FiiO Class A Headphone Amplifier and Preamplifier

4,000mW balanced headphone amplifier The FiiO CLASS A is a fully discrete Class-A desktop headphone amplifier and preamplifier built around a fully-balanced differential architecture. It combines up to 4,000mW + 4,000mW of balanced output power at 32Ω with five gain levels, independent bass and treble adjustment, balanced and single-ended connectivity, and a substantial linear power supply built around a custom 60W toroidal transformer. Fully-discrete Class-A amplification The amplification stage uses individually -elected transistors, resistors, and capacitors rather than an integrated power amplifier. FiiO pairs Toshiba twin transistors and complementary pairs with Sanken audio transistors, with quiescent current manually calibrated. The circuit is designed for the continuous-current operating characteristics of Class A amplification while supporting precise control across a wide range of headphone loads. Fully-balanced high-power architecture A fully-balanced differential circuit provides separate positive and negative signal paths for each channel. The CLASS A delivers up to 4,000mW + 4,000mW into 32Ω through its balanced headphone output, giving it substantial output capability for demanding over-ear headphones. A built-in DC servo circuit continuously monitors and corrects output DC offset to help maintain stable operation and protect connected headphones. Linear power supply with 20,000μF capacitance A custom 60W toroidal transformer feeds a split regulated power supply designed for the high quiescent-current demands of the Class A circuit. The transformer uses a continuous silicon-steel strip core, copper windings, magnetic shielding, and a resettable thermal switch. A 20,000μF capacitor reservoir with Nichicon audio capacitors provides stored energy for transient demands while helping reduce power-supply ripple. Five gain levels and tone control Five selectable gain settings — Low, Medium, High, Super High, and Ultra High — provide a broad adjustment range for headphones with different sensitivities and impedances. Independent bass and treble controls offer ±10dB of adjustment, allowing low- and high-frequency balance to be tailored without changing source components. Flexible headphone and line connectivity Three front-panel headphone outputs cover 1/4 in. (6.35mm) single-ended, 4.4mm balanced, and 4-pin XLR balanced connections. Analog inputs include 1/8 in. (3.5mm) single-ended, RCA, 4.4mm balanced, and XLR balanced. RCA and XLR line outputs allow the CLASS A to operate as a preamplifier for downstream power amplifiers or active speakers. Desktop system integration 12V trigger input and output allow compatible components to coordinate power control across a desktop audio system. A USB-C port is provided for firmware updates, while front-panel indicators show output mode and mute status. The illuminated volume control supports mute, output switching, and selectable indicator-light behavior directly from the knob. Protection for long-term operation Multiple protection circuits monitor operating conditions throughout the amplifier. These include DC output protection, power-input overcurrent protection, headphone-amplifier temperature protection, overvoltage protection, output-overload detection, and transformer thermal protection. Product highlights Fully discrete Class A headphone amplifier and preamplifier Fully-balanced differential amplification architecture Up to 4,000mW + 4,000mW balanced output at 32Ω Five selectable gain levels ±10dB independent bass and treble adjustment Custom 60W toroidal transformer 20,000μF capacitor reservoir Toshiba twin and complementary audio transistors Sanken audio transistors DC servo output control 1/4 in. (6.35mm), 4.4mm, and 4-pin XLR headphone outputs RCA and XLR preamplifier outputs 12V trigger input and output USB-C firmware update port Specs Color: Black or silver Dimensions: About 8.39 x 9.41 x 2.64 in. (213 x 239 x 67mm) Weight: About 7.72 lb (3.5kg) Power input: AC 100–120V / 220–240V, 50/60Hz Main controller: ESP32-S3 Amplifier transistors: 16 Toshiba twin matched-pair audio transistors and 8 Sanken Electric audio transistors Linear power supply: 60W custom toroidal transformer RCA / 1/8 in. input impedance: 5kΩ XLR / 4.4mm input impedance: 8kΩ Frequency response: 20Hz–95kHz, attenuation <3dB SNR: ≥126dB A-weighted Noise floor: <3.7μV A-weighted THD+N: <0.00046% at XLR output, 1kHz, -2dBV into 10kΩ Balanced output at 16Ω: Up to 2,000mW + 2,000mW Balanced output at 32Ω: Up to 4,000mW + 4,000mW Balanced output at 300Ω: Up to 1,360mW + 1,360mW 1/4 in. single-ended output at 16Ω: Up to 2,000mW + 2,000mW 1/4 in. single-ended output at 32Ω: Up to 2,850mW + 2,850mW 1/4 in. single-ended output at 300Ω: Up to 350mW + 350mW What’s included FiiO CLASS A amplifier Dust cap Fuse Warranty card AC power cord RCA cable Quick start guide