Moonriver 404 Reference integrated amplifier

Joy. It's all about the joy.

Joy manifests during those moments when the critical mind suspends, the lens clears, and only union between you and your experience exists. When joy arises, time stands still, all sense of separation vanishes, and only wonder remains.

Many of us live for those moments. Moments of understanding that transcend verbiage and mental chatter and affirm what is real and eternal about the human condition.

Music offers the opportunity to live in joy for more than a fleeting second. The sense of oneness can last for an entire live performance or recording. Suddenly, all distance between you, the artist, and their creation vanishes. During those transcendent moments, the acoustics of the hall and the quality of the recording or sound system mean naught. All that matters is the oneness, the sense that what you are experiencing is true and eternal.


It is in oneness that many of us experience pure joy. I'll never forget the morning when my dear friend Béla, his late sister Emilye, and her husband Lou visited my house in Oakland. I cued up a CD of Renaud Capuçon performing Brahms's Violin Concerto (Erato 2653). I don't know what was happening with my system that morning. All I know is that the combination of Pass Labs XA200.5 monoblocks, dCS Puccini CD/SACD player and Scarlatti Clock, and Wilson Audio Sasha speakers had us in rapt attention for 40 minutes. We were unable to utter a word as we were enveloped by beauty. When the music ended, we all uttered a collective sigh, hugged each other, and floated out of the room.

After those transcendent experiences, the critical mind may reassert itself. With Capuçon, I observed that his priority was beauty of tone rather than emotional expression. But during those moments of pure joy, we who love Keith Jarrett or Glenn Gould forget about all their noises and grunts and eccentricities. Who cares that Toscanini is singing along with his artists? We're swept away by the emotions he draws from them. We forget that Diana Krall sometimes seems to mumble and gesture her way through a song, as though carefully parsing out her life force. (John Atkinson is going to want my head for that one.) Or that Janis Joplin is ripping her vocal cords apart as she sings out her pain. Or that Callas's voice is on the edge of falling apart, and Joan Sutherland is reserving clear enunciation for another lifetime. Instead, their artistic brilliance and their imperfections transport us to another plane.


Thoughts of such experiences lead me to the subject of this review: the Moonriver Audio Model 404 Reference ($4995) integrated amplifier. The Moonriver 404 is a relatively low-powered class-AB design rated at 50Wpc into 8 ohms and 70Wpc into 4 ohms. Designed and manufactured in Sweden, it's the least expensive and least powerful integrated amplifier I've ever had in my current system. The 404 integrated amp is a modular design that comes in two versions: a basic unit ($3495) and a Reference unit ($4995) containing upgraded parts, the latter of which is new. There are options for phono preamp ($450 for MM phono, $550 for MM/MC phono), and a USB DAC option originally based on an AKM chip (footnote 1). Apart from the asynchronous USB DAC input and speaker outputs, all input and output jacks are single-ended.

Like Capuçon, Jarrett, Gould, Krall, Callas, and every other artist or component you can mention, the Moonriver 404 Reference integrated amplifier has its limitations. Yet Moonriver's chief engineer and founder, George Polychronidis, was so confident of its quality/price ratio that he encouraged me to compare its optional USB DAC to my reference D/A processors, the dCS Rossini/Clock combo ($31,500 plus lots of cables) and the HoloAudio May (Level 3) DAC ($4998). He also encouraged me to evaluate the quality of the 404 Reference's preamp stage by bypassing its amplifier section and connecting its preamp outs to my all-balanced D'Agostino Progression monoblocks ($38,000/ pair). Through all these configurations, I kept returning to one basic fact: No matter what I played through the Moonriver 404 Reference, it sounded right and consistently brought me joy.

There's such a lot of world to see
You may not have heard of Moonriver Audio (footnote 2). Polychronidis, 47, founded the company in 2015 and launched the 404 integrated amplifier in May 2019 at the High End Munich show. In only 18 months, the company's distribution network expanded into 17 countries.


Like many high-end audio designers, Polychronidis began fiddling with electronics and designing circuits as a teenager. Nine years ago, after he had begun to develop what would become Moonriver, he relocated from his native Greece to Sweden and worked as a service technician in a hi-fi shop. The knowledge he acquired in the field, along with his background in design, photography, and user interface and industrial design, contributed to the Moonriver 404.

