This is a review and detailed measurements of Gustard A20H DAC and headphone amplifier. It is on kind loan from a forum member. It retails for USD $850 on Amazon with free shipping (from China?). I am accelerating this review because it is on sale on massdrop for USD $700. Still not cheap but more reasonable.For your extra money you get a much larger and beefier enclosure with a large LCD display:I usually clean the units and touch them up in photoshop but in this case I choose to leave it alone so that you can see how well it shows smudges and scratches. Overall the enclosure is bland but OK.Claim to fame of this unit is stepped attenuator implemented using a bunch of relays. The volume knob therefor is a rotary encoder telling the unit where to set the volume. And therein lies the main usability issue I found: if you rotate the knob quickly, it will change very slowly! This is of course the opposite of what you want. If I play a loud track, or after I have changed to a more sensitive headphone, I want to be able to rapidly turn the volume down. If you do that, the counter on the display changes very slowly (once a second?) as will the volume. You have to rotate the knob at a slow to medium rate to get it to change quickly.Other than this, the menus are easy to navigate with up/down and knob to change setting.For this testing, I am only using USB input. I tested both balanced XLR and unbalanced RCA for most of the tests. Let's see how she did.As usual we start with our dashboard view:Our distortion measurement falls a bit short of published measurements. But if you look at the fine detail, you see that Gustard measurements are at -6 dBFS, not 0 dBFS as I test. Due to loudness compression, we tend to get a lot of music that reaches 0 dBFS so I like to see good performance at the limit. This puts the unit at the bottom of tier 2 of performance as far as distortion:As you see on that graph, unbalanced produces about 3 dB lower performance.Dialing down the level to -6 dBFS as Gustard has done, improves performance pushing SINAD to 108 dB using balanced connection.We can see this issue immediately when we run our intermodulation distortion test versus level:We see how both outputs start to rise in distortion levels as we approach 0 dBFS. This is likely due to the output buffer stage saturating.As the A20H uses the AKM Dac chip, its performance almost mirrors that of Topping DX3Pro Jitter distortion and noise is a bit disappointing although not of audible consequence:An ideal DAC would just show the main tone at 12 kHz and nothing else. Here, we see tons of jitter and distortion spikes in both balanced and unbalanced outputs.Gustard A20H nails the linearity though showing that it produces correct voltages all the way down to -120 dB (20 bits):That's the DAC performance. Let's switch to its headphone output and see what power we get with a 300 ohm dummy load using 1/4 inch unbalanced output:This is a disappointing showing. The unit falls short of the performance of Topping DX3 Pro which retails for nearly 1/4 of it. It has both higher noise and distortion and less power.Switching to 33 ohm load, we get this:We see slightly better showing here but still nothing to justify paying more.These values are far below the power specs from Gustard:Of course they have no details as to how these power numbers were computed. Perhaps they are for "balanced" XLR headphone out? Let's test that at 50 ohm:OK, we finally get decent amount of power. At 50 ohm, I am seeing nearly 1.7 watts which if one interpolates from the specs, seems correct.Channel balance is excellent due to digital control of volume/stepped attenuator:Likewise output impedance is a low 0.7 ohm which means it can drive just about any headphone without changing its frequency response:As usual, I started testing using my Sennheiser HD-650 whose 300 ohm impedance let's us compare the objective results with subjective listening. Here, there simply was not enough power. I could dial the volume to max of "60" and while it was loud, it just wasn't enough.Base impact simply was not there. Switching to Topping DX3 Pro, there was an authority and headroom that was quite satisfying and lacking in Gustard A20H.Next I switched to HifiMan HE-400i which with its 40 something impedance, attempting to match the objective to subjective again. Due to more available power at this low impedance, the situation was improved but I still preferred the Topping DX3 Pro. There was a bit more power in Topping and I got the impression of better resolution (could be placebo).If you plan to use the normal 1/4 "single-ended" output of Gustard A20H, my advice is to save your money and get much cheaper products such as Topping DX3 Pro. You actually lose both performance and out of pocket money by using Gustard A20H.Balanced mode has a lot more power but I can add a superb headphone amp such as JDS Labs Atom or Massdrop THX AAA 789 and be way, way ahead. It will be a two-box solution so if you want a tidy desk, and money is not a concern, then I guess the Gustard A20H fills that gap.Overall, the A20H is not a bad unit and seems to have decent engineering. I just can't figure out what it does all that better to justify its premium.-------------As always, questions, comments, recommendations, etc. are welcome.If you like this review, or even if you don't but wish for me to have lobster and steak for dinner tomorrow, please considerfunds using:or https://audiosciencereview.com/foru...eview-and-measurements.2164/page-3#post-59054 ).