The Only Alpine KTP-445U Review You’ll Need: A Tiny But Amazing 4 Channel Mini Amp

Sometimes getting good sound can be really tough – most especially if you have limited space. And it’s a shame, too, because often that means you’ll have to do without.

My, how things have changed!

This little power pack of sound is a modern-day solution to a decades old problem – getting great sound in a tight space. In my Alpine KTP-445U review I’ll provide a detailed an honest review of this fantastic like amp.

Alpine KTP-445U basics

Image of Alpine KPA-445U amplifier angle viewIn case you haven’t noticed yet, I’m a big fan of this little guy – and very happy with what Alpine has come up with! I don’t normally expect much from miniaturized amplifiers, but in this case I can honestly say I’m impressed.

First off, we need to set the stage by understanding what this little amplifier is and isn’t. It is not an end-all solution for the best audio quality money can buy. Let’s be realistic – you cannot get “perfect sound” in an incredibly tiny package for less than $150.

When it comes to sound, there are always compromises that must be made. It’s important to have reasonable expectations. Any good engineer will tell you the same.

What to bear in mind…

Also, it’s important to remember that as I’ll be explaining below, this is a class D type of amplifier. Class D amps have several pros and cons to be aware of (which I cover in detail). It’s important to remember this when you compare it to other amplifiers you may be thinking about buying.

I’ll be reviewing it based on my extensive knowledge of the technology and the amp both as an engineer and an installer. Also, I’ll be very fair – and very detailed – when I make comparisons to bigger and more expensive amplifiers.

Behind the technology: understanding the KTP-445U amplifier design

In only the last several years class D audio amplifiers have become one of the hottest audio technologies in the audio world. This modern technology has improved greatly since the first class D amplifiers hit the market years ago. I’ve found that despite this many brands still leave a LOT to be desired. Unlike the KTP-445U I have been very disappointed by some I’ve tried.

What is a class D car amp?

Simply put, audio amplifiers are all based off on one or more basic “classes”, or categories that classify the type of design they use. Despite what you might see thanks to advertising, a car amplifier class always fits into one of 3.

These range from Class A (fantastic clarity and ultra-low noise specs, but expensive and a power hog) to Class A/B and now class D. For the most part, any other kind you might run across is just a variation of one of those. (For a “class T” amp is still a class D – that’s just marketing).

Class D amps were once only used for subs but now are mainstream

Until recent years, Class A/B amplifiers were the most common because they’re cost-effective, relatively simple in design, and don’t waste as much power as Class A designs do. Also A/B amps provide low distortion and high power levels for a good watt-per-dollar value.

Despite their good points, conventional (A/B) amplifiers waste a lot of electrical power which is turned into heat rather than power to drive speakers. Today’s amps are still somewhat bulky and heavy due to the large metal body needed to dissipate the heat created.

A class D car amp is a newer type of amplifier technology used to produce audio power more efficiently.

How do class D amps work?

Diagram how a class D switching amplifier worksA Class D amplifier works by “modulating” (chopping up) the incoming audio signal and switching the transistors used to amplify it on and off incredibly quickly. This results in a fantastically efficient design without huge amounts of power being turned into heat like designs from the old days!

Class D amplifiers are based on a switching circuit design approach. This means the design modulates – or transforms – the incoming audio signal by chopping it up into a series of on-and-off waveforms as the input signal is received.

This is used to switch power-conducting transistors on and off thousands or hundreds of thousands of times per second. Older audio amplifiers (like class A or class A/B) conduct electricity nearly all the time they’re on.

While A/B type amplifiers are about 50-65% efficient, Class D amplifiers can achieve an incredible 85-90% efficiency!

Because of this the amount of power being consumed by a Class D amp is greatly reduced – resulting in no need for a huge, heavy amplifier body or lots of heat being produced. This was a huge step forward in technology.

Fun fact: Some bare-bones miniature class D amps are smaller than a pack of cigarettes!

Additionally, electronic component sizes have evolved to make these amps smaller and smaller. The decades-old problem of “How can I fit an amplifier into a tiny space in my vehicle?” is now just a bad memory.

