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Kenwood made their reputation building car amplifiers that offer no-nonsense reliability and superior sound quality. The compact KAC-8404 4-channel amplifier features a rugged cast-aluminum chassis more than 40% smaller than its predecessor, yet it'll still pump out 50 watts RMS to each of 4 channels — ideal for improving the performance of the front and rear speakers in your system. Or, you can bridge the amp to 2-channel mode and drive a couple of subs with 180 watts RMS each without straining your car's electrical system.

Built-in high- and low-pass filters adjust the amplifier output so you'll get the best sound possible from your speaker or subwoofer combo, while the variable bass boost lets you dial in up to 18 dB of bass boost, if you want to fatten up the sound.

The front-mounted controls allow you to tweak the sound easily, and convenient front-side connections make setup a snap. Signal sensing turn-on and speaker-level inputs allow these amps to hook up to factory radios that don't have preamp level outputs.

Product Highlights:

  • 4-channel car amplifier
  • 50 watts RMS x 4 at 4 ohms (75 watts x 4 at 2 ohms)
  • 180 watts RMS x 2 bridged output at 4 ohms (4 ohm stable in bridged mode)
  • 2-, 3-, and 4-channel operation
  • CEA-2006 compliant
  • high-pass (12 dB per octave) and low-pass (24 dB per octave) filters variable from 50 to 200 Hz
  • variable bass boost (0-18 dB at 40 Hz)
  • cooling fan
  • MOSFET power supply
  • speaker-level inputs with signal sensing turn-on
  • preamp-level inputs
  • fuse rating: 40A x 1
  • 8-gauge power and ground leads recommended — wiring and hardware not included with amplifier
  • 11-1/16"W x 2-5/16"H x 9-7/8"D
  • warranty: 1 year
  • Our 60-day money-back guarantee

My system has plenty of power. Who needs an amp?

You might think you don't need an amp because you have a 400-watt system in your car, or because your new stereo puts out 50 watts a channel. But those are peak wattage ratings, which may boil down to 15 or 20 watts per channel, using the more realistic RMS rating. An amp sends your speakers the power they need to deliver your music with clarity and impact, whether you're using factory speakers or high-performance components. And low-frequency reproduction requires lots of power, so an amp is an absolute must if you're adding a sub to your system.

Kenwood KAC-8404 Reviews

Average Customer Review:

6 Reviews

Good Amp

Written by: Dave from Mentor, OH on November 7, 2009

Crutchfield Customer Review (What's this?)

This is amp was perfect for the power i needed for my kenwood speakers. sounds
great, and gets loud! Im a proud owner of this amp now. the heart to my great
clean sound of car.



Very flexible, you can't go wrong

Written by: Michael from Bronx, NY on August 16, 2009

I can only speak of how this amp handles mids & highs, since I have a
separate dedicated amp for my subs. The sound is very crisp & clean. It's
powering 6.5-inch Kenwoods in the front and rear factory speakers of
my '02 VW Golf. It was a HUGE improvement over my last 4-channel amp
once I took the time to tweak the settings. I'm a perfectionist, so it took me
about a week to get it just right for my tastes. I'd keep the cover off for a
while as you'll find yourself making minor adjustments as you drive around.
I have the gain on the front channels slightly higher than the rears and
have both the front/rear channels on HPF at around 100 Hz.

Anyway, my only minor setback was slight engine noise. The only time I
heard it was when I paused my iPod or was using bluetooth, but it still
annoyed me. You always hear about the importance of a good, solid
ground. I originally had the amp grounded to a distribution block along with
my sub amp. Instead, I ran a slightly longer ground wire directly to the
grounding point. After that, all I heard was dead silence when I revved the
engine with the music paused and the windows up.

Aside from performance, I prefer amps like this one whose connection
terminals are all on one side so the install is cleaner. I have it mounted low
on the driver's side trunk wall. For the price and performance, I think
this amp is more than a fair value.



lots of solid, clean power.

