The Fosi Audio GR70 Class-A Tube Headphone Amplifier & Preamplifier combines four replaceable vacuum tubes, dual-stage amplification, and adjustable headphone impedance modes to deliver a warm, detailed listening experience. Featuring 3.5mm and 6.35mm headphone outputs, stereo RCA input/output connections, independent bass and treble controls, and up to 300mW of maximum headphone output power into 32 ohms, the GR70 offers flexible integration with headphones and home Hi-Fi systems. With its CNC-machined aluminum enclosure, distinctive orange-accented controls, exposed vacuum tubes, and included 12V/3A power supply, the GR70 brings classic tube audio character to a compact desktop design.
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Fosi Audio GR70 Class-A Tube Headphone Amplifier & Preamplifier – Orange

Experience the warmth and character of traditional tube audio with the Fosi Audio GR70 Class-A Tube Headphone Amplifier & Preamplifier. Designed for music enthusiasts who appreciate detailed sound and vintage-inspired Hi-Fi equipment, the GR70 features a pure vacuum-tube amplification circuit with four replaceable tubes, adjustable headphone impedance modes, and independent bass and treble controls. Delivering up to 300mW of maximum headphone output power into 32 ohms, the GR70 provides a versatile solution for enjoying music through compatible headphones or integrating tube amplification into an existing stereo system. Its premium CNC-machined aluminum enclosure, elegant orange-accented controls, and exposed vacuum tubes create a distinctive desktop listening experience.

At the heart of the GR70 is a dual-stage Class-A vacuum-tube amplification architecture featuring two 5654W tubes for voltage amplification and two 6Ж4/6Ж8 tubes for power amplification. This four-tube configuration brings the rich harmonic character and smooth musical presentation associated with traditional tube audio to a compact modern component. The replaceable tubes also provide opportunities for personalization, allowing enthusiasts to experiment with electrically compatible replacements to explore different sonic characteristics. With a carefully engineered analog signal path, the GR70 is designed to deliver natural vocals, engaging instrument reproduction, and an immersive listening experience across a wide variety of musical genres.

Designed to accommodate a broad selection of headphones, the Fosi Audio GR70 features both 3.5mm and 6.35mm single-ended headphone outputs, making it easy to connect compatible in-ear monitors and full-size headphones without relying on a separate adapter. A convenient front-panel impedance selector provides two operating modes: Low for headphones rated from 16 to 120 ohms and High for models rated from 120 to 300 ohms. This flexibility allows the GR70 to accommodate headphones with different impedance requirements, while its large top-mounted volume control offers precise, convenient listening adjustments. Independent bass and treble controls provide additional flexibility for tailoring the sound to your headphones, music, and personal listening preferences.

In addition to its headphone amplification capabilities, the GR70 functions as a dedicated stereo tube preamplifier. A rear-panel stereo RCA input allows connection to compatible analog audio sources, including external DACs, CD players, music streamers, and turntables equipped with a built-in or external phono preamplifier. A separate stereo RCA output sends the processed analog signal to compatible powered speakers, integrated amplifiers, or dedicated power amplifiers, bringing the GR70's vacuum-tube character into a larger Hi-Fi system. The preamplifier output delivers up to 1.2V, and the independent bass and treble controls remain active during both headphone and preamplifier operation.

The GR70 combines thoughtful construction with a simple, intuitive interface. Its CNC-machined aluminum alloy chassis features dual-side ventilation openings to help manage heat, while exposed tubes and subtle ambient illumination contribute to its classic aesthetic. The large top-mounted volume knob doubles as the power control, providing a streamlined layout that keeps operation straightforward. With a manufacturer-rated signal-to-noise ratio of at least 97dB and a frequency response of 20Hz to 20kHz, the GR70 delivers capable analog performance in a compact desktop design. The included 12V/3A power adapter, vacuum tubes, and tube protection covers provide the essential components needed to begin enjoying a dedicated tube listening setup.

