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JL Audio HD Series HD600/4

4-channel amplifier
150 watts RMS x 4

26 Reviews


Our take on the JL Audio HD Series HD600/4

HD Series amplifiers reproduce your music with exceptional accuracy, so you'll hear high-fidelity sound even under the most demanding conditions. JL Audio uses Single Cycle Control™ technology to eliminate the excessive signal distortion that's plagued Class D amplifiers in the past. Differential-balanced inputs eliminate noise before it hits the preamp stage, and allow you to connect the amp to just about any in-dash stereo. You'll hear clear, true, studio-quality audio, exactly what you expect from JL Audio.

Small amps, big power

JL Audio's HD Series amplifiers offer high performance from an ultra-compact chassis. These Class D amplifiers use less power, take up less space, and generate less heat than traditional amp designs — you can even stack them up to create a sweet-looking installation.

View of control panel

JL Audio technology goes to work for you

HD Series amplifiers reproduce your music with exceptional accuracy, so you'll hear high-fidelity sound even under the most demanding conditions. JL Audio uses Single Cycle Control™ technology to eliminate the excessive signal distortion that's plagued Class D amplifiers in the past. Differential-balanced inputs eliminate noise before it hits the preamp stage, and allow you to connect the amp to just about any in-dash stereo. You'll hear clear, true, studio-quality audio, exactly what you expect from JL Audio.

4 channels of reliable power

The 4-channel HD600/4 amplifier pushes 150 watts RMS per channel to your speakers or subs, from a 2" tall chassis that's about the size of a sheet of computer paper. The regulated power supply allows this amp to deliver its rated power to a wide range of impedances, even when voltage levels drop during heavy use. Removable power and speaker plugs make it easy to pop this amp out if you need the space in your cargo area.

Some extra touches

You can use JL Audio's optional stack kit to mount one HD Series amp on top of another, so you can maximum power from minimum space. JL's wired remote allows you to control your HD amp's volume from your front seat.

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Product Highlights:

  • 4-channel subwoofer amplifer
  • 150 watts RMS x 4 (rated power from 1.5 to 4 ohms)
  • 300 watts RMS x 2 bridged (rated power from 3 to 8 ohms)
  • variable high- and low-pass filter (50-500 Hz 12 or 24dB/octave)
  • subsonic filter and output polarity control
  • removable power and speaker plugs
  • optional wired remote for level control
  • optional HD stacking kit for stacking multiple HD amps together
  • Class D amplifier design
  • MOSFET power and output stages
  • differential-balanced inputs eliminate noise from your vehicle's electrical system
  • speaker- and preamp-level inputs (speaker-level input requires an optional adapter)
  • preamp outputs
  • 4-gauge power and ground leads and a 50-amp fuse recommended — wiring and hardware not included with amplifier
  • no onboard fuses — when installing multiple amps in a system, an additional 50-amp in-line fuse between the distribution block and the amplifier is recommended
  • 10-13/16"W x 2"H x 8-7/8"D
  • warranty: 2 years
  • Our 60-day money-back guarantee

I've been using this for a year and love it. I run a JL stealthbox and a three way focal set with it. It's silent where it should be and extremely loud where it should be. Very happy.

Rob, Omaha, NE

What's in the Box:

  • Four-channel class-D full-range amplifier
  • Power/Ground/Turn-On plug
  • 2 Speaker connection plugs
  • 4 Mounting brackets
  • 2mm Allen-wrench
  • 2.5mm Allen-wrench
  • 3mm Allen-wrench
  • 3.5mm Allen-wrench
  • 4mm Allen-wrench
  • 5mm Allen-wrench
  • 4 Mounting bolts
  • Owner's Manual

JL Audio HD Series HD600/4 Reviews

Average Customer Review(s):

(26 Reviews)

Very happy

Rob from Omaha, NE on 4/30/2017

Crutchfield Customer Review (What's this?)

I've been using this for a year and love it. I run a JL stealthbox and a three way focal set with it. It's silent where it should be and extremely loud where it should be. Very happy.

