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50 of 52 people found the following review helpful
on October 23, 2012
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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52 of 57 people found the following review helpful
on June 6, 2014
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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27 of 28 people found the following review helpful
on July 26, 2012
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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8 of 8 people found the following review helpful
on October 4, 2013
you can hide it anywhere, more than enough if you are replacing stock speakers and want a bit more umph!!
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7 of 7 people found the following review helpful
on February 23, 2014
Great amp. Really improved the speakers. Made the sound much brighter.
Small amp but great for cars with limited space.
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9 of 10 people found the following review helpful
on January 24, 2013
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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6 of 7 people found the following review helpful
on February 3, 2015
Let me first say that I currently own a car that has a aftermarket system in it that consist of one 12" JL subs running off a alpine monoblock pdx amp @ 2ohms/800 watt RMS, components up front and 6x9's in the rear running off a 4 channel 550 watt pdx alpine amp and it rocks hard. So with that said I know car audio and have been building out system for over 20years. Well I bought a 2014 ram 1500 Quad cab 5.7 HEMI 4x4 big horn edition with the 8.4 radio with the stock speakers. Wasn't a bad stereo system for the average person to listen to, but like most factory stereos it lack quality sound due to poor speakers and a crappy head unit(radio/deck). Well like most new vehicles, the 8.4 radio in this truck is tied to several features like the heating and cooling controls, navigation, backup camera, sat readio, settings for the truck, and several other feature as well. So replacing the head unit is not really an option I'd like to explore with this new truck. So I started to look around for a small foot print amp that didn't require running a power line with inline fuse from the battery to the amp and that could be placed somewhere behind the dash. I came across a few brands like clarion, fosgate, some off name brands, and this alpine unit, KTP-445U. Already having alpine amps in my other car, I knew I couldn't go wrong with it, so I made the purchase. Along with the amp I figured I'd order speakers to go with it. I decided on the Kicker-41KSC354 3 1/2 for the dash, Kicker-40CS654 6.5in for the front doors, and the Kicker-41KSC694 6x9's for the rear doors. The installation of the amp was simple and straight forward. Seeing how factory radios don't have RCA outputs, this amp allows you to cut the ends of the RCA inputs off each channel (it's a four channel amp) and use the lines for direct connect to the factory radio harness speaker lines. This also eliminated the need for a remote wire to turn the amp on because the amp detects the connection of the speaker lines and automatically turns the amp on when there is a signal coming over the speaker wire from the head unit. The best part was that this amp fit perfectly behind the factory radio and I was able to mount it to a cross support that was behind the radio. After installing the amp I next did the speakers throughout the truck. Another pretty simple straight forward thing to do. After everything was completed and put back, I reconnected the battery and fired it up and all I can say is fricking WOW!!! This little thing sure packs a punch. It turned this weak head unit/stereo system into something enjoyable. It's not a competition stereo, but boy was I shocked at how good it sounded. No engine noise of any kind! even with the headlights on. The gains are only turned up 25% of the way and it's running full range. For the cost of this amp and the ease of installation this thing is a winner. It will turn any boring head unit into a monster of sound. I should mention that this alpine amp will work with any factory head unit and most speaker configuration. If your vehicle has an upgraded factory system that already has an amp you will need to check out how many channels your factory amp is using and how many speakers your car has. My dodge has six speakers but the front dash speakers and front door speakers are tied together by the factory so they share the two front channels coming off of the amp while the rear uses the other two channels. So for any of you out there looking to do a inexpensive upgrade to your factory radio for better sound, this is your best bet. Are there other options or bigger amps you can install, why yes, but it's at a cost that most people don't want to spend. This little amp will please.
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3 of 3 people found the following review helpful
on September 22, 2014
This unit was exactly what I needed for my 2013 Ford Edge. In the newer model Fords, you cannot replace the factory head unit as it is integrated into the electronics of the car. So, when I decided I needed something better, I went with a JL Audio CL441DSP CleanSweep OEM Audio Interface, and this unit to power my new Alpine Type-R SPR-60C component sets for front and rear doors. Due to its size, I was able to easily wire this in to my factory harness and tuck it into the dash, just underneath the factory head unit. Once the CleanSweep was calibrated, the power this little power house puts out was astounding. I was blown away be the power and clarity of the sound. If you want to upgrade your factory sound system and cannot replace your head unit, this is definitely the amplifier for you!
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3 of 3 people found the following review helpful
on October 6, 2013
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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8 of 11 people found the following review helpful
on November 19, 2013
I recently had this amp installed in my 2013 Tacoma. I love my non-JBL touch screen head unit, but didn't like the quality of music it produced with the factory speakers. I replaced all four speakers with Infinity speakers and the sound was not much better which was expected. The head unit just doesn't have enough push and the lack of bass coming from the rear speakers was beyond disappointing. I went out looking for an amp that wouldn't make my ears bleed, but would make my Infinitys sound like they were meant to. This amp does exactly that. Deep strong bass from all four speakers plus the highs and mids are very crisp. I was pleasantly surprised by how loud I could push them. I stopped before they did. Plus, one of the best parts is the amp fit perfectly behind my double DIN head unit so no speaker wires to run under the seats. Cheap and easy upgrade that makes a world of difference.
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