's 92nd Street Y and Carnegie Hall, London's Wigmore Hall, and other prestigious venues.

From orchestra level—even from row C—Field Hall's acoustics favored the midrange, shortchanged treble brilliance, and truncated reverberation: good for talks and theater, not so good for unamplified music. Also problematic was the piano, a Steinway D that lacked warmth and richness because it was still recovering from a player piano mechanism–ectomy.

These shortcomings mattered not once the music started. The program consisted of compositions by the three members of the love triangle of Clara Schumann, Robert Schumann, and Johannes Brahms. The performances were so heartfelt, so filled with poetic give and take, that the greatness of music and artistry transcended the limitations of both hall and piano.

What was true for that live performance in Field Hall is also true for performances reproduced on audio systems: A system can be less than technically perfect yet still transmit with eloquence every iota of care and feeling that artists and engineers put into recordings. Perfection is not an essential component of musical truth. Inspiration is.

Lest readers think this preamble is intended to suggest some shortcoming in the component under review, the Accuphase A-300 monophonic power amplifier ($51,900/pair), let me reassure you at the outset: Time and again, the A-300, like Jeremy Denk's artistry, inspired a state of wonder. The more I listened to the A-300 monoblocks, the more I wanted to listen. In my too-busy life, every occasion for listening was an occasion indeed, a special event.

Inside
"To reduce noise is very important to sound reproduction. We've been pursuing reducing noise throughout Accuphase's 51-year history. So, after the A-250 monoblock was released in 2017, we redesigned it all over again." So spoke Takaya Inokuma, Accuphase's director of engineering, near the start of a four-person Zoom chat that also included Accuphase International Marketing Manager Kohei Nishigawa and Axiss Audio USA's new owner, Cliff Duffey.

"Before we tune a component's sound, it is very important to make the performance perfect," Inokuma said. "First, we focus on the performance—on noise, speaker driving ability, and so on—and adjust as necessary. After all that is complete, we start to tune the sound to our ideal. We don't listen to amplifiers from other manufacturers; instead, we listen to the latest Accuphase model so we can better it and better reproduce the dynamism, intonation, and emotion of music.

"All music is the same. It's not just sound. All music has atmosphere. There's something the performer wants to tell the audience. The challenge of audio is how to transfer those kinds of feelings to listeners. That is the most important thing.

"Ensemble is also very important. In live performance, performers try to breathe together before the first sound comes out. That inhalation is very important for an Accuphase amplifier. We try to revive that kind of atmosphere—the timing of what happens just before the sound comes out. It's not a case of which amplifier has more bass or less bass or sounds 'better'; instead it's about how to transmit the emotion, the atmosphere, and the feelings to the listeners."

Inokuma oversees all aspects of Accuphase's engineering, design, and development; Nishigawa described him as Accuphase's "Sound Master." So he was the best person to ask how the company tunes the sound of its products. First, Inokuma focuses on capacitors. "Capacitors are the most sensitive parts that influence sound quality," he said. "Changing caps is the easiest way to change and control the sound. We have a lot of capacitors in the A-300. Changing the filtering capacitor has the most effect on sound quality. We use many types of filtering capacitors, from many different companies. For example, the big capacitor in the amp is custom-made. We discuss with the manufacturer what we want to hear, and we try different capacitors with different values and sleeves until we get it right."

The A-300's output specs are impressive. The monoblock outputs 125W into 8 ohms and doubles down each time the impedance halves: 250W into 4 ohms, 500W into 2 ohms, 1000W into 1 ohm. "Its performance is extremely linear," Inokuma said. "With a speaker like the Alexia V, whose nominal impedance is 4 ohms, the first 60 or so watts is pure class-A."

Accuphase's literature describes the A-300 as a class-A amplifier—so why is class-A limited to the first 60W? I asked Stereophile Technical Editor John Atkinson to explain. "The Accuphase is what I would call a 'high-bias' class-AB amplifier. With such high power, running it in true class-A up to the clipping point into low impedances would be impractical, as the heatsinks would have to be the size of a house."

I also wrote to Duffey, who relayed the question to Inokuma and forwarded his response. "Here are our thoughts and technical approach to the question. For a push-pull output stage using a bipolar transistor as the output device, it operates as class-A up to twice the idling current flowing to the output device when the output is zero. If more than this amount of current flows through the speaker, one of the output devices, operating as a +/– pair, will turn off. Of course, current can be supplied to the outputs without any problem, and this is called class-AB amplification.