Pros: Loud, clean, sexy, dependable. Just like me.

Cons: Could be a little warmer.

JL Audio HD Series HD600/4

sam from lkn, NC on 1/1/2017

i have 2 cars powered by these amsp about to have a third. one is a 2000 town car L model and its pushing 2 pair or morel virtus 602. the sound is amazing. the second is a 97 mark 8 lincoln. this car came with factory jbl separates. i had 2 pair of morel virtus 603 installed they surface mounted the tweets and used the facroty tweet postion for the 3.5 inch midrange. this is the only am i will run for any system. its incredibly loud and clear

Pros: best amp out there

Cons: dolla dolla bills....lots of hem

Good power

Rick from Mount Prospect, IL on 12/2/2016

Crutchfield Customer Review (What's this?)

Well....if digital amplifiers sound like this I do not want any part of them. The high end sounded like there was a sheet of glass between me and the speakers. The amp did have some nice dynamic range and solid bass. But as a purist who simply wants a kick bass to sound like a kick bass and a cymbal to sound like a cymbal, this amp does not do it for me especially on the high end. My source of music are live recordings at 24 bit 192Khz.

Pros: Good stable power.

Cons: High end sounds like the cymbals are garbage can lids!

JL Audio HD Series HD600/4

jose from Elmhurst, NY on 10/17/2016

Crutchfield Customer Review (What's this?)

this amazing the power is unbelievable love it



JL(Not Justice League) Rocks!!

Elias from Walnut Creek, CA on 7/24/2016

Crutchfield Customer Review (What's this?)

These amps run cool, play hot, and are pure explosive fun! I've heard that class D amps are inferior, but after comparing them to my old A/B amps, I find no negative difference in musicality. At all! These bad boys are musical and extremely powerful, especially when you consider their size(think Ant-Man!) Thanks JL, for making my drive to and from work a blast!!

Pros: Size, Power, Musicality, Flexibility,

Cons: Not Available in Black??

Jl 600 Hd

Steven h from Vancouver b.c. on 5/28/2016

I have a jl hd 600 running my system which is a set of focal 165 as3 components in the front stage and a jl audio 10 inch truck wedge behind seat and a kenwood x-998 hu and it sounds amazing , strong punchy lows sweet mids and smooth highs at any volume level

Pros: Plenty of power for size

Cons: None

Not quite what I was looking for...

pohlevj from Little Falls, NY on 5/12/2016

Crutchfield Customer Review (What's this?)

I purchased this amp to power two sets of JBL 670GTI component speakers in my Jeep. These speakers are rated at 150 watts RMS/ch and 300 RMS per set, so I figured this amp would fit the bill perfectly. Now let me say that for the most part this amp made the JBLs sound very nice, but I like to listen very loud and the JBLs are competition speakers so they are meant to get very loud. The problem for me with this amp was that many times there ended up being something missing from my music. For example, when you would hear a cymbal or the snap of a snare drum, instead of it being nice and snappy and in your face it just sort of faded out into the distance. Same thing occurred with the vocals in many songs. Another thing that would happen often is when turning it up to a decent volume level, the vocals especially would start to break up. The overall sound is warm which is nice, but at the same time it makes most music sound almost lifeless and boring. Like one of the other reviewers had mentioned: it made me say "meh" and left me scratching my head. I know these speakers can play much louder without introducing distortion, and that is why I went with another amp. I returned this one and am currently auditioning a Rockford class AD hybrid amp. Once I hooked it up I noticed immediately that it was way cleaner and could get much louder before distortion was introduced. I am curious if going class AB is the solution to cleaning up the sound to the level that I am seeking.

Pros: Small footprint, lightweight, stays cool, extremely efficient, regulated power supply so impedance matching isn't much of an issue, makes your speakers sound great but only up to a certain volume level before distortion is introduced.

Cons: Overall sound produced by this amp tends to be lifeless and boring, do not get this amp if you really like to turn it up loud because distortion is quite easily introduced at high volume levels, especially with vocals and drums, certain elements of the sounds produced by this amp tend to fade into the distance making the sound seem unbalanced and flat

Great amp!

