The Fosi Audio MC331 Tube Integrated Amplifier combines two replaceable 5654W vacuum tubes, Texas Instruments TPA3221 Class-D amplification, and a built-in DAC to deliver up to 105 watts per channel of maximum rated power into 4 ohms. Featuring Bluetooth wireless streaming, USB, optical, coaxial, and RCA inputs, along with a 3.5mm headphone output and preamplifier output, the MC331 offers versatile connectivity for desktop and home Hi-Fi systems. With a vintage-inspired VU meter, adjustable bass and treble, replaceable vacuum tubes, and an included infrared remote, this compact stereo amplifier combines classic audio styling with modern convenience.
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Fosi Audio MC331 Tube Integrated Amplifier with DAC & Bluetooth

Bring vintage-inspired style and modern Hi-Fi performance to your listening space with the Fosi Audio MC331 Tube Integrated Amplifier with DAC & Bluetooth, a versatile all-in-one audio solution designed for music enthusiasts who appreciate the character of vacuum tubes and the convenience of modern connectivity. Combining a hybrid tube preamplifier design, Texas Instruments TPA3221 Class-D amplification, and a built-in digital-to-analog converter, the MC331 delivers up to 105 watts per channel into 4 ohms at its maximum rated output. With Bluetooth wireless streaming, USB, optical, coaxial, and RCA inputs, along with a built-in headphone amplifier and classic analog VU meter, the MC331 brings multiple audio components together in one compact and stylish desktop amplifier.

Designed to combine the character of traditional tube audio with the efficiency of modern amplification, the MC331 features two replaceable 5654W vacuum tubes that contribute to its distinctive sound and appearance. These tubes work alongside the Texas Instruments TPA3221 amplifier chip to deliver an engaging listening experience with clear vocals, detailed instruments, and dynamic musical reproduction. The front-panel analog VU meter adds a classic Hi-Fi aesthetic, displaying audio signal activity with a moving needle that responds to your music. With its exposed vacuum tubes, retro-inspired styling, and compact enclosure, the MC331 makes an attractive centerpiece for desktop listening stations, bookshelf speaker systems, and smaller dedicated Hi-Fi setups.

Connectivity is one of the MC331's greatest strengths. Bluetooth wireless streaming with SBC and AAC codec support makes it easy to enjoy music from compatible smartphones, tablets, and computers, while USB, optical, and coaxial digital inputs allow direct connections to digital audio sources. A dedicated stereo RCA input accommodates traditional analog components such as CD players, external DACs, and turntables equipped with a built-in or external phono preamplifier. The integrated DAC supports digital audio playback up to 24-bit/96kHz through compatible USB, optical, and coaxial connections, providing a convenient way to enjoy high-quality audio without requiring a separate DAC.

Beyond driving passive speakers, the Fosi Audio MC331 includes a dedicated 3.5mm headphone output for personal listening with compatible headphones rated from 32 to 300 ohms. A rear-panel preamplifier output also allows connection to additional compatible audio equipment, including powered subwoofers, making it possible to expand into a 2.1-channel system. Independent bass and treble controls provide convenient sound adjustments, allowing you to tailor playback to your speakers, room, or musical preferences. The included infrared remote adds another level of convenience with control over power, volume, input selection, Bluetooth playback, bass, and treble from your listening position.

Powered by an included 24V/4.5A adapter, the MC331 delivers flexible stereo amplification in a compact enclosure that fits comfortably into a desktop or entertainment center setup. Its multifunction volume knob provides quick access to input switching and power control, while front-panel indicators make it easy to identify the selected source. The replaceable vacuum tubes allow enthusiasts to experiment with compatible alternatives such as 6AK5, 6AK5W, 6J1, and 6Zh1P to personalize their listening experience. Whether you're streaming music wirelessly, playing CDs, connecting a computer, or enjoying a private headphone listening session, the Fosi Audio MC331 combines modern functionality with the visual appeal of classic tube Hi-Fi equipment.