No longer do you just have to settle for a weak 15W per channel stereo head unit. You’re now able to get many times the sound in a package that’s far smaller than anything imagined possible only 10 years ago.

Alpine vs the competitors

Something you might not be aware of is that there’s a lot of junk out there. Many of today’s car amp brands are no longer selling unique designs of their own. Sadly, many amplifiers on the market today, including compact Class D designs, are rebadged models that share the same internal components and mediocre design and only have minor cosmetic differences on the outside.

Over the years, lower-end brands were bought out by larger companies and exist only for marketing purposes, not for quality.

I’ve even bought one of these competing amps for test purposes (perhaps one day I’ll do a write-up) and was very disappointed with the design & sound quality. Noise levels were unacceptable and upon examining it I realized quickly it was another low-end version of an “amp on a chip” design.

In the audio engineering world, this means shortcuts were taken at the expense of sound quality and performance.

Alpine has relied on its great engineering resources and the KTP-445U is different from the competition because it’s an original and fresh design. I was not disappointed to find it has the trademark Alpine quality and innovation that became my personal favorite over the years.

Also, Alpine doesn’t use misleading power ratings and specifications, unlike other brands. The power ratings and sound quality specifications I’ll go into below are realistic and honest.

This is important to me not just as an installer and an engineer, but because I need to be confident in anything I review and recommend. I know how it feels to spend your hard-earned money on products that disappoint.

KTP-445U features and specifications


One of the biggest selling points is its size. The amp measures an amazingly compact 7 7/16″ x 1.5″ x 2.5″ (189 x 38.2 x 64.5 mm) in size. That’s smaller than pretty much any comparable amplifier available anywhere in the world today! I’m not kidding – I was expecting it to be much bigger. Basically all other high-quality Class D amplifiers below $200 today are at least 4 x the size of the Alpine.

mage of Alpine KPA-445U mini amplifier in my hand

Hard to believe how small it is. An amp with comparable power only a handful of years ago would have been 5 x times bigger. This one is small enough to hold in your hand!

Built-in high-pass crossovers

Originally I had expected the amp to be a “plain Jane” amp with NO features whatsoever, but it turned out I was wrong.

The amp actually, to my surprise, includes optional high-pass filters with selectable frequencies for the high-pass feature ( 60Hz, 80Hz, or 120Hz) to allow you to cut off speaker-distorting subwoofer bass if you like. Of course, you can always switch if off and run your speakers in “full range” mode if you like, but I normally prefer to block the lower bass frequencies.

My custom-installed 6.5″ speakers can’t handle the lower bass frequencies (they don’t do well below 50 Hz or so, so 60Hz is pretty close) so that’s very important to me.

High and low level inputs

Of course, I didn’t expect the Alpine to disappoint, but again they’ve done a great job in the design. The amp can work with both aftermarket head units via the or RCA inputs OR  speaker-level inputs from a factory stereo! In other words, you can use the KTP-445U to get a more powerful and better sound even if you have a factory-installed stereo in your vehicle.

The included color-coded wiring harness makes it easy and it’s a feature I’m sure a lot of buyers just like you will appreciate.

Quick tip: When adding an aftermarket amplifier to a factory system and connecting to speaker-level outputs, be sure to plan for getting some small-gauge speaker wire. Plan ahead for enough length to go from the speaker wiring connections to the amp (and back again, if powering factory speakers).

One thing I’ve learned in my years of car stereo installation experience is that the ability to connect to factory-installed stereos is a huge plus. The Alpine can be connected directly to factory speaker wiring in order to “tap off” and get a good audio signal to feed into the amp.

While not as good as being fed from an aftermarket head unit via the RCA inputs, it’s still a great option and in my experience, when done correctly, still sounds clean and there’s very little distortion or breaking up at higher volumes.

You can also disconnect the factory speakers once the KTP-445U is connected to avoid any distortion issues if that’s a concern for you.
Image of Alpine KPA-445U mini amplifier input harnessThe included signal input harness allows connecting both RCA (low-level) inputs or speaker-level inputs to the amplifier easily. Inputs are color-coded and explained clearly in the owner’s manual. A similar harness is used to connect to the output (to connect to speakers you’d like to use)

There are switches for audio controls on the bottom of the amp if you need to choose speaker level inputs or change crossover functions. As an added bonus, even if you’re using 4 speakers and only have a 2-channel input, the amp can provide a signal to all 4 outputs. You won’t have to buy a pair of RCA Y-adapters.

