Accuphase A-300 monoblock power amplifier

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.

"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.

Footnote 1: See

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."

Accuphase Laboratory Inc.
2-14-10 Shin-ishikawa, Aobaku
Yokohama 225-8508
(615) 419-1522

georgehifi's picture

How nice it is to see real audio amplifier measurements/pics/graphs that don't need to use "cloaking test gear devices" to hide the faults that other classes need to look respectable, and have wattage "load tests" that go well below 4ohm also

Cheers George

Gunhed67's picture

record still stuck , I see

remlab's picture


jellyfish's picture

that a component that costs $50,000, has the rear panel look of a $300 receiver. this is all too common with so called high end gear. cheapo gauge black anodized steel plate, t-shirt type silkscreening, visible fasteners. this happens on even cost no object components. and the reviewers are fine with it because mention is not made. hahahahahaha

Auditor's picture

Accuphase is expensive, but at least you know you're buying something that's well engineered and well built.

You can't say so much about some of the other gear that's reviewed in this magazine.

Ortofan's picture

... the output power from the Accuphase A-300 rarely exceeded 62.5W.

Yet, in a previous review he claimed that a D'Agostino Progression Mono amp excelled in dynamic contrast in comparison with a Pass Labs XA200.8's because the D'Agostino amp was capable of a 1,000W output versus only 400W for the Pass Labs amp.

JohnnyThunder2.0's picture

semi fact checker, explain to us what difference this makes.

georgehifi's picture

"Accuphase is expensive, but at least you know you're buying something that's well engineered and well built."

For $52kusd!!!!, not quite as good as you think even though it looks impressive.
Instead of just 2 massive "can" type caps, I would have been far more impressed to see 2 banks of 24 or so smaller ones to equal the same value, this improves the ESR of the power supply to a much better figure and therefore the bass slam and dynamic speed performance.

Cheers George

JohnnyThunder2.0's picture

you know so much more about audio engineering than the heads of Accuphase! I mean they would be so grateful because your "army of smaller caps" idea obviously eluded them. Maybe Accuphase engineered this amp exactly like they wanted to and liked the way it sounded without your suggestions. Based on how JVS described the sound of Accuphase vs. the D'agostino, I'd take the Accuphase in a heartbeat.

georgehifi's picture

You should'nt be naive about it, read up about "Low ESR" in solid state power supplies.
And how capacitors effect this greatly.

Curiousland's picture

If arrays of smaller caps can do better, why Accuphase special made those huge ones assuming smaller ones also cost less?

I did measured the runtime (after 30 minutes, at low output level around 65-70dB to a pair of Harbeth 40.3 XD) temperatures on the left side middle spot of their heatsinks of a pair of A-300 (earlier production units than this L2Y188), found they are around 96F and 102F, not even, but much lower than 120F. Runtime/idle wattage of these 2 amps are not even also, so they are going back to Accuphase Lab for inspection/repair.

Always curious

georgehifi's picture

Please that's being naive, they don't make their own caps, they are re-badged from a major cap maker, and far easier for production to have in a production amp, than 50 odd smaller ones and more pcb's and labor that has to go with them.
Like these 2 story, double stack ones in this amp,

And Gryphon and other amps use the same philosophy

Curiousland's picture

Naive?? No one said special made means in house. For a system house like Accuphase, unlikely. Given the limited quantity and high price per unit, hard to imagine production/assembly cost be a major factor for consideration by any stretch. We don't know if there are other factors such as error margin of different sizes of caps, etc.

Note nearly all Accuphase amps of recent decades, class A or AB, all using 2 large caps for some reasons. So you can be their new Chief design/production engineer to bring in revolution.

bhkat's picture

I love the look and it measures and sounds great. Nice.

Auditor's picture

Accuphase is not a cost-no-object ultra-hifi manufacturer. Their market segment is not the One Percent, it's well-to-do audiophiles who are prepared to invest a good chunk of money in their stereo system. When they design a product, Accuphase certainly have to make several engineering decisions based on their cost. Perhaps they could have chosen different capacitors, but that might have taken the amplifier beyond the maximum price they were aiming for. I trust they strive to maximize the sonic value they can get, given the cost and pricing decisions they have to make.

georgehifi's picture

"Perhaps they could have chosen different capacitors, but that might have taken the amplifier beyond the maximum price they were aiming for."

Auditor is correct, everything is built to a price, including this amp as good as it is, others here that think that it's the best they can do, are living in a dreamworld and being very naive.

Cheers George

JohnnyThunder2.0's picture

with the design philosophy of this amp. I know full well that Gryphon uses a lot of caps and Luxman uses two more than the Accuphase. I have a circa 1982 Luxman integrated - 100wpc class AB - and it has 2 large caps. So what are your credentials as an audio engineer/cirucit designer? Or do you just like to pick apart things that don't adhere to your Taliban-like rigid view of what constitutes good equipment? Or are you a bargain hunter like Ortofan ? Do you read ASR and get goosebumps when the science nerds measure their music instead of listening to it and feeling it ? Sheesh. You guys are really something else. I'm not sure what psychological classification you fall into...

georgehifi's picture

I've done the A/B's between what's being discussed here.
Same amp 2 x massive HQ caps vs many smaller HQ caps

Those with any good tech knowledge of power supply "ESR" know (speed of stored capacitance release when called for) "equivalent series resistance".
In "bass control and speed of dynamic swing", the many smaller ones same combined value win out every time, due to their "lower combined ESR" than the slower release of the 2 x massive size caps.

Just read and educate yourselves about "capacitor ESR" if you can, instead of just foaming at the mouth without any posted technical knowledge to back it?

