Amazon.com: OSD Audio 300W Mono-Channel Class A/B Subwoofer Amplifier, Auto Sensing, 4 -8 Ohm Stable : Electronics
Infinity Primus 3000A 300W RMS Power Compact Mono Subwoofer Car Amplifier System Bundle with 12" 1200W Max Power High-Performance Car Audio Subwoofer and Amplifier Wiring Kit - Road Entertainment
Subwoofer Amplifier Board 300w Low Pass Filter Subwoofer Pure Home Theater Active Subwoofer Amplifier, Amplifier For Subwoofer - Home Theater Amplifiers - AliExpress