Hotm8r from Sainte Genevieve, MO on 11/29/2015

Crutchfield Customer Review (What's this?)

Great amplifier - best power in its class!



Jl audio hd600/4 review

B from Tuscaloosa, Alabama on 10/17/2015

I'm gonna give it to you straight,because that's how I'd want someone to do me. If you are even considering this amp at all then buy it. If you have heard a slash series amp before then that's all great and stuff but the slash amps don't even compare to the HD series.. I'm the type of audiophile that won't quit until my stereo Sq is absolutely perfect. As good as Alpine pdx digital amplifiers were, I had to try the jl audio hd600. And once again no comparison. I had jl audio ZR650CSI components (front & back) and dynamated my whole vehicle and a hd750/1(which I did not like dew to no bass boost and lack of power. I bought 2 jl audio W7 10's but took them out because even though they hit extremely hard and drop really low, I found that they were a little sloppy for my taste due to the huge surrounds. I prefer tight, punchy bass so I dropped down to the W6's and they were much better. So u see I must have perfect and to me the Jl Audio Hd600/4 makes mediocre stereos sound ABSOLUTELY PERFECT! OMG! WOW! As jl audio claims, the HD amps actually takes the sound from your cd receiver and corrects the signal that you don't even realize needed any corrections and brings out brilliance that will actually approach the sound quality of home audio like Marantz, denon, Harmon kardon, onkyo, and klipsch which any true audiophile knows is nearly impossible to do in a vehicle. BUY THIS AMP OR NEVER HEAR TRUE BRILLIANCE! THIS IS AS HONEST AS I CAN BE!

Pros: Sonic brilliance! Buy it or regret it! Bring the sounds of Harmon kardon, onkyo, and klipsch to your car!

Cons: A little pricey but all the best stuff is! You get what you pay for really applies here!


richardd from Kentucky on 9/3/2015

Crutchfield Customer Review (What's this?)

Driving JBL 660gti components (150 rms each continuous, 600 watt peak each) and the sound is absolutely perfect, even at full power with no distortion. Replaced a Polk Audio PA660 and the sound is so clean and balanced now that I was able to completely clear all EQ adjustments (the PA660 required moderate treble boosting and mid-range pull down to be balanced). I've owned many makes and models of amps over several decades and the JL Audio HD series is by far, the cleanest sounding, easiest to install amps I've ever owned (have HD1200/1 driving a 13W7). While a little pricey, if you are running high end speakers it is definitely worth the money. Due to the power levels it achieves I do not recommend this amp for low end speakers.

Pros: Very easy to install and set via a voltmeter and test tone. Came with all necessary tools (except voltmeter and test tone). High power that is very clean and well balanced across the entire range. Compact and power efficient. Very robust and accurate built-in crossovers.

Cons: none

Highly recommend

Johnny a from California on 8/5/2015

Crutchfield Customer Review (What's this?)

This amp is exactly what I hoped it would be. Very easy to install. Lots of power. My music is so loud and clean.

Pros: Everything

Cons: Nothing

4 channel amp for MIds and highs

Algie from Norfolk,Va on 10/2/2014

Crutchfield Customer Review (What's this?)

Amp is very strong, perfect for those screaming MIds and highs!?

Pros: Very compact for under seat mounting

Cons: None


Fletch from Fayetteville, NC on 1/6/2013

Crutchfield Customer Review (What's this?)

This is truly an amazing amp. I have it hooked into a Kenwood 6190HD head unit and "stock" Dynaudio speakers. You have to give it time to break in. But when it does, it sings. The control is amazing. Imaging is fantastic. Voices and instruments hang in the air like they would in a high-end home audio system. I like road trips now, because I get to listen to my music on this gear. Very pleased.

Pros: Amazing sound and control. Not too large. Runs pretty cool.

Cons: Takes some time to break in.


