JBL MS-A1004

4-channel car amplifier — 100 watts RMS x 4

  • JBL MS-A1004


  • JBL MS-A1004

  • JBL MS-A1004

  • JBL MS-A1004

  • JBL MS-A1004

  • JBL MS-A1004

  • JBL MS-A1004

  • JBL MS-A1004

  • JBL MS-A1004

  • JBL MS-A1004

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Item #: 109MSA1004

Review Summary

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Our take on the JBL MS-A1004

by Buck Pomerantz

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.

JBL's Tiny amps

JBL's stylish MS Series "Tiny" amps measure only 7" by 8" so you can tuck one into virtually any hiding place that has adequate ventilation. Or you can mount one in a prominent spot to show off the bright digital display with its tone and gain settings. These unique amps come with a setup CD and include built-in indicators that help you set the input level perfectly. They also feature preamp and speaker-level inputs so you can hook them up to almost any system.

MS-A1004 display

Read more

Digital signal processing

The MS-A1004 sends 100 watts RMS to each of your front and rear speakers for clear, powerful reproduction of your music. You can also switch the MS-A1004 into 2-channel mode to drive a couple of subs with 200 watts RMS each, and you can run the amp safely with 2-ohm subs in bridged mode. Digital processing gives you a wide selection of crossover points and a choice of three filter slopes to get just the right tone from your system.

Sophisticated circuitry

An optional remote bass controller does much more than just turn this amp up and down. This wireless controller works with multiple MS Series amps at the same time, coordinating the low frequencies of all the amps to blend smoothly so you don't get a bunch of mud when you boost the bass. A signal-sensing turn-on circuit eliminates the need for a separate lead from your receiver, and a special input mode allows this amp to work even when there's a factory amplifier in your car's system.

MS-A1004 inputs MS-A1004 power and speaker connections


  • 4-channel car amplifier
  • 100 watts RMS x 4 (2 to 4 ohms)
  • 200 watts RMS x 2 (2 to 4 ohms)
  • CEA-2006 compliant
  • selectable high- and low-pass filters (20-20K Hz; 6, 12, or 24 dB/octave)
  • optional wireless remote bass controller (automatically pairs with multiple JBL MS Series amps)
  • Class-D amplifier design
  • digital signal processing — settings stored in non-volatile memory, no settings lost if power is disconnected
  • input mixer distributes signal without need for Y-cables
  • speaker-level inputs (RCA adapters included)
  • "Hi2" input setting provides factory system amps with output loads, eliminating "speaker disconnected" error messages
  • CD for system setup included
  • preamp inputs and outputs
  • output level controls
  • fuse rating: 30A x 2
  • 8-gauge power and ground leads and an 60-amp fuse recommended — wiring and hardware not included with amplifier
  • 7-1/4"W x 2-13/16"H x 8-13/16"D
  • warranty: 1 year
  • Our 60-day money-back guarantee

Hands-on research from the Crutchfield Labs (what are the Labs?)

Features and Specs
RMS Power Output (Watts x Channels) 100 x 4
Peak Power Output (Watts x Channels) N/A
Power at 2 Ohms (Watts x Channels) 100 x 4
Bridged Power (Watts x Channels) 200 x 2
Minimum Impedance Bridged 2
Minimum Impedance Unbridged 2
Best Frequency Response 10-27000 Hz
THD at Rated RMS Power 1%
Signal to Noise Ratio 80 dB
Input Voltage 14.4v
Amplifier Class D
Low-Pass Crossover Frequency 20-20 kHz
Low-Pass Slope (dB/octave) 6, 12, 24 dB/oct
High-Pass Crossover Frequency 20-20 kHz
High-Pass Slope (dB/octave) 6, 12, 24 dB/oct
Bass Boost Optional remote only
Bass Boost Frequency N/A
Fan Cooled No
Fuse Rating 60
Speaker Level Inputs RCA
Preamp Outputs 1 pair
Width (inches) 7-1/4
Height (inches) 2-13/16
Depth (inches) 8-13/16
Parts Warranty 1 Year
Labor Warranty 1 Year
Product Research
What's in the box?

Download owner's manual

  • 4-Channel amplifier
  • Two 30-amp ATO fuses (installed)
  • 4 Speaker wire to RCA adapters
  • 4mm Allen wrench
  • 2.5mm Allen wrench
  • Setup CD
  • Owner's manual

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 open the box, verify contents, 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.



Digital Signal Processing: The MS-A1004 is a four channel amplifier with a digital signal processor (DSP) built in to control input mixing, crossover settings, and output level. Once the gain is adjusted for the incoming signals, they are converted from analog to digital and routed through the DSP, then to the Class-D amplifier.

