MOON 641 and 681

In 2023, MOON by Simaudio revised its top line with what it initially called the ‘North’ Collection. This is a sextet of products that span the upper atmosphere of the company’s output. The first out the gates were the Network Streaming Preamp and Power Amp from the 700 range. MOON’s 641 integrated amplifier and 681 Network Streaming DAC followed. The upmarket 891 Streaming Preamp and spine-busting 861 power amp top the range.

We tested the MOON 791 streaming preamplifier and 761 power amplifier here. We concluded that they are extraordinarily flexible products that take on the highest of high-enders. However, the MOON 641 and 681 integrated amp and Network Streaming DAC will be even more significant.

Long history of amps

The 641 comes from a company with a long history of making great amplifiers. It represents the top of the company’s integrated amplifier tree. The dual-mono amplifier delivers 125W into eight ohms loudspeaker loads and doubles its power exactly into four ohms. This signifies a good amplifier design with a suitably ‘stiff’ power supply. That supply can cope with the most comprehensive range of loudspeakers. MDCA (MOON Distortion-Cancelling Amplifier) design features an independent circuit with precise signal correction to significantly lower noise and distortion. This is the latest development of MOON’s long-standing amplifier noise-reduction circuits. 

You can’t get far talking about a MOON amplifier without discussing volume controls. MOON is once obsessed with volume controls. The result is a delight to use, thanks to its revolutionary BRM-1 intelligent remote control. This smart pebble control sits in the hand well. So well, I’d be tempted to use it even if the amplifier itself was at my fingertips. However, it’s no simple potentiometer. The 641’s volume control is a sophisticated signal attenuation system. It places the volume in the optimum spot in the circuit itself. MOON calls its third-generation electronic gain control M-VOL3. 

Good, solid high performance

The amp has four RCA inputs and one XLR input. It’s a line-only design, with no internal module space for optional on-board DACs or phono stages. There is a single set of RCA outputs and network connections purely for linking the MOON 641 and 681 together. This link works for upgrades, too, and there is a 12V trigger. That’s it. There is no headphone amplifier and no tone stack. It’s just a good, solid, high-performance amplifier.   

The significant external changes are a more rounded styling with a chassis that gets rid of external screw heads. It also features clever use of internal heat channelling through the logo on the top plate.  

It also has an easy-to-read 4.3’’  colour graphic display screen instead of the large red LED readout you could see from space in previous models. MOON also looked to what designs sold best and did away with the all-black and all-natural versions, with just the ‘panda’ scheme (black chassis with natural aluminium side cheeks) available in the new collection. It shares this new set of design cues with the 681 Network Streaming DAC.

Back in DAC

Where many companies making an amplifier at this level will include a built-in DAC, MOON knows that packing a good dual-mono preamplifier, power amplifier and a DAC in the same chassis is rarely the best way to get high-end performance. Something usually has to give, and almost invariably, it’s DAC performance. This isn’t a lack of capacity or digital engineering prowess at MOON; the same company makes the Ace and 200 and 300 Series integrated amplifiers with built-in devices. But at this level, it would be a compromise, and that’s not in the MOON North lexicon. So, you are back to a separate DAC.

The 681 is currently the best standalone Network DAC in the MOON line-up, replacing the popular 680D and up-scale 780D v2 at a single stroke, despite costing less than the previous range-topper. And like that former flagship, the 681 can take a power supply upgrade. 

At the heart of the 681 is the MDE1 ( MOON Digital Engine 1), which is based on an FPGA and an ESS 9028Pro chipset. The FPGA achieves re-clocking with pico-second accuracy, and two sets of four DAC channel outputs are summed in the analogue stage.  It can decode MQA and DSD with alacrity. Equipped with MOON’s popular MiND2 network player (so it can synchronise with other MiND2 products in the house), the 681 accesses music from TIDAL, Qobuz, Deezer, and HighResAudio. It is compatible with Bluetooth, AirPlay 2, Spotify Connect, and TIDAL Connect. It is also Roon Ready. In short, digitally speaking, you name it, it does it.