Cheers George

JohnnyThunder2.0's picture

I'm not looking for brawn. I'm looking for grace. I don't need an amp for massive home theater like 100 db outbursts. I'm not trying replicate at home the sound levels of the Ramones at CBGB's in 1976/7. What you are mandating is not a requirement but a question of design philosophies and as we all know there isn't only one.

Gunhed67's picture

“ yawn”

georgehifi's picture

"I'm not looking for brawn. I'm looking for grace. I don't need an amp for massive home theater like 100 db outbursts."

Now your trying to twist things, lowering the ESR in a powersupply does not mean loosing grace or going for home theater/disco crap sound.
It's just a small part of getting the "very best" out of everything in poweramp design even in a 50w poweramp, having low ESR has the same effect in them as it would do in these beasts.

But there are those here seem to think that these Accuphase mono's are the end game, they're not.

JohnnyThunder2.0's picture

you aren't going to change minds. I dont want my mind changed. I'm not buying an Accuphase. The review is written. It's JVS's opinion. If you don't agree based on some empirical data that seems corrupt feel free to write to Accuphase. Other than that, no one really gives an s about what you think. What I object to you is you and others lecturing us about what we SHOULD be listening to. A dictatorship w lots of caps and low price tag (because I doubt you own a Gryphon. Im also sure that by the time the next review of a high priced Gryphon integrated appears, Ortofan or you will point out that the Parasound measures better at 100th the cost.

georgehifi's picture

Whatever, like I said "can't see the forest for the trees".

JohnnyThunder2.0's picture

about the caps still makes no sense in the design of this amp. Look at the photo of it. more caps or smaller transformer? smaller heat sinks. this amp looks put together w surgical precision ! more caps is more labor to match them all. more things to go wrong. silly really. it's a thing of stunning beauty. why criticize it at all when YOU HAVENT LISTENED TO IT. You're just reacting to the observations of a different human in the Pacific Northwest.

georgehifi's picture

Like I said, "can't see the forest for the trees"!

David Harper's picture

about an imaginary issue. They're only audio amplifiers guys. It's not rocket science. These amps (minus the placebo effect) will "sound" the same.

hiendmmoe's picture

Every time I start reading these comments the same negativity is always followed by the usual suspects.
Why do such people feel a need to dissect every component that they will never be able to afford and feel a need shed their negativity upon others?
The only expertise they seem to have is in the area of jealousy, negativity and the need to share it with others every month!

teched58's picture

Hey, hiendmomo, when you complain about people making the same old comments, you must be talking about yourself and the late johnnythunders.

Can't you shills for expensive equipment come up with a better insult than your go-to of "oooh, you're just jealous you can't afford it"?

When someone says this, they are actually voicing their own economic insecurity.

I think it's more the case that most of us with $50k would prefer to spend it on something that delivers a superior price-value proposition. That doesn't mean this particular amp isn't a good purchase for those who want it. It just means it's not for all of us.

Glotz's picture

Make your point, lose the judgmental negativity.

georgehifi's picture

Because of price/value, and dreamers and their followers (shills maybe) that post up that it's the end game for amp design. (it's not)

Cheers George

Auditor's picture

Well, it sure is amusing to watch grown men having a fistfight over capacitors.

georgehifi's picture

"Amusing to watch grown men having a fistfight over capacitors"

To quote you Auditor: "Accuphase is NOT a cost-no-object ultra-hifi manufacturer."
But other uneducated ones here think they are.
And it shows that Accuphase didn't go the extra mile by using those 2 x massive far (slower dynamic release caps into low impedances) that have higher esr, compared to same value of many good much faster low esr smaller ones.

Cheers George

Glotz's picture

result in lower ESR, and sonically, can more quickly adapt to fast transients with lower stress (if well-implemented). It's an expensive consideration for any mfg, obviously.

Glotz's picture

Those things are friggin' HUGE! That's a ton of stored energy.

ok's picture

..BIG capacitors look like:

georgehifi's picture

"Those things are friggin' HUGE! That's a ton of stored energy."

Granted that is a massive amount of stored energy, but it comes down to how fast it can be released instantly to the output stage ("flow rate" for want of a better word), to get the best dynamic range/tightest bass especially into low impedances bass speakers.

This is from an article on stored capacitance and it's dynamic release.

Cheers George

Jason Victor Serinus's picture

That is the bottom line.


David Harper's picture

It must be because it costs so much. We all know that price determines sound quality. Especially when it comes to amplifiers. And wires. And anything else that we can imagine. Which includes pretty much everything in "high end" audio. The key to understanding this is "imagine".

volvic's picture

Nothing Accuphase makes has ever disappointed.

skinzy's picture

Nice review Jason. I am considering this amp for my Alexx V's. I know your reference amps are the Momentum M400 MxV. Which of these amps would be the best match. Thanks

Jason Victor Serinus's picture

I've done my best to describe their differences. They're both superb amplifiers. It's a matter of preference and system synergy (which includes room interaction). This is something no reviewer can predict.

ChrisS's picture

...eyes, stop reading.

These aren't the amps you are looking for.

Go back to the 99cent store.

All will be well.

Jason Victor Serinus's picture

Someday, Chris, we must meet. Until then, long may you post.


ChrisS's picture

Meanwhile, keep up the great reviews!

The comment section will always be rife with "material"...

georgehifi's picture

Yep at nearly all our A/Bing listening sessions, a philomath will keep the romantics inline with measurement/specs etc, and the romantics will supply the philomaths with whatever it is they're using to sway them.

Cheers George