Polychronidis designed everything in the Moonriver 404 except for the core of its optional USB DAC, which was based on an AKM chip. I say "was" because after I had spent a long time evaluating the DAC and was prepared to sing its praises, the AKM factory in Japan went up in flames and, with it, this version of the Moonriver's DAC. (The remaining supply of DAC chips has been bought up already, and it could be a year or more before more chips are available.) As I write this, Polychronidis is contemplating designing a new DAC from scratch—possibly based on an ESS Sabre chip. If he does, the new DAC will handle PCM, DSD, and perhaps MQA.

Both Moonriver's basic and Reference 404 integrateds are hand-soldered and assembled in Sweden. They undergo a minimum of two days of factory burn-in to ensure reliability. Another 50 hours of consumer burn-in is recommended before they're at their best.

Polychronidis shared more about the 404's build-out. "The output stage of the amplifier is not discrete and is not formed by two bipolar transistors," Polychronidis said toward the start of an internet-based chat. "It's actually an integrated circuit based on an LM3886 chip that was originally designed by National Semiconductors and is currently produced by Texas Instruments. It has also been used by Simaudio Moon and Jeff Rowland and is limited to an output of approximately 50Wpc into 8 ohms and 70Wpc into 4 ohms. Actually, it is even less than 50W without measurable distortion. What's important, however, is not the amount of watts but how it sounds, how it performs, and how it drives the speaker." Polychronidis's statement

challenges the common assertion that the power rating is a critical factor in defining an amp's ability to drive a speaker. So, this raised more questions. Top of my mind was the recently reviewed Yamaha A-S3200 integrated amplifier ($7499.95), which is specified to output 100Wpc into 8 ohms and 150Wpc into 4 ohms. Were the Yamaha's limitations in reproducing and controlling bass adequately in my reference Wilson Alexia 2 loudspeakers due to its power rating, or were other factors at play?


"There is a big misunderstanding about power," Polychronidis continued. "Power is always measured by a constant, stable frequency in the lab—a single continuous sinewave without alterations of the level in time—when the major question is how much power an amplifier can deliver instantly, not constantly. Measuring with a stable frequency doesn't tell you much about how an amplifier will handle musical dynamics, follow precisely music's chaotic and complex transients, and drive the speaker. It's a number that doesn't apply in real life. Because it is common for an amplifier of hundreds of watts to be incapable of driving a difficult speaker load, you have to listen to see if it will drive the speaker."

Polychronidis acknowledged that because many speakers are low in sensitivity or present challenging loads, most people are insecure about investing in an amplifier that outputs less than 100Wpc into 8 ohms. "Some amplifiers don't drive well because of their preamp design, power supply design, and power supply placement," he continued. "The power supply should be as close to the output stage as possible in order to deliver instant power to the speaker. As a service technician, I've worked on hundreds of amplifiers with dozens of speakers. I have a sense of what can and can't drive well—let me remind you of the legendary NAD 3020 (footnote 3) that changed the perception about hi-fi forever when it came out in 1978—and I have some particular tests I conduct to be sure."

According to Polychronidis, the power supplies for both the amp and preamp sections are at the heart of the unit. Although the basic 404 and the 404 Reference have the same power output rating, the 404 Reference's power supplies have double the capacitance of the basic unit. This improvement, he claims, enables the Reference to better handle incoming signals and deliver more detail, low-level information, instrumental texture, and dynamics. The Reference model, he asserts, also produces a deeper and more articulate soundstage and better controlled, more authoritative bass. It has WBT nextgenTM speaker terminals, and the chassis includes additional vibration-absorbing materials and is said to provide better support.


Polychronidis believes that the most significant factors in amplifier design are voicing and timing, not the price of its components or the complexity of its design. "When you design something that's affordable, you have to choose between better performance/sound or better specs. It's one or the other, except when you design cost-no-object; in that case, you don't have to choose. The Moonriver Reference 404 may not be the quietest-measuring amplifier on the market, but it performs better than those with superior specs because it was designed for optimal performance/sound rather than specs.

"The secret to this integrated amplifier lies in its preamp," Polychronidis said. "Everything is about timing in music reproduction, and the preamp is the conductor that gives the amplifier the timing and tempo. The preamp decides when the note starts, how it will get louder, and how it will fade out. It kicks the power amp and produces big dynamics as well as microdynamics. A good preamp can elevate an amplifier's driving capability to the maximum level. In my opinion, it is the most important part of any system after the speakers.

