JL Audio JD400/4


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JD Series 4-channel car amplifier — 75 watts RMS x 4

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SKU: JD400/4 Categories: , , Brand:


Power up your music

JL Audio’s JX Series amplifiers were very popular with our customers, garnishing rave reviews citing their tremendous performance and value. We think their latest JD Series amps will follow in their footsteps, offering superior power and serious features for your dollar. The JD400/4 four-channel amplifier will send 75 watts RMS to each of your front and rear speakers, guaranteeing you’ll hear and feel your music clearly over road and engine noise. JL Audio designed this amp to power high-performance speakers like their premium C3 and C5 Series components. If you’re just looking to fill your ride with bass, you can configure this amp for two-channel operation in order to power a pair of subwoofers with up to 200 watts RMS each.

Convenient features

Variable high- and low-pass filters allow you to tune the amplifier to match your particular speaker or subwoofer system. The amp includes speaker-level inputs with signal-sensing amp turn-on, along with preamp inputs and outputs, so it’s ready to work in virtually any system. Differential-balanced inputs plus JL Audio’s NexD™ amp technology keep the signal sounding pure and noise-free at all times.

Product highlights:

  • 4-channel car amplifier
    • 75 watts RMS x 4 at 4 ohms
    • 100 watts RMS x 4 at 2 ohms
    • 200 watts RMS x 2 bridged at 4 ohms (4-ohm stable when bridged)
  • full-range Class D amp design with NexD™ switching technology
  • frequency response: 12-22,000 Hz
  • variable low- and high-pass filter (50-500 Hz, 12 dB/octave)
More Info:
  • preamp inputs and outputs
    • differential-balanced inputs prevent noise
  • speaker-level input via speaker wire to RCA adapters
  • signal-sensing turn-on with speaker-level inputs
  • wiring, fuse, and hardware not included with amplifier
    • 4-gauge power and ground leads and a 40-amp fuse recommended
  • 9-7/8″W x 2-1/8″H x 7-1/2″D

What’s in the box:

  • 4-Channel amplifier
  • 2.5mm Hex key
  • 3mm Hex key
  • Owner’s manual

Product Research


Overview: The JL Audio JD400/4 is a 4-channel full-range Class D amplifier. It’s effectively two full-range 2-channel amps built into one chassis (labeled CH. 1&2 and CH. 3&4). Each section of the amp is bridgeable, so it can be wired as 4-channel, 3-channel, or 2-channel.

Amplifier Power Ratings:

  • At 14.4 volts: 20 Hz-20 kHz, <1% THD+N
    • 4Ω: 75 watts RMS x 4
    • 2Ω: 100 watts RMS x 4
    • Bridged 4Ω: 200 watts RMS x 2
  • At 12.5 volts: 20 Hz-20 kHz, <1% THD+N
    • 4Ω: 60 watts RMS x 4
    • 2Ω: 90 watts RMS x 4
    • Bridged 4Ω: 180 watts RMS x 2

Clipping LED: Using a sine-wave test tone (50 Hz for a subwoofer or 1 kHz for full-range speakers) recorded at 0 dB reference level (not included), the clipping LED helps you set the gain control to the maximum unclipped level.

Crossovers: Each 2-channel section of the amplifier has an independent 12dB/octave crossover; each can be set to high-pass, low-pass, or off (full range). The crossover points are independently variable from 50 Hz to 500 Hz.

Protection Circuitry: The JD400/4’s protection circuitry automatically turns the amplifier off if thermal limits are exceeded, a short circuit is detected in the speaker wiring, or the input voltage drops below 11 volts.


  • Input Sensitivity: rotary controls (independent for each 2-channel section); used to match your source unit’s output voltage to the input stage of the amplifier for maximum clean output; the range of the dial depends on how the Input Voltage switch is set
  • Input Voltage: 2-position switch:
    • Low: input sensitivity control (gain) range is 200mV-2V; used with the preamp output of typical aftermarket radios
    • High: input sensitivity control (gain) range is 800mV-8V; used with speaker level outputs and high output preamps
  • Crossover Mode: 3-position switches (independent for each 2-channel section):
    • Off: crossover is bypassed
    • HP: High-Pass
    • LP: Low-Pass
  • Crossover Frequency: rotary controls (independent for each 2-channel section); continuously variable from 50-500 Hz
  • Turn-on Mode: 3-position switch:
    • Remote: use when the source unit has a +12 volt remote turn-on wire (preferred method)
    • Offset: the amp reads a small DC signal typical on the speaker level output of factory radios (senses the offset on the channel 1 input)
    • Signal: detects a midrange speaker level signal on the input; turns off after approximately 30 with no signal
  • Input Mode: 2-position switch; set to the number of inputs used:
    • 2 Channel: in 2-channel mode the signal on the channel 1&2 inputs feeds all four output channels
    • 4 Channel: each output channel has a dedicated input


  • Power: The power, ground, and remote turn-on connections are set-screw terminals:
    • Power and Ground: accept up to 4-gauge wire (4-gauge minimum recommended); the included 3mm hex key is used to tighten/loosen the set-screws
    • Remote Turn-on: accepts up to 10-gauge wire (18-gauge minimum recommended); the included 2.5mm hex key is used to tighten/loosen the set-screw

Note: The amplifier is not equipped with a fuse. An external 40-amp fuse (not included) must be installed on the power wire. If a wiring kit is used which includes a fuse with a value other than 40-amps, the original should be replaced with a 40-amp fuse.

  • Speaker Output Terminals: The speaker outputs are set-screw terminals. They accept up to 8-gauge wire (16-gauge minimum recommended). The included 2.5mm hex key is used to tighten/loosen the set-screws.
  • Signal Inputs: Two pairs of stereo RCA input jacks accept either preamp or speaker level signals. When connecting speaker level signals, speaker wire to RCA adapter is useful.
  • Preamp Outputs: The stereo RCA preamp outputs pass the signal connected to the channel 1&2 inputs, so another amplifier can be added easily. The output is not affected by the JD400/4’s gain or crossover controls. The preamp output signal is buffered to prevent noise.

Note: When the input voltage switch is set to Low, the voltage of the RCA output matches the input; when set to High, the output voltage is attenuated -12 dB.