The Fosi Audio GR40 Tube DAC, Headphone Amplifier & Preamplifier combines an ESS ES9028Q2M DAC and two replaceable 5654W vacuum tubes to deliver detailed high-resolution audio with classic tube character. Featuring Bluetooth 5.1 with aptX HD and aptX Low Latency, USB-C, optical, and coaxial inputs, the GR40 supports PCM up to 32-bit/384kHz and DSD256 while providing a 3.5mm headphone output and stereo RCA preamplifier outputs. With independent bass and treble controls, headphone-priority switching, and a compact metal enclosure, the GR40 offers a versatile solution for desktop headphone listening and home Hi-Fi systems.
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Fosi Audio GR40 Tube DAC, Headphone Amplifier & Preamplifier

Bring the character of vacuum tube audio and modern digital connectivity to your listening space with the Fosi Audio GR40 Tube DAC, Headphone Amplifier & Preamplifier. Combining an ESS ES9028Q2M digital-to-analog converter, two replaceable 5654W vacuum tubes, and a dedicated headphone amplifier, the GR40 offers a versatile solution for high-resolution music playback and personal listening. With Bluetooth 5.1, USB-C, optical, and coaxial digital inputs, along with stereo RCA and 3.5mm headphone outputs, the GR40 brings modern convenience and classic Hi-Fi styling together in one compact desktop component.

At the heart of the Fosi Audio GR40 is the ESS ES9028Q2M DAC, designed to deliver detailed and accurate digital-to-analog conversion for your favorite music. Through its USB connection, the GR40 supports PCM audio up to 32-bit/384kHz and DSD256, providing compatibility with high-resolution music files and playback software. Optical and coaxial digital inputs offer additional connectivity for compatible CD transports, televisions, and other digital audio sources. The GR40's tube preamplifier stage uses two 5654W vacuum tubes to introduce the rich harmonic character associated with traditional tube audio, creating an engaging listening experience that combines modern digital precision with vintage-inspired sound.

Wireless music playback is equally convenient with Bluetooth 5.1 connectivity, powered by a Qualcomm QCC3031 Bluetooth chip. Supporting SBC, AAC, aptX, aptX HD, and aptX Low Latency codecs, the GR40 allows you to stream music wirelessly from compatible smartphones, tablets, and computers. aptX HD provides enhanced Bluetooth audio quality when paired with compatible devices, while aptX Low Latency helps reduce audio delay when watching movies or videos. An included external Bluetooth antenna supports a reliable wireless connection, while front-panel input indicators make it easy to identify and switch between Bluetooth, USB, optical, and coaxial sources.

For dedicated headphone listening, the Fosi Audio GR40 includes a 3.5mm stereo headphone output designed for compatible headphones with impedances ranging from 32 to 300 ohms. The integrated headphone amplifier delivers up to 250mW into 32 ohms and 40mW into 300 ohms, offering flexible performance for a range of wired headphones. A headphone-priority system automatically mutes the rear RCA output whenever headphones are connected, making it easy to transition between private listening and speaker playback without manually switching outputs.

Beyond its headphone capabilities, the GR40 functions as a stereo tube preamplifier with a dedicated pair of RCA analog outputs. Connect the GR40 to compatible powered speakers, an integrated amplifier, or a dedicated power amplifier to bring its DAC and vacuum tube preamplification into a larger stereo system. Independent bass and treble controls provide additional sound customization, allowing you to adjust tonal balance to suit different recordings, connected equipment, and personal preferences. A multifunction volume knob also serves as the power and input-selection control, providing convenient operation without a complicated interface.

Designed for both performance and visual appeal, the GR40 features a compact metal enclosure, two exposed vacuum tubes, and decorative tube rings that bring classic Hi-Fi character to modern desktop audio systems. The tubes can be replaced with compatible alternatives, giving enthusiasts the opportunity to experiment with different tube characteristics. An external 12V power adapter supplies the GR40, while its USB-C connection is dedicated to digital audio data rather than power delivery. Whether you're exploring high-resolution music files, streaming wirelessly from your phone, or building a dedicated headphone listening setup, the Fosi Audio GR40 delivers an appealing combination of digital audio performance, tube preamplification, and everyday versatility.

