A Used Digital Amplifier Buying Guide

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A Used Digital Amplifier Buying Guide

Most families have some sort of music system in their home. Whether it is a dock for their iPod, an all in one stereo system, or the receiver in their entertainment centre,, they have something around to fill their halls with music anytime they want. With the focus on entertainment centres that we see in the electronics industry today, the satellite or cable receiver has become the major audio component in most people’s "sound system." There is only one problem. Those receivers are focused on providing control for video, with their audio capability being somewhat diminished. While it works, no true audiophile would be satisfied with the sound quality coming from their video receiver and entertainment centre.

For those audiophiles, a separate audio sound system, made of discrete components would be a must. Discrete components means that the system consists of separate amplifiers, CD players, phonographs and other audio components that are all connected together through the amplifier. That provides the best possible sound, for what is actually a reasonable price, especially if you buy used. Therefore, buyers should learn about the various features of an amplifier in order to find a quality used digital amplifier. Understanding those features allows the buyer the capability of making an informed decision about what type of used digital amplifier to buy, in order to meet their needs.

What to Look for in a Used Digital Amplifier

Since the amplifier is the heart of the stereo sound system, picking the right one is important. These can be expensive devices, but a lot of money can be saved by buying used. Although it is possible for a stereo amplifier to break, there is not much likelihood of it doing so. The most common cause of them dying is the final amplifier transistors becoming destroyed due to excessive heat. When this happens, it is most likely due to lack of adequate ventilation.

Number and Types of Connections

Since one of the main functions of the amplifier is to switch between the various audio sources, the number and type of inputs are critical. Almost all inputs are essentially the same, stereo RCA connections. The line output level of the various audio devices is essentially the same, making switching between these inputs simple.

There are two notable exceptions to this. The first is for turntables, used for playing vinyl records. These have a much lower output level than other audio devices. Amplifiers normally have a special input or two for "phono", which refers to the turntable. If another input has to be used, a preamp is required.

The second exception is for an iOS device. Apple has their own proprietary connection, which is incompatible with normal audio inputs. Many modern amplifiers come with an iPod dock, which also functions for iPhones. With the advent of the third generation iPad, Apple has introduced a new connector type, requiring an adapter to connect to the original docking station.

Regardless of how much equipment is currently in the sound system, there is always the possibility of adding more equipment later on. Therefore, it is a good idea to buy an amplifier with more inputs than desired, planning for the potential of this future expansion.

Number of Speakers

Almost all music is recorded in stereo, providing two separate channels of audio. There is a small quantity that has been recorded in quadraphonic, mostly in the 1970s. Quadraphonic never really took hold although some of it still exists.

Modern movies are almost all recorded in 5.1 surround sound. There is also a 7.1 surround sound. These have been developed to provide the listener with a more realistic viewing experience, putting them in the middle of the action, with things happening all around them. The number before the decimal point refers to the number of full-range speakers or speaker cabinets, while the "1" in that number refers to the sub-woofer. Amplifiers are designed for all of these speaker configurations. This chart shows which speakers are included in each recording format.

Recording Format

Front Left

Front Centre

Front Right

Back Left

Back Right


Side Right

















5.1 Surround Sound








7.1 Surround Sound








As the chart clearly shows, each of these formats adds additional channels and additional speakers that were not included in previous formats. If the home’s entertainment centre is going to be connected to the amplifier, using the audio system’s speakers instead of investing in a 5.1 or 7.1 surround sound amplifier is justified. However, if it is only going to be used for music, totally separate from the entertainment centre, then a stereo system is plenty.

Maximum Power

There are two different power numbers used for amplifiers, both stated in "watts of power". One is peak power, and the other is the maximum sustainable power. Many manufacturers, especially of lower cost units, like to use the peak power as it provides a more impressive number. However, the peak power is usually about three times that of the maximum sustainable power. Peak power is designed to signify the maximum power for things like gunshots in a movie, not the volume level for playing music.

