If you've decided to buy an amp for your mobile sound system, you've made a smart move. Whether you'll use your amp for boosting the power to your full-range speakers, or for powering subwoofers, an amplifier will make a big difference in your system's performance.

Your first step, of course, is to decide how powerful an amp you need. If you're uncertain about that, take a few minutes and check out the article on Powering Your Subwoofer for Peak Performance, as well as Todd Cabell's article Matching Car Speakers to Your Mobile A/V System for some valuable insights on what you'll need. Once you've decided on the basics, you'll need to decide which amp to purchase. With the number of choices available, deciding which one to buy can leave you scratching your head. You may find that there are several amps available that have the features and specs you're looking for, and the only difference you can see is the price.

If you're choosing between two similarly featured amps with a big price difference, is there a benefit in purchasing the more expensive model? Does it really matter which amp you pick?

To start answering these questions, let's first take a look at how amps work.

Understanding the fundamentals
Very simply described, there are three parts to a power amplifier. The preamp section is where the signal comes into the amp, and where devices like crossovers and equalizers are located. The power supply provides the energy to power the amplifier, where the signal boosting output transistors are located.

This very basic amp diagram shows the three main sections of an audio amp.

The quality and layout of the components in each part of an amplifier are crucial in determining how well the amp performs. A well-engineered and designed audio amplifier will have clean, uncluttered circuit boards, with all the elements carefully and logically laid out.

The power supply of the amplifier will do a better job of providing supplies of clean power if it has heavy-duty capacitors. This will ensure that there are adequate reserves of power available when you're bumping your tunes up to high volume.

In the amplifier section, powerful output transistors are essential to feed clean output to the speakers. It's very important that the output transistors have an effective way to dissipate the heat that is the byproduct of the amplification process. This will give you the cleanest possible sound.
Let's compare!
Let's take a look "under the hood" at two similar amps and see what the differences are. Amp #1 is a four-channel model, rated at 50 watts X 4 RMS, and sells for $129.99. Amp #2 is also a four-channel model, rated at 40W X 4 RMS, and sells for $100 more, at $229.99.

Comparing the internal layout of the two amps.

This look at the internal layout of the amps reveals something of the engineering that went into the two models. Amp #1, on the left, has a somewhat more disorganized look, as seen in the long wire runs, than Amp #2, on the right.

A closer look at the power supplies.

In this closer look at the power supplies (above) note how much more separation there is between the components in the more expensive Amp #2, as compared to Amp #1. The spacing of these crucial components allows for better heat dissipation and limits the possibility of interference in the signal path.

A close up look at the power capacitors.

In the close-up, above, note the relative size and ratings of the capacitors in the power supply. Amp #2 (on the right) uses two large 3300 microfarad capacitors to regulate the flow of power and keep a reserve of energy for peak demands. The less expensive Amp #1, on the left, uses smaller capacitors. Remember, Amp #2 is actually rated at lower power than Amp #1, yet it uses larger capacitors. Larger capacity components in a lower-rated amp is a good indication of the build quality and engineering that has gone into the design and construction of the amp.

The output transistors.

The output transistors, shown above, are an interesting illustration of the differences in the construction of the two amps. Amp #1, on the left, clamps the output transistors to the heatsink with simple metal bars, held in with screws. This is a pretty "low-tech" solution to the problem of keeping these vital components cool. By the way — the white substance around the transistors is called "thermal grease." It aids in conducting the heat away from the transistors.

Amp #2, on the right, utilizes a much more advanced solution. The output transistors in this more expensive amplifier are bonded to a multi-layer insulated metal substrate with a very low thermal resistance. This proprietary process increases the heat transfer from the output transistors, resulting in better reliability, power output, and stability. The manufacturer's commitment to developing innovative and improved technologies is one of the reasons that this amp is more expensive.

Let's take a look at one more interesting photo. When I first opened Amp #1 (below), I was surprised to see a small, square piece of cardboard glued to the top of the capacitors.

Cardboard?

I can only assume that this was placed there to prevent components from shorting out through contact with the amp's metal cover. While it works, the better design of Amp #2 ensures that "band-aid" solutions like this are not necessary.
Summing up
It's important to remember that both amps are made by respected audio companies, and both are excellent values for the money. Clearly, however, Amp #2 is better laid-out, uses heavy duty components, and employs more advanced technology to solve basic engineering problems, like heat dissipation.

While we're thinking about heat dissipation, the heat sinks molded into the actual body of the amp are an important part of the design. Audio amplifiers aren't very efficient — depending on the type of amp, up to 50% of the power they use can be turned into heat when the amp is running. Amp #2 uses high quality heat sinks made of heavy, cast metal that are noticeably heftier than Amp #1's thinner metal shell.

The heavy-duty components and superior design features of Amp #2 give it the ability to provide you with cleaner sound. Because it has better power reserves and can dissipate heat more effectively, it has more effective "headroom" — the ability to provide clean signal at the upper range of its power output.

So, does it make much of a difference which amp you choose? In short, yes! If your budget is limited, by all means buy the less expensive amp. If, however, you value the best possible performance and want your amp to last, the extra investment you'll make in a more expensive model is well worth it.