Infinity Kappa Four

4-channel amplifier — 125 watts RMS x 4

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  • Infinity Kappa Four


  • Infinity Kappa Four


  • Infinity Kappa Four

  • Infinity Kappa Four


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Item #: 108KAPPA4

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Expected: 10/27/2014
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Our take on the Infinity Kappa Four

by Gabrielle Thorndyke

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.

Infinity designed the latest Kappa Series amplifiers to deliver increased efficiency and performance from an extremely compact package. These slim powerhouses stand only 1-3⁄4" tall, so they'll fit easily in spaces where other amps just won't go. And efficient heat dissipation means these amps won't get too hot in tight quarters.

The Kappa Four 4-channel amplifier makes an ideal match for your high-performance Kappa speakers, dispensing 125 watts of clean power per channel. You can also bridge the amp to 2-channel mode, sending 300 watts each to a pair of subs. A built-in crossover and input selector switch let you configure your setup for the best possible performance.

Read more

The amp's Class-D design generates less heat, eliminating the need for large heatsinks. Non-stop Thermal Protection circuitry adjusts the amp's output so it runs cool no matter how hard you push your system. Balanced speaker-and preamp-level inputs reject engine whine and other noise from your car's electrical system. A unique detachable power/ground plug lets you connect and disconnect large-gauge power cables in one easy step.


  • 4 channel amplifier
  • 125 watts RMS x 4 at 4 ohms (150 watts RMS x 4 at 2 ohms)
  • 300 watts RMS x 2 bridged at 4 ohms
  • CEA-2006 compliant
  • variable high- and low-pass filters (32-320 Hz, 12dB per octave)
  • bass boost: 0-12 dB
  • frequency response: 10 Hz to 75 kHz
  • Non-stop Thermal Protection ciruitry
  • Class-D amplifier design
  • differential balanced speaker-and preamp-level inputs
  • 4-gauge power and ground leads and a 80-amp fuse recommended — wiring and hardware not included with amplifier
  • fuse rating: 40A x 2
  • 7-1/16"W x 1-3/4"H x 14-5/8"D
  • warranty: 3 years
  • 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) 125 x 4
Peak Power Output (Watts x Channels) 300 x 4
Power at 2 Ohms (Watts x Channels) 150 x 4
Bridged Power (Watts x Channels) 300 x 2
Minimum Impedance Bridged 4
Minimum Impedance Unbridged 2
Best Frequency Response 10-75k Hz
THD at Rated RMS Power 1%
Signal to Noise Ratio 85 dB
Input Voltage 14.4v
Amplifier Class D
Low-Pass Crossover Frequency 32-320 Hz
Low-Pass Slope (dB/octave) 12 dB/oct
High-Pass Crossover Frequency 32-320 Hz
High-Pass Slope (dB/octave) 12 dB/oct
Bass Boost 0-12 dB
Bass Boost Frequency 50 Hz
Fan Cooled No
Fuse Rating 80
Speaker Level Inputs RCA (adapter req)
Preamp Outputs No
Width (inches) 14-5/8
Height (inches) 1-3/4
Depth (inches) 7-1/8
Parts Warranty 3 Years
Labor Warranty 3 Years
Product Research
What's in the box?

Download owner's manual

  • 4-Channel amplifier
  • Two 40A ATO fuses
  • 4-Gauge terminal adapter (installed)
  • Instructions (English/ German/ French/ Spanish/ Dutch/ Italian/ Swedish/ Danish/ Finnish/ Polish/ Portuguese/ Russian)
  • Warranty/Product Registration card

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.



Class D/DirectFET Technology: The Infinity Kappa Four features high-power Class D circuit topology with DirectFET transistors, a design that increases power output and overall efficiency, with improved heat transfer from the transistors to the chassis.

CEA-2006 Compliance: The specifications given by Infinity for the Kappa Five comply with the CEA-2006 Amplifier Power Standard from the CEA (Consumer Electronics Association). All manufacturers who comply with the standard can display the CEA-2006 logo on their product.

4-Channel Design: This amplifier is designed to power four full-range speakers. All four channels are 2Ω stable; at 2Ω the power output is 150 watts RMS x 4. CEA-2006 compliance is maintained at 2Ω, with less than 1% THD+N. The amplifier's front and rear channels are individually bridgeable, so the Kappa Five can run 4, 3, or 2 channels. When bridged, the front and/or rear channel output is 300 watts RMS into 4Ω.

