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26 of 27 people found the following review helpful
5.0 out of 5 stars Looks confusing to install, but is actually straight forward
I installed two of these this past weekend. Both in new Jeep Wranglers. When I pulled it out of the packaging I was confused. I'll give you some pointers on installing this.

First of all you will need 4xRCA outs coming from your head unit. Most (if not all) decent aftermarket stereos include these. There may be two more for the subwoofer.

There...
Published 22 months ago by Pete

versus
1.0 out of 5 stars Horrible quality - Very unreliable
This was a huge waste of time and money. After about a week and a half, the left channel stopped working front and rear. A good friend suggested this amp because he had one and his amp blew days before mine. Do yourself a huge favor and select something else. I am so wishing I would have bought the Rockford ... pissed off and disappointed doesn't even begin to...
Published 3 months ago by Steven R. Goe


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26 of 27 people found the following review helpful
5.0 out of 5 stars Looks confusing to install, but is actually straight forward, October 23, 2012
By 
This review is from: Alpine KTP-445U 4-channel Power Pack Amplifier (Electronics)
I installed two of these this past weekend. Both in new Jeep Wranglers. When I pulled it out of the packaging I was confused. I'll give you some pointers on installing this.

First of all you will need 4xRCA outs coming from your head unit. Most (if not all) decent aftermarket stereos include these. There may be two more for the subwoofer.

There are two sides to the unit: the harness that plugs into the left is for your speakers, remote turn on lead, and power. All you have to do here is match up each wire with what comes off the wiring harness you bought for your stereo. Use solder to connect wires.

The harness that plugs into the right side is where the RCAs coming off the head unit plug in to. The RCA harnesses that come with the amplifier are labeled F/R, just make sure you match them up with the RCAs you have running off your head unit to the Alpine harnesses. When you have them connected you should test L/R and F/R on the head unit to make sure they are matched up properly.

You have to buy 2 sets of RCA cables as the amp does not come with them. After you buy your new RCA cables, run them from the back of your head unit, into the RCA adapter harness, then plug that into the right side of the Alpine amp.

That's it.

8 month update: Still works great and runs cool. It is still in my glove box without issue.
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14 of 15 people found the following review helpful
5.0 out of 5 stars For the money and power level, outstanding, June 6, 2014
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This review is from: Alpine KTP-445U 4-channel Power Pack Amplifier (Electronics)
So let's start with what this is NOT.

It is NOT a "big power" amp that is going to rattle your windows and piss off the neighbors. Nope. It's a small, Class "D" amp that roughly doubles to triples the power output of your existing head unit. To really take advantage of it you need RCA outputs from the head, although it will work with speaker-level outputs. This means that with a FACTORY head unit you will get much less than this amp can offer.

Let me explain -- an amplifier can only amplify what you feed it! If you feed it trash you get louder trash. Your head unit's amp is only so-so to start with (yes, even the expensive aftermarket ones because they figure if you care you'll use the preamp outputs instead!) so you're inherently limited. As a result if you want good sound quality you need RCA (pre-amp) outputs from whatever you're going to connect this to, and you also need to use decent-quality cables (don't waste your money on things like "monster" cables, but do get ones with 100% foil+braid shielding - you can tell they're reasonable in quality because they've got some thickness to them.)

Now let's talk about the amp itself. It's a Class "D" amp. A Class "D" amp is EXTREMELY efficient because the transistors in it are either "on" or "off." They thus dissipate very little power as heat. That's good. However, the way they work is by switching the power at extremely high speeds (typically at least 10x the maximum 20khz audible sound frequency) and then using a low-pass filter made up of reactive components to smooth the output. Due to the way these amplifiers work energy is reflected back up into the power supply as a natural part of their operation. You'll note that on the yellow (power) for this amp there is a black box with something inside it. That "something" is a choke (you can see the coil inside the box if you look carefully through the slot) and it is really important that you NOT cut it off! If you do there is a risk that some of the high-frequency energy the power supply generates inside the amp could be reflected back up into the car's power system. This is unlikely to make the car malfunction but you could easily wind up hearing it in the stereo's sound as it has a decent shot at making it into your head unit and if it does, it could color the sound (quite badly, in fact, especially in the high frequencies.) So in short don't cut that black box off the power wire in an attempt to shorten it up!

The (relatively) small size means you should be able to mount this amp under the dash or in another convenient place, and it's lack of heat generation means it won't overheat and cause trouble in that regard. It requires a 15A circuit (the fuse in it is a 15A one) so some care is required in terms of getting power to it, and of course a SOLID ground is necessary.