Brian from FL on 6/6/2012

started off with the hd1200/1 for my 13.5W7AE. blew me away, then i decided to buy this amp for my CDT HD series speakers. what an amazing difference this amp made in my vehicle. after putting this amp in you can clearly tell that my speakers are getting super clean power. setup is a breeze, amp is small, and 150 watts x4 RMS is plenty. the clarity is unbelievable with my EQ settings "Flat." sure its expensive but ive never looked back

Pros: small amp, efficient, clean power

Cons: this amp doesnt have a built in HD tuner (i kno that makes no sense but i had to put something in this dialogue box) :)

Over Rated & Way over priced

Solder32mp from Levittown,pa on 5/22/2012

First off this footprint is an ideal size and that's it ! I've been wanting to try this amp for awhile to complete my Jl set setup...HU alpine iva w205, Jl zr650csi, Jl tr650 all wiring Jl..its not what I expected at all for $$$$$ period I'm putting my polk pa660 right back in it seems even at 75 rms was warmer in sound and pushed the setup beyond it needed vs the HD and the gain isn't even 3/4.

Pros: Size, size, size

Cons: Better amps out there for less $$$$ your buying the name in this case...

dinero tirado a la basura - money thrown away

Daniel M. from Calexico Ca. on 10/28/2011

Acabo de recibir mi jl audio hd 600/4 y estoy un poco desepcionado, lo compre por que pense que sonaria mejor que mi alpine pdx 4.150 , pensando que el jl hd seria mejor, pero no fue asi, el hd tiene unos agudos un poco chillones , el pdx es bastante calido ,los ajustes y ganancias practicamente estan igual. sinceramente no valio la pena gastar 800 dlls cuando puedes comprar un alpine pdx 4.150, mi hu es una alpine cda-117,mis bocinas son dls iridium 6.3 3 way . <b>Translation provided by Crutchfield's Spanish Sales & Support team. Find more information en español here: <a href=""></a></b> I just got my hd jl audio 600/4 and am a bit disappointed, I bought it because I thought it would sound better than my alpine pdx 4150, thinking the hd jl would be better but it was not so, the HD has a slightly sharp sound, the pdx is quite warm, adjustments and gains are almost equal. honestly not worth it for the price when you can buy an alpine pdx 4150, my hu is an alpine cda-117, my speakers are 3 way dls iridium 6.3




My_Fast from Philadelphia, PA on 7/11/2010

Crutchfield Customer Review (What's this?)

This amp is awwweeesssooommmee. It's everything I was hoping for and looking for. Gets loud, has nice midrange punch I want and so dang crisp and clear! It's great. Highly recommend it!




My_Fast from Philadelphia, PA on 6/28/2010

Crutchfield Customer Review (What's this?)

Fantastic amp. Plenty of power, crisp, clean and just wonderful. It's very easy to setup. The instructions provide plenty of information to setup and tweak your system. I have been waiting a long time to order this amp, finally did and I absolutely love it. Highly recommend it, it's worth the money. I have it powering 2 pairs of Polk MoMo Component speakers in my 2008.5 VW GTI. I have 4 guage powering it, and 12 guage supplying the speakers from the amp. All connected to an Alpine iDA-X305 headunit.




juan from NEW ORLEANS, LA. on 5/12/2009

Not fair to compare this amp to anything else out there , nothing compares in size , sound quality and power . My only advice is, if you going to spend this much money on this amp ,don't go cheap with the speakers ,it would a crime to use this amp with the factory speakers or coaxials for that matter.



Amazing Product

Alan from Fort Lauderdale, FL on 3/27/2009

I've been a car stereo enthusiast for 3 decades, whether installing the equipment myself or getting lazy (lately) and having others doing it for me. When the salesman told me that the HD600 would have more than enough power to drive my set of 3-way components and a JL 12w3 Sub (in a Stealthbox), I was quite sceptical. Still, I thought why not try. I am amazed that this little Class D amp drives my entire system with ease. It only gets warm to the touch, is quiet and clear, and will allow my system to get as loud as my ears can handle (and body can shake due to the awesome 12w3 Sub). If you have not experienced JL equipment, you really need to. It's in a league of its own.



Pure sweetness....

