This is a review and detailed measurements of the Matrix Audio HPA-3B Balanced (input and output) headphone amplifier. It is on kind loan from a member. Even though the HPA-3B still a current product, I can't find a reliable price for it. Seems to have gone for less than US $500 and came out in 2017 I think. [edit: it came out in 2015]Like the HPA-3U , the HPA-3B comes in a beefy and very deep enclosure:The volume control is a bit stiff and slippery for my taste.The gain control is in the back unfortunately:Inclusion of AC mains power supply though is very nice in the way it declutters your desk.Note that unlike the HPA-3U, there is no DAC in this unit. Nor is there any RCA inputs. The latter can be easily solved though with an XLR to RCA cable while giving you most of the benefits of balanced input and its mains noise immunity.Here is our usual dashboard:Distortion is vanishingly small. THD+N and hence SINAD score is dominated by the power supply/mains noise at multiples of 60 Hz. Since our hearing sensitivity is poor in low frequencies, the SINAD score underestimates the good performance of HPA-3B. Rules are rules though and we have to go with the number we have in our rankings:Signal to noise ratio as well is impacted by the power supply noise:Frequency response is a bit less extended than I like:Power into 300 and 33 ohm loads show the HPA-3B to have very strong drive, capable of driving just about any headphone:As good as these numbers are, when you use the XLR "balanced" headphone output, you get lot more power still:I have revised the channel balance measurement with two cut off points:So depending how much attenuation you need, you may or may not experience channel balance issues.Output impedance is comfortably low at 1.2 ohm:Sorry, did not have a balanced DAC handy to test the HPA-3B. I suspect it will perform very well though given its power and similarity to HPA-3U.The world of headphone amplifiers has been turned upside down with a number of superlative units in the last 12 to 16 months. Prior to that, the HPA-3B would have been the king. Still, what is there has extremely low distortion and lots of power. Assuming you get it for a better price than $500, it makes a good option. As such,--------As always, questions, comments, corrections, etc. are welcome.Have you heard of pink panthers skiing? Me neither. It is snowing at the summit near us and panther saw that on TV and want to go and try it! Even renting the gear for them will be expensive let alone classes they need to take. So I implore you to open your wallet andaccount using : https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/ Amir