Fosi Audio M04 Mono Subwoofer Amplifier
- 100 watts into a 2-ohm load
- TPA3116 chip, NE5532 op-amp
- Sub or full-range mono mode switch
- Low pass filter with sub frequency control
- 19V/4.74A power supply included
Last refreshed Jun 20, 2026 · Based on the Amazon listing and published specifications, not hands-on testing.
A tiny, efficient amp for powering a passive subwoofer or a single speaker in a home or desktop setup. Power is rated into a low impedance load, so output falls with higher impedance speakers.
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ASIN: B07942M4MCModel: M04Category: Stereo Amplifiers
Overview
Fosi Audio packs a mono Class D amplifier into a mini chassis to drive a passive subwoofer or one full-range speaker. A switch picks sub or full-range mode, and a low pass control sets where the sub takes over.
It turns an unpowered subwoofer into a working one without a big amplifier. Output is quoted into a low impedance load, so expect less power from a typical higher impedance speaker.
Who it's for
Hobbyists adding a passive sub to a desk or small room system get compact, cool-running power. Listeners needing two channels for stereo speakers should get a stereo amp.
Pros and cons
- Drives a passive subwoofer
- Full-range mono mode too
- Adjustable low pass frequency
- Runs cool, Class D
- Power quoted into low impedance
- Input types not listed
- Only one speaker or sub per unit
Performance notes
Bass output depends on the subwoofer's impedance, since the rated power applies to a low impedance load. The low pass filter trims higher frequencies so the sub only plays bass. Class D switching holds heat down under heavy use.
Specifications
| Brand | Fosi Audio |
|---|---|
| Model | M04 |
| Capacity & performance | |
| Output Power | 100 watts into 2 ohms |
| Power & efficiency | |
| Power supply | 19V/4.74A, included |
| Included components | |
| Included Components | M04 amp, power supply, user manual |
| Other details | |
| Number of Channels | 1 (mono) |
| Amplifier class | Class D |
| Chipset | Texas Instruments TPA3116, NE5532 op-amp |
| Modes | Subwoofer or full-frequency mono |
| Filter | Built-in low pass, sub frequency control |
Frequently asked questions
Does the Fosi Audio M04 overheat with a subwoofer?
Fosi says its Class D design remains cool under demanding loads.
Can the Fosi Audio M04 power a regular speaker?
Yes. A selector switch changes it from subwoofer mode to full-frequency mono mode.
How much power does the M04 deliver?
100 watts into a 2-ohm subwoofer or speaker.
Is the Fosi M04 a stereo amplifier?
No. It is a mono amplifier with one channel.