Topping challenges the whole market of headphone amplifiers with its A90: an exceptional performance desktop headphone amplifier / preamplifier. With a SINAD up to 123dB (measured by Audio Science Review) on its balanced output and an incredibly low distortion of 0.000086%, the A90 significantly expands the boundaries of what most advanced home audio equipment can offer. Topping A90 has a stereo balanced input XLR 3-pole and an single-ended input stereo RCA connector on its rear face . It offers a balanced (XLR) / single-ended (RCA) as preamplified output. The connectors dedicated to the headphone amplifier are located on the front panel. A90 has all the connections necessary to easily connect headphones / IEM with various characteristics and requirements: a balanced output on XLR 4-pole connector, a second balanced output on jack TRRS 4.4mm connector.  Balanced headphone outputs are capable of delivering a power of 250mW and have an output impedance of 135 Ω. Finally the frontpanel offers an unbalanced output on 6.35mm connector with a power output of 125mW.