Shooting for the: Moon 681 Network Player and 641 Integrated Amplifier from Simaudio REVIEW


This is a review written by Chris Baillie May 2024.

An inside perspective

Launched towards the end of last year, The Moon North Collection from Simaudio represents a significant departure from the Canadian brand’s previous designs. I had the pleasure of hosting the Moon North 791 Network Player/Analogue Preamp and 761 Power Amp last November as part of a review for another publication. These components made a profound impression on me and are greatly missed. The Moon 681 Network Player and 641 integrated amplifier, which I am reviewing here, although smaller and slightly lower spec, follows a similar design philosophy, and the combination retails for a not inconsiderable £7000 less at £23,000.

The Moon 641, priced at £11,000, effectively replaces both the Moon 600i v2 and 700i v2. John Carroll from the company’s UK distributor, Renaissance Audio, told me that the Moon 641 outperforms both by a considerable margin, apart from ultimate power in the case of the 700i v2. Simaudio has also discontinued both the 680D and 780D v2 Network Player DACs. The company does not say this as much, but perhaps one could say that the Moon 681, priced at £12,000.00, replaces both, with the Moon 791 overlapping the 780D v2 whilst adding a full analogue preamp. The volume control of the 791 can be defeated, meaning users could hypothetically use the model as a Network Player/DAC only, although it would seem a shame to waste such a fine preamp.

As the owner of a Moon 780D and Moon 600i, I am in a good position to assess the performance of these newer models from the North Collection and help readers understand how they differ from equivalent models from the previous generation of components from the Moon brand.

Luxurious Design and Spec

I will get this part out of the way first. A high-quality integrated amplifier will, all things being equal, sound better without features such as a headphone socket, digital inputs, tone controls and switched speaker outputs, so the Moon 641 has none of these. I find it hard to read reviews that criticise this type of amplifier for not having such features when its sole purpose is to sound as good as possible at its price point. Similarly, almost all users with a turntable able to do justice to this level of amplifier will use their preferred phono stage, so the 641 doesn’t have one of those either.

Now that we’ve got that out of the way, I will describe this 125w Class A/B amplifier as well specified. Like every Moon Amplifier, this is a balanced design. The output of 125w per channel into eight ohms doubles when faced with a four-ohm load, a sign of a well-specified transformer and power supply. A highlight of the
previous generation 600i and 700i amplifiers was their volume control circuits, which were operated by satisfyingly large control knobs and offered particularly fine levels of graduation. Unlike many amplifiers I have owned and reviewed, the sound of Moon amplifiers is remarkably consistent across the volume range. The 641 builds on these qualities, albeit with a new set of graduations, which Simaudio calls M-VOL3. This volume control operates in 1db steps up to level 20 and 0.5db steps up to maximum level 80, which is typical in Moon amplifiers; I imagine this may confuse Spinal Tap’s guitarist.

Simaudio describes the integrated 641 amplifier as a preamplifier and dual mono amplifiers in a single box. The design is said to have zero global feedback, and in common with all the amplifiers in the North Collection, it contains what the company calls MDCA circuitry—MOON Distortion-Cancelling-Amplifier. This circuit replaces the feedback circuitry found in previous models with a proprietary audio comparator. This circuit compares input and output signals and creates a correction signal to eliminate noise and distortion.

Anyone familiar with Simadio components will have found that they sound best after being powered up for a few days. As a 600i and 780D owner, I concur that listening to music immediately after returning from a holiday can be a disheartening experience. Simaudio claims that a side benefit of the MDCA technology is that this is no longer such an issue. I will say that although this combo sounded great within an hour or so after setup, it continued to improve over five or so days in my system. I will add that my Townshend connecting cables do not like to be moved around too much, which, during the swap from my previous review kit, very much were, so this could have contributed to what I experienced. Each of the 641’s five inputs, 1 XLR and 4 RCA, is configurable and includes home-theatre bypass options.

A bright and clear 4.3” LCD display replaces the red LEDs of the previous generation of components on both the 641 and the 681. Being a full Network Player, the 681’s display shows high-resolution, full-colour artwork of any track streamed locally or via a streaming service over MiND2. Existing Moon users will be familiar with ‘Simlink’, which, for the North Series, has been replaced by Moonlink. Moonlink allows full communication between the two products, meaning the 641 gets an internet feed for update purposes. If you partner the 641 with DAC for the North Series, you will want to take advantage of Moonlink so the excellent
BRM-1 and the Moon MiND2 App can seamlessly control both components.

The BRM-1 is the finest remote unit I have had the pleasure of using. It features a full rotary volume control, which works in a similar fashion to the Moon North amplifier it is controlling. It includes a very clear display, which becomes intuitive after a few minutes of acclimatisation. This remote works over Bluetooth, which gives it a wide operating range. If, like me, you happen to have an older Moon remote in the house, many of the features of these new components can be operated by it, so obviously, there’s an IR receiver in them.

Every Simaudio component I have experienced has been built to a very high standard. My 600i and 780D are no exception, which is part of the reason I purchased them. Here, the bar has been raised again. Of particular note is the new heatsink design, feet which offer superior mechanical isolation, and smoother edges to the casing.

Components within the North Collection range are only available in the two-tone finish, which you can see in the photos. Personally, I have always felt this finish to be the natural choice. The Moon 681 has a comprehensive array of digital inputs, including a pair of optical, a pair of RCA SPDIF, an AES, a USB, Ethernet, and, rather impressively, an ARC HDMI input. The latter is a great idea, in my opinion, as it can save customers a lot of hassle if they want to hook up a TV or streaming box. There is a USB input for connecting an HDD or USB stick, but as the manual explains, this is not compatible with every type of device. As with the 791 I reviewed last year, I had no success with either of the ‘sticks’ I had in my draw. Others may be lucky, but since the manual explains that this is not the best path to high-performance replay, I don’t think it’s a deal breaker.