4-Channel Design: While four channel amps are typically used to power front and rear speakers, the input and output channels are labeled 1-4 for maximum flexibility without added confusion. Because the crossovers can be set to high-pass, low-pass, or band-pass with crossover points ranging from 20 Hz to 20 kHz, the MS-A1004 can be used to power almost any combination of speakers; four full range speakers, two tweeters and two midrange (powered separately), two full range speakers and a subwoofer (bridged), two subwoofers (both bridged), etc. Channels one and two share controls, as do channels three and four. Controls include input gain, input mixer, high-pass crossover, low-pass crossover, and output level.

Setup Disc: The included setup CD is used to correctly adjust the input gain. With the amp in setup mode, a test tone is output from the disc with the radio at full volume (the amplifier output is muted) and the amp measures the line voltage, guiding you with arrows on the display as you adjust the gain controls.

Signal Sensing: The MS-A1004 has a remote turn-on terminal that activates the amp with an input between +5 and 12+ volts DC. If the connected radio has no remote lead, or you prefer not to use it, turn on the signal sensing turn-on circuit and the amp will turn on whenever an audio signal is present at the inputs.

Crossovers: Each set of outputs (1/2 and 3/4) has independent high-pass and low-pass crossovers; they can be used individually or both can be used together as a band-pass crossover. The slope of each is adjustable (6 dB/oct, 12 dB/oct, and 24 dB/oct) and the crossover point has 98 options:

  • 20 Hz to 45 Hz in 2.5 Hz steps
  • 50 Hz to 130 Hz in 5 Hz steps
  • 140 Hz to 300 Hz in 10 Hz steps
  • 350 Hz to 800 Hz in 50 Hz steps
  • 900 Hz to 2 kHz in 100 Hz steps
  • 2.2 kHz to 5 kHz in 200 Hz steps
  • 5.5 kHz to 10 kHz in 500 Hz steps
  • 12 kHz to 20 kHz in 2 kHz steps
  • Off

Subsonic Filter: When powering a subwoofer, the high-pass crossover can be adjusted to act as a subsonic filter (20 Hz, 25 Hz, etc).

Audio Input: If your radio has no line-level outputs, use the included adapters to convert the speaker wires to RCA and plug them into the amplifier's inputs. The differential inputs will accept any signal from 100mV to 15.0V; set the input selector switch to Hi when using speaker-level inputs. The input selector switch also has a Hi2 position, used to present a speaker load to factory radios equipped with a circuit that turns the radio off when an amp is connected.

Wireless Bass Control: An optional MS-WBC wireless bass control (item number 109MSWBC, sold separately) is available to remotely adjust the bass output. The MS-WBC communicates via RF signal and requires no physical connection to the amp; it's also battery powered, but has an optional power wire if you prefer not to replace the battery periodically. When adjusting the bass output, the DSP also adjusts the crossover, so the tonal quality of the bass (and its apparent location) doesn't change.


Controls: Each of the following is set independently for the 1/2 channel and 3/4 channel outputs:

  • Input Gain: rotary knobs
  • Input Selector: three position switch; Lo (line-level RCA), Hi (speaker-level), or Hi2 (used only with factory radios having a circuit that turns the radio off when it sees no speaker load)
  • Input Mixer: one, two, three, or four inputs can be used with no need for Y-adapters; 1 (mono input 1 feeds both outputs), 1/2 (stereo inputs 1 and 2 feed the stereo outputs), 3 (mono input 3 feeds both outputs), 3/4 (stereo inputs 3 and 4 feed the stereo outputs)
  • High-Pass Crossover Slope: 6 dB/oct, 12 dB/oct, or 24 dB/oct
  • High-Pass Crossover Frequency: choose from 97 options from 20 Hz to 20 kHz, or off
  • Low-Pass Crossover Frequency: choose from 97 options from 20 Hz to 20 kHz, or off
  • Low-Pass Crossover Slope: 6 dB/oct, 12 dB/oct, or 24 dB/oct
  • Output Level: adjust from 0 to 80; important when matching tweeters and midrange, subwoofer and full range speakers, etc


Inputs and Outputs:

