This is a review and detailed measurements of the Crown XLi 800 pro Power Amplifier. It is on kind loan from a member. The XLi 800 costs just US $269 including free shipping. Hard to imagine so much electronics from a brand name company selling for so little.NOTE: my company (Madrona Digital) is a dealer for Harman and sells a lot of Crown amplifiers.Unlike some of the switching amplifiers from Crown, this is a class AB amplifier with seemingly linear power supply as it is quite heavy. From the outside though, it look like countless other commercial amplifiers:There are two gain controls in addition to very useful clipping indicators. Speaking of clipping, there is a compressor in there that limits power output to maximum no matter how much you increase its input. It is a nice feature that is surely there to stop the amp from stressing while saving a speaker from blowing up due to a mistake upstream.The back panel is as you expect:In use the unit never even got warm. I had headphones on so did not take note of when/if the fans came on.Let's see how the XLi 800 does in our usual dashboard at 5 watt output into 4 ohm using a 1 kHz tone:Ouch! We have very high distortion of 0.13 to 0.16%. The spec is 0.5% so it is within what they say but this is very high. Translated into SINAD (signal over noise and distortion) our 57 dB value sinks into the bottom range of all amplifiers measured so far:Signal to noise ratio at 5 watt is nothing to write home about either:Frequency response is fairly flat and predictable:Power into 4 ohm relative to THD+N gives us:That is a lot of power. And tremendous value at just 50 cents per watt.As one would predict, we lose some of that into 8 ohm:Determining maximum power and peak with 1% THD+N gives us these:We have fair bit of headroom there.I had a hard time measuring power across full spectrum at a given THD+N due to the amp limiting power (and hence distortion). Only managed to capture 0.9% and 0.5% THD+N power here:As we would expect, we get less power at low frequencies because they tax the power supply more. Oh, the text on graph is wrong: should say 1% not 0.1%.Finally, here is our frequency sensitivity relative to power and distortion+noise:Best distortion is usually at lower frequencies and here, the improvement is quite good at 20 Hz. Alas, we also get less power before clipping (orange).Otherwise, the lines are quite predictable with no funny non-linearity mid span as we get with some amplifiers.Crown advertises the XLi 800 as a PA (Public Address) amplifier and that is what it is. Distortion and noise is kept in check just enough to do the job with tons of power for so little money. I suspect it is reliably too given the dual fans to keep it cool. And the market it is being sold into.For hi-fi use, it is not something I would consider to drive full-range speakers. For subwoofer or active woofer duty, it would be fine.As it is, I can't recommend the XLi 800.------------As always, questions, comments, recommendations, etc. are welcome.Spent 4+ hours mowing our field today. Could have hired someone to do that and tested more audio gear. But I am too darn cheap with my own money. Your though could be put to that use so please make generous