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Alpine KTP-445U 4-channel Power Pack Amplifier
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- Compact Class D amplifier for factory and aftermarket receivers
- Universal plug lets you send signal from RCA outputs or speaker-level wiring
- Runs off same power circuit as receiver.
- 45 watts RMS x 4 at 4 ohms (CEA-2006 compliant)
- Dimensions: 7-7/8"W x 1-1/2"H x 2-9/16"D
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|Item Dimensions||7.5 x 9.25 x 3.25 in||7.5 x 9.25 x 3.25 in||7 x 8.5 x 2.5 in||3.54 x 5.51 x 1.34 in||9.06 x 12.99 x 4.33 in||9.06 x 12.99 x 4.33 in|
Universal Class D 4-Channel Head Unit Power Pack for Use with all Aftermarket & Factory Receivers
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I highly recommend this amp for giving extra punch to any aftermarket speakers you buy to replace OEM factory models. I wouldn't advise for factory speakers unless your factory head unit has poor output power.
The only con I could give the amp is with the intent being to mount in a hidden location that they didn't include a remote option to control the gain. With this in mind you will have to make your gain adjustments before final mounting of the amp and putting the dash back (or wherever you mount it if hidden away). Excellent price for the amp also.
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.
I installed this amp without RCA so I stripped it to connect it to the speaker wires to the head unit. I have a Pioneer DEH-X5800HD with Kicker 40CS654's in the front Rockford Fosgate Prime 165X3's in the rear (will upgrade to CS654's to match front). The speakers sounded great with the head unit 14W RMS and had some boomy bass. When I installed this amp, the clarity is crystal clear... Until I put an EQ, Loudness, Bass Boost, or any other sound tweak in general.. it starts to distort. It's not even like boomy distortion, it's punchy distortion which sounds super sharp.. almost like it's going to clip and shut off.
To be quite honest.. the head units MOSFET 14W amp is almost as loud (just lacked low end on low volume). If I were trying to save money, I would have just gotten an underseat subwoofer and stayed with the head unit amp.
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