Maximum sustainable power is the more important number, as it reflects the normal operation of the system for playing music. Many people want amplifiers that can produce 500 or even 1,000 watts of power. In reality, one watt of power, run through a quality set of speakers, can produce enough sound volume to drive people out of the room.

That does not mean it is not worth buying a high power amplifier. Higher power amplifiers also produce less noise and distortion at the lower power settings. The signal-to-noise ratio and the total harmonic distortion are measured at the highest volume settings. So when the volume is lowered, these numbers lower as well. If the amplifier’s output capacity is higher than the speakers input capacity, it is extremely easy to "blow out" a speaker. This does not happen at low volume levels, but if the amplifier is turned up to capacity, there is a very good chance of it happening.

Brand Name

It is worthwhile to spend the money to buy a brand-name amplifier. Generally speaking, the major brands became popular by producing superior products to the marketplace. These brands typically provide better quality sound, better features, and build better quality equipment.

Signal-to-Noise Ratio

The signal-to-noise ratio is one of the most important specifications on an amplifier. This refers to the amount of noise that is produced by the system as compared to the amount of actual sound. All sound systems produce some noise, and the important thing is that the noise is low enough as to not impede hearing the music.

Total Harmonic Distortion

All audio equipment distorts the sound to some extent. Manufacturers strive to maintain this distortion as low as possible, ensuring that the sound that comes out of the system is as identical as possible to the sound that was originally recorded. They check this by running a pure sine wave through the equipment and comparing the output to the input. A total harmonic distortion (THD) of 0.01 per cent is considered good.

The Advantage of Buying Used Digital Amplifiers

Digital amplifiers are fairly expensive, which is why many people buy all-in-one units, rather than buying discrete stereo components. However, discrete stereo components provide better sound and more control. Used digital amplifiers provide an excellent way of buying the heart of the sound system for a much more affordable price, well within the budget of most people.

As digital amplifiers are entirely made of electronic components, there is very little that can go wrong with them. Therefore, a used digital amplifier usually works just as well as a new one. The only exception is that an older digital amplifier can have some noise problems, especially if it has been used in a high heat environment. This noise comes from the degradation of electrolytic capacitors. It appears as a low frequency hum in the speakers. If a used digital amplifier has this hum, then it needs to be sent to a repair shop.

It is easy to test for this problem, as all that is required is to connect the used digital amplifier to a set of speakers and turn up the volume about one-fourth of the way, without any music going through it. If the hum doesn't show up at that point, there is no problem and the amplifier should work fine for a number of years.

Buying Used Digital Amplifiers on eBay

eBay is the best place to find a wide assortment of used digital amplifiers and other audio equipment. You can find just about as much used equipment for sale on eBay as you can find new equipment. While some of this equipment might be vintage, it is still perfectly good and capable of providing years of listening pleasure.

When searching for used digital amplifiers, it is necessary to define what type of amplifier one wants. The same term can be used to refer to equipment used in professional audio, automotive sound systems, and some amplifiers that are used in industry. If a search is done for "digital amplifiers" is done, and these other devices show up as well, then they can be eliminated by filtering the results and refining the search. Once buyers have found what they are looking for, they should read up on the product and the seller.


Buying a used digital amplifier is a great way to build up a home audio system. Even though used, the equipment is still good and able to provide years of enjoyable listening. As long as the equipment functions upon arrival, there is a high probably that it continue to function for years. The decision as to what type of amplifier to buy depends mostly on its intended use. Almost all music is recorded in stereo, while movies are mostly recorded in 5.1 surround sound. If the system is only going to be used for music, then stereo provides everything needed, but if it is going to be integrated with the home entertainment system, then 5.1 or 7.1 surround sound would be a better solution.

While the specifications on an amplifier are important, the most important specification is the amount of inputs that it has. It needs to have enough inputs to work with all the audio equipment that to be connected to it. An amplifier that cannot accept all of those inputs make the owner constantly have to change cables in order to listen to their music. The other important specification is the power in watts. This determines how much sound volume the amplifier can produce. Larger amps also produce less noise as they are working at only a fraction of their capability. eBay's search engine and various filters make the online shopping experience enjoyable and quick.

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