JL Audio RD900/5 RD Series Class D 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.

The RD Series is also available as the JL Audio RD500/1 monoblock subwoofer amplifier.

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 continuously variable
• Inputs: differential-balanced, switchable 200 mV – 2 V or 800 mV – 8 V RMS
• Automatic turn-on: signal sensing or DC-offset sensing
• 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 (sub channel, sold separately)

5-channel Class D system amplifier

The RD900/5 is designed as an all-in-one solution to power a complete system — four satellite speakers plus a subwoofer — from a single chassis. Using JL Audio's NexD™ switching technology, it produces 70 W x 4 into 4 Ω for the main channels and 500 W x 1 into 2 Ω for the subwoofer. Each pair of main channels is fully bridgeable, delivering 200 W x 2 into 4 Ω to run the amp as a powerful 3-channel unit.

Signal processing controls are located 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 voltage levels, with automatic turn-on via signal sensing or DC-offset sensing.

LED clipping indicators are fitted to each channel section, making it straightforward to set input sensitivity accurately without special equipment. The RD900/5 has a black powder-coated finish and a top-mounted dual-colour LED strip showing overall amplifier status. An optional RBC-1 remote level control (sold separately) allows subwoofer output to be adjusted from the driver's seat.

NexD™ switching technology

NexD™ is JL Audio's proprietary Class D switching technology, developed from the company's experience with the original 'Slash' subwoofer amplifiers. It delivers high fidelity, high efficiency and high power from compact amplifier designs.

A traditional fixed-frequency PWM switching amplifier varies pulse width based on the audio input signal alone, which assumes ideal conditions — such as a stable power supply — that rarely exist in a real car installation. Power supply sag under load causes distortion at all power levels, even well below clipping. Feedback can correct this at lower frequencies, making it workable for subwoofer amplifiers, but it becomes impractical at higher audio frequencies, ruling it out for full-range designs.

For the subwoofer channel, NexD™ uses an enhanced fixed PWM approach running at 240 kHz — approximately four times higher than most Class D subwoofer amplifiers. This extends bandwidth to at least 500 Hz with low distortion, improves efficiency, and keeps the circuitry compact.

For the full-range main channels, NexD™ uses a variable, ultra-high-speed self-oscillating modulator running at well over 400 kHz. A feed-forward circuit sends information about the instantaneous power supply voltage directly 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 reduces distortion throughout the audio band.