Yamaha A-U670 Review

These days it’s not uncommon for an integrated amplifier to include some digital connectivity along-side the analogue inputs of yesteryear. Designed to partner the CD-NT670 or CD-NT670D network CD players and the NS-BP401 bookshelf speakers to form the MusicCast MCR-N870 system, the Yamaha A-U670 takes things a step further. It may look like a simple integrated amplifier, but there’s some clever modern technology packed into that tiny chassis including a DSD-capable 384KHZ asynchronous USB DAC accompanying the single analogue input.

That DAC is powered by an XMOS controller and the ESS ES9010K2M 32-bit DAC chip, fully supporting both DSD64 and DSD128 content as well as PCM sampling rates of up to 384kHz. Class D amplification produces 70W per channel, with a low-pass filter coil made of oxygen free, OFC copper wire. Class D amplifiers are extremely efficient, meaning the A-U670 draws just 30W at full power and an eco friendly 0.5W in standby. The A-U670 features an optimised circuit layout with short signal paths and Yamaha’s pure direct circuit is fitted to optionally bypass the tone and balance control circuits as well as the back buffer amp for the purist sound quality.

Two models are available, the A-670 lacking the USB DAC function and paired with either a CD-NT670 or CD-NT670D network CD player and a pair of NS-BP301 speakers to form a MCR-N670 or MCR-N670D mini hi-fi system. The A-U670 is paired with either of the aforementioned CD players and a pair of the larger NS-BP401 speakers to form the MCR-N870 and MCR-N870D systems. The difference between those systems with an appending D to their model identifier is the inclusion of a DAB+ radio tuner. Both amplifiers are also available to purchase as stand-alone units.

The 2 amplifiers are largely identical besides the omission of the USB DAC on the lesser model, and that model offering less output power and therefore less power consumption (28W as opposed to 30W). The A-U670 is rated to deliver a maximum of 70W per channel at 1kHz into 6 ohm load at 10% THD, with a frequency response of 10 Hz – 40 kHz (+/-3dB). At 30W per channel, that distortion figure drops to 0.05% which is a far more acceptable value. It is for this reason that i prefer to think of the A-U670 as a 30W per channel amplifier, and it is that value I’d advise you take into account when choosing a matching pair of speakers.

In the box, you’ll find the amplifier itself along with some documentation and a system control cable. That cable connects to the matching CD player to allow the power and volume of the amp to be controlled by the player’s remote and of course the MusicCast control app. Weighing 3.3KG, the amp feels heavy for its size, and measuring 314 x 70 x 342 mm (W x H x D) it’s slightly larger than your average half-sized separate. It’s well made though, with contoured dials, a thick aluminium front panel and piano-effect side panels which lend it a sleek appearance when it’s sitting on the rack.

On the front, you’ll find a row of vertical dials for bass, treble and balance and a rotary dial to control the volume. There are buttons for power and pure direct, the latter with an LED which lights when the function is enabled. The amp doesn’t remember the status of the pure direct function, so you’ll need to re-enable it each time you switch on if you wish to use it.

Speaking of LED indicators, the amp doesn’t feature a sample rate display, instead a row of indicators to show the status of the DAC. It also lacks an input selector, instead switching to DAC mode when it detects a PC is connected. If you connect a compatible Yamaha network CD player, you can switch to the USB DAC mode using the input control on the front of the player, the player’s remote or the MusicCast app. Rounding out the front panel functionality is a full-size quarter inch headphone jack, specified for use with 32 ohm headphones. Connecting headphones mutes the speakers automatically as you would expect.

Around back, you’ll find a permanently attached power cable along with a set of speaker terminals which will accommodate bear wire or banana plugs. There’s a single mono sub woofer terminal, along with a pair of RCA analogue inputs, the system control jack and the type B USB computer input.

I’m a huge fan of the A-U670s design. I love the vertical dials, a hallmark of many a classic amplifier over the years, not to mention the solid feel of not only those dials but the casework itself. The parts are beautifully manufactured and the result is a product finished to a standard that is not always the norm when it comes to smaller hi-fi components. Typically such components are so feature laden that their build quality becomes something of an afterthought. That’s not the case here, Yamaha’s decision to opt for a simple design approach meaning that the attention to detail and the quality of the components in use hasn’t suffered.