  • Power and Ground Terminals: set screw terminals; accept up to 4 gauge bare wire; requires included 4mm Allen wrench
  • Remote Turn-on Terminal: set screw terminal, accepts up to 8 gauge bare wire; requires included 2.5mm Allen wrench
  • Speaker terminals: set screw terminals, accept up to 8 gauge bare wire; require included 2.5mm Allen wrench
  • Audio Inputs: 4 female RCA jacks; channels 1, 2, 3, and 4; compatible with a speaker level signal using the included adapters
  • Line Level Outputs: 2 female RCA jacks; top is summed from inputs 1 and 3, bottom is summed from inputs 2 and 4; no crossover is applied
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JBL MS-A1004 Reviews

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5 out of 5


Written By JBL AMP, texas on Saturday, March 09, 2013
Crutchfield Customer Review (What's this?)
This is one of my favorite amps ever!! really makes my kappa sound amazing
Small, easy install, digital display is amazing, easy to change settings and small enough to hide very well. good job !
Was this review helpful?    Yes | No
5 out of 5

JBL MS-A1004

Written By RichardM, Eugene, OR on Tuesday, October 18, 2011
Crutchfield Customer Review (What's this?)
I installed this amplifier 2 weeks ago, and it was entirely hassle free, if anything it's DPS features made it the easiest system set up I've ever done. Sound quality from it is amazing, class Ds have really evolved over the year. Even though it has a very small footprint it's power output ratings are very conservative, especially at 2ohm. I can also vouch for the fact it's 2ohm stable in bridged mode too.

I do have one complaint with JBL but not the item itself, Crutchfield shipped a new (not open box) but arrived with the MSA1004 box, but enclosed was a MSA5001 which required me to initiate an RMA. It is very unnerving when a company improperly packages something with a price tag like this has. It cost me several days to finish my install. But I'm only rating the amp itself and it is a solid 5 star and very satisfied with it.
5 out of 6 people found this helpful
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5 out of 5

JBL MS-A1004

Written By David V, Tampa, FL on Thursday, June 30, 2011
I have installed four of these amplifiers in my vehicle, and all are run bridged into two channels. Very stout construction. The amps sound good in my opinion as I had a concern about not sounding as good as a conventional class AB amp. I especially like how easy it is to set the gains on the unit, which is different and improved from any other amplifier I know of. I set my head units volume to max volume before clipping, play the setup CD, and set the input gains until the display tells me it is correct. Then the output side is set which can also be used as a level matching with the other amplifiers. Never had I ever had such easy and precise process setting amplifier gain.

Then instead of having another knob to turn for crossover slope, the digital display shows you exactly what frequency the crossover is set to. I do not need a real time analyzer now to precisely set crossover slopes.

The only thing that I wish were improved was more power output in bridged mode, such as is offered by the JL HD amps or the infinity Kappa amps, which are 300 watts a channel bridged. However, being an IASCA sound quality competitor this amplifier fits the bill of precise gain and crossover settings for me. And with the compact size I was able to install four of them in my vehicle.
9 out of 12 people found this helpful
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5 out of 5

JBL MS-A1004

Written By Brad, USA on Wednesday, June 01, 2011
I have installed a few of these amplifiers now into customer vehicles. I would like to say first that proper setup is decently complicated if you do not have experience with tuning vehicles. Secondly, I have found these amps (and the msa-5001) to have perfectly adequate output given their rating. It sounds to me like the other reviewer has an install or setup issue. My guess would be improper output settings or improper voltage drop; be it a poor ground, bad battery connection, etc.

This amp is not the most powerful, but honestly it will amplify a set of passive components without issue. I would typically give this amp a four star rating, BUT then there is the DSP capability.

Great flexibility in an amplifier without a dedicated piece of DSP equipment. Because of this, and it's price point, I gave it 5 stars.
14 out of 15 people found this helpful
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1 out of 5

Dissapointing in every way

Written By James, CT on Monday, May 02, 2011
Crutchfield Customer Review (What's this?)
This amp is in no way capable of providing anywhere near the promised output power. Show it any type of load and it will simply cut out for around 10 seconds. When it comes back on your settings may or may not be the same. I can't tell if the amp is trying to be 'smart,' or if the changes are just arbitrary, but the high/low pass and output gain are usually different afterwards. It's not the amp overheating either...it's barely lukewarm all the time and will cut out/reset immediately after turning on with the volume at a decent level. I am led to believe that this is some kind of design defect, as it will cut out at the same volume level whether I am running one speaker per channel, or two with the amp bridged. All setup instructions were followed...repeatedly...because I was sure I had done something wrong the first couple times, but it's going to have to go back.
10 out of 50 people found this helpful
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For a more in-depth review and enhanced detailed information on the JBL MS-A1004, please visit the Crutchfield website product page (/ISEO-rccbcspd/p_109MSA1004/JBL-MS-A1004.html ).