The number crunching inside the Moon 681 is carried out by what Simaudio call the MDE-1; this is based on an ESS 9028PRO DAC chip, which is re-clocked by an FGPA. The company is keen to point out that such is the extent of the processing involved here, so readers should not focus too much on the raw chipset. The MiND2 streaming end is as good as anything out there in my experience. I have used this App for many years with Android and IOS devices, and I have to say that apart from some glitchy text scrolling experienced when using some phones, it is pretty good, if not in the same class as something like JPLAY.

MiND2 works with Qobuz, Tidal, Deezer, Spotify and HRA ( All sorts of internet radio stations are available via MiND2, including the excellent Radio Paradise and all BBC stations. The 681 is compatible with MQA and is Roon Ready. Naturally, it plays every digital format that users will likely find and did not bat an eyelid when I fed it with DSD256 files.

How Do They Play?

Before the Moon 681 and 641 Network Player and amplifier arrived, my living room hosted the Musical Fidelity Nu-Vista DAC and 800.2 amplifier. Conveniently, these components are priced similarly to the Simaudio/Moon components we are looking at here. Whilst each of these combinations produces music in an involving and enjoyable manner, they go about it in quite different ways.

The Nu-Vista has a velvety smooth top end with a precise but slightly softer balance. The Moon North components immediately demonstrated a much richer and weightier sound. Here, musical notes are more defined and start and stop much faster, but in a natural and organic manner. You get the leading-edge definition here but with a body behind those notes. Many components sound fast; without mentioning names, I am thinking of products from well-known British manufacturers that produce music in a manner which ultimately becomes fatiguing and somewhat similar sounding. There are no such worries from the 681 and 641; play something like Joni Mitchell’s Hejira, and it sounds rounded and natural.

For sure, the system reveals certain limitations of the recording, but it sounds as it should. Where there is a rhythm or a transient, the system immediately makes you aware of it, far more obviously than with either the Nu-Vista’s or, indeed, my 780D and 600i. Anyone who knows this album will appreciate Jaco Pastorius’s contribution with his fretless bass. The 681/641’s resolving skills make his instrument easy to follow and appreciate his technical skills. Speaking of bass, I have never doubted the low-frequency ability of my 780D and 600i, but the North Collection takes this to a new level. The bass depth, tone, detail, definition and speed are easy to enjoy but in keeping with the rest of the audio band.

The system’s low levels of distortion and ability to swing a current give incredible control of the drive units of my Totem Forest Signature speakers. This newfound speed and control brought a new level of appreciation for my SACD rip of Pink Floyd’s Wish You Were Here album. The Moon 681 and 641’s timing qualities open up this complex piece, allowing me to follow the rhythm of each instrument within the soundstage or appreciate the homogenous effect. The penultimate part of the final track became a truly polyrhythmic extravaganza, which was totally involving. Within the limitations of my room and speakers, each recording I played via this system reflected the character of the recording rather than the Moon North components. It seemed to bring the best out of whatever I played.

Although I grew out of the band in my early twenties, I often use older U2 albums to catch out a component or system, bluntly because they are poorly recorded. I attempted to listen to War a few weeks ago via my 780D and 600i as part of a cable review; this was not an enjoyable experience. The 681/641 revealed the thin balance of this recording, but the rhythmic talents of these components made it possible to listen to the whole album and appreciate the guitar playing, even if it could not improve some of the lyrics!

One side effect of adding an Ethernet Port to an integrated amplifier is the potential for additional noise from this added circuitry. Helpfully, I had a device here from CAD at the same time as the components reviewed here, called the CAD Ethernet Control. This device is designed to reduce noise from Ethernet boards in audio components, and I had been enjoying the fine work it was doing in my Melco’s Ethernet input port. It improved the Moon 641’s performance, bringing a welcome added sense of space and depth to the soundstage and improving instrumental separation, suggesting that my theory concerning the Ethernet port having a slightly detrimental effect may be correct. To be fair to Simaudio, many other manufacturers follow a similar path, and at least CAD is on hand with a solution.

Should You Buy These Components?

Readers considering purchasing components from Moon’s North Collection will be interested in the sonic differences between the 681 Network Player and 641 integrated amp tested here and the 791 Preamp/Network Player and 761 amplifier. It has been six months since I had the more expensive components at home, and I have upgraded my server considerably.

However, I can confidently say that the 791/761 delivers an appreciably larger and more transparent soundstage. The 761’s 200wpc vs the 641’s 125wpc means that it can drive difficult speakers with greater ease and generally makes the sounds more dynamic. So, significant improvements are available for the extra £7,000 required to secure the Seven Series components, which also has a phono stage and allows users to bridge two 761s in mono mode.

The Musical Fidelity Nu-Vista’s 330wpc means it sounds similarly dynamic and expansive to the 791/761, but they are so large that they do not fit the average rack and are visually imposing. They also lack the MiND2 Streaming board and the timing and rhythmic qualities of the Moon North components, so, for my room and tastes, my heart heads North.

When you consider the build quality and finish of these components, Simaudio’s 10-year warranty and the way they can potentially integrate into so many systems, though not inexpensive, I cannot think of a better amplifier and Network Player at this price point. Not only does this combination sound fantastic, it is great to operate and makes me smile every time I look at it. Therefore, Simaudio Moon 681 and 641, as individual components or combined, receive my highest recommendation.

pecial Performer Award Website No Background

Simaudio Moon 681 Network Player/DAC – £12,000.00
Simaudio Moon 641 Integrated Amplifier – £11,000.00
Distributed in the UK by Renaissance Audio

moon 681 641 amp network player hifi review 2 website