No issue

That ‘does it all’ approach extends to its inputs and outputs and even the way it handles volume (I said it was a MOON obsession). You can squirt digital signals into the 681’s many ports, be it HDMI, USB, Ethernet, AES/EBU, S/PDIF or Toslink. There’s even a host USB connection. Add in the Bluetooth and AirPlay 2 links, and the only connection missing in action is probably I²S. Away from the digital domain, there are balanced and single-ended outputs, a 12V trigger and MOONLink on an Ethernet port. 

The 681 includes configurable outputs to serve as a line-level source with an integrated amplifier like the 641, a reference-level preamplifier, or a variable output source. The MOON Hybrid Volume (MHV) control in the 681 takes advantage of 32-bit processing to finesse inaudible digital attenuations with several analogue gain adjustments. This crafty algorithm results in a seamless volume control circuit designed for direct coupling with a power amplifier like the 761. Even the BRM-1 can be mapped to either the 681 or 641, while MOONLink controls both devices in perfect harmony.

Fit and finish

Before we get on to the performance of the MOON 641 and 681, it’s worth mentioning the overall fit and finish of these products because it’s exemplary. The control surfaces (especially the use of rotary controls on the handset and the 641) are exceptional, and the widescreen displays on both DAC and amp are legible and never garish. They make set-up and use easy. Most people will initially mash their fingers against the screens, thinking they are touch panels, but the operation is intuitive, both on the devices and with MOON’s MiND App. We tend to elaborately over-engineer audio electronics, but there’s a sense of appropriateness here. It’s built to withstand the rigours of domestic use, and although it’s solid enough to be parachuted out of a military transport, that build comes across as absolute authority. Nothing is vibrating here, ever!

There’s a reason we started discussing sound through the medium of build quality. The term ‘absolute authority’ applies perfectly and equally to both products. It’s a pity the term ‘competent’ sounds so pejorative because their competence makes these products so good. This pair are a perfect match for each other, and the pair are an ideal match for the most comprehensive range of loudspeakers and cables.  

Do one thing

Where so many good audio products are in the ‘do one thing brilliantly’ category, the MOON 641 and 681 duo are more universally excellent. While I have a lot of time for products that are remarkable in one aspect, I also think products with good balance win out in the end. Few of us get asked about audio as often as we used to, but when someone starts discussing good loudspeakers they like, it’s frequently tricky to find an easy partner in electronics. The MOON 641 and 681 duo are that easy partner. I know that any loudspeaker (that isn’t the size of a small asteroid and just as hard to drive) will sing with the MOON 681/641. 

So, what makes these two MOON products so universally good? It’s a perfect blend of insight and detail without sounding etched or exaggerated. That means a sophisticated and elegant sound that hangs together musically perfectly. It’s also a forgiving sound, thanks to all that refinement and elegance, but it isn’t masking anything. It’s just the kind of musical performer that makes you want to listen to more music. I find Muse a bit of a bellwether for this musical insight; There’s a great recording hiding somewhere in ‘Supermassive Black Hole’ by Muse [Black Holes and Revelations, Warner], and it is an excellent track I want to hear sometimes. A lot of similarly-specified electronics at this level focus on the squashed and compressed sound and not on the tonality and energy of the music. The MOON 600 models sidestep that compression and make the performance more enjoyable.

Loudness wars

When you move over to similarly recorded prog that is a casualty of the loudness wars of the 2000s, you get the complete package. Pick any Porcupine Tree or Steven Wilson album, and the room fills with a beautifully layered insightful sound that draws you deep into the musical mix.

The MOON 641 and 681 performed impeccably, to the point where the usual audio descriptions seem a little stale. The DAC’s network connection was always flawless, and it performed equally well when being fed a CD feed from a Hegel CD player, a USB feed from an Innuos Statement Next Gen or taking online streaming straight from an Ethernet switch (admittedly a good one from Nordost). The access via the App was quick and accurate. The display was both legible and informative. But most of all, the sound was quicksilver, detailed, dynamic and highly coherent.

