Moonriver The 404 Reference integrated amplifier

Following the runaway success of the Moonriver Model 404 (Standard), we decided to move a step further by improving on the already excellent design platform of the Standard 404 model. The Moonriver Model 404 Reference achieves even better performance over the Standard Model while retaining a sensible price point.

Just like the Standard Model 404, the 404 Reference amplifier will extract hidden elements and render textures from within any audio format, but it has the capability to drive any speaker on the market, despite its moderate power. Only the source, speakers and room will set the performance limit. Its culture will suit all music, as the Model 404 is, by design, set to define the faintest nuances of which tonal integrity is composed.

The power supply section has been improved to the maximum. The 404 standard uses a total of 57000 µF capacitance. The 404 Reference lifts the capacitance to a spectacular 107000 µF, of which 21000 are reserved for the preamp only.  This enormous increment expands the driving behaviour and the dynamic character and digs out more detail and low-level information. The deeper and more articulate soundstage and the vast space between instruments are contrasted by the greater authority and confidence of the bass than ever before.

The texture of each individual instrument is exposed exponentially in comparison with the standard version. A fully discrete preamp section serves to provide acute dynamic awareness, while a high output stage that is custom-optimised for bandwidth and distortion gives neutral character and transient fidelity. A careful choice of parts combines the design to avoid altering the sound, keeping it natural along the shortest possible signal path.

Furthermore, an integrated phono stage, a USB DAC, (two) preamp outputs and a tape monitor loop expand functionality to form an ideally flexible integrated amplifier.

Design & Ergonomics

We had a very clear vision when conceiving the Model 404 Reference amplifier: classic design with a modern touch; high-quality materials such as oversized aluminium controls, solid walnut cheeks, a sturdy chassis and an ergonomic user interface.

This design prioritises functionality over mere aesthetics, avoiding complicated displays and single multi-function knobs.

The heart of the Model 404 is pure and minimal, but the interface is user-oriented and easy to operate for anyone in seconds, with no need to resort to the user manual. Four knobs and three switches give direct access to any function.

Modular Architecture

The Moonriver 404 Reference amplifier is modular like its brother; it can accommodate an MM or MM/MC phono stage and a USB asynchronous DAC.  Fitting these modules is simple and can take place at any time, on or after purchase.  The USB DAC may also be upgraded with a newer version to meet future needs and technologies.

Balance Control

You may find this feature to be vanishingly scarce in audiophile products as a result of today’s ‘minimalist’ design mentality and the various myths accompanying it. However, balance control addresses a common problem: speakers that are positioned in asymmetry, in a non-balanced room environment. It therefore provides the simplest tweak towards achieving a proper soundstage.

Living rooms and house furniture are meant to serve everyday life and may not be positioned in an ideal listening spot, evenly distanced from each speaker to form an equilateral triangle. One speaker is often placed nearer room boundaries than the other, having various frequencies boosted in a more or less predictable pattern. More often than not, balance control is incredibly useful, as it drastically helps overcome volume-level unevenness and, in some cases, even reclaims the stereo effect and the resulting focused sound stage.

It is to be expected; the way the balance control is implemented on the Moonriver 404 Reference amplifier – in parallel – will not degrade or affect the signal in any way that is determinable.

Discovering the layout

Model 404 Reference, like the standard model, incorporates no less than 5 separate power supplies, each featuring overload protection. The power amplifier specifically runs in a dual-mono configuration, beginning with separate windings on the toroidal transformer.

WBT nextgen™ speaker terminals ensure the massive flow of current from the amplifier’s output stage is able to drive even “difficult to drive” speakers.

Signal switches are implemented via relays, while volume attenuation is trusted to the legendary blue ALPS pot.

A soft start circuit based on a 30A relay ensures that even the on/off switch is thought out to work with virtually no burden or wear for decades.

The 404 Reference chassis reduces unwanted resonant vibrations even further with absorbent materials and better integral mechanical support.

Components are carefully selected for both suitability and reliability. We make no use of surface mount in analogue circuits, despite the fact that through-hole production costs more and requires advanced space management & layout strategies.

Each element utilised has to be of proven stability and sustained higher performance – proficient implementation provided – before making it into our analogue paths.

As for the sound, we are not to say whether Model 404 Reference is virtually transparent or inherently forgiving. Voicing it to appreciate the playlist and respect the user at all times has been the sum of all of our effort: a sincere effort to achieve effortlessness.

The Importance of Tape Monitor Loop

Most of today’s manufacturers probably reject the idea of their product featuring a tape loop. Moonriver Audio has concluded that the tape monitor loop is essential. Not only does it add the option of monitoring the difference between recorded and source material in real-time, but it also, and most importantly, makes it possible to insert into the chain – at will – a digital or analogue room correction processor, a buffer, a noise reduction system or any other line device available to improve the sound of a connected source.

Stereo/Mono Switch

With the pristine era of analogue recording long gone, features like the stereo/mono switch have gradually become obsolete. Who wants to go back to one when they have two channels? “Less is more” and “more is better”. Well…

With the resurgence and interest in vinyl, whether it's the current rage, fashion or a real movement, countless monaural pressings emerge out there, often along with their digital… image.

Too many of them, among others waiting to be rediscovered, have currently become collectors’ items, 78 rpm direct-cut gems being no exception. This is not unreasonable, as what happened between, say, the 30s and the 80s in terms of both musical interpretation and recording technique is by many considered to be “most of the music” – this sentence doing perhaps no justice to stunning actual developments in creation and reproduction.

The stereo/mono switch allows you to enjoy significant recording milestones as they were originally intended, either in genuine mono or 2-channel, eliminating artificial phase discrepancies caused by a mandatory stereo mode.

So, ‘less’ may well be ‘more’, but ‘better’ is to have a choice.

Optional Phono Stage

Model 404 Reference comes with two options in the phono stage department; one is MM only, and the other is MM/MC selectable. Both follow the exact quality principles that Model 404 Reference is built on. Quality components and massive power supplies are also employed here to efficiently accommodate very low noise, high-performance op-amps.

The gain in the MM/MC phono can be adjusted simply by changing the dip switch position. The MC input load can be set also by replacing the original 100 Ohm input resistor with a higher or lower value. No soldering is required.

Optional USB DAC

What was desired for our USB DAC module was not to make an addition rather than an omission; instead, we had to be confident of substantially raising the true value and functionality of Model 404.

A new USB DAC is under development for the Moonriver 404 Standard and Reference.

Technical Specifications

• Inputs: 5 (line 1 and 4 optionally occupied by phono stage and USB DAC, respectively, 1 x tape loop)
• Outputs: 2 x preamp out, 1 x rec out
• Max output power: 50 W / channel into 8 Ω
• Frequency response: 10 Hz to 50 kHz
• Total harmonic distortion: 0.05%
• Signal-to-noise ratio: 85 dB (line)
• Idle Consumption: 22 Watts
• Dimensions (mm): 430 (W) x 390 (D) x 135 (H)
• Weight: 13 kg