Rockford Fosgate M400-4D Prime Marine 400 Watt Full-Range Class-D 4-Channel Amplifier

Rockford Fosgate M400-4D Prime Marine 400W Class-D 4-Channel Amplifier – Maximum Channels, Minimum Current Draw

Product Overview

The Rockford Fosgate M400-4D is a 400 Watt, 4-channel full-range Class-D amplifier purpose-built for marine and powersport environments. Delivering 75W x 4 RMS at 4 ohms (CEA-2006 certified), it powers four speakers cleanly and efficiently or bridges down to two channels for 200W x 2 at 4 ohms when a more subwoofer-focused setup is needed. The Class-D topology achieves an average efficiency of 80% at 4 ohms, drawing significantly less current from your charging system than equivalent Class-A/B designs a genuine advantage on boats and powersport vehicles where alternator capacity is limited.

Designed to handle the harshest Australian conditions on the water and the trail, the M400-4D features a marine-grade two-part epoxy coated PCB, cast aluminium heatsink with convection cooling, and tri-stage protection circuits covering thermal events, over-current, and short circuits. The compact chassis just 50 x 172 x 231 mm fits neatly under seats, behind panels, and into the tight spaces common in jet skis, UTVs, and small marine vessels.

Key Specifications

• Rated power: 75W x 4 @ 4 ohms (CEA-2006, ≤1.0% THD+N)
• Rated power: 100W x 4 @ 2 ohms
• Rated power (bridged): 200W x 2 @ 4 ohms
• Total power (sum of rated): 400W RMS
• Dynamic power: 79W x 4 @ 4 ohms / 138W x 4 @ 2 ohms / 255W x 2 @ 4 ohms bridged (PowerCube®)
• CEA-2006 compliant
• Class-D full-range circuit topology
• Frequency response: 20 Hz – 20 kHz ± 1.0 dB
• Efficiency: 80% @ 4 ohm / 75% @ 2 ohm
• Dimensions (H x W x D): 50 x 172 x 231 mm
• Shipping weight: 2.65 kg

Features & Benefits

• Class-D high-efficiency topology: Averages 80% efficiency at 4 ohms, meaning less heat generated and less current drawn from your boat or powersport vehicle's charging system. Ideal for setups running off smaller batteries or lower-output alternators common in Australian watercraft.
• Marine-grade two-part epoxy coated PCB: Circuit boards are sealed against moisture, humidity, and salt spray essential for open-water use in coastal and estuarine conditions around Australia.
• Tri-stage protection (thermal, over-current, short circuit): Three independent protection circuits monitor the amplifier continuously, shutting down safely before damage occurs. Reduces the risk of failures in hard-to-access install locations.
• On-board Punch EQ (+18 dB @ 45 Hz): Adds the signature Rockford bass punch without needing an external equaliser. Effective for wakeboard towers, transom-mount speakers, and powersport speaker pods where bass naturally dissipates outdoors.
• Bridgeable to 2-channel operation: Run the M400-4D as a stereo amplifier delivering 200W x 2 at 4 ohms bridged. Useful for systems combining full-range speakers up front with a bridged subwoofer channel at the rear.
• Variable crossover on all channels (50 Hz – 500 Hz, 12 dB/octave Butterworth): Independent crossover control on front and rear channels allows precise frequency management across different speaker types in the same system.
• 2/4 channel input switch: Use two RCA inputs to drive all four output channels, simplifying installation when a head unit has limited preamp outputs common on marine and powersport source units.
• Cast aluminium heatsink with convection cooling: Passive cooling with no moving parts. Reliable long-term in dusty, salty, and wet environments where fan-cooled amplifiers would accumulate contamination.
• Top-mounted controls: All gain, crossover, and EQ adjustments are accessible from the top of the unit. Makes setup and fine-tuning straightforward even in tightly installed locations.
• Compact chassis: At 50 x 172 x 231 mm, the M400-4D fits into installation locations that standard 4-channel amplifiers cannot. Ideal for smaller vessels and under-seat mounting in powersport applications.

Technical Specs

Compatible With

• Marine vessels: bow riders, pontoons, fishing boats, tinnies, and ski boats
• Powersport applications: UTVs, side-by-sides, jet skis, dune buggies, and ATVs
• Wakeboard tower speaker systems (4-channel full-range drive)
• Transom-mount and pod-mount marine speakers
• Bridged subwoofer configurations (200W x 2 @ 4 ohms bridged)
• Factory and aftermarket marine head units with 2 or 4 RCA preamp outputs
• Rockford Fosgate Prime and Punch marine speaker series
• Systems requiring compact amplifier footprint in space-restricted enclosures

Frequently Asked Questions

Is the M400-4D fully waterproof? The M400-4D features a marine-grade epoxy-coated PCB and corrosion-resistant construction, but it is not fully submersible. Mount it in a protected location away from direct water exposure and spray where possible.

Can the M400-4D be bridged to run a subwoofer? Yes. The M400-4D is bridgeable, delivering 200W x 2 at 4 ohms in bridged mode. This allows two channels to drive a subwoofer while the remaining two channels power full-range speakers.

What does the 2/4 channel input switch do? It allows two RCA inputs to feed all four output channels simultaneously. This is useful when your head unit only has one stereo preamp output, simplifying wiring without sacrificing all four amplifier channels.

How efficient is Class-D compared to Class-A/B for marine use? The M400-4D's Class-D topology averages 80% efficiency at 4 ohms, drawing considerably less current than a Class-A/B amplifier of equivalent output an important advantage when running off a boat or UTV's charging system.

What power wiring does the M400-4D require? Rockford Fosgate specifies 4 AWG power and ground wiring for the M400-4D. Confirm recommended fuse rating with your installer or the supplier prior to installation.