B4-X is a dual-mono balanced version. Its left and right channel are amplified by independent components, and power supply, tubes, and op amp are all independent and symmetric. So the degree of sound separation is higher than B4. B4-X adopts 2 groups of independent power supply(+12V and -12V) for 2 op amps, less mutual effects and can drive 300Ω headphones. The circuit adopts dual op amp parallel output, with higher output power. B4-X has 3.5mm and 2.5mm 2 kinds of output interface, suitable for most of balanced and standard headphones. High-end making material and craft: using gold-plated socket, original nichicon electrolytic capacitor, original DALE resistors and precision ring resistance.