In order to bridge the amp, you’ll also need to set the 2/4 ch. input switch to 2 channel as well.

Image of Alpine KPA-445U mini amplifier control switches

Selectable option switches on the bottom of the amp allow you to adjust the crossover functions or split a stereo input into 4 channels. Also, this is where you must select the audio source before powering up the amp.

Front and rear gain controls

Image of Alpine KPA-445U mini amplifier controlsSeparate front and rear gain controls allow adjusting the amplification level depending upon the input signal strength you have. Speaker-level inputs, for example, might require turning it down, while RCA-level inputs may require boosting it a bit. It’s highly dependent upon what kind of stereo you have. In either case, it’s easy to adjust. The KTP-444U can accept up to 4V RCA inputs which are considered a “higher end” signal strength for aftermarket units.

Not too much I have to say here – the front and rear controls are easy to use and easy to adjust. Also, the gain controls “feel” good because good quality components (potentiometers, which are just adjustable resistors) are used on the circuit board. This means that when you adjust the gain levels it won’t change over time and will have a good “feel” when you turn them.


The amp can deliver up to 45 watts per channel into both 4 or 2-Ohm speakers, which is surprising because most miniature amps in my experience cannot handle 2 Ohm speakers. This means you could add extra speakers in parallel (to a degree) if desired.

It’s important to understand that 45 watts isn’t enough for extreme sound levels or to drive large woofers if that’s your goal. This amp isn’t designed for that.

I’d estimated with a good set of efficient speakers, however, you can get close to around 100dB of clear sound before it begins to give out due to its limits. For most people with normal listening habits, it’s plenty of power and you need not worry.

For reference, it may be helpful to know that most in-dash car stereos can provide only around 15W-18W RMS or so per channel of usable power.

Sound quality

For me, sound quality is extremely important.

It seems like every little bit of irritating distortion or poor musical reproduction I’ve heard really grates my nerves.

I’m happy to report the KPT-445U has great good sound quality and is very impressive for a tiny amp! If you recall what I mentioned earlier, this is a Class D amplifier. The benefits of Class D amplifiers are a fantastic size, great efficiency, and a lower weight, but one of the drawbacks is reduced sound quality.

I can say with certainty (and don’t just trust me on this – check the multitudes of other happy reviews) that the sound quality is very good. Remember when I mentioned earlier about how I bought another brand of car amplifier and was disappointed?

It was because the noise levels (the noise I heard when no music was playing) was far too high compared to the many amplifiers I’ve installed and listened to over the years. Not so with Alpine – they’ve done a great job in minimizing noise.

I can say I was pleasantly surprised. I came into my review of the KTP-445U expecting an “ok” experience but was honestly very impressed with what Alpine has done.

Here’s an excerpt from the company themselves:

In order to ensure that Alpine sound quality is heard at your ears, we’ve created a platform that offers an unbelievably low noise floor, taking extra care to ensure a clean signal path, with no extraneous interference. The end result: The Power Pack boasts 1 Watt Signal-to-Noise Ratio of 82dB or better.Alpine Electronics

In my opinion, this says a lot. Why? Because it takes additional engineering time and manpower – in addition to planning – to make the effort to make better sound quality a design goal rather than a forgotten number on a spec sheet somewhere.

I’d much rather pay a bit more for something I know is designed right from the beginning and I know sounds great rather than just made to be “ok” and barely passable.

Quick tip: If you have to increase the gain level greatly it also increases your chance of hearing the base noise level in any amplifier, including this one. For best results, the amp should have a good, strong signal so that the gain can be turned down, resulting in the cleanest output possible.

And by the way, for you spec nerds like me, the specs on this little amp are great. According to the company, the Power Pack distortion actually decreases at higher frequencies, resulting in a clean and clear signal where your ear is most sensitive to distortion (less than 0.03% THD+N @ 1W, 1% THD+N at rated power).

