This is a review and detailed measurements of the NextDrive's SPectra X Dac and Amplifier USB dongle. It was sent to me by the company and costs $USD 189 including Prime shipping on Amazon. Clearly this is a lot more money compared to $9 dongles from likes of Apple and Google.The spectra X makes a very good first impression as dongles go:It is far more robust than the flimsy phone dongles. It is a metal tube and feels nice in the hand.The Spectra X comes with different end connectors. I asked for the USB-A version so I could test it using my computer.Spectra X was UAC2 compliant meaning you don't need driver. In my case though I got bit by the ASIO4ALL wrapper issue where the device for some odd reason shows up as a 16-bit device. NextDrive provides a set of drivers but it quickly quit saying I already have a more up to date eversion of "bravo HD" driver. I tried to use that but it quickly hung my Audio Precision analyzer application. I got around this partially but did limit the testing I could do.Per above, I could not use the ASIO interface to control the Spectra X. So instead, I played my 1 kHz tone through Roon which faithfully output 24 bit samples:We get a SINAD (signal over distortion and noise) of about 102 dB on average. Turning on the level by a few notches (in software) produced as high as 107 dB which is quite good for a dongle. As it is, it lands in our 2nd tier of all DACs tested:Unless my eyes and memory are failing me, this is better distortion specs than all the other dongles I have tested. So the unit lives up to the stated "high-resolution" audio standard, able to beat 16 bit distortion requirements (96 dB).We also have a nice 2 volt output which makes it as good as any desktop DAC for driving external amplifiers. Many dongles fail to get above 1 volt.Next I ran the J-test signal in Roon and measured jitter and noise:There are fair number of spurious tones which doulbe jitter or other sources of noise. I like to see these tones below 120 dB but here they are as high as -106 dB or so. Still, I don't consider them problematic. Compare this to the output of Apple and Google Pixel V2 adapters (inset) which are horror shows compared to Spectra X.Given the restrictions I have, I did not try to run more DAC tests. Let's jump into headphone amp measurements then starting with power with 300 ohm load:Note that these tests are in 16 bit noise so elevate the measurements some. That aside, there is more power here with Spectra X which is very important. We get 14 milliwatts against Apple's 4 milliwatts for example.Switching to 33 ohm we get:Ah, was wishing the same power advantage here but did not get it. We have 49 milliwatts which is more than Apple's 31 so it is higher, just not multiple times higher.How does this compare to other dongles tested? Here you go:Graph is sorted by 300 ohm power so the Spectra X finishes third there. It beats Dragonfly red which is a good thing. But loses big time to DACPORT HD which is a power monster in this class. Apogee Groove also produces more power.Output impedance is also comfortably low at just 0.9 ohm:As usual I started testing with Sennheiser HD-650. Here, power was clean up to max volume. This was listenable and just a hair loud. Bass was good but no match remotely for any desktop product.The situation with Hifiman HE-400i was a bit better with slightly more volume. I could listen at 75% to 80%. Again, I could not detect distortion at max volume which was good.The Spectra X delivers on pride of ownership and good DAC implementation. On the headphone amp side, there is more power than ordinary dongles but we are talking about a price that is 20 times higher. The DACport runs circles around it on this front but is ugly as sin compared to Spectra X.If you want to go with a dongle and money is not an object, the Spectra X is a good alternative to cheap throw-away ones both on performance and durability. Personally I would have wanted to see a lot more power out of it. But that is me. See Z reviews below on subjective power.------------As always, questions, comments, recommendations, etc. are welcome.Snow has melted but now I need gas money to go and pick up all the packages piled up at the post office. So please considermoney using: https://www.patreon.com/audiosciencereview ), or https://audiosciencereview.com/foru...eview-and-measurements.2164/page-3#post-59054 ).