How to Buy a Used Digital Amplifier

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How to Buy a Used Digital Amplifier

Buying a used digital amplifier is a great way of securing a high quality amplifier at a lower price. Many can be found in an excellent condition and can provide fantastic audio performance. A digital amplifier maintains and increases the size of the original sound signal's waveform in a digital format, rather than switching between analogue and digital. One of the main decisions to be made when buying a used digital amplifier is to select the right amplifier class. There are four digital amplifier classes that use different circuit configurations. Some offer enhanced signal replication and sound quality, while sacrificing energy efficiency. Other classes are more energy efficient, but offer poor sound quality. Selecting the right power, damping, and resistance capacities is also important.

Used digital amplifiers can be purchased from audio retailers and private sellers. Good quality digital amplifiers of all classifications and specifications can be found on eBay offering quality and value for money.

What is a Digital Amplifier?

A digital amplifier is used to amplify sound waves to increase the output volume. It is also used to enhance sound quality and channel the sound waves to speakers. This key difference has an impact on efficiency, output quality, and interference. The signal that is put into an amplifier is digital. In a traditional amplifier, this signal is converted to analogue, and in some cases it is transformed back to digital at the output. This can cause a loss of audio quality, and there is also a high chance of noise and interference occurring. Digital amplifiers do not require the signal to be transformed into an analogue signal, but instead carry the signal from input to output in a digital format. As the amplifier maintains the original signal in digital form, there is less signal and audio quality loss.

Used Digital Amplifier Classes

Digital amplifiers are categorised into four distinct classes. Each class has a variety of benefits and drawbacks. The amplifier class affects energy efficiency, sound quality, and how accurately the input signal is replicated. To produce good quality sound a digital amplifier must maintain the detail of the original signal while increasing the size of the sound waves of the input signal. The precision with which the detail is maintained is referred to as linearity and is one of the key differences between the amplifier classes.

Class A Used Digital Amplifiers

Class A used digital amplifiers are by far the most accurate. They greatly surpass other amplifier classes in terms of linearity, meaning that they offer the most true representation of the input signal. Class A digital amplifiers contain transistors that run at full power continuously. This means that there is no switching, which occurs when the transistors cycle on and off. So, transistors in class A digital amplifiers can replicate the sound waves of the input signal accurately, making the amplifiers the most precise at providing very high quality audio performance.

The continuous run of the transistors also means that class A amplifiers are very energy inefficient. They produce a great deal of heat and require good airflow and ventilation to stop them overheating. A heat sink may also be required to reduce the temperature. Class A digital amplifiers are very large and extremely heavy when compared to the other classes.

Class B Used Digital Amplifiers

Class B used digital amplifiers are extremely energy efficient and do not produce a lot of heat. They have two transistor sets. These amplifiers are commonly known as push-pull amps. One of the sets pulls the signal while the other pushes it. The transistor sets switch on and off alternately during the sound wave cycle. This allows each transistor a rest period, which is why they create less heat, thereby wasting less energy. However, the continual cycling on and off of the transistors means that the sound quality is diminished.

No single transistor captures the entire sound wave, meaning that some detail is lost. The cycling of the transistors also creates unwanted noise and distortion. The push-pull method of class B amplifiers requires that two output devices, such as speakers, are connected to the outputs of the amplifier, as the positive and negative halves of the signal are carried separately.

Class AB Used Digital Amplifiers

Class AB used digital amplifiers are an amalgamation of class A and class B technologies. They are the most common class of amplifier used in vehicles and households. Two transistor sets are used, as in class B amplifiers, but the switching cycle is slightly unbalanced. This means that the two opposing sets switch on and off slightly out of sync, allowing them to assist each other at the crossover point. This reduces the amount of noise and distortion produced by the speakers and improves the replication of the original signal. This assisted crossover allows more detail from the original signal to be maintained and enlarged. Class AB digital amplifiers are more energy efficient than class A models, but a little bit less efficient than class B, although they do not usually require a heat sink to reduce their temperature.

Class D Used Digital Amplifiers

Class D used digital amplifiers are often mistakenly thought to be a separate class of digital amplifier. They utilise rapidly switching transistors. The transistors turn off and on again at least twice during each sound wave cycle. The rapid cycling allows a very large percentage of the original sound wave to be captured accurately. Class D amplifiers are not energy efficient, but the sound quality is considered to be better than class B amplifiers, but unable to compete with class A or class AB models.

Factors to Consider When Buying a Used Digital Amplifier

Buyers need to take into account the technical specification when buying a used digital amplifier. Without the appropriate specification, the audio quality suffers significantly and the digital amplifier or speakers may be damaged.

Power and Resistance for Used Digital Amplifiers

Power and resistance are important concepts for used digital amplifiers. An amplifier should have twice the power capacity as the continuous power rating of the speakers. Choosing an amplifier that does not have enough power can cause it to overload, which in turn can damage the speakers. Buying a used digital amplifier with plenty of extra power capacity, known as headroom, ensures that it delivers the highest performance and can replicate loud, high and low frequency sounds accurately, without overloading and causing unpleasant distortion and feedback. The same theory applies to resistance. The resistance of the digital amplifier, measured in ohms, should be double that of the speakers to ensure the ultimate audio performance.

Damping Factor for Used Digital Amplifiers

Damping factor is another important factor when buying used digital amplifiers. Many amplifiers, if left to their own devices, continue to vibrate even after the signal has stopped. This creates unwanted reverberation and noise. Many buyers do not realise that this effect can be controlled by an appropriate digital amplifier. The damping factor is the impedance, or control, exerted on the speaker by the amplifier. The higher the damping factor, the greater the impedance and the more control the amplifier has over the speaker. The greater the control, the less reverberation and inappropriate vibration occurs, improving the audio quality and making it more true to the original signal.

Buying a Used Digital Amplifier on eBay

eBay has a range of used digital amplifiers available. Buyers can search for "used digital amplifiers" from the eBay home page by entering the keywords in the search box, and then narrow down their results by using the filters on offer. These filters allow the buyer to ensure that they only see used digital amplifiers, and to choose a price range.

When purchasing used digital amplifiers on eBay buyers should ensure that they read the description of the item carefully. They should ensure that the amplifier meets all of their requirements, and by looking at the photograph they should check the condition of the amplifier. If buyers require any more information or photographs they can contact the seller directly using an eBay message.


Feedback is the best way to ensure that the transaction goes smoothly for the buyer. Buyers are able to look at the opinions of other customers who have used the same seller. Feedback is left after the buyer has received their item. Sellers with a high percentage of positive feedback are more likely to offer a fast and excellent service.


A used digital amplifier can greatly enhance the performance of an audio system, whether in the home or a vehicle. Buying used items allows shoppers to save money and to buy a good quality audio device. Buyers need to decide whether they favour performance, or whether they are willing to sacrifice some audio quality in exchange for energy efficiency. Shoppers can choose to compromise by purchasing a class AB amplifier that provides the best of both sound quality and efficiency.

Buyers must also make sure that their used amplifier has double the peak current capacity and resistance of the speakers that it is paired with. If buyers experience reverberation and feedback from their speakers because they continue to vibrate after the signal has finished, a used digital amplifier with a high damping factor is a good choice. Used digital amplifiers of all types can be found at great prices on eBay.

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