Written by: septone from seattle, wa on October 7, 2008

Crutchfield Customer Review (What's this?)

I have a Kenwood KAC-8404 powering all of my door and dash speakers, some polk audio 4x6 in the dash, 6x9 in the rear deck, and infiniti 51/4" in the front door. I can turn it up to the point where it actually begins to hurt the ears without any distortion.

The highs are crisp and clean. :)

I'm very happy with this amp.



Put your Kenwoods together

Written by: Neal from Chicago on June 12, 2008

I put this Kenwood KAC-8404 with a Kenwood SR700 (sirius built-in satelite receiver). Pair of Kenwood KFC 1682ie 3way speakers and pair of Kicker 6 1/2" Midbass/subwoofer 04SSMB6. All which fit in the doors of my Colorado. Sound is excellant, size is great and power is perfect for vehicle.



Excellent choice when you're on a budget

Written by: Big Walt from Moreno Valley, CA on May 28, 2008

This amp sounds
AWESOME!!! I'm using
it to power a pair
of 5 x 7 Infinity
Reference Series
component speakers
and a pair of
Infinity 5 x 7 Kappa
Series 2 way
speakers with ZERO
distortion. Because
of budget issues(not
enough money LOL) I
have to wait to
install a sub, but
the mids thump hard
enough to keep me
content until then.
Originally I had an
Infinity 5 channel
amp, but it was just
too big, this amp is
perfect for the
amount of space that
I'm playing with.
You can't go wrong
with this amp.



Great Buy

Written by: Ashley from Clintonvile, WI on April 12, 2008

I used this amplifier to power a set of 6.5" component speakers and a 10" subwoofer. The flexibility of the variable crossovers and 3 way capability make this amplifier an excellent all in one amplifier. Plenty of power for the subwoofer, and the component speakers really sound great. Overall this amp combined with the new speakers added an amazing amount of depth to my music. Volume levels can be cranked up much higher now due to the clean boost in power.



Hands-on research

What's in the box?

Download owner's manual

  • 4-channel amplifier with 40-amp blade fuse inserted into the chassis
  • Allen wrench
  • Speaker level input harness
  • Rubber terminal cover
  • Four 3/4" Self-tapping screws
  • Instruction Manual (English/French/Spanish)
  • Warranty information

Product Research



CEA-2006 Compliant: CEA-2006 is a new system of testing & measurement methods for mobile audio amplifiers. This voluntary standard advocates a uniform method for determining an amplifier's RMS power output and signal-to-noise ratio. The criteria for measuring power uses a DC input voltage of 14.4 volts and the RMS power output is measured into a 4-ohm load, with 1% or less Total Harmonic Distortion (THD) plus noise, and at a frequency range (for full range amplifiers) of 20 Hz to 20,000 Hz. Signal-to-Noise ratio is measured in weighted absolute decibels (dBA) at a reference of 1 watt into 4 ohms. CEA-2006 allows consumers to compare car amplifiers and receivers on an equal basis. The Kenwood KAC-8404 under CEA-2006 regulations is rated at 50 Watts RMS x 4 channels with a 80 dBA signal to noise ratio.

Bridgeable: The Kenwood 4-channel amplifier features two stereo amplifiers inside one chassis that not only can be used in a 4-channel configuration but also can be bridged and used in a 2-channel or 3-channel configuration. The amplifier is rated at 180 Watts x 2 at 4 ohm in 2-channel mode and 50 Watts x 2/180 Watts x 1 at 4 ohm in 3-channel mode.

MOS-FET Switching Power Supply: The amplifier utilizes a MOS-FET switching power supply providing thermal stability and efficient switching speeds guaranteeing performance and dependability.

Control Cover: The Kenwood KAC-8404 features a brushed aluminum top cover that conceals all of its controls. This provides a very clean look as well as protects the amplifier's controls from being accidentally changed. The cover is held in place by two hex head screws. An allen-wrench is supplied to remove the cover.

