JL Audio RD900/5+ RD Series 5 Channel Stereo Subwoofer Amplifier 900w RMS

The JL Audio RD900/5+ is a 5-channel Class D system amplifier rated at 900 W RMS, from JL Audio's RD Series. It delivers 70 W RMS x 4 at 4 Ω plus 500 W RMS x 1 at 2 Ω (at 14.4 V), powering four speakers and a subwoofer from a single compact chassis.

This listing is for the RD900/5+. The original model is also listed as the JL Audio RD900/5. Remote subwoofer level control is available with the optional JL Audio RBC-1.

Key specifications

• Channels: 5 (4 main + 1 subwoofer), Class D
• Main channels (14.4 V): 70 W RMS x 4 @ 4 Ω, 100 W RMS x 4 @ 2 Ω
• Main channels bridged (14.4 V): 200 W RMS x 2 @ 4 Ω
• Subwoofer channel (14.4 V): 500 W RMS x 1 @ 2 Ω, 225 W RMS x 1 @ 4 Ω
• Crossovers: 12 dB/octave high-pass (main) and low-pass (sub), 50 Hz – 500 Hz variable
• Inputs: differential-balanced, switchable 200 mV – 2 V or 800 mV – 8 V RMS
• Fuse rating: 80 A; minimum power/ground wire 4 AWG
• Dimensions (H x W x D): 54 x 372 x 177 mm; weight 2.79 kg
• Remote level control: optional RBC-1 (subwoofer channel)

5-channel Class D system amplifier

The RD900/5+ is an all-in-one system amplifier designed to drive a subwoofer plus four satellite speakers. Using JL Audio's NexD™ switching technology, it produces 70 W into 4 Ω on each main channel and 500 W into the subwoofer channel. Each pair of main channels is fully bridgeable, delivering 200 W x 2 at 4 Ω for a powerful 3-channel configuration.

Signal processing controls sit on top of the amplifier beneath a removable protective cover. Each pair of main channels has a 12 dB/octave high-pass filter; the subwoofer channel has a dedicated low-pass filter. All three crossovers offer continuously variable frequency selection from 50–500 Hz. Dual-range, differential-balanced inputs accept a wide range of input voltages, and automatic turn-on is available via signal sensing or DC-offset sensing.

LED clipping indicators are fitted to each channel section, making input sensitivity setup straightforward without specialist equipment. The amplifier has a black powder-coated finish and a top-mounted dual-colour LED strip showing overall status. The subwoofer output level can be adjusted from the driver's seat using the optional RBC-1 remote level control (sold separately).

NexD™ switching technology

NexD™ is JL Audio's proprietary Class D switching technology, developed from their long-standing expertise in Class D amplifier design. It delivers high efficiency, low distortion and high power from compact amplifier chassis.

A standard fixed-frequency PWM design varies pulse width based solely on the audio input signal, which leaves it vulnerable to distortion caused by power supply sag — an issue common in real in-car environments. Feedback can correct this at lower frequencies but becomes impractical as audio frequency rises, limiting it to subwoofer applications.

For the subwoofer channel, JL Audio use a fixed PWM approach running at a switching frequency of 240 kHz — approximately four times higher than most Class D subwoofer amplifiers. This extends usable bandwidth to at least 500 Hz with minimal distortion, improves efficiency and keeps the circuitry compact.

For the full-range main channels, a variable self-oscillating modulator switches at well over 400 kHz. A feed-forward circuit sends information about the instantaneous power supply voltage to the modulator, combining it with the input signal to cancel distortion caused by supply voltage fluctuation before feedback is applied. This simplifies the overall feedback loop and maintains clean, accurate audio at all power levels.