Protection Circuitry: The amp features protection circuits and will shut itself down in the following cases:

  • DC Output: DC voltage is detected on the amplifier output
  • Over/Under Voltage: Voltage at the +12V (Battery) terminal is too high or too low
  • Short Circuit: Short circuit in speaker or speaker wire

Non-Stop Thermal Protection: Kappa amps protect themselves against excess heat with circuits that cool the amplifier down by gradually reducing output, instead of shutting down completely.

Status LEDs: Three LEDs on top of the chassis indicate the status of the amplifier. Two Power LEDs indicate the amplifier is on. The Protection LED indicates one of the protection circuits has engaged.


Front Input Select:

  • Front/Rear: choose which inputs feed this side of the amp (no Y-adapters needed when using only one input)

  • Stereo/Left/Right: choose stereo, or which channel is output when this side of the amp is bridged

Rear Input Select:

  • Front/Rear: choose which inputs feed this side of the amp (no Y-adapters needed when using only one input)

  • Stereo/Left/Right: choose stereo, or which channel is output when this side of the amp is bridged

Input Level: 2 rotary controls match the level of the preamp input signals for front and rear channels; 200mV to 6V.

Crossovers: The Kappa Four has independent 12 dB per octave crossovers on the front and rear outputs. Each is continuously variable from 32-320 Hz and selectable; low-pass, high-pass, or full range.

  • Frequency: 2 rotary controls set the crossover points for the front and rear channels; continuously variable from 32-320 Hz.
  • Crossover Switches: 2 switches set the front and rear crossovers to low-pass, high-pass, or full range.

Bass Boost: The Bass Boost control allows you to enhance the bass output from the rear channels; 0 to 12 dB at 50Hz.


Power: A 4-Gauge terminal adapter is installed on the power/ground/remote terminals; if removed, it reveals three 8 gauge set screw terminals (Infinity recommends 4 gauge power and ground when the power cable is more than 4 feet)

  • +12V: Set screw terminal for power wire from battery; handles up to 2 gauge wire
  • Remote: Set screw terminal for remote turn-on lead; handles up to 12 gauge wire
  • Ground: Set screw terminal for ground; handles up to 2 gauge wire

Front and Rear Channel Inputs: 2 pairs of RCA inputs. The amp will accept a speaker level signal through the RCA inputs. A speaker wire to RCA adapter is needed (136XDCLR2S, sold separately).

Speaker Output: 8 set screw terminals (4 pair) for connecting speaker wires; handles up to 8 gauge; front left, front right, rear left, and rear right.

Fuses: 2 Slots for 40A fuses (installed).

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Infinity Kappa Four Reviews

Average Customer Review:

11 people say:

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5 out of 5

infinity kappa four

Written By Ted, Marshall MI on Wednesday, April 16, 2014
Crutchfield Customer Review (What's this?)
Great amp love it
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5 out of 5

Good Amp.

Written By DS, Chagrin Fall,s Oh on Thursday, January 16, 2014
Crutchfield Customer Review (What's this?)
Nice amp for the price . Make sure your speakers can handle the power though It cranks pretty impressively .
Was this review helpful?    Yes | No
5 out of 5

Infinity Kappa Four

Written By James, Puerto Rico on Thursday, April 12, 2012
Crutchfield Customer Review (What's this?)
I can just say, WOW.
2 out of 7 people found this helpful
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5 out of 5

Infinity Amps are amazing

Written By Zane, Mattoon, IL on Wednesday, August 17, 2011
I bought this amp to replace a cheap 4 channel amp. Let me just say that it was truely a night and day difference! The minute I hooked it up, well I was hooked. I know that Infinity is not "known" for their amps, but this will start to change that. I currently have it powering Infinity Kappa 6x9's and Infinity Kappa 6.5 components, and let me say that these really come to life with this amp. I have the gains on both channels around 40% or so, and that is plenty. This amp really puts out the power and sound quality. I just can not say enough great things about it. If your looking for a hi-quality amp, this is the one.
11 out of 11 people found this helpful
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4 out of 5

