Adding an amplifier to your classic car stereo system will push more power and cleaner power to your speakers.  Power is the answer for improved sound quality, volume, and clarity.  Think of your stereo and speakers as a large rock.  I might be able to bend over, reach down, and pick that heavy rock up.  Or, I could have a crane pick up and move the rock.  Me picking up the rock is the built-in power in your radio.  The crane is the equivalent of using an amplifier.  

Why You Need an Amplifier 

Yes, we said, "Need."  You should consider adding an amplifier to your classic car because it will create a significantly better driving experience.  You just invested a significant amount of time and/or money into your classic car, and you can take your driving experience to the next level with a stereo system that sounds amazing.  An amplifier may cost $200-$700.  But, imagine this...

You are driving your car on a nice sunny day, the windows are down, and you have your favorite song playing.  You turn it up because you like the song, and the more you turn it up, the better it sounds.  It actually sounds so good, you think that they are playing the song right there for you, and you can't help but smile and maybe turn it up a little bit more because it just sounds that good.  

That's what an amplifier does.  The stereo systems that come in new cars today sound pretty freakin' good and there is a reason for that.  Most new cars that have come with a "Premium" or "Bose" or "Bowers and Wilkins" or B&O" or whatever name stereo system, sound incredible.  You can have that sound quality and probably better in your classic car for usually less than $1000.  When it comes to the cost of the car, it usually isn't that much in terms of a percentage.  But, what you get in return is so so worth it.  "Smiles per Mile"

There are some important steps to help you figure out which amplifier is right for you.

1. How many speakers are you going to power?
2. Are you powering speakers or subwoofers?
3. What is the RMS power rating of the speakers and/or subwoofer(s)?

How Many Speakers are you Powering?

Most classic cars that have upgraded the stereo system have four speakers.  There are typically two speakers in the front, either in the kick panels or in the dash location, and two speakers in the rear deck, typically 6x9s.  If you have a truck, or if you have a coupe such as a Thunderbird or Corvette, you may have less than 4 speakers.  Regardless, count the number of speakers in your vehicle.

Do you have or do you want a subwoofer?

If you have a subwoofer, or if you plan to add a subwoofer, you will need an amplifier to power it.  Typically we power subwoofers with monoblock amplifiers or 5 channel amplifiers.  The monoblock amps are amplifiers that are designed to specifically power subwoofers and 5 channel amplifiers allow you to power 4 channels and a subwoofer with a single amplifier.

What is the RMS power rating of the speakers and/or subwoofer?

When looking at the power rating on speakers, we only care about the RMS rating.  Peak power handling is not important.  If your speakers are rated at 75W RMS, you ideally want to be somewhat close to that.  You will be fine with 45 watts of power and you will be fine with 100 watts RMS from your amp.  If your speakers are rated at 75W RMS and your amp is putting out 100W RMS, you want to make sure that you don't have the gain turned up all the way.

Now that we have that info...

Amplifier Channels

• Monoblock, Mono, or Subwoofer Amplifiers - These are single-channel amplifiers that are designed to power subwoofers.  Most subwoofer amplifiers can power 1 or 2 subwoofers, depending on the power rating of both the subwoofers, the amplifier, and how it is wired.
• 2 Channel Amplifiers - 2 Channel amplifiers are typically used to power two speakers.  A two-channel amplifier can power 4 speakers and it can also be bridged to power a single speaker or subwoofer, but the most common application is for a 2 channel amp to power 2 speakers.  It makes sense.
• 3 Channel Amplifiers - There aren't many three-channel amplifiers.  JL Audio is the only company that makes these.  A 3 channel amplifier is designed to power two or four speakers and either one or two subwoofers.  With a three-channel amplifier powering 4 speakers, you lose the ability to fade between the front and back.  
• 4 Channel Amplifiers - These are one of the most popular amp configurations for classic cars.  A four-channel amplifier is typically used to power 4 speakers.  You can bridge a 4 channel amplifier to power 2 speakers and a subwoofer, but it isn't that common.  A four-channel amplifier can power up to 8 speakers at 2 ohms.
• 5 Channel Amplifiers - 5 channel amplifiers are very popular among classic car owners that want to power both their speakers and a subwoofer.  A 5 channel amplifier lets you power your 4 speakers and a subwoofer while only needing to install one amplifier.

Amplifier Brands

Keep It the Same as the Speakers

Don't make it more complicated than it needs to be.  Unless you really know car audio amplifiers, the easiest thing to do is to use an amplifier from the same brand as your speakers.  If you have Kicker speakers, go with a Kicker amplifier.  The same thing holds true with Rockford Fosgate, JL Audio, Kenwood, etc.  

Some Exceptions

The only exception to this rule is Hertz.  The affordable Hertz amplifiers aren't that good.  Hertz makes great speakers, but when it comes to amplifiers, go with the Audison SR series, Rockford, or JL Audio.  JBL and Infinity amplifiers work fine, we probably like the Audison, Kicker, Rockford, Kenwood, and JL Audio amps better.

Frequency Ranges, Filters, and Crossovers

Amplifiers will have frequency ranges, filters, and crossover specifications that allow you to control which signals go to which speakers.

Frequency Range

Outside of monoblock amplifiers, two, three, four, and five-channel amplifiers will be able to power your speakers without having to worry about the frequency ranges.  On 3 channel amplifiers and 5 channel amplifiers though, the subwoofer channels are designed to play subwoofer frequencies, typically below 200 Hz.  You can't use the subwoofer channels on 3 and 5 channel amplifiers to effectively power and send the proper signal to full range speakers.

Filters

• Hi-Pass Filter - Allows the high frequencies through to the speakers and cuts out the low-level frequencies below the selected crossover point.  This is typically used when you have a subwoofer.  You turn on the high pass filter and set it at 80 Hz.  This keeps most of the sub-bass frequencies from going to the speakers.  Your speakers don't try to reproduce frequencies they weren't designed to reproduce
• Low Pass Filter - Allows the low frequencies through to the speakers and cuts out the high-level frequencies above the selected crossover point.  This is typically used when you have a subwoofer and it is used on the subwoofer channel.  With the crossover set at 80 Hz, this keeps the frequencies above 80 Hz from going to the subwoofer.  Your subwoofer doesn't try to produce high frequency sounds that it wasn't designed to reproduce.
• All-Pass Filter - Let's all of the frequencies through to the speakers and/or subwoofer

Crossover Slope

The crossover slope is typically shown as 12 dB/octave or 24 dB/octave.  This number tells you the slope of the fall-off at the crossover point.  If we have the crossover set at 80 Hz, a 24 dB/octave crossover is going to "fall off" much faster than a 12 dB/octave crossover.  Most amplifiers have 12 dB/octave crossovers and it is more than enough.  Don't overthink this.

Product Recommendations

These are some of our favorite amplifiers that we offer

4 Channel Amplifiers

• Kicker CXA360.4t
• Rockford Fosgate R2-300x4
• Rockford Fosgate R2-500x4
• JL Audio RD400/4
• Audison SR4 300
• Kenwood Excelon X302-4

5 Channel Amplifiers

• Kicker CXA660.5t
• Rockford Fosgate R2-750x5
• JL Audio RD900/5
• Audison SR5 600
• JL Audio XD700/5
• Kenwood Excelon X901-5

Mini Amplifiers

• Rockford Fosgate PBR400x4d
• JL Audio MX280/4
• Rockford Fosgate T400x4ad
• Kicker KEY200.4
• Rockford Fosgate T1000x5ad

You can't go wrong with any of these products.  They all sound great.