Specifications

• Brand: Fosi Audio
• Model: MC331
• Product Type: Hybrid tube integrated stereo amplifier with DAC, Bluetooth, and headphone amplifier
• Amplifier Configuration: Hybrid vacuum tube and Class-D amplification
• Audio Channels: 2.0-channel stereo
• Supported System Configuration: Stereo or 2.1-channel with compatible powered subwoofer
• Amplifier Chip: Texas Instruments TPA3221
• Vacuum Tubes: 2 × 5654W
• Tube Configuration: Replaceable vacuum tubes
• Compatible Replacement Tubes: 6AK5, 6AK5W, 6Zh1P, 6J1, 6J1P, EF95, and other compatible tube models
• Tube Warm-Up Time: Approximately 15 seconds after powering on
• Built-In DAC: Yes
• Built-In Headphone Amplifier: Yes
• Maximum Rated Speaker Output Power: 105 watts × 2 into 4 ohms
• Supported Speaker Impedance: 4–8 ohms
• Frequency Response: 20Hz–20kHz (±1dB)
• Signal-to-Noise Ratio: At least 100dB
• Dynamic Range: At least 100dB
• Total Harmonic Distortion: 0.03% or less
• Total Audio Input Types: 5
• Analog Audio Input: 1 × stereo RCA pair
• USB Audio Input: 1 × USB
• Optical Digital Input: 1 × TOSLINK
• Coaxial Digital Input: 1 × coaxial S/PDIF
• Wireless Audio Input: Bluetooth
• Input Modes: RCA, Bluetooth, USB, optical, and coaxial
• Maximum USB Audio Resolution: PCM up to 24-bit/96kHz
• Maximum Optical Audio Resolution: PCM up to 24-bit/96kHz
• Maximum Coaxial Audio Resolution: PCM up to 24-bit/96kHz
• Bluetooth Audio Codecs: SBC and AAC
• Bluetooth Wireless Range: At least 10 meters (approximately 33 feet) under suitable conditions
• Bluetooth Antenna: External antenna, included
• Total Audio Output Types: 3
• Speaker Outputs: 1 stereo pair of binding-post speaker terminals
• Headphone Output: 1 × 3.5mm stereo headphone jack
• Preamplifier Output: 1 × 3.5mm stereo pre-out
• Headphone Impedance Compatibility: 32–300 ohms
• Headphone Priority: Inserting headphones mutes the passive speaker outputs
• Powered Subwoofer Compatibility: Supported through the preamplifier output with an appropriate connection
• Speaker A/B Selector: No
• Speaker Pairs Supported: 1
• Volume Control: Front-panel multifunction rotary knob
• Bass Control: Independent front-panel bass adjustment
• Treble Control: Independent front-panel treble adjustment
• VU Meter: 1 front-panel analog needle-style meter
• Input Indicators: Front-panel LED source indicators
• Remote Control: Included infrared remote
• Remote Functions: Power on/off, mute, volume adjustment, previous track, play/pause, next track, input selection, Bluetooth mode, Bluetooth pairing reset, bass adjustment, and treble adjustment
• Power Control: Multifunction power, input selection, and volume knob
• Power Input: DC 19–24V
• Included Power Supply: 24V/4.5A DC adapter
• Amplifier Design: Compact desktop enclosure with exposed vacuum tubes
• Dimensions: Approximately 10 × 2 × 2.7 inches (manufacturer-listed dimensions)
• Apple AirPlay: No
• Wi-Fi Connectivity: No
• Built-In Music Streaming Services: No
• HDMI Inputs: 0
• HDMI Outputs: 0
• 12V Trigger Input: No
• 12V Trigger Output: No
• Built-In Phono Preamplifier: No
• App Control: No
• Manufacturer Warranty: 24-month limited warranty
• Included Accessories: Fosi Audio MC331 amplifier, 2 × 5654W vacuum tubes, 2 × tube covers, Bluetooth antenna, infrared remote control, 24V/4.5A power adapter, and user manual