Here are some of the most basic specifications you need to know:

Image of Alpine KTP-445U technical specifications

Note: the KTP-445U mini amp – despite its tiny size and simple design can drive 2 ohm speakers up to 45 watts each. I was honestly impressed and didn’t expect that.


Alpine KTP-445U under seat installation

Great for installation under seats and just about any small space you can think of.

The great thing about the size is that you can fit it in incredibly small spaces which were unheard of years ago. A great example is some of today’s vehicles in which there’s extremely tight space inside the dashboard, perhaps beside or behind the current stereo.

It’s a great solution to the most difficult installation problems which years ago would have required either a ton more money to be spent by customers or unfortunately cause some people to just “give up’ as there weren’t any other options.

It’s also a great fit for boats as well but you’d need to ensure it is protected against corrosion and exposure to the air and saltwater since it’s not marine rated. You can mount the tiny powerhouse by using the included zip cable ties to attach it to the nearest available wiring or mount it permanently using the included brackets and self-tapping screws.

Don’t forget that because of its light weight you could also use double-sided adhesive tape or Velcro if desired for convenience.

Note: Because it is so efficient and draws less electrical current than traditional amps, you won’t need to get a heavy-gauge wire installation kit and run extra wire. It’s possible to connect it to a nearby 12V supply from your car stereo, for example.

Accessories included with the KTP-445U

Image of Alpine KPA-445U included items

  • Mounting brackets (2)
  • Self-tapping screws (4)
  • Cable ties (2)
  • Required wiring harnesses

I would definitely suggest getting a few inexpensive items to make sure you’re better prepared for installation, such as:

  • A roll of speaker wire
  • 14 or 16 gauge power and negative wire for installations placed further way
  • Wire crimp connectors (“butt connectors”) and a crimp tool
  • A small bag of 6″ or 8″ zip wire tie

Bridging the amp

Need more power? Amazingly – and to my surprise – it’s not a problem with this amp.

Just switch the 2/4 channel input switch to the 2 ch. input mode. Then connect the output speaker wiring in bridged mode and you’re done!

You’ll have 90W RMS per channel of high-quality sound at your disposal. Honestly, I didn’t expect that for an amp so small, but once again the engineering quality made all the difference.

Just one more reason I’m impressed with it.

KTP-445U vs KTP-445A

Alpine KTP-445A image

The KTP-445A looks very similar to the KTP-445U. However, it’s designed specifically for Alpine head units 2005 and later, not for RCA or high-level inputs from others.

When shopping it’s important to be aware of the KTP-445A model as it can cause a bit of confusion and comes up in search results.

The KTP-445A is a model of the KTP-445U (where “U” stands for universal; “A” stands for Alpine head units) designed only to work with Alpine model car stereos. The wiring harnesses included don’t allow using RCA connectors and the standard speaker-level inputs.

Aside from that, both share the same basic design and performance.

There are a few drawbacks to know…

I would have liked to have an optional low-pass crossover feature in addition to the high pass design. Perhaps it was a cost-cutting or design compromise decision that had them remove it. I’m not sure.

I have somewhat mixed feelings regarding the location of the switches used to control sound options. They’re located on the bottom, whereas ideally, they’d be accessible from the side or top. But ultimately that’s a minor complaint.

Review score & summary

All in all, in my opinion, the KTP-445U is a wonderful little 4-channel amplifier with great sound quality. It’s truly a dream come true if you want great sound but have especially limited space.

It’s not for those who need extreme power and volume levels. You can’t drive subwoofers or very high-volume speaker systems with this amp, but what it does it does well!

Alpine KTP-445U review featured imageHead over to check out the current price and see the fantastic buyer reviews at Amazon.

  • Quality - 9.5/10
  • Sound quality - 8.7/10
  • Installation ease - 9.5/10
  • Features - 7.5/10

A well-designed and great sounding miniature car amplifier. One of the best compact amps I've seen.

Alpine has done it again with their approach to getting the most power and sound out of a tiny package. It’s a great upgrade for weak aftermarket or factory stereos. Thanks to its design it’s a great general-purpose 4-channel amp that can fit a wide variety of installation and audio system needs. You’re paying a few extra dollars for better sound and better design – and that’s exactly what you’ll get. You won’t be disappointed.