The DAC was unfazed by dynamic classical pieces (Rachmaninov’s Symphonic Dances, Zinnman, Telarc) or avant-garde jazz (Eric Dolphy’s Out To Lunch, Blue Note). These are often problem sounds for a DAC to process. In the former, the scale and dynamic range can be a problem. The latter relies on a lot of leading-edge detail. Most DACs can do one well, and the other suffers. The 681 does both well. To find something better means spending more money on cabling the boxes together than the cost of the 681.

Return to the amp

If the DAC feeds the amplifier an excellent signal, the amplifier more than rises to the occasion. It never once sounded like an integrated amplifier, with power to spare and a sense of stereo separation and detail typically found in pre/power systems. This comes with excellent soundstaging properties, a good depth understanding, and even height in the proper settings.

The combination of staging, refinement, and muscularity is a rare gift, making for a sound that is incredibly solid yet light and airy. This sounds like a contradiction, yet I think that’s because we are too used to amplifier systems that don’t tick all the boxes. The 641 – like its larger MOON North siblings in the 700 models – shows we can have our cake and eat it, too.

The telling recording here is ‘The Ghost’ by Anna B Savage [in|FLUX, City Slang]. This (literally) haunting song is atmospheric and sparse. It needs to be enveloping, claustrophobic and almost visceral in its staging. And that’s precisely what you get through the 641. There’s a word I don’t use that often, but it fits perfectly here – this product has ‘slam.’ Part of the reason I don’t use it is that it also lacks finesse… but not here!

Perfectly matched

It’s hard to break up the band. However, of the two, I would say the 681 is probably the better. Not in performance terms – they are perfectly matched and on par with one another – but the increased flexibility of the DAC puts it a notch ahead of the amp. And, for the record, I preferred placing the volume control in the DAC… but not by much. The amp is every bit as good in sonic terms. It is also straightforward to use and is the perfect partner for the amp. However, its minimalist specification sheet might deter the ‘Top Trumps’ collector.

More fool the collectors, both amplifier and DAC, are remarkable performers. You are onto a couple of winners when ‘criticism’ is the lack of headphone sockets in a market not known for playing headphones. Both MOON 641 integrated amplifier and 681 Network DAC are a perfect ‘add loudspeakers’ audio system. They can cope with almost anything without fuss. That it also sounds excellent in the process is the icing on the cake.

Like the 700 pre/power models I tested in 2023, the 641 amp and 681 DAC are perfect ‘dingers’.  They are products that will happily ring the bells of almost anyone with any loudspeakers or cables. The MOON 641 and 681 are built to last and sound excellent, too! 

Technical specifications

Moon 641 integrated amplifier

• Output Power (Stereo 8 Ω) 125 W
• Output Power (Stereo 4 Ω) 250 W
• Input Sensitivity 300 mV – 6 V
• Input impedance 22 kΩ
• Gain 37 dB
• Frequency response 2Hz–90kHz (+0 dB/-3 dB)
• Crosstalk -109 dB
• Signal to Noise ratio 109 dB
• Total Harmonic Distortion + Noise (@ 1W) 0.008 %
• Total Harmonic Distortion + Noise (@ 125W) 0.003 %
• Intermodulation Distortion 0.06 %
• Damping Factor 700
• Dimensions (W×H×D) 48.1. × 10.2 × 46.5cm
• Weight 26kg
• Price (at time of testing) £11,000/$11,000

Moon 681 Network Streaming DAC

• Analogue input impedance 50 Ω
• Analogue Output Level 2 Vrms / 3.5 Vrms / 6.5 Vrms
• Crosstalk -125 dB
• Frequency response 2Hz–200kHz (+0 dB/-3 dB)
• Signal to Noise ratio 125 dB
• Dynamic Range 125 dB
• Total Harmonic Distortion + Noise (@ 0 dBFS) 0.0003 %
• Intermodulation Distortion 0.0002 %
• Dimensions (W×H×D) 48.1. × 10.2 × 42.7cm
• weight 18kg
• Price (at time of testing) £12,000/$12,000

Manufacturer

MOON by Simaudio

www.simaudio.com

UK distributor

Renaissance Audio

www.renaissanceaudio.co.uk

+44(0)131 555 3922

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