Reviewed by a sort of audiophile with a touch of electronics analysis

Written By Tony S, Sierra Vista, AZ on Sunday, February 13, 2011
Installed in my 2-door Ford Explorer. For testing, I connected an AGM battery to it with short cables and used an O-scope to monitor voltage at the amp's power and speaker lugs. Connected 4 Kappa 682.9CF speakers 100 W. After confirming music was well over 100 W RMS, the input voltage varied 0.3 Volts at most and the speakers were popping badly so these measurements were brief. I tried the truck's stock 18 AWG wiring and tried 12 AWG fine mesh wire. Neither made a difference to improving control of popping. I question these 100 W speakers now. I guess I'm asking too much from a 5x7 speaker. Well, it was worth a shot. Two issues. First, the amp has variable low freq boost and crossover controls for only 2 of the 4 channels. Bummer because this boost really accentuates the low, low freqs, making these speakers sound really impressive if they didn't pop so much. My Kenwood KDCX994 HU has low frequency boost but it's not as low as this amp's. Second, the amp has hiss I can hear even with music and the engine running. Turning the input gain down to half way minimizes this hiss to just an acceptable level, being noticeable only with the engine off and nothing playing. Disconnecting my head unit made no difference. My test music is highly dynamic and much has extensible deep bass, the kind that shakes your pant leg next to the speaker. The amp seems well made. The controls have a high quality feel to them. I dropped a star due to the noise issue.
10 out of 22 people found this helpful
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2 out of 5

Good sound; zero longevity

Written By Aaron, Lubbock, TX on Thursday, December 16, 2010
This amp sounded great for a while, but it just inexplicably shut down a few days ago, a month after the warranty ran out. I expect more for this price. This time, I'm just going to get the Alpine PDX that I should have bought in the first place.
10 out of 14 people found this helpful
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5 out of 5

Just fantastic.........

Written By Christopher, Charlotte, NC on Friday, June 18, 2010
This amp simply rocks! I would recommend this to anyone wanting a high power 4 channel amp. The highs and mids are mindblowing and the bass is quite good as well. I do have all Inifinity kappa speakers matched to it. I took it on a 7 hour trip recently and played it at moderate to loud volume with no issues. I like my music loud and clear and this amp does just that. Get it, you will not be disappointed!!!!!
5 out of 6 people found this helpful
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5 out of 5

Power and Quality

Written By C-Machine, Manhattan KS on Sunday, May 23, 2010
This is the best amp i have ever had the chance to hear. JL and Rockford have nothing on this when it comes to quality. I have two Infinity Kappa 6X9s that scream the meds and highs and two 10" Polk Momos that rock to lows. I have had a cheap Pioneer amp, a JL 250/1, and a 700.2 and none of them power subwoofers as clean as this Infinity. The the JL 250/1 was slightly louder and the 700.2 tried to tear my trunk door off but could not play the lows as cleanly as the Infinity. The amp is easy to set up and tune and is great at keeping the lows from going to the 6x9's. Waiting to get the Infinity Kappa One for the subs so i can free up two channels for the front speakers. Want everything but your subs to be loud as possible and to hit every note the way it was ment to be played, give this amp a try. This thing makes me grin ear to ear every time I get into my car. Thanks Infinity.
10 out of 11 people found this helpful
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4 out of 5

Tons of power in a tiny package

Written By Buck, Enola, PA on Wednesday, March 24, 2010
Crutchfield Customer Review (What's this?)
I can't be happier with this amp. The performance for the size of it is just
utterly fantastic. I'm using it to drive 2 12" Infinity 1224W subs (Mounted in a
ported enclosure) in bridged 2 channel mode, and it's doing the job wonderfully
Instructions/information booklets are sufficient, but could be alot better, so i
took away one star for that.
7 out of 7 people found this helpful
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5 out of 5


Written By aphexacid, Chicago IL on Saturday, October 31, 2009
I had to replace a JL audio 300/4 after i blew a channel on it. I figured i might as well get an amp with more oomph. I decided on this one becaiuse it put out the right amount of power, and is class D.

I have it powering a pair of Boston Acoustic Pro 5 1/4 components, and Boston Acoustic 6x9's in the back. The sound is amazingly detail and clear. and about 1000x LOUDER than my JL Audio. I've never heard my components put out sound like this!

My components are 3 ohms, so theyre sucking a bit more power than your normal speaker. That might be why the amp isnt "cool" like the other guy said. I was blasted it for at least 30 minutes, and it wasnt hot, more like warm. but not cool. Excellent amp!
7 out of 7 people found this helpful
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5 out of 5

Best upgrade ever!!

Written By Leon, Brazoria, Tx. on Thursday, March 12, 2009
Crutchfield Customer Review (What's this?)
I just replaced my Infinity 475A with the Kappa 4 amplifier. Let's just say
this is money well spent. The sound quality is clearer than ever before,
even at high levels. The amp is currently pushing 2 Kappa 6x9's and 2
Kappa component 6.5's for my highs. This is the perfect addition for my
Punch 800@2 with 2-12" HX2's. This amp stays cool even when played at
high levels and compact enough to be mounted under the seat. I hope this
helps with your selection.
41 out of 41 people found this helpful
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