  • Amazingly small size!
  • Great sound, low distortion, and low noise design
  • Can handle 2 ohm speakers (4 channel mode)
  • 4 channel outputs
  • Bridgeable to 90W RMS x 2 channels
  • Selectable 2/4 channel input switch (no Y adapters required)
  • Speaker level inputs
  • Installation accessories included
  • Great power: 45W/channel
  • Built-in optional high-pass crossovers
  • Simple installation / no large wire required


  • No low-pass crossovers
  • Option switches are located on the bottom as opposed to top or sides
  • Could use more zip ties in package

Your comments are welcome!

    • Hi there – you’re right. Somehow I made an error – it is bridgeable to 2 x 90W RMS.

      I’m not sure how I missed that. I’ve updated my post to correct this.

  1. I am very interested in this amp for my 2008 gl1800 goldwing. Just trying to figure out the best front 6.5″ and rear 5″ to replace stock speakers. Any suggestions? Also what would be the next upgrade for a amp? I do have concerns about the heat buildup with amp mounted in the small trunk.

    • Hi Bruce! I am very sorry about replying late to your comment & questions. Unfortunately I wasn’t feeling well at all yesterday so I couldn’t reply sooner.

      To answer your questions:

      1. For the front 6.5″, I recommend a plastic cone pair of great-sounding coaxial speakers. Unlike paper cone speakers, they’re a lot more resistant to moisture. Additionally, these are pretty efficient (produce a good volume for the power applied) which is important for motorcyles.

      Have a look at these great Polk Audio DXi651 coaxial speakers. For the 5″, see my comments etc below.

      2. Regarding the amp, what are you currently using, and how much room do you have for an amp?

      My advice would to get an amp with no less than 45-50W per channel. The Alpine KTP-445U is a very nice amp and you can bridge it to get 90W/channel if you wanted to run only the front. However, you can get pretty good volume and sound with what it provides.

      3. With an amp like the KTP445U, there’s nothing to worry about with regard to heat. Class D amps (especially this one) run very cool and won’t have heat problems.

      Regarding the 5″ speakers, do you have any speaker opening measurements? 5″ isn’t a standard size, so most likely you’ll need to use 5 1/4″ or 4″ speakers with adapters to fit. But it’s important to know the mounting hole size before I can say more.

      I checked online but so far came up short in finding the specs for your model Goldwing.

      I hope this helps – just post a reply and we’ll go from there. Thanks for the comment, and for stopping by!

      Marty :)

      NOTE: You might also considering stuffing some Polyfill (polyester pillow stuffing material, sold by the bag) behind the speakers to get the best sound. The more you block off the rear of the speakers, the better.

      Speakers open to the air or without a decent sealed enclosure have fairly bad sound and will reach distortion levels too soon.

  2. Oh man, I just typed a whole page of information and did not put in Name and email before submit. Lost everything. OK condensed version.
    Called Alpine Tech line three times. Two said no go to add KTP445U to existing system. One said yes.
    Until I heard that I was going to keep stock amp and cut in a KTP445U for the new front speakers bridged and a KTP445U bridged for the new rear speakers.

    1. Polk Audio DXi651 coaxial speakers. YES
    2. Stock amp on goldwing 60×4 watts. Powerful yes but I want more. Located above rear tire. Would prefer not to remove and replace but time will tell. Would rather add the new amp or amps.
    Plenty of room for almost any size amp. Three different large storage compartments. Problem is cooling.
    3. yes probably 5 1/4s Suggestions for nice ones?
    Note. Will do on turkey stuffing.

    Marty. Thank you for your time, I really appreciate it. I am linking this information to my followers on the gl1800 website.

    If you go to Crutchfield and look up this amp, play the video and around the three minute mark, he states that it is not desirable to add this amp to existing factory amp. Just a FYI

    • Hi again, Bruce. I checked out the video, but he’s incorrect. There may be a few exceptions but his statement doesn’t make sense especially given that this is a “universal” amp.

      One reason I say that is because aftermarket amps are very frequently used to replace, or are added alongside, factory amplifiers. There are some cases where it’s not possible for a variety of reasons, but that’s usually not the case. I’ve installed quite a few in both situations.

