Yamaha A-U671 Stereo Amplifier with USB DAC Function

Great amp/headphone amp/DAC for pc or mac audio. No issues driving several sets of bookshelf speakers including a pair of Legacy Audio Studios with a 4ohm nominal rating. No significant heat, protection circuitry untriggered.Interestingly for an amp, the housing isn't ventilated. Unlike class A or AB amps, class D amps are more efficient which results in cooler, more energy efficient operation. Regardless, another class D amp I own is ventilated. It's almost ten years old which I suppose suggests that class D amps continue to evolve and have become even more efficient. .Wide format support with the Yamaha HiFi USB driver up to and including DSD. Very clean playback across the audio spectrum. No clicks, pops, hiss or hum. I have it connected to a UPS with voltage regulation and an emi/rfi filter which may help.For the best sound quality according to Yamaha, there's an option called Pure Direct. They say this improves audio quality by bypassing certain circuitry. When in this mode, the bass and treble controls are bypassed along with the subwoofer. I've tried it and noticed no difference when compared to playback without it (treble and bass set flat, sub disconnected) but it's there and available to use.Perhaps most importantly, the driver for pc/mac playback is stable and well designed. Once the software is installed, it's a set and forget exprerience. Post installation, no issues. In my experience, Yamaha's software is a benchmark for what this type of software should be. For Foobar users, Yamaha thoughtfully includes configuration info in their download site. Lastly, you'll need to thoroughly review Windows Sound options to make sure you're fully utilizing the capability of this DAC/ amp.Pros:Very clean and natural sounding playback.Powerful class D amp. Capable of driving a wide range of bookshelf speakers to realistic volumes. Even with a pair of speakers nominally rated at 4ohms, the amp never got hot.Rock solid, 'set and forget' firmware/software. Benchmark software interface in my experience.Bass and treble control knobs! Not common these days. Having to dig into a menu system to make quick tweaks is annoying.Size. Not as small as some mini-amps but small enough to allow for more placement options than a full size component.A subwoofer pre-out.USB input for a clean digital transfer from a PC or Mac.Minimalist remote.Cons:Limited connection possibilities. No coax, toslink, wifi, bluetooth or HDMI inputs - only USB and RCA inputs. This is first and foremost a pc/mac playback device.Pricey relative to some full size amps with more features, power and connection options.

An excellent amplifier, with very good sound and good features. The only details are the absence of digital connections.

This amp has a lot going for it — it's simple, has all the controls you typically need, a subwoofer output, remote, small footprint, and just two inputs. For a minimalist like me, it's perfect. Unfortunately, it has a constant buzzing noise from the headphone output. This was on the original and replacement unit, so I can only assume it's a flaw in the product. I'm not paying $500 for an amp, that's advertised on Yamaha's site as a "high-quality headphone amplifier" yet has a cruddy headphone buzz. Returning.

When it arrived I plugged it into my Mac. The Mac recognized it right away. Before I hooked it up to my speakers I figured I would get a listen with headphones to get a real opinion of the sound quality. I could hear the music but with lots of hissing and noise. I changed cables, headphones, pretty much everything you could think of to fix the issue but nothing worked.There are LED indicators on the front to tell you what the bitrate is, but none of them lit up. I own several USB DACs and have never had an issue like this before. I have been a long time Yamaha fan, I own much of their equipment already. I am very disappointed that this made it past the QA department.I returned this and ordered a NuForce DDA120 Powerful Integrated Digital Amp with BTR1 Bluetooth Receiver Dongle Included (Black) instead. Hopefully it does a better job.

I had previously purchased (and returned) a NAD D 3020 integrated amplifier from a different company. I was impressed with its clarity, but disappointed by it’s thin, brittle, sterile sound. This Yamaha A- U671 amplifier sounds terrific. Crystal clear on top but with tight , punchy bass and warm full sound. If you were considering going the D 3020 route, you need to consider this guy for sure too. I am impressed. Nice, warm, punchy, clear, detailed, sound. Not bombastic at all. You can tell that its the same type of amp as the D 3020, but there is more oomph...I had pressed the bass boost button on the NAD and this Yamaha sounds punchier than when it was on. Not bloated, just has some presence. Keep in mind I use Wharfedale bookshelf speakers here so not rattling the rafters, but I am hearing things I couldn't before and bass is punchy and present.Also, I must say that the THD 10% rating MUST be a typo... These type D amps have a certain civility to them that I noted w the NAD D 3020. Everything seems calm and collected...like the amp is saying, "Would you like to listen to some nice music sir?" You get the sense that there is nothing added and nothing taken away. Certainly not a "Giant Killer" amp by any stretch. But I was planning to spend much more for a new amp to achieve what I seem to have found here.

Good amplifier with very nice DAC built inside. However, the noise is a little bit high when paired with normal sensitive speakers. If you place your speakers within 50cm, you can sure hear it. This noise presents as long as the power is on, it does not disappear even if you turn the volume all the way down to zero. So I suppose it is the noise from the final Class-D amp stage.