Fully discrete NFCA also create wonderful amp: A90 Discrete uses fully discrete components to redesign the NFCA (Nested F eedback Composite Amplifier) module. 4 built-in NFCA-Discrete modules which each them uses 39 transistors build up fully balanced structure. The optimized Voltage Current hybrid feedback architecture along with UHGF (UItra High Gain Feedback) technology provide excellent DC and AC performance. Benefiting from the new design, the output capability is stronger than ever,which allows the amp driving low impedance headphones even more effortlessly. 2 Gain settings :The A90 Discrete has two gain options, which enough to cover a wide variety of headphones: low gain to drive the IEMs with high sensitivity, and high gain to drive fullsized over-ears.Combined with the 0.2uVrms ultra-low noise,even sensitive IEMs will not suffer from any noise. Ground Loop Noise Terminator: Ground loop noise may be encountered when multiple devices are used in combination. A90 Discrete adds a GND/LIFT switch to solve this problem. When in normal use,set it to GND; and when ground loop noise is encountered,switch it to LIFT. Then the ground loop noise is eliminated. A Headphone Amp, also a Preamp: The A90 Discrete is not only able to drive the headphones but also served as a preamp.When it is in preamp mode,you can get the same high performance as the headphone amp mode, and the 20ohm SE and 40ohm balanced output impedance are widely suitable for various power amplifiers. Also support the output from all at the same time . The A90 Discrete provide you 1 X XLR and 1 X RCA stereo inputs, but when it working with a Ext90, they could provide totally 4 X XLR and 2 X RCA stereo inputs.