"Class-A amplifiers can reveal even small microdynamic detail that a normal class-AB amplifier can't, but so can a good preamplifier. Our preamp is a discrete design with bipolar transistors; it is not based on an integrated circuit because, in a preamp, ICs lack transparency and drive. ICs don't negatively affect transparency in a power amplifier. If you could achieve the same transparency and drive in a preamp with an integrated circuit, I would use it."

Polychronidis's background as a technician informed his design choices. The 404's front panel has a single on/off power button that activates a soft-start circuit. He decided to eliminate the rear-panel power switch and standby function from the 404. "With standby, you have an active circuit inside the amp that runs power 24/7 and will break at some point," he said. "A simple power switch with soft-start increases reliability. I know this isn't very good for some people, but I want to build something that will last for many decades or even a lifetime."

For more longevity, he made the 404 Reference easily serviceable: It has a removable bottom that gives access to both sides. "When you have through-hole components rather than surface-mount components, and you have access to both sides of the PCB [printed circuit board], you can service the amplifier very easily," he said. "The chip I use has a very short signal path and doesn't have crosstalk or interference between the discrete transistors that are usually used in a power amplifier. It also includes essential protection circuits that guard against damage from overheating, short circuits, and voltage spikes. This creates the kind of transparency that only single-ended amplifiers have.

Footnote 1: The recent fire at the AKM factory destroyed inventory and has impacted a number of companies, including Moonriver, that use their DACs in production.

Footnote 2: Yes, the company name was inspired by the Johnny Mercer/Henry Mancini song "Moon River."

Footnote 3: The diminutive NAD 3020 integrated amplifier output 20Wpc into 8 ohms, 38Wpc into 4 ohms, and 72Wpc into 2 ohms.

Moonriver Audio
North American distribution: On a Higher Note
P.O. Box 698
San Juan Capistrano, CA 92693
(949) 544-1990

MatthewT's picture

That is a very attractive piece of gear, a bit of vintage Sansui.

michelesurdi's picture

midfi is sad

Anton's picture

From JVS' conclusion: "...that makes it difficult for me to proclaim the Moonriver 404 Reference integrated amplifier a new benchmark for sonic excellence in an integrated costing $5000 or less. But I'm tempted to anyway, because it does justice to complex and demanding recordings and it sounds tonally spot on, well balanced, clear, and musical.

For some of you, the Moonriver 404 integrated may be the longed-for component, just waitin' round the bend, that transports you to audio nirvana. With dutiful attention to setup and component matching, the Moonriver Model 404 integrated amplifier can deliver Class A sound at a Class B price, and joyful listening."

Mid Fi?

How so?

Jack L's picture


Too true!

Like it or not, this is human weakness !

Jack L

solarboy297's picture

JVS...The first three paragraphs of this article speak to the essence of the experience better than any description I've ever read. I've shown it to several people who have asked "What is it with sitting in the dark listening to music?" Thank you so much for putting into words what I have been unable to express but have felt strongly over my lifetime of listening.

Jason Victor Serinus's picture

Thank you.


CJThiel's picture

my big takeaway from those first four paragraphs is that I shouldn't quit my day job

Long-time listener's picture

Interesting comments about Toscanini singing along with his orchestra. His intense shouts of encouragement can be heard in his 1951 Verdi Requiem recording (in the Dies Irae), and he hums along briefly in the final section of his last studio recording of Strauss' Death and Transfiguration.

Long-time listener's picture

So, it doesn't meet its claimed power ratings and it doesn't measure that well in some respects. But it sounds WONderful, blissfully so. That could well be. I might like it myself. But at the same time, I'm skeptical of components that don't measure well, and probably won't buy them, insofar as my budget allows. I trust components that are well designed and meet their power requirements, have low noise and distortion, and nice square waves. Measurements, for me, tend to confirm, or disconfirm, what a reviewer is saying, and certain aspects of measured performance, for me, correlate importantly with what I like. (I like 21 bits of resolution a lot more than 18, for example.) But all this also points up a fact which JVS and all of us need to face, which is that enjoyment of music isn't necessarily correlated, ever, with sound quality. I enjoyed listening to California Dreaming or Cast Your Fate to the Wind as a kid on transistor radio in the '60s as much as I now enjoy Strauss' Four Last Songs on my fine stereo or headphones. Maybe knowing that the amplifier wasn't that expensive or powerful freed our reviewer from worrying about critical listening so much and freed him to simply enjoy the music. Or maybe it does what poorly measuring tube amps do -- transport us back to the days of distorted sound in our childhood when we really enjoyed music.

