Fosi Audio M04 Subwoofer Amplifier Mono Class D 100W

The Fosi Audio M04 is a compact mono Class D amplifier built to drive passive subwoofers or a single low-frequency speaker, delivering up to 100 watts into 2 ohms with selectable subwoofer or full-frequency modes.

Small but capable, the M04 combines a Texas Instruments TPA3116 power stage with an NE5532 op-amp to punch out deep low frequencies without taking much rack or shelf space. It adds practical controls such as a low-pass filter, sub frequency adjustment, and a mode selector so you can tailor the output for a dedicated subwoofer or a full-range mono output. The amp ships with a compatible 19V/4.74A power supply and a user manual, making it ready for fast integration into a home theater or stereo setup.

How does the M04 improve bass in a home theater?

The M04 focuses amplifier power and filtering specifically on low frequencies to add weight and control to your system’s bass. Using its built-in low-pass filter and sub frequency control, it isolates and amplifies the sub region while keeping mids and highs clean through your main speakers.

• Built-in low-pass filter for precise bass-only output
• Sub frequency control to tune roll-off to room and subwoofer size
• 100W peak output into a 2-ohm load for robust low-end impact
• Class D efficiency reduces heat and power draw during playback

What connectivity and controls will I find on the M04?

The front and rear panels put key adjustments and input options within reach so setup is quick. A mode selector switches between subwoofer and full-frequency mono operation, while input jacks and gain controls let you match the amp to preouts or receiver lines.

• RCA line input compatible with most preamp and receiver sub outs
• Mode selector for subwoofer vs full-frequency mono operation
• Gain and frequency controls for level and crossover tuning
• Compact terminal/output connectors for passive subwoofers or speakers

How loud and efficient is this mini amplifier?

Thanks to its Class D design around the TI TPA3116 chip, the M04 delivers strong bass output with high power efficiency. That means you get louder low frequencies with less heat buildup compared with many linear-class amplifiers of the same size.

• Efficient Class D topology for minimal heat under load
• Designed to deliver up to 100W into a 2-ohm sub or speaker
• Compact footprint preserves shelf or rack space in small rooms
• NE5532 op-amp for improved signal handling and cleaner lows

What’s included and how straightforward is installation?

The package includes the M04 amplifier, a matched 19V/4.74A power supply, and a user manual so you can get the amp operating quickly. Typical installation requires connecting an RCA sub/preamp output or line-level source and running speaker wires to your passive subwoofer or single speaker.

• M04 mono amplifier unit with front and rear controls
• 19V/4.74A external power adapter for safe, reliable power
• User manual with wiring and control guidance
• Simple line-level and speaker connections—no complex calibration tools

Who is this for? The Fosi Audio M04 is aimed at home theater enthusiasts and compact-system builders who want stronger, more tunable bass without adding a large powered subwoofer. It suits users upgrading passive subs, converting a passive speaker into a dedicated low-frequency driver, or adding mono bass power to a small listening room or media center. If you need a space-saving, efficient amplifier focused on low frequencies with flexible controls, the M04 is a practical, budget-friendly option.