This is a review and detailed measurements of the SONOS Amp wireless/wired networked amplifier. It was kindly purchased by a member and drop shipped to me for testing. It costs USD $599 and seems to be price protected. This is the second generation amplifier from SONOS. The first one lasted until now from company's beginning.If you are not familiar with SONOS, they pioneered easy, plug-and-play networked/wireless multi-room audio. They aimed high as far as fit and finish, often compared with what Apple would design if they were in this business. Their offerings became so popular that they took the company public. Alas, they have lost direction in the last few years, missing the boat on voice recognition and smart speakers from likes of Amazon and Google.Back to the product, from industrial design point of view, it is quite a departure from the original SONOS Amp:Amplifiers don't usually have "pause/play" on them but this one does as it is an end-point in a streaming platform. So music piped to this Amp can be put on pause or played using the center icon. The left set of dots lowers the volume and the right, raises it. What is wrong with the traditional up/down symbols to have needed reinvention is beyond me.The circle above may make you think it is a subwoofer but it is not. It mates with the bottom of the unit allowing you stack them without much of a seam between them.The back of the unit exemplifies what happens when the company has too much cash on hand and wastes it on useless things:I am referring to the power socket on the left. It seems to be a proprietary connection, mating with a beautifully made power cord. It looks very nice when plugged in but why on earth would I care what the back of the unit looks like in this regard? Granted, the cord is flexible and feels nice in hand when you plug it in. I shutter to think how much it cost to tool the socket and power cord including the regulatory and safety costs. If the final outcome is that if I need a longer cord I have to go to SONOS, they deserve a few curse words on that.Somewhat similarly there are banana sockets but they are flush and custom made in metal. You are then given adapters like the one I have plugged in on the "LEFT" channel if you want to connect bare wire. The metal banana jacks are very tight and provide a nice secure connection. But again, I hate to think how much was spent on mechanical engineering and single sourcing of these jacks.For the first time (?) there is analog input and SONOS shows this playing from a turntable in their promotional videos. The jack seems to be smart in that if nothing was connected to it, it would refuse to "play" from that source.There is a sub output which I like but did not test. Likewise there is an HDMI input but since it does not pass through, I could not test with it.The paint on the SONOS Amp feels very nice but is a huge smudge magnet. It picks up oil from skin from barely touching it and I could not wipe them clean with a microfiber. You will need some kind of solvent to keep it clean.There are dual Ethernet inputs. Why, I am not sure. There is of course wireless input. Just plugging the unit in allowed the SONOS app on Android to find it but could not talk to it. I had to push the button on top left to enable it to find it. As is typical here, it immediately wanted to update the firmware in it. Overall, I found the messaging in the app cryptic and uninformative.The rest of the user interface is also rough as far as usability. Why do I need to "browse" to select the line in as an input? Why is the unit called a "speaker" in settings?There is airplay support which allowed me to stream content to it from my Roon player. It takes priority over line in so if you are playing from that input, it will be overridden and streaming content will play. While there is a volume control in SONOS app, when you stream using airplay, it takes the volume control from source player. This provided quite a surprise when I streamed 0 dBFS reference tone from my player and watched the power meter in my analyzer peg to max! Thankfully I was not using any speakers connected to amp.Speaking of volume control in the app, at least on Android, it has very coarse steps to control line in volume. I don't know how this is usable in practice. A single step would go from 6 to 12 watts of output or some such thing. The front panel controls seem to do the same thing (?).In advanced settings, there is a sensitivity selector from 1 to 6 (?) with 2 being the default for AV components. There are others for itunes, etc.Browsing local content on my phone was fast and trouble-free.I connected the analog output of my Audio Precision analyzer to Line in and used balanced connection to analyzer/dummy load to measure performance at nearly 5 watts with 4 ohm load (280 milliwatts output level from analyzer):This is pretty disappointing. Looking at the FFT spectrum we see that the distortion products are below 100 dB yet our SINAD is only 67. This tells us that the SINAD/THD+N is dominated by noise, not harmonic distortion. We can verify this by separating the two in the Audio Precision analyzer:The figure on the left includes THD+N meaning it has both Total Harmonic Distortion (THD) plus Noise. Using signal processing we can separate the THD out of it and compute that part as shown on right. As we see, the THD component is 1/6th of the total, confirming that noise is our enemy here, not distortion.Thinking that the line in may be different than digital streamed content, I used Roon player to stream the same 1 kHz tone to Amp and got this (ignore Gain):Wow, quite an improvement! How is this possible? In the streaming scenario, a full amplitude digital file is played and volume is controlled in software. In other words, the front-end of the unit gets full signal. In the case of Line in, I am keeping the volume at max and lowering the input level to get to same power output. So it seems that the front-end noise is an issue for Line In.Using full amplitude of 2 volts we still get rather disappointing performance:85 dB? This is far worse than CD (96 dB).Frequency response of Line In gives us clues as to what is going on here:We have a very sharp brickwall filter at around 20 kHz. It is causing peaking/attenuation in the "transition band" depending on which channel you look at. It is clear they are digitizing the input but why use such a low sampling rate? Aren't turntable folks going to get upset that you can't even reproduce 20 kHz cleanly?On the low end, there is a drop but part of that is because I had to select AC input which puts a 10 Hz high-pass filter. Measurements with DC input on the analyzer completely confused the measurement system (due to input DC offset?).Power measurement using 4 ohm load produced this:SONOS rates the Amp at 150 watts into 8 ohms. Here we are seeing over 200 watts of power using 4 ohm which is excellent. During the test I could barely detect the Amp getting warmer so efficiency is quite high. Alas, so is the noise level. Again, this is using Line In with its higher noise level. Best case though at maximum power is in entirely different category than our reference quality Hypex NC400.Wideband FFT spectrum give us insight into operational design of the unit:We see a peak in noise at nearly 98 kHz. This "smells" like a power DAC running at that sample rate. Therein lies the issue with power DAC (or "digital amplifiers") in that their switching frequency is very close to audio band unlike class D amps which switch in hundreds of kilohertz. Peak level is -53 dB which indicates good filtering.Line input (in red) shows secondary anomaly. It has a peak at 21 kHz. Guessing what is going on, there is noise shaping in the ADC which explains the rise prior to that frequency. And then some kind of sharp filter to cut off everything after that.It seems to me that SONOS has partially lost its way, overspending on mechanical engineering, and underspending on features people really wanted (e.g. voice control). Usability of the software is worse than I expected just the same.Line in input is really poorly implemented. I don't know why any self-respecting turntable fan would want to use it. It might come in handy though to route TV sound through it that way.The highlight of the unit is copious amount of power at 4 ohm in such a small and cool running package. I am not sure there are many options in the market with so much power.Subjectively, that great amount of power may cover the sins I am seeing elsewhere. Objectively though, I would have wanted to see more engineering go into unit to keep its noise level at bay, than making fancy power cords for it.Overall, I am going to leave the SONOS Amp without a recommendation one way or the other.------------As always, questions, comments, recommendations, etc. are welcome.Weather is supposed to get warmer so I am thinking of cleaning up the RV to get it ready for trips and need money for Diesel fuel. So I am going to pass the had to collect some money using: https://www.patreon.com/audiosciencereview ), or https://audiosciencereview.com/foru...eview-and-measurements.2164/page-3#post-59054 ).