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JBL GX-A604

4-channel car amplifier — 60 watts RMS x 4

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Our take on the JBL GX-A604

by Buck Pomerantz
JBL

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.

Power for clarity

JBL has been designing and building sound systems for decades, so they know a thing or two about power. Their GX-A604 4-channel amplifier can send 60 watts RMS to each of your front and rear speakers, about five times the power of most factory radios. The GX-A604 includes speaker-level inputs, so it's perfect for upgrading the power in a factory system. 

Versatile tone filters — versatile amp

You can also use the GX-A604 in 3-channel mode, using the front channels to power your front speakers, and bridging the rear channels together to drive a subwoofer with 170 watts RMS. A high-pass filter cleans up the sound by removing extreme low bass from small full-range speakers, allowing them to play louder and cleaner. You can switch the rear filter to low-pass mode when you're driving a subwoofer, while the built-in bass boost adds some punch when you're in the mood.

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Highlights:

  • 4-channel car amplifier
  • 60 watts RMS x 4 at 4 ohms (85 watts RMS x 2 at 2 ohms)
  • 170 watts RMS x 2 at 4 ohms in bridged mode (4-ohm stable in bridged mode)
  • switchable high-pass filters (80 Hz, 12 dB/octave) on front channels
  • variable high- and low-pass filters (32-320 Hz, 12 dB per octave) on rear channels
  • switchable bass boost (0, 12 dB at 45 Hz) on rear channels
  • preamp and speaker-level inputs
  • fuse rating: 20A x 2
  • 10-gauge power and ground leads recommended — wiring and hardware not included with amplifier
  • 11-13/16"W x 2-1/16"H x 8-1/8"D
  • warranty: 1 year
  • Our 60-day money-back guarantee

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

Features and Specs
Performance
RMS Power Output (Watts x Channels)
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60 x 4
Peak Power Output (Watts x Channels)
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---
Power at 2 Ohms (Watts x Channels)
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85 x 4
Bridged Power (Watts x Channels)
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170 x 2
Minimum Impedance Bridged
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4
Minimum Impedance Unbridged
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2
Best Frequency Response
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20-20000 Hz
THD at Rated RMS Power
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1%
Signal to Noise Ratio
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75 dB
Input Voltage
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14.4v
Features
Amplifier Class
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AB
Low-Pass Crossover Frequency
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32-320 Hz (R)
Low-Pass Slope (dB/octave)
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N/A
High-Pass Crossover Frequency
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80 (F) / 32-320(R)
High-Pass Slope (dB/octave)
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N/A
Bass Boost
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0, 12 dB (R)
Bass Boost Frequency
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45 Hz
Fan Cooled
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No
Fuse Rating
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40
Speaker Level Inputs
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Harness x2
Preamp Outputs
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No
Width (inches)
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11-13/16
Height (inches)
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2-1/16
Depth (inches)
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8-1/8
Parts Warranty
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1 Year
Labor Warranty
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1 Year
Product Research
What's in the box?

Download owner's manual

  • 4-Channel amplifier with two 20A ATO fuses installed
  • Two 8.25" Speaker-level input harnesses
  • 4 Self-tapping screws (Length=3/4")
  • 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.

Features
Controls
Connections

Features

Power Output: The JBL GX-A604 Class AB 4-channel amplifier delivers the following power output (RMS Power Output @ 1% THD+N, 14.4 VDC):

  • 60 watts x 4 @ 4 ohms
  • 85 watts x 4 @ 2 ohms
  • 170 watts x 2 bridged into 4 ohms

Protection Circuitry: The amplifier features protection circuitry for thermal overload, over- or under-voltage (<9V or >16V), and short circuits. The LED on the end of the amp glows red if the amp goes into protection mode.

Controls

Input Level: The GX-A604's rotary gain control let you match the amp's input sensitivity to the output of the source unit. There are independent input level controls for the front and rear channels. The input sensitivity range of the amplifier is continuously variable between 200mV and 12V. A small screwdriver (not included) is required to set the gain.

Input Mode: The amp's 4 channels can be driven by input signals from 4 channels. If you only have 2 channels of input, the Input Mode can be switched to "2CH" and all four channels will receive audio signal from the two connected inputs. The switch should remain at "4CH" if there are 4 inputs connected.

Crossover: The amp features separate crossovers for the front and rear channels. For the front, there is a selectable 80Hz high-pass filter with an On/Off switch. The rear channels feature a 32Hz to 320Hz variable crossover. A 3-way switch lets you configure the crossover for high-pass or low-pass operation, or switched to "flat" to defeat the crossover.

Bass Boost: The GX-A604 has a switchable 12dB bass boost, centered at 45Hz, for the rear channels. This is useful when using the rear channels of the amplifier in bridged mode to power a subwoofer.

Connections

Terminals: The JBL GX-A604 uses screw terminals for the +12V power, ground, turn-on (remote) lead, and speaker outputs. The screws can be tightened/loosened with a Phillips-head or flat-head screwdriver (not provided).

Power/Ground: The +12V Power and Ground terminals will accept spade connectors up to 1/2" wide. It is recommended that you use an 8 AWG power wire to the battery, with an in-line 50A fuse installed no more than 18" from the battery terminal. An 8 AWG ground wire (minimum) should be used, and attached to a metal area close to the amplifier.

Remote Turn-On: The Remote screw terminal will accept a spade connector up to 3/8" wide. Typically, an 18 AWG turn-on lead is included in an amplifier wiring kit.

Speaker-Level Input: The amp includes two Speaker Level Input harnesses for connecting the amp to a factory radio or aftermarket head unit without preamp outputs. You should splice left and right speaker wires from the head unit to each harness and plug the harnesses into the amp.

Line-Level Inputs: The amplifier is equipped with two pairs of RCA inputs for connecting stereo RCA patch cables from the head unit to the amp. If you are bridging the amplifier's rear channels and have only one input for the rear channel, a "Y"-adapter will be needed to connect the left and right rear RCA inputs.

Speaker Outputs: The amp features screw terminals for connecting speakers in 4-channel, 3-channel, or 2-channel configurations. In 3-channel mode, the front channels are connected in stereo and the rear channels are bridged (using Left + and the Right - terminals). For 2-channel mode, both pairs of speaker terminals are bridged. The terminals will accept a spade connector up to 3/8" wide.

 
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For a more in-depth review and enhanced detailed information on the JBL GX-A604, please visit the Crutchfield website product page (/ISEO-rccbcspd/p_109GXA604/JBL-GX-A604.html ).