"In the case of the A-300, the idling current is applied so that the class-A range into 8 ohms is 125W. The amplifier operates as class-A up to 62.5W into 4 ohms and 31.25W into 2 ohms."

This inverse relationship between class-A power and load impedance is easily understood when you consider that current—idle current—determines an amplifier's class-A range and that power equals current squared times load impedance: Cut the impedance in half and the power is halved as well. "So, the A-300 does in fact provide 125W of class A power into 8 ohms," Duffey wrote. "Into 4 ohms, though, the amplifier's fixed amount of 'idle current' can support just 62.5W of class-A power." Inokuma's response included a table relating impedance, rated power, class-A range, and maximum power at clipping rated at 1% THD. The table showed that the clipping power easily surpasses the rated maximum output power at each load impedance, reaching 1100W into 1 ohm. How much power does a person need?

"The A-300 is equipped with a real-time watt meter that measures the actual current and voltage flowing and displays output power," Inokuma wrote. "When you have time, check how much power your speakers require at the volume you normally use."

The Accuphase A-300 monophonic power amplifier's balanced input section is fully discrete. The output stage uses 20 push-pull MOSFETs in two parallel power-amplifier modules said to have very low output impedance. A gold-plated, glass-cloth, fluorocarbon-resin printed circuit board with big, gold-plated bus bars helps lower that output impedance. So do the large, easily tightened speaker terminals, rectangular wire coils, and short, thick signal paths. The A-300's damping factor is specified as 1000 (footnote 3), sufficient to tightly control driver motion in loudspeakers. In case this isn't enough power, the A-300 has connections and switches that allow it to be bridged with a second A-300 or used in a biamped configuration.

Created to help celebrate the company's 50th anniversary year, in 2022, the A-300 is claimed to have 20% less noise than its predecessor, the A-250. Central to the amp's low noise is an amplification section that operates like an instrumentation amplifier, equalizing input impedance on the + and – sides. Equally important are "assigning a high gain (12.6×) in the signal input section" and implementation of a "double MCS+ circuit." What is a double MCS+ circuit? The website puts it this way. "By placing the voltage amplification stage in a two-parallel circuit layout, the MCS+ (Multiple Circuit Summing-up) circuit theoretically reduces the noise floor by about 30%. The A-300 comes with two MCS+ circuits in a double MCS+ circuit configuration." Another listed feature, "Balanced Remote Sensing," is said to "lower the amplifier's output impedance [via] negative feedback with signal sensing from nearby the speaker terminals," improving damping factor, total harmonic distortion, and intermodulation distortion.

In addition to its robust power supply and high-efficiency toroidal transformer, the A-300 contains two large, specially designed 100,000µF filtering capacitors. The position of both devices has changed from the A-250. The power transformer now sits farther away from the input amplifier, which helps minimize leakage flux from the transformer.

Importantly for such a powerful amplifier, protection circuits protect against excess output current, excess temperature, and short circuits. Such protections reflect longtime Accuphase company policy. "We produce high-quality products with high reliability, high performance, and safety," he said. "We try to make products that are unbreakable, with long-lasting components and very simple circuit architecture that people can use for a long, long time."

On the outside
Several features made the A-300 one of the easiest big amplifiers to install and repack to visit my music room. The large handles on its front and rear are a reviewer's dream, and the very large, easily adjusted speaker terminals make connection a cinch. The packaging is equally well thought out; it includes an inner cardboard amplifier holder with thoughtfully positioned indentations that allow for easy lifting, Styrofoam protectors labeled by position (eg, bottom front), and a removable cloth cover that is light years ahead of the slippery, tight plastic component protectors—I call them condoms—that ironically make lifting and repacking heavy equipment a disaster waiting to happen. You will not pinch your fingers as you and a helper remove this amp from its heavy cardboard packaging or when you repack it.

Equal kudos for the multi-language manual. Its easy-to-comprehend instructions and diagrams are as complete as you would expect from a 51-year-old Japanese company.

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Footnote 1: See Musiconthestrait.com.

Footnote 2: The week before, the Takács String Quartet and pianist Garrick Ohlsson opened the festival.

Footnote 3: According to Accuphase A-300's Technical White Paper, its damping factor of 1000 is "the same as the A-250, but the actual measured value is over 2000, which is 43% higher than the former model."