Features
Controls
Connections

Features

RD Series: The JL Audio RD series amplifiers feature big audio performance from a small footprint. With exclusive NexD switching technologies, the RD amps run cooler than most other amplifiers. Because the RD amps employ smaller cast alloy heat sinks, they can be installed in smaller spaces. RD amplifiers feature a black powder-coat finish with a brushed aluminum cover for the controls.

Four-channel Class-D Amplifier: The RD400/4 is a Class-D 4-channel amplifier, designed specifically for full-range operation, but can be used to power subwoofers. The amplifier is stable down to 2 ohms in stereo, or bridged to a 4 ohm load.

Amplifier Rating: The RD400/4 has the following power output:

• 75 Watts RMS x 4 channels at 4 ohms
• 100 Watts RMS x 4 channels at 2 ohms
• 200 Watts RMS x 2 channels at 4 ohms bridged

Differential-Balanced Inputs: The RD400/4 features differential-balanced input architecture to effectively control noise and ensure compatibility with a wide variety of source units, including many OEM systems. Without resorting to line output converters, you can directly connect most OEM source units to the amplifier without creating any noise or compatibility issues. Unlike conventional single-ended inputs, the differential-balanced design does not connect one side of the audio signal to chassis ground. This eliminates any voltage sensitivity between one input terminal and ground and greatly reduces the incidence of alternator whine in a typical car audio installation.

Protection Circuitry With Status Indicator Lights: The amp features a bi-color LED light strip on the top panel of the amplifier to indicate the amplifier's operating status:

• Temporary Red: When the amplifier is powering up, the light strip turns red for 3 seconds and audio output is muted.
• Constant Blue: The LEDs light blue to indicate that the amplifier is turned on and operating normally.
• Constant Red: The LEDs light constant red to indicate that the amplifier has exceeded its safe operating temperature, putting the amplifier into a self-protection mode, which mutes the power output of the amplifier. The red LEDs will shut off and the amplifier will return to normal, full-power operating mode when the temperature drops back to a safe level.
• Momentary Red: The light strip will light red for 1/2 second and the output will be muted to indicate that an over-current condition has occurred. Over-current condition can be caused by a speaker impedance lower than the optimum load impedance range for the amplifier or a short-circuit in the speaker wiring.
• LEDs Off: The only condition that will shut down an undamaged RD400/4 completely is if battery voltage or remote turn-on voltage drops below 10 Volts. The amplifier will turn back on when voltage climbs back above 11 Volts.

Cooling System: The outer shell of the JL Audio amplifier is designed to remove heat from the amplifier circuitry. For optimum cooling performance, this outer shell should be exposed to as large a volume of air as possible.  Enclosing the amplifier in a small, poorly ventilated chamber can lead to excessive heat build-up and degraded performance.

Controls

Control Panel Cover: The RD400/4 features a brushed aluminum Control Panel Security Cover which protects and hides the amplifier's controls. When installed, the cover ensures that the amplifier's settings are not accidentally changed while creating a clean aesthetic look for the amplifier and your installation. The control panel security cover is pre-installed at the factory and must be temporarily removed to access the amplifier's controls. The security cover screws can be removed with the supplied 2.5mm Allen wrench.

LED Clipping Indicators: The amplifier is equipped with onboard LED clipping indicators which let you quickly and accurately set the amp's input sensitivity without special equipment. The simple, 7-step procedure using a Test CD and a screwdriver properly sets the input sensitivity to its optimum level.

Flexible Input Section and Active Crossover Network: The RD400/4 amplifier provides a flexible input section and a comprehensive crossover network to fine tune your system effectively and accurately. This 4-channel amplifier is divided into two separate pairs of channels, each with their own crossover:

• Filter: The front and rear channels are equipped with a 12 dB/octave Butterworth filter which can be configured as a low-pass (LP) or high-pass (HP) filter, or turned off. You can set the Filter Mode via a three-way switch.
• Filter Frequency: The filter frequency can be selected using the rotary control. There are markings at 50Hz, 60Hz, 80Hz, 120Hz, 200Hz, and 500Hz. You'll need a small screwdriver (not included) to set the frequency.

Turn-on Options: The Turn-on Mode Switch lets you choose the method for turning the amplifier on and off:

• +12V Remote Turn-on Lead: The preferred method for turning the amplifier on and off is by running a turn-on lead from the source unit and connecting it to the Remote terminal. When +12V is present at the terminal, the amplifier will turn on. When the +12V is turned off, the amplifier will shut off. The set screw connector on the Remote terminal will accept 18 AWG to 12 AWG wire.
• DC Offset-Sensing: The amplifier will turn on and off when the presence of a very small DC signal (or offset) is detected on the amp's RCA left channel input. The amplifier will turn off when this DC Offset is no longer present. This method is designed for high-level (speaker-level) input signals, not for low-level (line-level) signals.
• Signal-Sensing: The amplifier will turn on and off by detecting the presence of a full-range audio signal at the left-channel input. The amp will turn off approximately 30 seconds after the audio signal is no longer detected. This method is designed for use with high-level (speaker-level) input signals and not for low-level (preamp level) signals.

Input Controls: You can select the Input Voltage and Input Mode via two way switches:

• Input Voltage: The amp will accept a wide range of signal input voltages, from 200mV to 8V. The range is split into two sub-ranges: "Low" for preamp level signals from 200mV to 2V, and "High" for high-output preamp level signals and speaker level signals from 800mV to 8V.
• Input Mode: The Input Mode switch lets you send four discrete channels into the amplifier, or use only two channels to feed all four amplifier channels. You can set the Input Mode to 4 CH or 2 CH.

Connections

Power/Ground/Turn-On Terminals: This JL Audio RD amplifier features set screw clamp terminals for the power, ground, and remote turn-on connections. A 2.5mm hex-wrench is supplied for tightening or loosening the set screws.

• Power and Ground: The amplifier's set screw clamp Power and Ground connections are designed to accept up to 4 AWG power wire, as recommended by the manufacturer.
• Remote Turn-On: The amplifier's set screw clamp turn-on lead will accept 18 to 12 AWG wire.

Speaker Output Terminals: The JL Audio RD400/4 features eight set screw clamp speaker terminals for easy connection. Markings showing the proper way to bridge the amplifier are provided on the speaker terminals. The terminals will accept 16 to 8 AWG speaker wire.

Preamp Inputs: The amplifier features two sets of differential-balanced RCA jack inputs, each with an Input Voltage switch and rotary Input Sensitivity control. The amplifier's input voltage range is 200mV-2V (LOW) and 800mV-8V (HIGH).

Preamp Outputs: The RD400/4 incorporates a buffered pass-through preamp output section, so that additional amplifiers can be easily added to the system. The preamp output signal is not affected by the amp's crossover networks. The pass-through preamp output is a summed stereo signal (Channels 1&3 / Channels 2&4) to another amplifier.