Opamp applied to: Little Bear B4-X Headphone: Hifiman HE4XX Pre- vs Post- opamp: High end tamed while maintaining most if not all of its dynamics. Instruments separation seems to be improved. Tonality remains somewhat the same which it’s a plus. In my case, the biggest improvement is when paired my upgraded B4-X with my iPhone through the 3.5mm dongle. Pretty satisfied with the result, can’t wait to see what it brings after the burn-in. (Installation is pretty straightforward, just need to be patient when removing the old opamps as those pins could break off if yanked at a wrong angle)