      As long as you have access to the factory amp’s wiring it shouldn’t be too hard adding the Alpine and leaving the original there if you don’t want to remove it.

      I have tapped off of factory amp wiring (audio signal and power wiring, too) for this very reason by stripping the original wiring and soldering the other amp’s wiring to it. This avoided cutting up the original wiring.

      In the case of the KTP445U, you won’t need large gauge wire, so that makes it even easier.

      For the 5.25″ speakers, have a look at these water & moisture resistant Polk DB522 speakers.

      They’re recommended for motorcycles as well.

      Thanks for following up and I do hope this information will help others as well!

  3. All right then. So if I leave the stock amp where it is and just cut the wires at each stock speaker (wiring that in to input signal to the amp) and a new set of wires going from the output to the new speakers I should be OK. Using the speakers you suggested, would I want to use 1 or 2 Alpine KTP-445U or a completely different amp? Also, how do you make money off this info? Sell stereo equipment or ?? I do not expect this valuable information for free.
    Thanks again!!! Bruce

    • Hi again, Bruce.

      Ideally you would be able to unplug the connectors to the factory amp (unless you’re still using it for some speakers) and cut the original wiring as you said. Then connect to the amp. Of course, be sure to tape off the bare ends of the speaker wiring from the amp if it’s still powered on to prevent shorts.

      The good thing is you have some nice flexibility with the Alpine. You can leave it as-is and get 45W RMS to each of 4 speakers, or you can bridge it for more power and volume to each (90W x 2 when bridged).

      If you’re happy with the factory amp’s volume, if it were me I would try 1 amp first and see what you think.

      One reason I say that is because the factory amps are not usually rated accurately, so the KTP445U will likely be more powerful than the factory one.

      The Polk speakers are fairly efficient (produce good sound volume per wattage) so that should also help the volume you’ll get.

      Yes, I do make a tiny commission if someone buys recommended products through Amazon via my links. But, I would still have tried to help you for free, because I like helping others. (What can I say, I’m still a small-town guy inside, ha ha!)

      I have an affiliate disclaimer at the bottom of my site, to be upfront about this way of earning money.

      My pleasure, I’m happy to help! Let me know if anything else comes up. Those Goldwings are really nice and I’ve always thought they were cool.


  4. Hi Bruce,
    Just was wondering on your thoughts on alpine PSS-23WRA . Just got a 2018 Jeep JL. And want a better sound . I like alpines plug and play system for jeep.and sub and amp under seat . Or price wise , do you think I should do something eles, ?

    • Hi Alan & thanks for dropping by.

      I took a look at the PSS-23WRA. I am familiar with the 8″ PWE-S8 powered sub it includes. In my opinion the cost for the system is far too high and if you don’t mind less installation convenience you could get much better results for a fraction of the cost.

      I would recommend something like this, depending on your space requirements:

      – KTP445U amp under seat or Alpine MRV-F300 (preferred) or other compact higher power class D amp

      – Same or similar tweeters. You can get some great tweeters with crossovers under $65/pair

      – Preferably a real subwoofer in a ported or sealed enclosure. While you could bridge 2 of the 4 channel amp’s outputs, a second mono amp would be much better to drive it. 10″ or 12″ would do well.

      Another great option would be to use a powered subwoofer like this nice Rockville 12″ with the amp built in. In either case, using straps or brackets to hold the box in place in the cargo area should work.

      If you go this route you can easily save 1/2 the cost vs the Alpine and get much better sound. The tradeoff is that’s it’s not super-convenient like the PSS-23WRA’s ready-made connectors and brackets. Therefore installation takes more time and effort.

      If theft is a concern for the subwoofer, in the install shop we used quick-disconnect connectors for the subwoofer box wiring so it can be removed easily and avoid the temptation for thieves.

      I hope this helps!


  5. Thank you very much for sharing your knowledge and experience. Your website is very informative and very helpful with my limited knowledge of speakers. The Alpine KTP-445U is exactly what I am looking for to get more volume from my factory stereo.


      • I’m getting alot of distortion from the 6×9 speakers powered by the alpine ktp-445u amp. The door speakers powered by the head unit are clear in sound. The distortion comes and goes I believe as the amp heats up. Could it be the amp or the speakers.

