How to Buy a Stereo Amplifier

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How to Buy a Stereo Amplifier

A stereo amplifier is an electronic device that is used to increase the power of an audio signal that is delivered to an external speaker. Stereo sound is developed by basically recreating audio signals from one location to another, and the amplifier is a critical component in the process of recreating those signals. Stereo amplifiers are found in a variety of different types from those that are internal components of a stereo receiver to stand alone components that can be added to a home or car stereo system.

Amplifiers have the job of providing the power necessary to make the entire stereo system operate properly, so it is important for those shopping for a new amplifier to understand the basics of what to know and look for. Understanding the different aspects of an amplifier and how they actually operate helps prospective buyers shop for an amplifier that properly suits their needs.

How a Stereo Amplifier Works

Sound is basically a pressure wave that moves particles around in the air and causes them to vibrate. This creates pressure fluctuations that human ears can pick up and translate as electrical signals that are transferred to the brain for processing. Electronic stereos operate with the same basic principle in that a microphone is used to produce an electronic signal that is recorded and then replayed through speakers.

Speakers have a cone that moves back and forth to recreate the original pressure wave recorded from the microphone. The main problem with this process is that the microphone diaphragm only has to move a small distance to create the pressure waves and vibrations that are recorded, and in order to reproduce these sounds through much larger speaker cones, the signal must be dramatically increased in order to move the large diaphragms in the speakers.

Importance of the Audio Signal

In order to boost the audio signals to a point where they can move the speaker cone, they must be amplified through a stereo amplifier. The amplifier increases the audio signal output while maintaining the same pattern of vibration that was captured by the original recording. The amplifier does more than just increase the electronic strength of the audio signal, it increases it while maintaining its original intent. It does this by taking the original signal and recreating it in a more powerful version that is an entirely new signal based on the original signal.

The Significance of Watts

Watts measure how hard an amplifier works in order to operate the drivers of a speaker. The drivers of a speaker are the various tweeters and woofers that pulse back and forth and create the sound pressure waves and vibrations that produce the actual music that is emitted from the stereo system. The higher the level of watts a stereo system has, the more power it has to operate the speaker’s drivers. This becomes important when larger speakers are needed to play louder music in larger spaces. Various amplifiers feature different levels of wattage output and the higher the level, the more expensive the amplifier is. Wattage is an important measure of how effective a system’s potential is, but the number of watts are only as important as the speakers capability to handle that amount of power.

Watt Utilisation

Generally, speakers that are more efficient are able to utilise less wattage more effectively. A set of efficient speakers can fill a normal sized room with approximately 25 watts of power, where a set of less efficient speakers might need 40 to 50 watts to equal the same level of performance. It is important to match the wattage of the amplifier with efficient speakers that can make the most effective use of the power. It makes no sense to purchase an expensive high-powered amplifier if the speakers cannot handle the load.

Stereo Amplifier Channels

Amplifiers are classified in terms of the number of channels they have. In simplified terms, the larger the number of channels, the more capabilities the amplifier has to handle speakers and subwoofers. Small stereo systems that have two speakers are effectively served by a two channel amplifier, which controls left and right channels. A two channel amplifier controls a speaker on the left and right sides. A bridged two channel amplifier adds the addition of a mono channel to the amplifier and gives it the ability to operate the left and right channels as well as a subwoofer.

The human ear cannot distinguish the direction of bass, so a mono output is all that is needed for the woofer. If the buyer intends to run two speakers and a subwoofer, then they should make sure to purchase at least a bridged two channel amp for the task. Amplifiers can come in many different channel configurations from one to 12 channels and even a mono channel amp that is designed specifically for a subwoofer usage.

Stereo Amplifiers for the Car

Car amplifiers designed for automobiles can vary in both wattage and the amount of channels they have depending upon the requirements of the sound system. For people who have two speakers and merely want to upgrade their automotive system, a two channel amplifier can be added to increase the systems output. Automotive systems that feature four speakers are best served by a four channel amplifier that controls both right and left output as well as front and rear output.

If a subwoofer is added to the stereo system, a five channel amplifier is well suited to the application as well as a six channel amplifier. There are also specialised units known as Class D amplifiers that are specifically designed for subwoofer applications because of their high power capabilities. There are also specialised marine amplifiers that are suited for wet environments and harsh weather.

Stereo Amplifiers for the Home

Much like automotive amplifiers, home stereo amplifiers come in a variety of power and channel options depending on the needs of the user. A two channel amplifier powers a two speaker system effectively, and unlike automotive systems, home stereo speakers usually can produce effective levels of bass so a stand alone subwoofer is not needed. If more speakers are going to placed into service, a four channel or greater amplifier is needed. If a user upgrades to a four channel amp, the two channel amp can be adapted into the system to power a subwoofer or additional speakers that might be added in the future.

How to Buy a Stereo Amplifier on eBay

Searching for the right stereo amplifier for your needs is not as difficult as one might think. The key to finding the right amplifier is having the ability to search through a large spectrum of amplifiers in order to find the best unit at the best price. The most effective way to do this is to use the powerful search tools available on eBay. Start your search at the eBay homepage by entering a keyword such as "stereo amplifiers" into the search box. A list of auctions is displayed that relate to that search term.

You can browse through each listing until you find the right stereo amplifier for your needs, or you can select from various categories that can refine the search results by amplifiers for the home or vehicle or other applications. By selecting from the various categories, you can significantly narrow the search results to display only the exact type of amplifier you are looking for.

Finding a Seller

Once you have selected the proper amplifier for your stereo system, the next step is to verify the feedback rating of the seller. The eBay community provides feedback about the seller on every transaction that is conducted, and a positive feedback rating means that the seller has consistently completed their auctions in a honest and professional manner. Always seek out sellers with a positive feedback rating, and those that have been listed as a Top-Rated Seller.


Stereo amplifiers are one of the most critical components of a stereo system. Without amplification of some sort, sound recreation from recording to playback would be severely limited and the high fidelity audio that is currently enjoyed through speakers would be impossible. Amplifiers take the original recording and recreate it into a more powerful signal that can be processed by the speakers. Without this amplification, the original recording would not be powerful enough to operate the drivers within the speakers and create the actual sound.

When buyers shop for a stereo amplifier, it is important that they understand how many watts they need from their amplifier in order to properly power the speakers they plan to use. Understanding how many channels they need from their amp is also good information to have prior to purchasing. Once buyers understand exactly what type of amplifier they need, the next step is to take advantage of the excellent variety of amplifiers and the great savings they can realise when shopping on various websites and online auctions such as eBay.

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