Specifications

• Brand: Fosi Audio
• Model: GR40
• Product Type: Tube DAC, stereo preamplifier, and headphone amplifier
• Audio Channels: 2-channel stereo
• Amplifier Design: Hybrid digital audio conversion and vacuum tube preamplification
• DAC Chip: ESS ES9028Q2M
• Bluetooth Chip: Qualcomm QCC3031
• Vacuum Tubes: 2 × 5654W
• Tube Configuration: Replaceable vacuum tubes
• Compatible Replacement Tube Types: EF95, 6AK5, 6AK5W, 403A/403B, 6J1, 6J1P, and other electrically compatible alternatives
• Built-In DAC: Yes
• Built-In Headphone Amplifier: Yes
• Built-In Stereo Preamplifier: Yes
• Total Audio Input Types: 4
• USB Audio Input: 1 × USB-C
• Optical Digital Input: 1 × TOSLINK
• Coaxial Digital Input: 1 × coaxial S/PDIF
• Wireless Audio Input: Bluetooth 5.1
• Selectable Input Modes: Bluetooth, USB, optical, and coaxial
• Maximum USB PCM Resolution: 32-bit/384kHz
• Maximum USB DSD Resolution: DSD256
• USB Function: Digital audio data connection only; does not power the GR40
• Bluetooth Version: 5.1
• Bluetooth Audio Codecs: SBC, AAC, aptX, aptX HD, and aptX Low Latency
• Bluetooth Wireless Range: At least 10 meters under suitable conditions
• Bluetooth Antenna: External antenna, included
• Bluetooth Pairing Reset: Dedicated rear-panel reset button
• Total Audio Output Types: 2
• Headphone Output: 1 × 3.5mm stereo headphone jack
• Analog Preamplifier Output: 1 × stereo RCA pair
• Headphone Impedance Compatibility: 32–300 ohms
• Headphone Output Power at 16 Ohms: 300mW
• Headphone Output Power at 32 Ohms: 250mW
• Headphone Output Power at 250 Ohms: 50mW
• Headphone Output Power at 300 Ohms: 40mW
• Headphone Priority: Yes; RCA output is muted when headphones are connected
• Signal-to-Noise Ratio: At least 103dB
• Dynamic Range: 104dB
• Frequency Response: 20Hz–20kHz (±1dB)
• Bass Control: Independent front-panel rotary control
• Treble Control: Independent front-panel rotary control
• Volume Control: Multifunction front-panel rotary knob
• Power Control: Press-and-hold multifunction knob
• Input Selection: Front-panel multifunction knob
• Input Indicators: Front-panel LED indicators
• DSD Indicator: Dedicated front-panel indicator
• Tube Warm-Up: Approximately 15 seconds recommended before playback
• Power Requirement: DC 12V
• Included Power Adapter: 12V DC power supply
• Enclosure: Compact metal chassis with exposed vacuum tubes
• Tube Accessories: Decorative rings for both vacuum tubes
• Compatible Speaker Systems: Powered speakers or passive speakers driven by an external amplifier
• Built-In Speaker Amplification: No
• Speaker-Level Outputs: No
• Stereo Speaker Pairs Powered Directly: 0
• Analog RCA Inputs: 0
• Phono Input: No
• Balanced XLR Input: No
• Balanced Headphone Output: No
• 6.35mm Headphone Output: No
• Wi-Fi Connectivity: No
• Apple AirPlay: No
• Built-In Network Music Streaming: No
• HDMI Inputs: 0
• HDMI Outputs: 0
• 12V Trigger Input: No
• 12V Trigger Output: No
• Remote Control: No
• App Control: No
• Manufacturer Warranty: 24-month limited warranty
• Included Accessories: Fosi Audio GR40, 2 × 5654W vacuum tubes, 2 × decorative tube rings, 12V power adapter, Bluetooth antenna, and user manual