What It's Great At

• Classic Tube Sound with Modern Amplification: Two replaceable 5654W vacuum tubes combine with efficient Texas Instruments TPA3221 Class-D amplification to deliver an engaging listening experience with the distinctive character of tube-based Hi-Fi equipment.
• Versatile All-in-One Audio Connectivity: Bluetooth, USB, optical, coaxial, and stereo RCA inputs accommodate a wide range of digital and analog sources, reducing the need for multiple separate components.
• Powerful Stereo Speaker Amplification: With a maximum manufacturer-rated output of 105 watts per channel into 4 ohms, the MC331 provides capable amplification for compatible passive bookshelf and compact floorstanding speakers.
• Dedicated Headphone and Preamplifier Outputs: A 3.5mm headphone output supports compatible headphones from 32 to 300 ohms, while a separate pre-out provides flexibility for connecting additional audio equipment or a powered subwoofer.
• Classic Analog VU Meter Design: The front-panel VU meter and exposed vacuum tubes create a vintage-inspired visual presentation that adds personality to modern desktop and home Hi-Fi systems.
• Convenient Sound Customization and Control: Independent bass and treble adjustments, replaceable vacuum tubes, a multifunction volume knob, and an included infrared remote make it easy to tailor and manage your listening experience.

FAQ Section

Q: What is the Fosi Audio MC331 Tube Integrated Amplifier?
A: The Fosi Audio MC331 is a 2-channel hybrid tube integrated amplifier that combines a vacuum tube preamplifier stage, Class-D speaker amplification, built-in DAC, Bluetooth connectivity, and headphone amplification. It allows you to connect multiple digital and analog audio sources while powering compatible passive speakers or wired headphones.

Q: How much power does the Fosi Audio MC331 deliver?
A: The MC331 has a maximum manufacturer-rated output of 105 watts per channel into 4 ohms using the included 24V/4.5A power adapter. It supports passive speakers rated between 4 and 8 ohms. This is a maximum output specification rather than a continuous RMS power rating.

Q: Does the Fosi Audio MC331 support Bluetooth and wireless music streaming?
A: Yes. The MC331 includes Bluetooth wireless audio connectivity with SBC and AAC codec support, allowing you to stream music from compatible smartphones, tablets, and computers. It does not include built-in Wi-Fi, Apple AirPlay, Spotify Connect, or other independent network streaming services.

Q: What audio inputs does the Fosi Audio MC331 have?
A: The MC331 features five selectable input types: stereo RCA, USB, optical digital, coaxial digital, and Bluetooth. Its built-in DAC supports digital audio playback up to 24-bit/96kHz through compatible USB, optical, and coaxial connections.

Q: Can I connect headphones to the Fosi Audio MC331?
A: Yes. The MC331 includes a dedicated 3.5mm headphone output designed for compatible wired headphones with impedances from 32 to 300 ohms. When headphones are connected, the amplifier automatically prioritizes headphone playback and mutes the passive speaker outputs.

Q: Can I connect a subwoofer to the Fosi Audio MC331?
A: Yes. The MC331 includes a rear-panel preamplifier output that can connect to a compatible powered subwoofer using an appropriate cable. This allows you to expand a traditional stereo speaker setup into a 2.1-channel system. The MC331 does not include a dedicated speaker-level subwoofer amplifier or adjustable subwoofer crossover.

Q: Can I replace the vacuum tubes in the Fosi Audio MC331?
A: Yes. The MC331 features two replaceable 5654W vacuum tubes. Compatible alternatives include 6AK5, 6AK5W, 6Zh1P, 6J1, and other electrically compatible models. Changing tubes allows enthusiasts to experiment with different tube characteristics. Always power off the amplifier, disconnect it from power, and allow the tubes to cool completely before replacing them.

Q: Does the Fosi Audio MC331 have a remote control and adjustable bass and treble?
A: Yes. The MC331 includes independent bass and treble controls on the front panel, along with an infrared remote that supports power, volume, mute, input selection, Bluetooth playback, and tone adjustments. A multifunction volume knob also allows convenient operation directly from the amplifier.