There is a set of DIP switches on the back side that set high-pass filtration if you want it (if you're routing low frequencies to a sub this may be helpful, although most head units have a decent high-pass filter in them as well) as well as whether you are using speaker-level or the RCA-level inputs. Again, I STRONGLY recommend against using speaker-level if you can avoid it.

As for sound level this amp will roughly add 3db over what a non-amplified head unit will produce. It's maximum power draw is 180 watts before the fuse blows, and it's rated 45W/ch -- while it can drive either 2 or 4 ohm loads there is no boost to output driving a 2ohm load as there is with some other amplifiers. It's not going to be a lot louder (doubling perceived sound level requires a 10db change -- and 10x the power!) but it will be somewhat louder and, more-importantly, MUCH cleaner audibly.

Make sure you correctly set the input attenuation by the input plug. If you have a 4 or 5V RCA output head unit you will need to turn those pots down quite a bit; if they're turned up too far you will raise the noise floor (and be able to hear it in the form of hiss) along with rendering a large part of your volume control on your head unit worthless since you'll run out of power in the amp first. The best way to set these is with an oscilloscope to be able to "see" the clipping, but few people do that -- as a guideline if you have a 4 or 5V output head unit (most modern units are either 4 or 5v in an attempt to get better noise immunity) having the input settings somewhere between 9 and 10 o-clock is probably about right. If you have low-level RCA outputs you will need to raise the setting commensurately.

Properly installed and set up this little amp is awesome for what it is. Just understand what it is and what you are and are not buying. It isn't a beast, but rather provides a nice but modest boost and a very material cleaning-up of sound quality without having to deal with everything that goes into mounting and dealing with the cooling and power requirements for a "traditional" Class AB car power amplifier.

For a bit over $100 that's pretty darn good.
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9 of 10 people found the following review helpful
5.0 out of 5 stars Compact, powerful and well... awesome!!, July 26, 2012
By 
Patrick (Northern California) - See all my reviews
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The Alpine KTP-445U is a great amp hands down!! It was easy to install, I have experience installing amps so it was probably easier for me than if you have never done an amp before. First thing I love is you don't need an amp installation kit as this unit uses the factory or after market power wires which saves time and money on the installation. Your options for mounting are increased because of it's compact size. This amp sounds great... replaced a stock factory amp that had failed and the quality was even better than what the car had come with and it saved him $800 over what the dealer wanted to put an inferior stock amp back in the car.
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4 of 4 people found the following review helpful
5.0 out of 5 stars its great, October 4, 2013
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you can hide it anywhere, more than enough if you are replacing stock speakers and want a bit more umph!!
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5 of 6 people found the following review helpful
5.0 out of 5 stars Great Simple Product, January 24, 2013
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This review is from: Alpine KTP-445U 4-channel Power Pack Amplifier (Electronics)
I bought this not knowing anything about this type of amp and didn't even know it existed but it works awesome and the improvement of sound is very noticeable
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2 of 2 people found the following review helpful
5.0 out of 5 stars great amp, March 19, 2014
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This review is from: Alpine KTP-445U 4-channel Power Pack Amplifier (Electronics)
Great Amp. Couldn't Hear A Thing Over Eighty On My Motorcycle Now I Can Hear Well Up To Triple Digits.
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2 of 2 people found the following review helpful
4.0 out of 5 stars Great amp. Small size., February 23, 2014
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This review is from: Alpine KTP-445U 4-channel Power Pack Amplifier (Electronics)
Great amp. Really improved the speakers. Made the sound much brighter.
Small amp but great for cars with limited space.
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2 of 2 people found the following review helpful
5.0 out of 5 stars Great., October 6, 2013
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Fast shipping. Exactly what I ordered. Compact and light. Used it for stereo on motorcycle fairing. Driving 4 Polk DB521's. Sound is fantastic.
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2 of 2 people found the following review helpful
5.0 out of 5 stars great amp, February 18, 2013
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I paired this amp with an alpine head unit and what a great combo. It sounds so much cleaner and powerful worth it upgrade.
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4 of 5 people found the following review helpful
5.0 out of 5 stars An improvement with stock HU, November 11, 2013
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I have a 2012 Subaru Impreza with stock HU, Polk mm651 front door coaxials, CDT CL-6EX rear door coaxials, Kicker 11HS8 underseat sub, and the Subaru/Kicker upgrade in-dash tweeters. This amp is all I need to drive the door speakers more than loud enough, and with little distortion. With the gain set up 40%, the amp maxes out around 33 (of 40) on HU volume control and still sounds clean.

One BIG tip: run a new ground. Using the factory harness ground will give a lot of alternator whine (at least it did for me).
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Alpine KTP-445U 4-channel Power Pack Amplifier
$150.00 $112.44
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