HarrisonZ from Jacksonville, Fl. on 11/18/2008

I bought this to replace 2 amps. I have speaker system up front with a 8" in the door, 3" Mid in the kick, and 1.1" in the dash and had a 5 channel Alpine MRV-F450 running bridged to 2 channel at 120watts pushing them before. Had a FD2200 amp pushing my JL Audio VR-650CXi's in the rear doors. Now that I have the JL HD600 in there, the system sounds so much better. The 8" in the front doors slam, the whole system is crystal after a few adjustments on the Fosgate 360.2 processor. My question to the people who are having noise issues.... did you use a volt meter to set the "Input Sensitivity"? I have no issues and no complaints. I am waiting for my HD750 to get here in 2 days for my 12W7 and I'll be a happy camper. In the 17 years I've had systems, I can honestly say that this is the BEST amp I have EVER owned, and I have had way too many to count. Small, compact, clean, and powerful. Fantastic buy everyone. You'll be happy.



awesome amp

Michael from tampa, FL on 11/13/2008

i hooked this amp up to the stock head unit in my 08 honda accord coupe with NAVI. I didnt use any processors like the cleansweep. There is absolutely no noise, no turn on pop, the sound is loud, clear, and smooth. I am running a set of JL C5 splits off the front channels and a JL sub off the rear channels bridged. The clarity and volume out of such a small amp is unbelievable. I had an old RF BD1000 running my sub before this and the 300 watts from this amp are almost as loud, but much more musical than the 1000 watts from the BD1000. I couldnt be happier with this amp.



JL does it again

DJV from Ma on 10/2/2008

Crutchfield Customer Review (What's this?)

This amp is AWESOME! Small, runs cool, loud as you will ever need, and plays so wonderful. I replaced a pair of 300/2 amp with this and I have to say this amp sounds better than the other two. Clearer, cleaner, and way smaller. Worth every penny.



Awesome amp

Bruce from Canton, Ohio on 9/3/2008

I purchased this amp to replace my Alpine PDX 4.150 which was too noisy. This amp is incredible. I have no noise as stated in previous review, and the sound quality is better than the Alpine PDX by far and on par with my JL slash 4x75 amp. I am powering 2 sets of Boston 6.5"s and 1 12 inch woofer. If you want to save space and want top quality sound, this is your amp. I would rate it on par with my last set that were running my components.



Good power a little noisy

kenny from Italy on 7/27/2008

Crutchfield Customer Review (What's this?)

I purchased this this amp to power my Boston Acoustics Pro50 components and one JL 12w3 Sub. I was immediatly impressed by the amount of power for such a small amp, I couldn't believe it! I don't have any complaints with the clarity of the amp but then again I didn't have another amp to compare it to. However, the compliant I do have is the noise in the signal. It seems to be a bit loud even though its rated at 109db then again it might be my patch cables too, not sure but I'll try a different pair. Overall, I'm very happy with performance of the 600HD.



Price does not justify performance.

NO KA OI from Maui,HI. on 7/13/2008

Crutchfield Customer Review (What's this?)

Was very excited to try amp out for my 2 sets of Infinity Kappa 6.1 Perfects.I must say I was impressed by the size and can really feel the power but the clarity just wasn't there.It left me scratching my head,but I was not worried because Crutchfield has an excellent return policy.So I put my JL 450/4 back in and that alone sounded great like always.So in my conclusion for the money and clarity it did not sound cleaner than the JL 450/4 and justify me spending another $800.00 for my system.And a big thumbs up for Crutchfield,excellent service and fast shipping.




Hands-on research

Product Research



Four-Channel Full-Range Amplifier: The JL Audio HD600/4 is a Class D four-channel, full-range amplifier that is rated at 150 Watts RMS x 4-channel in 1.5 to 4-ohm at 20 to 20kHz with a signal-to-noise-ratio of 110 dB and a total harmonic distortion of 0.03% while receiving 11 to14.5 Volts. The amplifier can also be bridged to output 300 Watts RMS x 2-channel in 3 to 8-ohms.

