Fosi Audio GR70 Tube Headphone Amplifier

The Fosi Audio GR70 is a compact tube headphone amplifier and preamp designed to deliver the warmth and character of classic tube sound with modern control and flexibility. Built for both headphone listening and home audio integration, it supports a wide range of headphones and active or passive systems.

Using a true multi-stage tube amplification design and adjustable output impedance, the GR70 allows listeners to tailor both sound signature and system matching while maintaining clean, stable performance.

Features

• Pure tube-based amplification designed to deliver natural warmth and smooth analog character
• Quad vacuum tube design with two-stage amplification for balanced and textured sound
• Replaceable tubes allow users to fine-tune the listening experience
• Switchable low and high impedance modes to properly match a wide range of headphones
• Supports headphones from 16 Ω to 300 Ω, including IEMs and full-size over-ear models
• Integrated bass and treble controls for subtle tonal adjustment
• Functions as both a headphone amplifier and a tube preamp for home audio systems
• Front-mounted 6.35 mm and 3.5 mm headphone outputs for convenience
• Rear RCA input and output for integration with DACs, powered speakers, or power amplifiers
• CNC-machined aluminum alloy chassis for durability and refined appearance
• Compact footprint with dual-side ventilation for effective heat dissipation

Specifications

• Amplifier type: Tube headphone amplifier / preamp
• Vacuum tubes: 5654W × 2, 6Ж4 / 6Ж8 × 2
• Inputs: RCA
• Outputs: RCA, 6.35 mm headphone, 3.5 mm headphone
• Rated output power: 90 mW @ 32 Ω
• Maximum output power: 300 mW @ 32 Ω
• RCA output level: 1.2 V
• Signal-to-noise ratio: ≥ 97 dB
• Headphone impedance (low mode): 16 Ω – 120 Ω
• Headphone impedance (high mode): 120 Ω – 300 Ω
• Power input: DC 12 V / 3 A

What’s in the box

• Fosi Audio GR70 main unit
• 6Ж4 / 6Ж8 vacuum tubes (2)
• 5654W vacuum tubes (2)
• Tube protection covers (2)
• DC 12 V / 3 A power supply
• User manual