Vintage Tube Sound Meets Modern HiFi Performance

The Fosi Audio GR70 Tube Headphone Amp is a premium hybrid desktop tube headphone amplifier and preamplifier designed for audiophiles who appreciate warm analog sound, rich musical texture, and versatile desktop HiFi functionality.

Combining authentic vacuum tube amplification with modern audio engineering, the GR70 delivers smooth, natural, and immersive sound for headphones, powered speakers, and home stereo systems. Featuring quad vacuum tubes, adjustable bass and treble controls, dual headphone outputs, and low/high impedance switching, the GR70 provides a refined tube listening experience for both casual listeners and serious headphone enthusiasts.

Perfect for desktop HiFi systems, audiophile headphones, music streaming, vinyl setups, and home audio integration.

Pure Tube Amplification for Warm Analog Sound

The GR70 is engineered around a true vacuum tube amplification design that reproduces the classic analog warmth and musicality beloved by audiophiles.

Tube Amplification Benefits:

• Rich harmonic texture
• Warm natural vocals
• Smooth treble response
• Spacious soundstage
• Relaxed fatigue-free listening

Unlike sterile digital amplification, the GR70 delivers a more organic and emotionally engaging listening experience ideal for long music sessions.

Perfect for:

• Jazz
• Classical
• Vocal music
• Acoustic recordings
• Vinyl listening setups

Quad Vacuum Tube Architecture

The GR70 features a carefully designed four-tube amplification stage for balanced, transparent, and dynamic sound reproduction.

Tube Configuration:

• 2 × 5654W vacuum tubes
• 2 × 6Ж4 / 6Ж8 vacuum tubes

Amplification Stages:

5654W Tubes

• Voltage amplification
• Improved signal detail
• Enhanced tonal richness

6Ж4 / 6Ж8 Tubes

• Power amplification
• Dynamic output delivery
• Stronger headphone driving capability

This dual-stage tube architecture produces:

• Improved sound layering
• Better instrument separation
• Rich midrange presentation
• Smooth analog tonality

Two-in-One Headphone Amplifier & Preamplifier

The GR70 functions as both a dedicated headphone amplifier and a desktop preamp for home audio systems.

Connectivity Options:

Inputs:

• RCA Input

Outputs:

• RCA Preamp Output
• 6.35mm Headphone Output
• 3.5mm Headphone Output

This flexibility allows easy integration with:

• Powered speakers
• Stereo amplifiers
• DACs
• Turntables with phono stages
• Desktop HiFi systems

Perfect for building compact tube-based desktop audio setups.

Supports Both Low & High Impedance Headphones

The GR70 includes dedicated impedance switching modes to optimize performance across a wide range of headphones.

Headphone Modes:

Low Impedance Mode

• Supports 16Ω–120Ω headphones

High Impedance Mode

• Supports 120Ω–300Ω headphones

This ensures:

• Better headphone matching
• Improved dynamics
• Cleaner amplification
• More accurate sound reproduction

Compatible with:

• Audiophile headphones
• Studio headphones
• Over-ear headphones
• In-ear monitors
• High-impedance headphones

Powerful Compact Tube Amplifier

Despite its compact desktop footprint, the GR70 delivers impressive amplification performance.

Output Performance:

• Rated Power Output: 90mW @ 32Ω
• Maximum Power Output: 300mW @ 32Ω
• RCA Output Voltage: 1.2V
• Signal-to-Noise Ratio: ≥97dB

This provides:

• Warm yet detailed sound
• Dynamic musical presentation
• Clean low-noise amplification
• Satisfying headphone drive capability

User-Friendly Analog Controls

The GR70 is designed with intuitive physical controls for a classic HiFi user experience.

Front Panel Features:

• Large volume control knob
• Bass adjustment
• Treble adjustment
• High/low impedance switching
• Dual headphone outputs

These controls allow quick sound customization without software or menus.

Perfect for:

• Tailoring sound signatures
• Adjusting headphone performance
• Matching different music genres
• Personalized listening preferences

Premium CNC Aluminum Construction

The GR70 combines elegant retro aesthetics with durable modern construction.

Build Features:

• CNC-machined aluminum alloy chassis
• Durable metal housing
• Dual-side ventilation design
• Compact desktop-friendly footprint
• Premium tube amplifier styling

The robust chassis improves:

• Heat dissipation
• Structural durability
• Electromagnetic shielding
• Long-term reliability

Technical Specifications

• Product Type: Tube Headphone Amplifier & Preamplifier
• Tube Configuration:
  • 2 × 5654W
  • 2 × 6Ж4 / 6Ж8
• Inputs:
  • RCA
• Outputs:
  • RCA Output
  • 6.35mm Headphone Output
  • 3.5mm Headphone Output
• Rated Power Output:
  • 90mW @ 32Ω
• Maximum Power Output:
  • 300mW @ 32Ω
• Headphone Impedance:
  • Low Mode: 16Ω–120Ω
  • High Mode: 120Ω–300Ω
• RCA Output Voltage:
  • 1.2V
• Signal-to-Noise Ratio:
  • ≥97dB
• Power Supply:
  • DC 12V / 3A
• Chassis Material:
  • CNC Aluminum Alloy

Key Features

• Pure vacuum tube headphone amplifier
• Quad tube amplification design
• Warm analog HiFi sound
• RCA preamp integration
• 6.35mm & 3.5mm headphone outputs
• Low/high impedance switching
• Bass & treble controls
• Compact desktop tube amp
• CNC aluminum chassis
• Audiophile desktop HiFi solution