High-Fidelity Class D (HD) With Single-Cycle Control: The JL Audio HD600/4 utilizes patented Single Cycle Control Class D technology for all channels. This technology delivers reference-grade sonic performance while requiring far less current from the vehicle's electrical systems than a conventional amplifier. Single Cycle Control is a unique approach to controlling a full-range Class D amplifier. By tracking the audio signal, comparing it to the real PWM waveform and then correcting it in each and every cycle (over 400,000 times per second), a multitude of distortion-causing mechanisms can be tightly controlled to enable pristine amplification. While there are certainly less expensive ways to make a full-range switching amplifier, no other Class D control system works faster or more accurately than Single Cycle Control.

Compact/Efficient Design: The JL Audio Class D amplifier on average is 13% smaller overall and over 1/2-inch shorter in height than most class AB amplifiers. The HD600/4 features outstanding overall efficiency (80% at 1/2 rated power) which allows for huge power from a tiny chassis and is easy on your vehicle's charging system, drawing 60% less current than a class AB design of equal power.

R.I.P.S. (Regulated, Intelligent Power Supply): R.I.P.S. stands for "Regulated, Intelligent Power Supply" and is a central feature of the JL Audio's JL Audio HD amplifier. The JL Audio R.I.P.S. System ensures consistent power delivery over a wide range of battery voltages and load impedances. This technology provides optimum power at any impedance level between 1.5 ohm to 4 ohm per channel and at any vehicle voltage level between 11V and 14.5V.

  • Regulated Power Supply: "Regulated" means that the power supply adjusts its operation so as to maintain the amplifier's rated power output and low distortion operation over a wide range of vehicle voltages (11V-14.5 V). This allows the JL Audio JL Audio HD amplifier's the rail voltage and clean power output to remain stable in real-world car-audio systems, resulting in superior fidelity and stability.
  • Intelligent Power Supply: The "Intelligent" portion of the R.I.P.S. System is a circuit that actually monitors output current to optimize the amplifier's output power over a wide range of load impedances (1.5 ohm to 4 ohm per channel). The R.I.P.S. System detects the actual impedance being driven and adjusts output rail voltages to deliver optimum output. The entire process is seamless, automatic, and results in incredible dynamics for satellite channels and consistent power output for a wide range of subwoofer configurations. It also takes into account the real impedance of your car-audio system, rather than relying on often inaccurate assumptions based on a speaker's rated impedance.

RealSink Heat Management With Rollback Protection: This JL Audio amplifier employ and advanced type of heat management, called RealSink. This features takes advantage of convection and radiation effects to remove heat from the amplifier circuitry. For optimum cool performance, the vertical heat sinks located at the sides of the amplifier should be exposed to as large a volume of air as possible. If a JL Audio HD amplifier should ever reach an unsafe temperature, its unique Advanced Rollback Protection circuit also adjusts power until the amplifier cools down, without ever shutting your music down.

Differential-Balanced Inputs: The JL Audio amplifier features differential-balanced input architecture to effectively control noise and ensure compatibility with a wide variety of source units, including many OEM systems. Without resorting to line output converters, you can directly connect most OEM source units to the JL Audio amplifier without creating any noise or compatibility issues. Unlike conventional single-ended inputs, the differential-balanced design does not connect one side of the audio signal to chassis ground. This eliminates any voltage sensitivity between one input terminal and ground and greatly reduces the incidence of alternator whine in a typical car audio installation. The JL Audio HD amplifier provides range switching on each of its inputs via the "Input Voltage" switch. This permits connection to a wide range of source voltages while retaining excellent sensitivity setting precision.

Note: You will need two speaker wire to RCA adaptors (136XDCLR2S, sold separately) to connect this amplifier to your headunit via speaker-level.

Protection Circuitry With Status Indicator Lights: There is a single multi-color LED on the control panel of the amplifier to indicate the amplifier's operating status.

