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Diamond Audio D400.1

Mono amplifier — 400 watts RMS x 1 at 2 ohms

Item # 114D4001

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Our take on the Diamond Audio D400.1

The Diamond D400.1 mono amp sends up to 400 watts RMS of clean, pure musical power to your subwoofer or speaker, with no audible coloration or distortion. The D400.1 comes with a remote level controller, so you can adjust the amount of bass from the front seat.

Sturdy internal components

Diamond Audio D400.1

From the outside, the uncommonly heavy aluminum chassis with its cool flying D logo tells you that this Diamond Audio amp is something special. And when you consider what's inside — high-grade components mounted on military-spec multi-layer circuit boards — you'll know you're looking at an amp that's built to last.

Full-range mono amp

The Diamond D400.1 mono amp sends up to 400 watts RMS of clean, pure musical power to your subwoofer or speaker, with no audible coloration or distortion. The D400.1 comes with a remote level controller, so you can adjust the amount of bass from the front seat.

Heat management

heatsink system Overheating destroys an amp's sound quality and longevity. Diamond's designers developed the focused mass heatsink, which draws heat away efficiently by attaching 75% of its mass directly to the components that create the most heat. The amp's output transistors also mount to the heatsink using a special system that provides better heat flow than commonly used clips.

More features that ease setup

The D400.1 features a variable low-pass filter, a bass boost, and a phase switch so you can tune your sub system to sound its best. But keep in mind that this is a full-range amp with a high-pass filter — you can use a pair of these amps to power component speaker systems with great results. A pair of preamp outputs make it easier to add more amps when you want, without having to run a new RCA cable to the receiver. And you'll also find speaker-level inputs for hooking the amp to a factory stereo that doesn't have RCA outputs.

Confused about impedance? Check out our article on matching subs and amps.

Product Highlights:

  • mono subwoofer amplifier
  • 250 watts RMS x 1 at 4 ohms (400 watts RMS x 4 at 2 ohms)
  • variable high- and low-pass filters (50-250 Hz, 12 dB/octave)
  • variable bass boost (0-12 dB at 50 Hz)
  • phase switch
  • remote level control included
  • focused mass heatsink improves cooling
  • Class AB amp technology
  • PWM MOSFET switching power supply
  • frequency response: 20-20,000 Hz
  • nickel-plated, low-resistance connectors
  • speaker-level and preamp inputs
  • preamp outputs
  • fuse rating: 30A x 2
  • 4-gauge power and ground leads recommended — wiring and hardware not included with amplifier
  • 13-1/2"W x 2-5/16"H x 8-11/16"D
  • warranty: 1 year
  • Our 60-day money-back guarantee

What's in the Box:

  • Mono amplifier
  • Remote level control
  • 16' Remote level control cable (RJ-14 connectors on each end)
  • Four 30 amp ATO fuses (2 installed/2 extra)
  • 12" Speaker input harness
  • Four 5/8" Self-tapping screws
  • Two 3/8" Self-tapping screws
  • Six split lock washers
  • Six flat washers
  • Installation manual
  • Diamond Audio logo badge (adhesive backed)

Hands-on research

Product Research



Full-Range Mono-Amplifier: The Diamond Audio D400.1 is a mono-amplifier that is capable of powering either a subwoofer or full-range speaker. It features a switchable crossover; low-pass, high-pass, or full range (crossover is bypassed).

2Ω Stable: The D400.1 can power loads as low as 2Ω; the RMS power output is 250 watts at 4Ω and 400 watts at 2Ω.

Remote Level Control: The amp has an RJ-14 jack for use with the supplied wired remote level control. The remote's rotary knob allows you to adjust the amp's output level between no output (minimum) and the gain setting on the side of the amp (maximum) from your listening position. The remote has integrated mounting flanges and includes two mounting screws to secure it to a flat surface in the front of the vehicle. The dimensions are 2" wide x 15/16" tall x 1-5/8" deep (2" including knob).

LEDs: Power and Protection LEDs are located on the side of the amplifier. A blue Power LED illuminates when the amplifier is turned on and operating normally. A red LED illuminates when any of the amplifier's protection circuits engage; thermal, short circuit, or too low an impedance.


Gain: The amplifier's input gain setting is adjusted to match the incoming signal voltage. The gain is continuously variable, line level from 150 mV to 5.0 V and speaker level from 5 V to 24 V.

Bass Boost: The bass boost, centered at 50 Hz, is variable from zero to +12 dB.

Subsonic Filter: This high-pass filter is designed to prevent frequencies below the audible range from being directed to the speaker. The subsonic filter improves subwoofer performance and power handling, particularly in vented enclosures. The subsonic filter can be turn on or off.

Crossover Switch: The internal crossover can be set to low-pass, high-pass, or full range (crossover is bypassed).

Crossover Frequency: The crossover frequency is continuously variable from 50 Hz to 250 Hz. The slope is 12 dB/oct.

Phase: If needed, the phase of the D400.1 can easily be reversed to blend better with the rest of the system; choose 0° or 180°.


Power Connections: The power and ground terminals are nickel plated set screws and will accommodate up to 4-gauge wire. The remote turn-on terminal will accept up to 10-gauge wire. 4mm (power and ground) and 2mm (remote) Allen wrenches (not included) are required to tighten/loosen the terminals.

Dual Speaker Terminals: The amplifier features two pair of speaker output terminals so you can easily connect two subwoofers. The nickel plated set screw terminals will accept up to 8-gauge wire. A 3mm Allen wrench (not included) is required to tighten/loosen the terminals.

RCA Inputs: The D400.1 features a pair of RCA input jacks for easy connection to the source unit's line level output. The RCA input jacks are nickel plated to resist signal degradation caused by corrosion.

Speaker Inputs: Use the included speaker-level input harness to supply signal to the amp when the receiver has no RCA outputs.

RCA Outputs: The amplifier also features a pair of Pass-Thru RCA jacks, providing a convenient method of daisy-chaining an additional amplifier without running an extra set of RCA cables from the front of the vehicle. The RCA output jacks are nickel plated and are unaffected by the D400.1's crossover and bass boost circuitry.

Remote: An RJ-14 jack is provided for connecting the included remote level control. The remote adjusts between no output (minimum) and the gain setting on the side of the amp (maximum).

Our Product Research Team

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