        • My first thought is that most likely it’s the amp.

          If you’re only driving the one pair of speakers you could drive them in bridged mode and see how that works out.

    • I bought the A version to hook up to my alpine headunit..confused as to the amperage radio fuse is 10 amp..amp needs i had to cut the power wire and tap into 15 amp circuit..strange they would make you do that for soething that is plug and play

      • Hi Ira Thanks for the heads up regarding that as those who buy the “A” version will want to know that.

        [For those who aren’t familiar, the “U” version is a stand alone amplifier to work with factory or aftermarket head units while the “A” version can connect to Alpine head units.]

        Honestly that’s the only way a “real” amp could work – with a separate higher current power connection. That’s because a head unit’s wiring can’t provide enough to the external amp unless it’s a much weaker amp. I’ve seen similar before with a variety of add-on amps etc.


  6. I know understand the “A” model has different wiring harnesses for connection to Alpine head units, but could you simply cut off the harnesses and then wire in the amp like you would the “U” model? (For my specific application that would be speaker level input into the amp) Are there any other differences I’m not picking up on?

    • Hi there Josh. You can’t use the “A” model (Alpine dedicated unit) like you can the “U” (universal) model. There are several differences between the two:

      – The U model has gain controls. The A model doesn’t
      – The A model doesn’t offer RCA inputs like the model
      – I have not been able to confirm it yet, but I believe the A model is also missing the high-pass crossover feature too
      – I believe it may not have the 2/4 channel input switch option either

      You can use if that’s ok with you and if you’re only connecting to speaker outputs from a head unit (and not RCA jacks). However, there’s the possibility that you’ll need to adjust the gain, so that may be an issue.

  7. My local car stereo installer is recommending this unit as a lower cost alternative over a regular amplifier, to be installed on the factory head unit in my 2017 Kia Forte5 (it has aftermarket component speakers up front and coaxials in the rear). However they cannot guarantee that I will get better sound unless they also install a summing device between the head unit and the amplifier. I fully understand the purpose of the summing device, but do you think it’s true that my system may not sound better if I go with just adding the powerpack?

    • Hi Kevin. Well, there are certainly plenty of budget amps that sound good and cost less than the Alpine. However, the compact size makes the Alpine great for installations especially in small cars.

      Yes, it’s true that it may not sound better, but it’s not the amp’s fault. I’ve heard the sound in another Kia and the issue was the head unit’s sound quality, mainly.

      Ultimately, if you’re keeping the factory stereo you’re limited to the sound quality provided by it. As you have aftermarket component speakers, if they’re connected to their crossovers they should be able to provide good sound. If they’re not it’s possible the sound quality will be affected.

      The summing device, assuming it’s used correctly, just passes a full-range signal to the amp unless it has some EQ functions built in.

      So yes, unfortunately if you’re keeping the factory stereo you won’t get “great” sound, but you can expect somewhat better sound when using the amp if the installation is set up right. Ideally they’ll connect the component speakers to their included crossovers and then to the amp as they’re intended to be used.

  8. Yes, there are crossovers that I found wired up under the dash. My local tech did have a listen to my system and was surprised that it sounded pretty decent (no distortion at full volume). I just want to take it the next step up. I’d like a little more ommph (especially in songs that don’t have a lot ooomph to begin with). I noticed if I turn the fader to just to use the back speakers, the sound is very flat and low, despite them being aftermarket decent coax speakers. I noticed this in my previous cars too. It seems that vehicle manufacturers and their head units, concentrate the better sound to the front speakers. It is my guess that the summing interface,would greatly improve the sound to the back speakers, and thus I would have a more submersive experience with my music?

    Regarding your comment about there being cheaper amp options over the Alpine power pack, sure that’s true, but my tech told me that the labor cost is much more expensive going the regular amp route.

    • Hi Kevin, I understand where you’re coming from regarding the rear speakers and your other notes. It definitely depends on the rear speaker signal coming from the head unit, but also in my installation experience, in some cases the rear acoustics can be terrible and can result in poor sound.

