This is a detailed measurement and comparison of SMSL iDEA and AudioQuest Dragonfly Black DAC and headphone amplifiers. Both of these are diminutive devices in the form of "USB thumb drives." The SMSL iDEA is $86 with prime shipping from Amazon. The Dragonfly Black will cost a few more ice cream bars at $99 with prime shipping.Note that connectivity is different with the SMSL iDEA having a micro USB jack whereas the Dragonfly comes with a normal USB plug.The SMSL iDEA was kindly loaned to me from a member whereas I purchased the Dragonfly Black last fall (2017) through Amazon.The SMSL iDEA comes in a slick aluminum package. Due to strength of material they are able to make it much thinner than the Dragonfly Black DAC. It also has volume controls which the Dragonfly lacks. Alas, every time you plug it in, it reverts to a lower volume so be mindful of that if you are doing any comparisons or measurements.The SMSL iDEA supports many more formats going up to whopping 768 kHz in PCM and DSD 512. The Dragonfly Black lives in the yesterday with support limited to 96 kHz. Indeed the SMSL iDEA beats some desktop DACs with its extensive format support. Here is what Roon reports for SMSL iDEA:I should say that I tried to play DSD with Roon through SMSL and all I got was noise or clicks. Not sure where the issue is.Dragonfly Black DAC is limited to 96 kHz as mentioned above:In operation the SMSL iDEA warms up just a tad but nothing to be concerned about. The Dragonfly on the other hand is completely cool to touch.I did however run into a serious problem with the Dragonfly DAC. If I connect or disconnect the headphone to it while it was playing, it would mute its output and I could not get sound from it unless I plugged and unplugged it! It didn't do it all the time though. Seems like it has a protection circuit that kicks in but then does not reset.OK, let's dig into measurements and see what we find. Please read my tutorial on my setup and how these tests are conducted: https://www.audiosciencereview.com/forum/index.php?threads/understanding-audio-measurements.2351/ . Naturally all of these tests are performed using USB input. I have expanded my USB tests some but they still are not as complete as the ones that operate over S/PDIF.Let's start easy with frequency response measurements:Frequency response flatness is fine with the SMSL iDEA dropping just a hair at 20 kHz while the AudioQuest Dragonfly Black peaking just a bit.What is significant however is the much higher output of SMSL iDEA by over 4 dB. This was clearly audible and significant advantage for SMSL iDEA. Here is the output impedance using a 33 ohm dummy load at 1 kHz (corrected from the first draft of the review):I will provide subjective impressions as a result of this later in the review.Jumping to jitter and noise we get:Unfortunately neither matches the ultra clean output of desktop DACs. Various noise spikes are visible in both. The difference between the main tone at 12 kHz and highest peak was the same for both DACs: 120 dB.However the SMSL iDEA pulled way ahead in signal to noise ratio with having 4 dB higher output and 6 dB lower noise level.Let's look at harmonic distortion of a full amplitude 1 kHz tone:This is a clear win for SMSL iDEA with higher signal to noise ratio and significantly less harmonic distortion.This gets reflected just the same in THD+Noise versus level:Past -10 dB both of them have more distortion. Problem is with Dragonfly you would be operating it at its full output given the anemic drive so that problem is even worse there. So another clear win for SMSL iDEA. It distortion and noise here is excellent matching desktop products.As another confirmation we can look at reproduction of a very low level, -90 dB sine wave (24 bit format, 44.1 kHz):The SMSL iDEA stomps the Audioquest Dragonfly black by showing a very good sine wave. The output of the Dragonfly Black on the other hand is lower, and marred by lots of noise.Overall the SMSL iDEA wins the measurement race.I tested both units with three of my headphones: Sennheiser HD650, HiFiMan HE400i, and Grado SR 60e. If levels are not matched, the SMSL iDEA easily blows away the Dragonfly Black. With HD650 especially, the Dragonfly Black simply has insufficient drive. It produces anemic and too low of a level to be usable for my ears. On the other hand, the much more efficient Grado SR60e works well with it. So keeping the advantage of SMSL iDEA output level makes this an easy win for it.Level matching is challenging as my one means was using Roon volume control. And that unfortunately is not very exact. Getting it close most of the time the two units sounded similar. In a couple of instances I thought the Audioquest had slightly better high frequency but then the darn thing died in the middle of AB switching and I gave up.The Audioquest Dragonfly Black despite its higher price loses to SMSL iDEA. Given the much more extensive format support, better measurements, and higher output level, my recommendation is easily for SMSL iDEA.Sadly that is the one I have to return.Edit: here are the power consumption figures while playing a 0 dBFs 1 kHz tone at 48 kHz sampling:: 0.05 amp no headphone, 0.06 amp Sennheiser HD650 headphone: 0.13 amp no headphone, 0.13 with Sennheiser HD650 headphone----If you like this review, please consider donating funds for these types of hardware purchase using Patreon ( https://www.patreon.com/audiosciencereview ), or upgrading your membership here though Paypal ( https://audiosciencereview.com/foru...eview-and-measurements.2164/page-3#post-59054 ).