What It's Great At

• High-Resolution Digital Audio Conversion: The ESS ES9028Q2M DAC supports PCM up to 32-bit/384kHz and DSD256 through USB, making it an excellent foundation for enjoying high-resolution music files.
• Classic Vacuum Tube Sound: Two replaceable 5654W tubes bring the distinctive harmonic character of tube preamplification to headphone listening and compatible stereo audio systems.
• Versatile Digital and Wireless Connectivity: Bluetooth 5.1, USB-C, optical, and coaxial inputs accommodate computers, smartphones, CD transports, televisions, and other compatible digital music sources.
• Dedicated Headphone Amplification: A 3.5mm headphone output delivers up to 250mW into 32 ohms and supports compatible headphones from 32 to 300 ohms, with headphone-priority switching for convenient private listening.
• Stereo Tube Preamplifier Functionality: A dedicated stereo RCA output allows the GR40 to connect to powered speakers or external amplifiers, bringing its DAC and vacuum tube sound character into a larger Hi-Fi system.
• Customizable Sound and Tube Design: Independent bass and treble controls, user-replaceable vacuum tubes, and convenient front-panel operation make it easy to personalize your listening experience.

FAQ Section

Q: What is the Fosi Audio GR40 used for?
A: The Fosi Audio GR40 is a combined digital-to-analog converter, vacuum tube stereo preamplifier, and headphone amplifier. It converts digital audio from Bluetooth, USB, optical, and coaxial sources into analog sound for compatible wired headphones or a stereo system connected through its RCA outputs.

Q: What audio inputs and outputs does the Fosi Audio GR40 have?
A: The GR40 features four selectable audio input types: Bluetooth 5.1, USB-C, optical digital, and coaxial digital. It offers two analog output types: one 3.5mm stereo headphone output and one stereo RCA preamplifier output. It does not include analog RCA inputs, balanced XLR connections, or speaker-level outputs.

Q: Does the Fosi Audio GR40 support Bluetooth music streaming?
A: Yes. The GR40 features Bluetooth 5.1 with SBC, AAC, aptX, aptX HD, and aptX Low Latency codec support. This allows wireless music playback from compatible smartphones, tablets, and computers, while aptX Low Latency can help reduce audio delay when used with a compatible transmitting device. The GR40 does not include Wi-Fi or independent network streaming services.

Q: Can the Fosi Audio GR40 play high-resolution audio?
A: Yes. The GR40 includes an ESS ES9028Q2M DAC supporting PCM audio up to 32-bit/384kHz and DSD256 through its USB input. Actual playback resolution depends on the connected source, connection type, software, and audio format.

Q: How much headphone power does the Fosi Audio GR40 deliver?
A: The GR40 delivers 250mW into 32 ohms, 50mW into 250 ohms, and 40mW into 300 ohms, with a published measurement of 300mW at 16 ohms. Fosi Audio specifies a recommended headphone impedance range of 32 to 300 ohms, making it suitable for a variety of compatible headphones.

Q: Can I use the Fosi Audio GR40 as a tube preamplifier?
A: Yes. The GR40 features stereo RCA preamplifier outputs for connection to compatible powered speakers, integrated amplifiers, or dedicated power amplifiers. This allows you to use its DAC and vacuum tube preamplifier stage as part of a larger Hi-Fi system. It cannot directly power passive speakers.

Q: Can headphones and RCA outputs play simultaneously?
A: No. The GR40 uses headphone-priority output switching, meaning the rear stereo RCA outputs are automatically muted when headphones are connected. To resume playback through connected speakers or an external amplifier, disconnect the headphones from the front-panel jack.

Q: Can I replace the vacuum tubes in the Fosi Audio GR40?
A: Yes. The GR40 includes two replaceable 5654W vacuum tubes. Electrically compatible replacement models include EF95, 6AK5, 6AK5W, 403A/403B, and selected 6J-series tubes. Always power off the unit, disconnect its power supply, and allow the tubes to cool completely before replacing them.