This is a review and detailed measurements of the Devialet Expert 200 Amplifier, DAC, Phono premaplifier and wired streamer. It seems to be a generation behind the current products offered by Devialet. The Expert 200 cost US $9,650.The Devialet line of amplifiers made quite a buzz when originally announced given its unique, lifestyle packaging which has not changed yet:A combination of class A amplifier and class D current source is used to keep the size down, and efficiency up.Innovative for its time was inclusion of an SD card and online configurator to change the operation of the unit including re-purposing the back RCA connectors:The thin package creates real compromises here with the exclusion of balanced analog inputs or preamp outputs.Usability suffers quite a bit as well with the display being on top of the unit which simply is not visible from afar. There is provision for wall-mounting but come on, no audiophile is going to do that and then dangle the cables from it.There is a very substantial remote but strangely has no display on it. That would consume a lot more power, likely requiring a charger and such.Trying to troubleshoot a problem let me to going to their configurator site and downloading SD images some 10 times. I have to tell you, it gets old taking the SD card out of the unit, plugging it into a PC, making a simple change, put it back in the unit, wait for a restart, to see the effect. Granted, you only do this once in a while but during experimentation is quite tedious. In this day and age, such configurator should be inside the unit and activated vi an app or with a browser. The data on the SD card is very small anyway (some kind of simple text file). So it is not like it is data intensive.Overall, I think looks are put way ahead of function on Davialet amplifiers.I had planned to do a much more extensive review of this unit but sadly, right after my first power sweep, it shut down and no longer powers back on.The online brochure talks extensive about protection measures. Clearly they are not enough as I suspect the microprocessor board has failed as opposed to the amplifier that has health monitoring. I am hoping Devialet is responsive to this review and failure and make good on repairing this unit. I have never had an amplifier fail in such a simple sweep that keeps the power max for just a few seconds.Anyway, I had accumulated enough data that I thought it is worthwhile to post it while waiting for a response from Devialet.The Devialet amplifiers digitize their analog inputs so I thought I start with our dashboard of 5 watts driving using USB input:Distortion products are quite low at < -110 dB. However, the noise floor is high in low frequencies causing our SINAD to suffer a lot, ending with a metric of 92 dB. This is well above average compared to all the amplifiers we have measured but way short of state-of-the-art:Analog input creates a lot of harmonic distortion and with it, drags down SINAD a few notches still:I don't understand how their ADC could distort so much in a product this expensive. It can't even clear 15 bits of distortion-free range.There are some lofty numbers like -130 dB noise floor is thrown around by Devialet. I am not sure how that is computed. Using analog Line-in for consistency with other amplifier measurements we get rather ordinary numbers:Crosstalk is good but again, not state of the art:At this point I went to measure a simple frequency response and got stomped big time. No matter what I did, the output would drop off randomly between 8 and 10 kHz. As mentioned, I messed with the configurator, doing everything in my power to turn off filters, tone controls, etc., nothing helped. So I dug in with just feeding the amp a 15 kHz tone and noticed that the output would jump up and down especially in one channel! What the heck is going on????My frequency response testing is at 5 watts as that is what I use in my dashboard. Turns out this amplifier cannot reproduce high frequencies reliably at 5 watts! It has some kind of limiter that kicks in and pulls power back. It also does that at low frequencies but at or past maximum power. That I can sort of understand but not the high frequency hold back. To see this in action, I ran my THD+N vs Level vs Power test:Focus on the red line first. That is at 20 kHz. Notice how it actually zigzags back and forth as input level is increased, but output level does not. Or even goes backward! This must be the "good" channel as it produced 10 watts. The other channel was more finicky and as noted, would get upset at even 5 watts.Problem severity goes down with frequencies but still there at 10 kHz as indicated by the light blue line which zips back at around 180 watts or so.At lower frequencies, the amp simply refuses to increase power and not go into clipping.With this knowledge, I reduced output power to below 1 watt and ran my frequency response sweep:This is line-in so is digitized. It produces about 48 kHz of bandwidth which is fine. What is not so fine is that there is a phase shift between channels as frequencies go up:Some kind of filter is active here that is causing a phase shift between channels. Even if there is some processing active (which there shouldn't be as I disabled tone control and "SAM" speaker EQ), it should affect both channels equally as far as phase.Our story ends with my power measurement as noted:This is healthy amount of power at 269 watts with both channels driven into 4 ohms.While the Devialet is an elegant looking audio device, it clearly sacrifices usability and reliability/performance to get there. There is something clearly wrong in the way it handles high frequencies. No, this is not just me saying that. It is also buried in the stereophile measurement of another one of their units: https://www.stereophile.com/content/devialet-d-premier-da-integrated-amplifier-measurements A $10,000 amplifier can't produce more than 20 watts at high frequencies without "power supply collapsing?" Conclusions like this don't help:No, this is not a testament to how good an amplifier can get. No amplifier should power limit to just 20 watts (or lower in my case) in high frequencies. We have issues with class D amps generating out of band noise that causes measurements to be low in this regard. But they are producing full power. Not so with Devialet.Then we have the phase shift. Poor usability with "sneaker net" style of shuffling SD cards back and forth to make simple changes.And of course the total failure of the unit under a simple industry standard test of power sweep.I feel sad that an amplifier has failed under my watch. I hope Devialet steps up and makes this right for the owner.------------As always, questions, comments, recommendations, etc. are welcome.Too unhappy to ask for money. But if you are so inclined, please donate unis: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/