MB Quart RA1-280.4 Reference 4-Channel Amplifier

The MB Quart RA1-280.4 is a compact four-channel car amplifier for powering front and rear speakers from an aftermarket or factory-based audio system. Its four-channel layout makes it suited to common full-range speaker upgrades where a head unit alone does not provide enough clean output. It is designed for universal vehicle applications and supports 2- or 4-channel operation.

Rated at 50 watts per channel into 4 ohms and 70 watts per channel into 2 ohms, the RA1-280.4 is intended for efficient power delivery to compatible full-range speakers. This makes it a practical match for many door-speaker, component-speaker, and coaxial-speaker installations. Independent crossover sections help tailor the signal for the speakers being used.

The amplifier uses MB Quart's Class SQ Class D topology, combining compact Class D efficiency with a four-channel configuration. A Q-Stasis low-noise preamplifier stage and FLUID-FETS output-device technology are part of its signal and output design. The specified signal-to-noise ratio is greater than 101 dB, with total harmonic distortion rated below 0.09%.

Variable high-pass and low-pass crossover controls are provided for channels 1 and 2 as well as channels 3 and 4. Each channel pair can be set to full-range, high-pass, or low-pass operation, with a 50 to 250 Hz adjustment range. A 0 to 9 dB bass-boost control provides an additional low-frequency adjustment when appropriate for the system.

For factory-audio integration, the RA1-280.4 includes DC Signal Sense auto turn-on capability. This feature can allow the amplifier to power on when it receives a signal, reducing the need for a separate remote turn-on lead in applicable installations. It uses RCA inputs and is intended to be installed with properly sized power, ground, speaker, and signal wiring.

Key Features

• Four-Channel Configuration: Powers up to four compatible full-range speaker channels.
• Class SQ Class D Design: Provides efficient multi-channel amplification in a compact chassis.
• 50/70-Watt Channel Ratings: Delivers 50 watts at 4 ohms or 70 watts at 2 ohms.
• Variable Electronic Crossovers: Lets each channel pair run full-range, high-pass, or low-pass.
• DC Signal Sense: Supports automatic turn-on from an incoming signal.
• 0-9 dB Bass Boost: Adds adjustable low-frequency output control when needed.

Design & Installation

The RA1-280.4 uses an aluminum heat sink to dissipate heat and heavy-duty connection hardware for power, ground, and speaker wiring. Its power supply is a MOSFET pulse-width-modulation design, while nickel-plated RCA inputs are designed for secure signal connections. The black amplifier chassis measures 11.0 inches long, 6.0 inches wide, and 2.25 inches high.

Install the amplifier on a secure surface with adequate ventilation and do not mount it upside down. MB Quart specifies 4 AWG power and ground cable requirements and accepts up to 12 AWG speaker wire at the terminals; the amplifier uses a 40A external fuse. Set each channel pair's crossover mode and 50-250 Hz crossover point to suit the connected speakers, and use compatible 2- or 4-ohm speaker loads.