This is a review and detailed measurements of the Dense Audio Adapt Reference DAC and Headphone amplifier in a "dongle" configuration. It was kindly sent to me by the company to review last fall and I am only getting to test it now.The Adapt has a retail price of US $209.99 but I see it on sale for $169.99. That is up there as far as price although there are likes of Audioquest that charge as much and more. There is apparently a "Standard" version as well at lower cost.The Adapt dongle is a little box with USB-C connection at one end and 3.5mm adapter at the other end:It is a metal (aluminum?) case and super light and small as you can tell from the picture.It is plug-and-play with Windows and that is how I tested it.As usual, we start with our dashboard view to see how the device produces a pure 1 kHz tone into high impedance (as if it were a desktop DAC):Happy to see full 2 volt output which makes it comparable to a desktop DAC and bodes well for output power into high impedance headphones. SINAD if nearly 110 dB is clearly desktop class and places the Dense Adapt into our highest tier of all DACs tested regardless of class and price:Noise level is also quite low for a dongle:32-tone signal resembling "music" also shows very low levels of distortion:Jitter test shows some unwanted signals but they are well below threshold of hearing:Linearity is perfect and better than some desktop DACs:IMD shows that classic "hump" due to use of ESS DAC chip but it is not extreme:The most important measurement for any portable headphone amplifier is amount of power. These little devices usually lower power due to footprint and cost issues and that seriously hurts performance. You lose bass response and with some headphones you won't even be able to get enough volume for best dynamics. Let's start with 300 ohm load where this usually manifests:That's decent amount of power with excellent, low level of distortion with zero clipping (i.e. you can enjoy the music to max volume with no distortion).33 Ohm load is a bit harder on the device:Still, power is readily available as we see in these summary charts:Output impedance is very low making it a non-issue for any headphone:Performance with both Sennheiser HD-650 and Hifiman HE400i was very good. Plenty of bass and volume. With superb content, you get superb fidelity with these combinations.I expected serious problems with my very inefficient, Ether CX headphones at just 25 ohms but that did not occur. Except for some extreme tracks where at max volume I could hear some distortion, the combination was quite usable. This is not so with vast majority of dongles and even desktop products.The Dense Adapt Reference is part of a class of premium dongles which cost a lot but also provide excellent performance in the form of essential transparency with enough power for even difficult headphones. They are desktop headphone amp and DAC that are as small and lighter than a car remote key. With no battery to fuss with, they are a great way to take high fidelity with you on the road for both computer and phone/tablet use.The Dense Adapt Reference is well designed and engineered. I am happy to put it on my recommended list.------------As always, questions, comments, recommendations, etc. are welcome.One of the panthers started to cough. I told him to cough into his elbow as to not spread germs but he would not listen. Kept telling me he can't bend his neck to do that. What excuse.... Made me quite mad. The only thing that counteract that would be some money in my pocket. So pleasewhat you can using