Jack L's picture

.....quoted Moon River founder.


Agreed to what you state: "it doesn't meet its claimed power ratings and it doesn't measure that well in some respects. "

Stereophile measured the amp clipped at 39.5W@8ohm load & its lowest distortion 0.016% at 3.5Wrms output power.

However good it may sound, this amp was measured far inferior to what the manufacturer claimed.

I can only suggest that Sterophile lab measurement used a simulated loudspeaker load vs this Moon River amp was measured with a 8ohm resistance dummy load.

Surely simulated loudspeaker load reflected the more realistic performance of the amp.

Jack L

Jack L's picture

........ with sound quality." quoted Long-time listener.

Yea, "One day when we were young"! I would call it 'evolution'.

Decades back, when we were junior school kids, AM radio was our only entertainment centre to enjoy free music off the air at home. How nice!

Todate, science evolution has brought us hi-tech audio which demands "critical listening" to justify the high costs involved.

That said, many musicians, & music industry personnel still enjoy bigtime music from Lo-Fi audio. Apparently, they don't think they need hi-end audio at all !

My elder son is a live example. He does not own any hifi & enjoys music-to-go from his iPhone earbuds & from labtop mini speakers at home. Mind you, he earned his first class honour of Classical Piano in theory & practice from our city's Royal Conservatory of Music when he was only 18 before entering university. He is still a perfect pitch !!

Listening is believing

Jack L

Charles E Flynn's picture

Some companies have to learn the hard way that if something is to be shipped, it must be able to be tossed without incurring damage.

It is regrettable that there seems to be no obvious way to buy Shockwatch indicators in small quantities. Someone should choose to fix this.

USM Haller uses Shockwatch indicators on at least some of its furniture shipments. I do not know whether Herman Miller does, but they can tell just how many feet a crate was dropped onto a loading dock, by lookng at the damage. I once described damage to a chair to a Herman Miller support rep, and he said, "That requires a minimum drop of fifteen feet to a hard surface".

Shockwatch® Indicators - 50G

Jack L's picture

......without incurring damage." quoted C. Flynn.

Ideally it SHOULD be so. But this is not an ideal world, my friend.

Ask any electric appliance store managers if any damage on delivery of fridges or stoves, let alone small household items, you will be surprised so much claims of transit damages from customers daily !!

If you take a look inside the Moonriver deceiver, you would be surprised to see how vulnerable is the entire component layout to transit damage.

The most bulky & heaviest item: the toroidal power transformer is mounted on the SAME circuit board of the entire amp !!!!

The flimsy PCB is NOT designed to hold such heavy load !! The power transformer should have been installed directly onto to the rigid baseplate of the receiever. Period. Totally separated from the main PCB !!!

It is therefore the receiver makers design gross error in the first place. Damage could be done even the courier dropped off the box at the doorway not so gently for the receipient to sign off.

It is the physical layout design error to warrant for undue transit damage !!

Jack L

Ortofan's picture

... a few hundred dollars to buy a basic oscilloscope so that he (and we) could know if a relatively low-powered amplifier, such as this 404, is ever being driven into peak clipping when driving his Wilson speakers?

Also, should the simulated loudspeaker load, that JA1 uses for his tests, perhaps be revised to more closely emulate the impedance of a speaker such as the Wilson Alexia?
Up through the midrange, the impedance of the existing simulated load never drops below 6Ω, while the impedance of the Alexia approaches 2Ω at several points.

Charles E Flynn's picture

wellington12's picture


I've listened to the Moonriver and agree with you,
it is a lovely and powerful amplifier. As a result, I am considering purchasing the amp. However, since most of my
listening is via streamer. I am wondering if using
a Roon Nucleus, as the streamer, and connecting the Roon
via a USB cable to the onboard dac is a good idea? Or
would suggest a different approach. Thanks