This is a review and detailed measurements of the Geshelli Labs Archel2 headphone amplifier. It was kindly sent to me by the company. I am told the Archel2 will sell for US $149.99 but there is an early order discount down to $119.99.The industrial design with metal box and clear/smoked Plexiglas is similar to other Geshelli products:Hitting the power button once turns on the unit. Hitting it again lights up little LEDs inside.Next is an input switch which works overtime as a gain switch as well. Hold it down 3 seconds and it will toggle the gain with a corresponding red LED lighting up on the right.The volume control is on the smaller side but feels solid and good.As you see, you have just one output in the form of 1/4 inch headphone jack.I am told the Archel2 will come in multiple stock colors (red, white and purple) and others on request.The back panel shows two inputs which you can independently select:I have included the power supply so you can see how small it is. It outputs 12 volt at half an amp. The small size is very much welcome although I suspect it may limit the amount of current available to the unit for low impedance headphones.In corresponding with Sherri and Geno at Geshelli, I am impressed with their operation. They took excellence in performance to heart, and purchased an Audio Precision APx555 analyzer. In addition, the company is vertically integrated with their own pick-and-place unit (PC board automated assembly). Most importantly, they put the product fully through FCC and regulatory certification. For such a small operation, this approach is surprising and certainly appreciated on my part.As usual, we run our dashboard in unity gain with 2 volt in, 2 volt out for unbalanced devices:You are seeing what I am seeing? There are essentially no distortion products down to whopping -150 dB. That small tick may actually be in my analyzer. This is just stunning performance with no help from THX feed-forward technology as some of our other headphone amplifier champs use. Naturally, the Archel2 takes the crown for the lowest distortion amplifier and possibly audio device I have tested so far:The good story continues to noise performance:Wow, 125 dB full power signal to noise ratio:It should also be quite noise-free with sensitive IEMs:Intermodulation+noise performance in low gain is exceptional as well:High gain raises that some but still in very good territory with distortion levels that beat even our champion Drop THX AAA 789 in high gain by a bit.Same is reflected in THD+N versus power level into 300 ohm load:Note that as I have mentioned before, this measurement is not with highest performance mode of my analyzer. Turning that on (not shown) resulted in even lower distortion in low-gain mode!We have plenty of power here, easily breaking past my requirement of 100 milliwatts of power in high gain mode.Switching to 33 ohm maintains the excellent performance but power is not as high as I like to see:The JDS Labs Atom in contrast produced 1 watt of power.Given use of analog volume control, we have the usual channel imbalance:The low gain mode is unity-gain (what goes in, is what comes out) so maybe you don't need as much attenuation. High gain is 4X by the way.Output impedance is very low seeing how my fixture itself is about 0.9 ohm:EDIT: forgot to include this.Frequency response is dead flat as it should be:I started with my very low impedance (25 ohm) closed back Drop Mrspeakers Ether CX . In high gain there was plenty of volume to get loud. I was however able to push the Archel2 into distortion and cutting out. Mind you, I would not be listening at this level but this is a test that other high performance amplifiers pass.The situation turned around completely with Sennheiser HD-650 headphones. There was incredible amount of power, detail, authority and fidelity to die for. It is as if this amp and the headphone are made for each other.Yes, we have another state-of-the-art audio product. Not just headphone amplifier but audio product. And from a company with a one-person designer. Yet we have much larger companies making excuses for the performance of their unit.You now have no less than 5 choices in high-performance headphone amplifiers that areThey respect the content you play by not polluting it with noise and distortion, letting its fidelity to shine through.Headphone users are living the golden age of amplification. It is so gratifying to see companies like Geshelli putting performance first rather than some mythical story as to why their device sounds better.The only weakness here is that you can't drive low impedance headphones to deafening levels.It is------------As always, questions, comments, recommendations, etc. are welcome.A local university researcher specializing in glues of all things has approached me to glue the head to the beheaded pink panther. He says with some grant money, he can do that without a trace that the head had even blown off! So, please help me help him byusing : https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/