This is a review and detailed measurements of the Monoprice THX AAA Desktop DAC and balanced headphone amplifier. It is on kind loan from a member. It costs US $480 from Monoprice direct including free shipping. The only other desktop headphone amplifier with THX AAA amplifier is from massdrop and it doesn't have a DAC, nor is it easy to find. So if the Monoprice performs, it will be a major win seeing how it also includes a DAC for only $80 more than Massdrop.I previously tried to measure this unit when it first came but unfortunately it failed on my bench The industrial design is good:The display looks a bit grainy to my eyes but it does the job. What doesn't is the volume control. It is digital which is fine. Not so fine is that it runs way behind the volume knob if you turn it quickly. You can literally take your hand off and watch it keep going for a few seconds. And it is not just the display: the volume adjusts in sync with it meaning if you play something quite loud, it may take a while to get the volume down. The logic for this needs to be modified in the firmware to skip values when the knob is turned quickly (i.e. have acceleration).Sadly there is no remote control.Here is the connectivity:It is always a pleasure to see balanced inputs to get around potential ground loops. Inclusion of AES/EBU (XLR) digital input is also helpful in this regard.I am sure you all are interested in measurements so let's get into them. There is a ton here as I had to measure the unit both ways: using digital USB input and then XLR analog input.For this test, I manually set the headphone output to 2 volt, not realizing until later that there is a fixed mode setting in the menus. Regardless, I think this is close enough to not merit re-measuring it:Second harmonic distortion is at -120 dB. Since out SINAD is at much lower -- 107 dB -- it indicates that there is fair amount of noise to reduce performance that much. As it is, the Monoprice THX desktop falls in second tier of our performance ratings:Jitter performance is excellent with almost no spurious tones:Linearity is very good and just shy of excellence:Multitone test shows extremely even performance across the board:The high frequency dynamic range between test tones and top of the distortion spikes is about 105 dB which should do justice to any CD rate music for sure.Intermodulation distortion versus input level shows the same higher noise level as indicated in the dashboard:We only get better performance than Topping DX3 Pro ($250) until we get to max level where noise becomes less material.Here is the power versus distortion and noise using 300 ohm headphone load:I had to set the volume level to +6 dB to get it to produce the max volume/clip. Otherwise it would end a bit early in power level. Once again the Topping DX3 Pro in low gain has a noise advantage over Monoprice THX desktop. Power level though is excellent and a match for topping at 129 milliwatts (I like to see > 100 milliwatt).There seems to be more current available to drive lower impedance loads such as 33 ohm:Now the Monoprice pulls ahead producing one watt of output using its 1/4 inch jack. At higher volumes it is also able to maintain lower distortion. This seems to be the benefit of inclusion of THX technology.Output impedance for the 1/4 inch jack is an excellently low 1.3 ohm:So don't worry about it changing the frequency response of your headphones.For historical reason, I am running high power headphone amps at 5.8 volts output using XLR input at 4 volts:As noted, this is quite a bit lower performance than Massdrop THX AAA 789 . Distortion spike is now up to nearly -102 dB which is dominating the SINAD score.Instead of one signal data point, we can see the THD+N versus power at different input levels:We are not in the same class as Massdrop to be sure. Nothing is broken though and we have excellent amount of power. Noise is also slightly lower if you don't go above 0 dB.Same picture emerges when we change the load to 33 ohm:Running a "fully balanced" chain from XLR input to XLR headphone output at 50 ohm we get:Power nicely quadruples as I like to see. Noise level though rises so don't use it unless you need the extra power.Examining the nature of the noise and distortion relative to power showed something odd:The rising distortion relative to noise is unfortunate but there is a sudden drop indicating that the frequency response is limited. I ran the test up to 40 kHz and got this:So a roll off is occuring. Are the analog inputs digitized? They seem to be given the perfect channel balance relative to volume knob:I ran the signal to noise ratio only in XLR analog input:If the inputs are digitized then I should go back and run them again with USB. For now, we are falling short in both measurements with the 50 millivolt not being all that good:The power versus distortion+noise are a power predictor of subjective performance and such was easily the case here. Using either my Sennheiser HD-650 and Hifiman HE-400i, I had thundering bass, detail, dynamic range and as much gain as I wanted. No issues at all subjectively using these headphones. And if you need more power, you can always have it using balanced output.The Monoprice THX AAA Desktop DAC and headphone amplifier seems to have one issue: higher noise level. If it didn't have this issue, it would easily match the performance of our reference stand-alone headphone amplifiers (Massdrop THX AAA 789 and JDS Labs Atom). Performance otherwise is predictable and solid. There is ample power to drive anything you throw it and subjectively, delivers all that you would want in a desktop headphone amplifier and DAC. And importantly, one that you can buy now.In this regard, I say it is a very good alternative to Topping DX3 Pro, albeit at double the price and with usability quirks (volume control) and lack of remote.All in all I am happy to put theon my recommended list.------------As always, questions, comments, recommendations, etc. are welcome.I noted in my last review that the pink panthers were threatening to go on strike, complaining about too many hours of work (lazy bastards). Well, they did go on strike. The one in the picture above is the only one that crossed the picket line. He is now getting death threats so I appreciate if you all donate money so that I can get him a body guard using: https://www.patreon.com/audiosciencereview ), or https://audiosciencereview.com/foru...eview-and-measurements.2164/page-3#post-59054 ).