Whether you're looking to add the distinctive character of vacuum tubes to your headphone listening experience or introduce a tube preamplifier into an existing Hi-Fi system, the Fosi Audio GR70 offers an appealing combination of traditional audio design, versatile connectivity, and convenient everyday control. Its replaceable vacuum tubes, adjustable impedance modes, dual headphone connections, and stereo RCA preamplifier output make it a compelling choice for listeners seeking a more personalized approach to high-fidelity music reproduction.

Specifications

• Brand: Fosi Audio
• Model: GR70
• Version: Orange-accented
• Product Type: Vacuum tube headphone amplifier and stereo preamplifier
• Amplification Class: Class-A
• Amplifier Architecture: Pure vacuum tube amplification
• Audio Channels: 2-channel stereo
• Total Vacuum Tubes: 4
• Voltage Amplification Tubes: 2 × 5654W
• Power Amplification Tubes: 2 × 6Ж4/6Ж8
• Tube Configuration: Dual-stage vacuum tube amplification
• Tube Replacement: User-replaceable with electrically compatible vacuum tubes
• Headphone Output Power: 90mW rated at 32 ohms
• Maximum Headphone Output Power: 300mW at 32 ohms
• Supported Headphone Impedance: 16–300 ohms
• Low-Impedance Mode: 16–120 ohms
• High-Impedance Mode: 120–300 ohms
• Headphone Impedance Selection: Front-panel High/Low switch
• Total Audio Input Types: 1
• Analog Audio Input: 1 × stereo RCA pair
• Input Signal Type: Analog line-level audio
• Total Audio Output Types: 3
• 3.5mm Headphone Output: 1 × single-ended stereo headphone jack
• 6.35mm Headphone Output: 1 × single-ended stereo headphone jack
• Analog Preamplifier Output: 1 × stereo RCA pair
• RCA Output Level: Up to 1.2V
• RCA Output Function: Stereo analog output for compatible powered speakers or amplifiers
• Frequency Response: 20Hz–20kHz (±1dB)
• Signal-to-Noise Ratio: At least 97dB
• Dynamic Range: At least 97dB
• RCA Output THD+N: 0.26% or less
• Headphone Output THD+N: 0.5% or less
• RCA Output Noise: 20µV or less
• Headphone Output Noise: 56µV
• RCA Output Crosstalk: -63dB
• Headphone Output Crosstalk: -65dB
• Bass Control: Independent front-panel rotary adjustment
• Treble Control: Independent front-panel rotary adjustment
• Tone Control Compatibility: Applies to both headphone and RCA preamplifier outputs
• Volume Control: Large top-mounted rotary potentiometer
• Power Control: Integrated with volume knob
• Vacuum Tube Warm-Up: Allow at least 20 seconds before playback
• Simultaneous Output Support: Headphone and RCA outputs can operate simultaneously; individual output use is recommended
• Chassis Material: CNC-machined aluminum alloy
• Exterior Styling: Dark metal chassis with orange-accented controls
• Cooling: Passive cooling with dual-side ventilation openings
• Vacuum Tube Protection: Includes 2 tube protection covers
• Ambient Illumination: Decorative tube-area lighting
• Power Input: DC 12V/3A
• Included Power Supply: 12V/3A external adapter
• Built-In DAC: No
• USB Audio Input: No
• Optical Digital Input: No
• Coaxial Digital Input: No
• HDMI Inputs: 0
• HDMI Outputs: 0
• Bluetooth: No
• Wi-Fi: No
• Apple AirPlay: No
• Built-In Music Streaming: No
• App Control: No
• Remote Control: No
• Built-In Phono Preamplifier: No
• Passive Speaker Amplification: No
• Speaker Binding Posts: No
• Speaker A/B Selector: No
• 12V Trigger Input: No
• 12V Trigger Output: No
• EAN: 6976136960904
• Manufacturer Warranty: 24-month limited warranty
• Included Accessories: Fosi Audio GR70 headphone amplifier/preamplifier, 2 × 5654W vacuum tubes, 2 × 6Ж4/6Ж8 vacuum tubes, 2 tube protection covers, 12V/3A power adapter, and user manual