Sound wise the A-U670 is a very neutral amplifier. The highs are clean with plenty of top end detail, as are the mids. The bass is tightly controlled, though realistically with 30W of power at acceptable distortion levels you can’t expect the A-U670 to offer earth-shaking sound unless you pair it with some particularly efficient speakers. It’s certainly capable of providing more than enough volume in an average domestic setting however, running my reference Tannoys to very high levels with admirable control. After all, a good hi-fi is designed to faithfully reproduce a piece of music as the artist intended, not to reproduce it as loudly as possible.

Noise levels are reasonable, though the amp does generate some hiss that will be evident if you connect high sensitivity speakers with particularly revealing tweeters. It handles sensitive headphones very well though, easily on a par with any integrated amp at this price and beyond, and better than some dedicated headphone amplifiers. The sound through headphones is much like that delivered through the speaker outputs – detailed, involving and true to the source material.

The A-U670 is a worthy choice if you’re looking for a simple, compact and relatively affordable integrated amplifier. It’s equally at home as part of a compact hi-fi setup where space is at a premium as it is on a desktop where its USB DAC makes it the ideal companion for high-resolution computer audio. Pair it with a CD-NT670 for the ultimate mini hi-fi system. Highly recommended.

By Ashley

I founded Audio Appraisal a few years ago and continue to regularly update it with fresh content. An avid vinyl collector and coffee addict, I can often be found at a workbench tinkering with a faulty electronic device, tweaking a turntable to extract the last bit of detail from those tiny grooves in the plastic stuff, or relaxing in front of the hi-fi with a good album. A musician, occasional producer and sound engineer, other hobbies include software programming, web development, long walks and occasional DIY. Follow @ashleycox2


  1. Hi Ashley, enjoyed reading your review and wondered if you could provide some advice on the Yamaha MCR N870 mini system.
    I’m looking to replace my old Denon D F102 from around 2007, so obviously a bit dated and now almost being outshone by my Acton Marshall Bluetooth speaker. I live in Hong Kong so a bit limited in set up space and strangely buying options, so I’ve narrowed my search to:
    Denon CEOL n10 (only sold as package with associated Denon speakers) package approx £420
    Yamaha WXA-50, with either Q Acoustic 3020i, or DALI Spektor 2 amp + plus speaker £600
    Yamaha MCR N870 (can only source package with related Yamaha speakers) £780
    Had convinced myself that paying extra for N870 was worth it, until reading a few tech reviews which had the WXA-50 out performing the A U670 and also stating that the Q Acoustic and DALI, were much better options than the Yamaha speakers.
    Any thought, advice much appreciated?
    Cheers C

  2. Hi, I am looking for some headphones to use with the A-U670 (together with the CD-NT670). What would you suggest from Yamaha ? The pro (500) series or the MT (8) series ? Thanks

    1. The MT8s if you want an accurate, detailed sound and a more comfortable headphone, the pros if you want something slightly warmer. My preference would be for the MT8.

      1. Thanks. That was my though as well. I like to be able to identify each piece of the music. And the pros do seems relatively uncomfortable due the rigid construction.

  3. Hi Ashley

    What are your thoughts on pairing this amp with Mission MX3 floor standers [8ohms, 35-150w] in a smallish lounge. I tend to play music at ‘background’ levels but I do use my amp/speaker combo for TV sound and tend to turn the volume up to hear dialogue [an age thing, I’m afraid].

    Kind regards


  4. Hi,

    Is the DAC only relevant for components connected via USB, or does it apply to music streamed through the 670D? I also have a portable music device (Hidizs AP100) that can act as a DAC I believe, so it might be possible to just plug that into the 670D’s USB input and go from there. I’m trying to work out whether the extra expense of the AU amp is worth it vs the much more affordable lower model…

    Any help appreciated!


    1. The DAC is only relevant for the USB input. The 670D connects via the analogue RCA inputs and thus contains its own DAC. Your audio player appears to have a line out jack (which could be combined with the headphone jack, I’m not entirely sure). Either way you could connect it directly to either of these amps via a 3.5Mm to RCA cable. I’m not sure whether you’d be able to connect your player to the USB input of the 670D. The 670D’s USB input is intended to accept mass-storage devices. If your player acts as a standard mass-storage device it may work. You certainly wouldn’t be able to use your player with the USB input of the A-U670, as it is designed for connection to a computer only.