      Most of the time the rear speaker channels are just a fader-controlled duplicate of the front, with the exception of higher-end “premium” amplified speaker systems. I’m not 100% sure in this case.

      Yes, you’ll save money with the Alpine as it won’t require a heavy amp gauge/amp wiring kit + separate mounting which is more in terms of parts & labor costs.

      My thought is that yes, the summed output of the adapter could be used to run to the rear input RCA jacks of the Alpine and you’ll know 100% you have the same signal as the front channels. (Or the adapter may have a second set of outputs to use as the rear channels, it depends).

      The best thing to do is try that and see how it sounds to you once it’s done. Hopefully you’ll find the sound to your liking at that point. I’m not sure what model the summing adapter is, but hopefully it offers EQ functions as that would allow you to tweak the sound as you like.

  9. When I put the my ear close to the speakers, I definitely can hear more range in the front speakers. When I play bass heavy music and I put my hand to the speakers, I can feel the front speakers thump but when I turn the fader to the back, I barely anything from the rear speakers.

    The summing interface that my shop wants to sell me, is the Audiocontrol LC7i. Looking online I see that less expensive option is the LC6i. Both have output level adjustment knobs on them (but no EQ adjusting). The LC7i has a “Accubass” function while the LC6i doesn’t. Accubass is supposed to correct bass rolloff from factory head units. I wonder if I really need that since I’m not adding a subwoofer?

  10. Hi Marty,
    After reading your review, I have purchased this Alpine KTP-445A to match the OEM Alpine HD145BT headunit that came with my Alfa Romeo 4C coupe. Being a tiny amp, it answered the concern of storage location.
    Since there is only space for front speakers, glad you mentioned the power is bridgeable. Now I know to switch to 2 channel when installing.
    So glad Alpine came out with a complementary product to improve their current head units. Loving the plug n play wiring features.
    Your article also convinced me to purchase a compact powered sub. Will surely lock out 80hz at the very least, or should I go the max?
    Kudos to this very helpful review.

    • Hi Les I’m glad you found the review helpful! Yes, I would keep the 80hz crossover frequency as it’s about right for most cases. (If I understand your question correctly). But certainly it doesn’t hurt to try adjusting it if you have the option and see how you like it.


  11. :( I would love if the pictures are going to be back again.

    I have this amp in my car and i dont hear och feel any different in the sound .

    • Hi there Carlos. Yes it can be, but the problem is that is doesn’t have a low-pass crossover feature built in. You’ll either need a head unit that has it built in or add your own if you want clean bass from the subwoofer.


  12. Marty, if I read this correct – if my car radio only has two channels (left & right speaker level outputs) & I connect them to this amp on just the front channel Left & Right speaker inputs, then this amp can still power its 4 output channels at 50W rms. Would I have to set the input switch to 2 or 4 channels ?

    • Good morning, Max. I doubled-checked and yes, it appears you’ll set the 2/4 input switch to “2” when connecting only the 2 channels of speaker inputs. You can definitely drive all 4 amp channels or even bridge it to 2 for more power if you like.

  13. So I working with a 2014 malibu Ls. First I added a 10.1 android head unit which took an interface harness with steering wheel controls. Had a huge impact on the front factory door speakers and completely cut out both rear door factory. I just installed 4 kicker 6.5 DSC650 Coaxials and installed and modified the rear deck panel with 2 kicker 6×9 KSC6930 Coaxials. I bought the alpine ktp-445u to power the 6 speakers but I also just added a kicker compr 12″ sub. Once I get an amp to power the 1 subwoofer could someone help me figure out the best way to bring everything together with wiring? Thanks

    • Hi Drew. It can be done, but the KTP-445U isn’t really a great match for 6 speakers. You only have 45W/channel, so that means if 4 speakers share one pair of amp channels, they’ll be limited to around 22.5W each. That’s only a few more watts than your average head unit can put out.

      Probably the best way to go about this, since most people keep the front speakers at a higher level than the rear, is to use:
      • Front channels: front speakers
      • Rear channels: Rear door & deck speakers, in parallel

      That will work since the amp is 2Ω capable. Ideally, however, you’re better off with a bigger amp or even a 6 ch. amp for example. I would try what I mentioned and see how it works out for you & how you like it then go from there.



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