What It's Great At

• Authentic Class-A Tube Amplification: A dual-stage amplification design featuring four replaceable vacuum tubes delivers the distinctive harmonic character and smooth musical presentation associated with traditional tube audio.
• Versatile Headphone Compatibility: Adjustable Low and High impedance modes accommodate compatible headphones rated from 16 to 300 ohms, with both 3.5mm and 6.35mm headphone outputs for convenient connectivity.
• Integrated Stereo Tube Preamplifier: A dedicated stereo RCA input and output allow the GR70 to serve as a tube preamplifier for compatible powered speakers, integrated amplifiers, and dedicated power amplifiers.
• Personalized Sound Adjustments: Independent bass and treble controls make it easy to fine-tune music playback, with adjustments available for both headphone and preamplifier operation.
• Customizable Vacuum Tube Design: Two 5654W voltage amplification tubes and two 6Ж4/6Ж8 power amplification tubes can be replaced with electrically compatible alternatives for additional personalization.
• Premium Desktop Construction: A CNC-machined aluminum alloy enclosure, orange-accented controls, exposed vacuum tubes, and dual-side ventilation combine classic Hi-Fi styling with practical heat management.

FAQ Section

Q: What is the Fosi Audio GR70 used for?
A: The Fosi Audio GR70 is a Class-A vacuum tube headphone amplifier and stereo preamplifier. It amplifies analog audio for compatible wired headphones and can also send a tube-processed audio signal through its RCA outputs to powered speakers or an external amplifier. It does not contain a built-in DAC or speaker power amplifier.

Q: How much headphone power does the Fosi Audio GR70 deliver?
A: Fosi Audio specifies 90mW of rated headphone output power into 32 ohms, with a maximum output of 300mW into 32 ohms. Actual output varies with the headphones being used and the selected impedance mode.

Q: What headphones are compatible with the Fosi Audio GR70?
A: The GR70 supports compatible headphones with impedances ranging from 16 to 300 ohms. Its Low mode is designed for 16–120-ohm headphones, while High mode accommodates models rated from 120 to 300 ohms. Both 3.5mm and 6.35mm single-ended headphone connections are available.

Q: Can I use the Fosi Audio GR70 as a stereo preamplifier?
A: Yes. The GR70 features a stereo RCA input and stereo RCA output, allowing you to connect an analog audio source and send the processed signal to compatible powered speakers or a separate amplifier. Its tone controls also operate when using the RCA preamplifier output.

Q: Does the Fosi Audio GR70 support Bluetooth, Wi-Fi, or music streaming?
A: No. The GR70 is a dedicated analog headphone amplifier and preamplifier without built-in Bluetooth, Wi-Fi, Apple AirPlay, or network streaming services. To enjoy wireless or digital music, connect a compatible external DAC, Bluetooth receiver, or music streamer with analog RCA outputs.

Q: Can I adjust the bass and treble on the Fosi Audio GR70?
A: Yes. The GR70 includes independent bass and treble controls on its front panel, allowing you to customize the tonal balance of your music. These adjustments operate during both headphone listening and RCA preamplifier playback.

Q: Can I replace the vacuum tubes in the Fosi Audio GR70?
A: Yes. The GR70 includes four replaceable vacuum tubes: two 5654W tubes for voltage amplification and two 6Ж4/6Ж8 tubes for power amplification. Replacements must be electrically compatible with the specific tube positions. Always disconnect power and allow the tubes to cool completely before removing or installing them.

Q: Can the Fosi Audio GR70 play through headphones and powered speakers simultaneously?
A: Yes. The GR70 supports simultaneous audio output through its headphone connections and stereo RCA preamplifier output. However, Fosi Audio recommends using one output at a time for the best listening experience. The unit requires approximately 20 seconds of tube warm-up after powering on before playback begins.