AIYIMA D03 Bluetooth 5.0 DAC Amplifier 150 Watt x 2 Stereo HiFi 2.1 CH Digital Sound Amplificador 24Bit/192kHz Class D Power Amp USB Coaxial Optical OLED AptX, Support Subwoofer & with Remote

I wanted to upgrade my audiovisual setup in my new house, and needed a small stereo amp, with just three specific features: an optical input, a subwoofer output, and a usable remote control for at least volume. After scouring the Amazon website, I settled on the Aiyima D03. While I have had mixed results when buying electronics from an unknown mainland China manufacturer, this product was the simplest one available with the right combination of features. I wanted the optical input, because my entire signal chain is digital: HDMI from the BluRay DVD/CD player, into the Samsung TV, out via the TV's optical port, through a Bluetooth transmitter (for using Apple AirPods), and then out to the amp. I also needed the subwoofer output to drive an existing powered speaker, and finally, the remote volume control was also mandatory. The product also supports Bluetooth, although I won't be using that.This product fit the bill perfectly, and I have been very pleasantly surprised by it. The D03 is truly tiny; the cord-bump power supply is actually bigger than the amp. While it has a volume knob and input selection controls, the remote provides that, along with bass and treble controls, input selection, and more. When I connected it to my Klipsch bookshelf speakers, I got excellent sound performance, and completely quiet operation, no noise or hum.The amp features a nice graphic display which unfortunately, and owing to the tiny size of the amp, cannot be read from more than a few feet away. No matter, in my application, I really don't need to see it, since I'll only be using the optical input.The product came with a Bluetooth antenna (which I won't be using) and an optical cable, but without the necessary AAA batteries (x2) needed for the remote.Despite the five star rating I'm giving this product, no product is absolutely perfect, and I do have a minor criticism or two. The binding posts for the speaker outputs are really tiny, and a challenge to use with my stubby fingers. They also won't work well with heavy gauge speaker wire, so it makes sense to use 18 ga. or smaller wire, and abandon the myth that speaker cable gauge has anything to do with sound quality, especially with nearby bookshelf speakers. The instruction guide is also rather minimal, albeit sufficient.Class D amp design, something which I did professionally until my retirement, is truly amazing, in terms of reducing the size and weight of amplifiers. While class D amps have their challenges, they have the advantage on not needing massive amounts of iron and copper for transformers, as well as big heatsinks. As for the power output, I never believe the power rating claims of manufacturers like these, because they never specify the conditions for such a test. However, suffice it to say that the amp is far more powerful than it needs to be, to drive the Klipsch bookshelf speakers.Of course, since I only just installed this amp 24 hours ago, reliability will be my chief concern, and I would reserve the right to edit my review, should things go pear-shaped. However, once past the infancy failure stage, audio electronics can run for a very long time; I once had a Technics receiver in my office which remained turned on continuously for well over 20 years, until it finally failed. We'll see if Aiyima holds up as well.UPDATE: I've had this product since last May, and bought a second one for my daughter in August. I'm knocking off one star, for a couple of small problems in both that might be annoying to users. First, the IR remote control has a particularly weak output... it requires pointing the remote directly at the amplifier, and unless there's a clear and direct view, it often fails to work. Second, the volume control, via the remote, is difficult to use; each 'step' results in a very small volume change, so it takes a lot of clicks to meaningfully raise or lower the volume.Aside from those two issues, I still consider it to be an excellent product.

The first thing to understand about either of these is that they are dac-amps. When you are using digital inputs the signal stays digital all the way through except for the final output to the speakers. There are just a few amps that work this way but as digital inputs become the most common sources this is truly ideal because you are avoiding both dac adc conversions when using a digital amplifier - and you don't need a high end dac to get good sound. The downside is that the analog input must go through an analog digital conversion and that is not a strong point of this amp. So as you read others' comments its critical to know what inputs they used. And, of course, bluetooth is not hifi either.I will say that using the digital inputs both of these are truly excellent. I have had many amps including an Aiyama A07, Sabaj A10, Hypex digital, several tube amps, and several class AB amps. In terms of top to bottom detail both the Hypex and D03/D05 are standouts. I did not find the Aiyama A07 as good in soundstage and 'rhythm'. The high end of the Sabaj felt more digital, a bit harsher and flat.But don't forget that dac's can make a huge difference. I have some high end dac's including an RME and Marantz DAC1 so I know what a decent dac should do. The precision, imaging, and soundstage you get from D03/D05 are competitive.I highly doubt there's a significant power difference between them despite the specs since they both provided the same power supply (same as the A07 also). They had more power than I could use with the KEF Q100's I was driving. Sound of the two were very similar with the top end feeling a bit more lively with the D05. Both provide an exciting, detailed sound that felt 3d with the instruments suspended in space.I like the aesthetics and creature comforts of the D05 much more, however. It's a bit lower, longer, and narrower with a larger volume knob and more space for the speaker posts on the back. When you change settings the display changes so that you can see what's changed from a distance. There's a loudness contour that's useful at low volumes. And you can blank out the screen if you want. I haven't found any use for the eq settings. Note that a long press on the display button switches to hi gain which is about the same gain as the D03. Overall, the D05 is worth a few extra bucks.