MTX Thunder TM904 4-Channel Marine Amplifier Waterproof MOSFET four-channel power amplifier delivers 75 Watts x 4 RMS @ 2 ohms; 45 Watts x 4 RMS @ 4 ohms Conformal coated circuit boards, corrosion-resistant materials, plexi-covered controls to guard from water Selectable High- and low-pass filters at 85Hz with 18dB/octave slope; subsonic filter (24dB at 15Hz) MOSFET power supply with high-quality heatsink/components for effective heat transfer and efficiency MXT surface mounting design to withstand to withstand vibrations or hard impacts