Crossovers: The KAC-8404 has built-in high pass and low pass crossovers. The high pass crossover's slope is 12 dB/octave and is continuously variable from 50Hz to 200Hz and can be controlled independently for the A (Front) and B (Rear) channels. The low pass crossover's slope is also 12 dB/octave and continuously variable from 50Hz to 200Hz and can be controlled independently for the A (Front) and B (Rear) channels. The amplifier can also be operated at full-range simultaneously for both A (Front) and B (Rear) channels.

Bass Boost: A fixed bass boost of 18dB at 40Hz can be engaged for Amplifier B (Rear) only. There is no bass boost for Amplifier A (Front).

Stereo/Mono Operation: You can independently switch Amplifier A (Front) and Amplifier B (Rear) from Stereo to Mono operation. When switched to Mono, the signal from the left channel input only is used.

Line Level Inputs: Amplifiers A (Front) and B (Rear) each have separate line-level RCA inputs with independent gain (Input Sensitivity) controls. The Input Sensitivity controls will accept an input signal of 200mV to 5.0 Volts.

Signal Sensing Speaker Level Input: The KAC-8404 comes with a 4-channel speaker level input harness.  This feature makes it easier to add an amplifier to a factory radio or a receiver with no preamp outputs. You don't need to connect the remote turn-on wire when using the speaker-level input harness because the power of the amplifier is turned "On" and "Off" as the amp detects input signal from the unit's speaker level input.

Built-In Fans: There are two fans and two vents located on the back side of the amplifier to help dissipate heat and ensure cool, reliable operation. Make sure not to block these vents or fans when you install the amplifier.

Power Indicator: When the power is turned on to the amplifier, the Power indicator will light up red. This indicator will turn off with the amplifier and will turn off if the amplifier goes into protect mode. The amplifier also features a Blue LED lamp on the top of the amplifier which illuminates when the amplifier is on.

Protection circuitry: The amplifier features protection circuits that will turn the amp off in case of the following events to protect the amplifier and your speakers:

  • Speaker output contacts ground
  • Speaker wire short-circuits
  • Unit malfunctions and DC is sent to speaker output
  • Internal temperature is too high
  • Loss of ground of head unit or amp


Top of the Amplifier: All of the amplifier's controls are found on top of the amp under the removable brushed aluminum cover.

  • A-Channel Crossover: High Pass/Low Pass/Off
  • A-Channel Operation Mode: Stereo/Mono
  • A-Channel Crossover Frequency: 50-200 Hz
  • A-Channel Input Sensitivity: 200 mV-5 V
  • B-Channel Crossover: High Pass/Low Pass/Off
  • B-Channel Operation Mode: Stereo/Mono
  • B-Channel Crossover Frequency: 50-200 Hz
  • B-Channel Input Sensitivity: 200 mV-5 V
  • Bass Boost (B-Channel only): On/Off


Front of the Amplifier: All of the amplifier's connections are found on the front of the amplifier for easy access.

  • Fuse: 40 amp
  • Power: Gold-plated screw terminal (0.5625" wide)
  • Ground: Gold plated-screw terminal (0.5625" wide)
  • Remote Turn-On: Gold-plated screw terminal (0.3125" wide)
  • Speaker Outputs: Gold-plated screw terminals (0.3125" wide)
  • A and B Line In: Two pair of gold-plated RCA inputs
  • Ground Screw: Phillips-head screw for RCA signal ground if needed
  • Speaker-Level Input: Multi-pin input for use with included speaker level input harness

Note: The amplifier features a brushed aluminum top cover used to hide the unit's controls and which also needs to be removed to access the Power, Ground, Turn-on, and Speaker terminals. The cover is held in place by two small hex-head screws which are removed using the supplied hex-key. Once all connections and control adjustments are made, the top cover should be re-installed.

Our Product Research Team

At Crutchfield, you'll get detailed, accurate information that's hard to find elsewhere. That's because we have our own in-house Product Research team. They verify what’s in the box, check the owner's manual, and record dimensions, features and specs. We stay on top of new products and technologies to help people make informed choices.