  • Flashing Green: When the LED is flashing green, the amplifier is powering up and audio output is muted.
  • Constant Green: This LED lights green to indicate that the amplifier is turned on and operating normally.
  • Constant Red: This Red LED lights to indicate that the amplifier has exceeded its safe operating temperature, putting the amplifier into a shelf-protection mode, which reduces the power output of the amplifier. The red light will shut off and the amplifier will return to normal, full-power operating mode if the heat sink temperature drops back to a safe level.
  • Constant Yellow: This amber LED lights to indicate that the impedance of the speaker load connected to the amplifier is lower than the optimum impedance load range for the amplifier. When this light is on, a protection circuit engages and reduces the power output of the amplifier. The amber indicator will also light when a short-circuit is detected in the speaker wiring.
  • Alternating Red/Green: The LED alternated between Red and Green to indicate that the amplifier is experiencing a fault that may require service of the amplifier, its wiring, or the vehicle's operating system. Audio is muted when this fault occurs.

Note: There is only one condition that will shut down the HD600/4 completely and that is if the battery voltage of your vehicle drops below 10 volts.

Mounting Options: The HD600/4 has two mounting option to choose from during installation.

  • Standard Mounting: The standard method of mounting requires removal of the four corner caps with the 3/16-nch he-wrench included with the amplifier. Using the appropriate mounting screws (not included), you can then secure the amplifier in all four corners and replace the corner caps.
  • Lateral Mounting Feet: Lateral Mounting Feet are also included with the HD600/4 to provide an alternative mounting option. Each mounting foot should be attached to the bottom of the amplifier by screwing the provided bolts into the bottom of the amplifier and up into the corner cap with the supplied 1/8-inch hex-wrench. Then, using the appropriate mounting screws (not included), you can secure the amplifier by its four lateral mounting feet.


Control Panel Cover: The HD600/4 features a Control Panel Security Cover which protects and hides the amplifier's controls. When installed, the cover ensures that the amplifier's settings are not accidentally changed while creating a clean aesthetic look for the amplifier and your installation. The control panel security cover is pre-installed at the factory and must be temporarily removed for access the amplifier's controls. The security cover is secured by a single 2.5mm hex-head screw.

Simplified Gain Setting: The amplifier's R.I.P.S. feature also allows for easy gain setup. Because the amplifier will always deliver the same amount of power within its operational range of impedances and supply voltages, the maximum, unclipped output is very predictable. This makes setting the gain level of the amplifier via the input sensitivity control very simple. All you need is Digital AC Voltmeter (142TK12V, sold separately) and a Test CD Disc (503CD104, sold separately) with a sine-wave test-tone recorded at 0 dB reference level in the frequency range to be amplified for that set of channels (50 Hz for subwoofer channels, 1 kHz for a midrange application).

Flexible Input Section And Active Crossover Network: The JL Audio HD amplifier provides a flexible input section and a comprehensive crossover network to fine tune your system effectively and accurately. The variable filter design employed in the JL Audio HD amplifier crossover sections allow you to seamlessly switch slopes, easily change filter frequencies and address what frequencies the preamp outputs will pass. The HD600/4 offers the following independent crossover adjustments for the front and rear channels along the unit's front panel, behind a removal cover plate.

  • Input Mode: This switch allows operation of all four amplifier channels with only one pair of input signals (2-CH Input Mode) or with independent front and rear input signal pairs (4-CH Input Mode). You will only need to connect the front RCA inputs when placing the amplifier in 2-CH input mode.
  • Filter Mode: The amplifier features a Full-Range, variable Low-Pass or variable High-Pass filter mode for the amplifier's preamp input section.
  • Switchable Slope on all filters:12dB/octave Butterworth or 24dB/octave Linkwitz-Riley alignments allowing for more precise integration of subwoofer and speaker channels.
  • Variable Frequency: Fully-variable frequency selection from 50-500 Hz for high-pass or low-pass crossovers.


Power/Ground/Turn-On Plug: The amplifier features a Power/Ground/Turn-On plug which detaches from the amplifier to make connecting your power, ground, and remote turn-on lead wires more convenient. Once your connections are made the Power/Ground/Turn-On connector simply plugs into the amplifier.

