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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