NEW TOPPING A30Pro Headphone Amplifier 4 pin XLR / 4.4mm / 6.35mm Output Balanced Input A30 PRO Hi-Res Amplifier AMPFeatures: APX555B limited our measurement againThe THD+N of A30Pro is no higher than 0. 00006%which means the A30Pro accurately restores 99. 9994% of theoriginal sound, what you get is what you input. Because noise of A30Pro is low enough, so APX555B limits the noise measurement of it, resulting in the need to amplify the noise of A30Pro by 100 times for indirect measurement. 4PIN XLR+4. 4mm+6. 35mm outputSince then, buying headphones does not have to