  • Power and Ground: The JL Audio amplifier's set-screw Power and Ground connections found on the detachable Power/Ground/Turn-on plug are designed to accept 8 to 4 AWG power wire. A 4mm hex-wrench is supplied for making connections.
  • Remote Turn-On: The JL Audio HD amplifier's set-screw turn-on lead found on the Power/Ground/Turn-on plug will accept 18 to 8 AWG wire. A 2.5mm hex-wrench is supplied for making connection.

Note: The Amplifier is not equipped with a fuse. An external 50-amp AFS, AGU, or MAXI 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 50-amps, the original should be replaced with a 50-amp fuse

Speaker Output Plugs: The amplifier features two Speaker Output plugs which detach from the amplifier for easier speaker wire connection. Once your speaker wires are connected to these plugs, they simply push into the amplifier. Each Speaker Output plug features four set-screw terminals. The HD600/4 amplifier's eight set-screw speaker terminals found on the Speaker Output plugs will accept 16 to 8 AWG speaker wire. A 2.0mm hex-wrench is supplied for making connections.

Preamp Inputs: The amplifier features two sets of differential-balanced RCA jack inputs. The amplifier features a dedicated Input Sensitivity gain control for the front and rear channels of the amplifier. These controls are designed to match the input sensitivity of the HD600/4 to the specific signal source that is feeding it. The amplifier's input level can be set independently for the front and rear channels to Low (200mV-2V RMS) when connecting the amplifier to a low-level preamp signal or set to High (800mV-8V RMS) when connecting the amplifier to a high-level speaker signal.

Preamp Outputs: The HD600/4 incorporates a pass-through preamp output sections, so that additional amplifiers can easily be connected to the same signal(s) feeding the HD600/4. These preamp output signals are buffered to prevent noise and are always preamp level, regardless of the level of signals feeding the HD600/4's inputs. The amplifier's set of preamp outputs can be configured two different ways.

  • Front: The preamp output delivers the same signals that is connected to the HD600/4's front RCA inputs. This mode is useful for feeding a subwoofer amplifier when the HD600/4 is being used to drive front and rear speaker system. In this mode, the preamp output level will track with the signal level of the front input signals, allowing you to fade the rear channels in and out, without affecting the subwoofer level.
  • F+R: This mode delivers a sum of the signals being fed to the front and rear RCA inputs of the amplifier. When the HD600/4 is being used to drive front and rear speaker systems, this preamp output mode will deliver a summed front/rear signal to the subwoofer amplifier, while permitting fading of the front and rear speaker system fro the source unit.

Remote Level Control: The amplifier features a standard telephone connector for adding an optional wired remote level control. With the addition of the optional wired Remote Level Control (136HDRLC, sold separately), you can control the volume of one or both channel pairs of the HD600/4 form the front of your vehicle. This is useful for subwoofer level control or even as a master volume control for your system. If desired, multiple HD amplifiers can be controlled from a single HD-RLC controller using a simple phone line splitter and multiple phone cables (all sold separately).

Note: All inputs and outputs are located on the rear side of the amplifier to make installation of the amplifier simple and neat.

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Staff Reviews

Product reviews from the Crutchfield Labs

Harold Jones, winner of Virginia's IASCA Sound Quality Challenge, was kind enough to drop by Crutchfield headquarters to show off his impressive ride.

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Customer Q&A

Crutchfield asked  
Why did you buy this?

Great Class D amp. Sounds fantastic, has generous output and I haven't had any problems with it! [ M  Feb 08, 2017 ]
Unbeatable performance [ CHARLES D  Nov 18, 2016 ]
suppose to be the best of the nest [ Albert  Sep 25, 2016 ]
Because I wanted the best of the best. Buy it cheap, buy it twice as they say. [ Vincent  Aug 31, 2016 ]
Past experience with this product. Excellent! [ Elias  Jul 09, 2016 ]
Need more power for my speakers [ Edward  Jun 08, 2016 ]
Reputation for quality, crossover and bi-amp options. [ Chris  Mar 30, 2016 ]