【Fully Discrete NFCA for Superior Sound】 – The TOPPING A90 Discrete features 4 NFCA-Discrete modules with 39 transistors each, ensuring high output, strong current, and low impedance for effortless headphone driving. 【Re-Optimized Circuit for Ultra-Low Noise】The TOPPING A70 Pro’s newly developed input stage boosts noise performance and input impedance (20kΩ) for better device compatibility, while the gain architecture minimizes noise at high gain settings. 【Ground Loop Noise Terminator】 – Use the GND/LIFT switch to eliminate ground loop noise. Set to GND by default, switch to LIFT if noise occurs for uninterrupted audio. 【Headphone Amp & Preamp in One】 – Functions as both, with 20Ω SE and 40Ω balanced output impedance, ensuring compatibility with various power amps. 【Expanded Inputs with Ext90】 – The A90 Discrete has XLR and RCA inputs but expands to 4 XLR and 2 RCA with the Ext90, plus a 12V Trigger for easy device sync. 【Precision R2R Volume Control】 – Uses relay and resistor networks for precise, durable volume control, ensuring accurate channel balance and remote convenience. 【Volume Memory for Convenience】 – Remembers volume settings for PRE, HPA, and PRE+HPA modes, restoring previous levels automatically for seamless use. The TOPPING A90 Discrete features fully discrete NFCA modules with 39 transistors each for exceptional power, clarity, and low impedance. It offers 2 gain settings for IEMs and headphones, a GND/LIFT switch to eliminate noise, and works as both headphone amp and preamp. With precision R2R volume control, memory function, XLR/RCA inputs, and Ext90 compatibility, it's built for high-end audio versatility.