      1. Incredibly helpful, many thanks. The site is great by the way, I’ve just found you guys.

        My player has an option to connect as either a mass storage device or a DAC when connected via USB. It has a separate line out jack next to the headphone jack so it can bypass the headphone amplifier.

        Is there an appreciable difference in sound quality between streamed hi-res audio files opposed to if the computer was connected via USB in the A-U670? Or between connecting my player via 3.5mm cable in the 670D or it’s USB port? If the USB connection on the A-U670 is ONLY useful for connecting a computer physically, unless the sound quality is better it’s probably no use as I’d likely stream it from the sofa etc.

        Many thanks for your help


        1. You’re welcome, thanks for your kind comments on the site! I suspect the USB DAC option on your player is for use with a computer. When connected in that way, it would bypass the sound card in your computer and allow you to use the DAC and headphone amp in the player to listen to music from the computer. That looks to be a high-quality portable player, and I’d imagine it would sound fine connected to the amp via a good quality 3.5MM to RCA cable. No need to spend a fortune on audiophile cables though. You might hear a slight improvement connecting a computer to the A-U670, as it is technically the better interface. When you mention ‘high-resolution’ audio, take care not to be sucked into the ‘high-res hype’ as I like to call it. A lot of the high-res content out there is no better in quality than the 16/44.1 resolution of a CD, particularly classic albums original recorded on analogue tape, the fidelity of which is nowhere near that of a 16/44 CD. High-resolution audio is only worthwhile if the source material is true high-resolution. The clever marketing and the publications who fall for it will have you believe that bigger numbers are always better, but that’s not always the case. Just something to keep in mind. With that said virtually any DAC made today is good enough.

          1. Basically I’ve got an all-in-one Onkyo mini system with some Sony speakers, which I’ve been using for years but would like something technically better, with more finesse. I appreciate the presentation of the music more than pure clinical/technical reveal too. I have some Sony V6 headphones which are great for a more ‘monitor’ type sound but just like over-sharpened, hyper detailed digital photography, I often prefer the less clinical, harsh and I guess less ‘digital’ presentation of music and I get the impression Yamaha still have that ‘musical’ approach. Don’t get me wrong, I like it to be accurate, but also enjoyable.

            I know exactly what you mean re. Hi-Res audio, and don’t worry, I haven’t fallen into that trap. I use the term in relation to FLAC rips of my CD’s, which probably doesn’t fit the technical description of it but it’s the way to point out it’s lossless. I also have quite a few 24/96 FLAC vinyl rips, which I also know aren’t ‘Hi-res’ either but rather just larger, better sounding (higher dynamic) recordings. I’m not fussed with the numbers and I’m not convinced the differences are audible, the mastering of particular pressings however certainly are super important. And high quality, lossless vinyl rips are the next best thing to the actual vinyl.

            Sounds like the DAC in the A-U670 is probably not necessary for me, and I need something affordable so that helps! If you have any recommendations let me know. I know the speakers are probably the most important component, a lot has been written about Q Acoustics etc but am wary of cabinets that look like big computer speakers and have places like C-Net and What Hi Fi sing their praises so highly – I found their headphone reviews to be completely inaccurate! Yamaha have real ‘musical’ pedigree and reputation which gives me more confidence.

            1. Yamaha are certainly tonally accurate. They tend to go for the neutral approach in my opinion, whereas the tone of Marantz gear is more musical and, I think, the more enjoyable. With regards to speakers, typically good speakers do involve a hefty cabinet of some kind. I’ve not spent any real time with q-acoustics products but I do know a couple of readers here who like them, I’m a Tannoy guy personally. I couldn’t possibly comment on the inaccuracy of the reviews in certain publications, save to say I’m not at all surprised and that is exactly the reason I started Audio Appraisal in the first place when, as a consumer, I was frustrated by the dishonesty, brand bias and the apparently lack of consideration that consumers spend large amounts of money based on a publication’s reviews. That is why brands don’t pay us anything or advertise with us, because that only encourages dishonesty which then leads to mistrust and ultimately disappointed consumers. Anyway. I’d recommend you go and demo some components if at all possible. Personally if you want a sound that is neutral in character and somewhat analytical, I’d consider Yamaha. If you want a sound that is more musical I’d consider a marantz. it would be helpful to know how much you’re willing to spend and whether that budget needs to include an amp and speakers. I’d also recommend you try some different speakers as the quality of speaker is of far greater importance than the quality of the amp. Source first, speakers second, amp third.

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