An Amplifier Buying Guide

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An Amplifier Buying Guide

Amplifiers are used to enhance electronic performance. Most often, amplifiers are used in the process of sound reproduction. An amplifier works by increasing the power of a signal inputted by an external energy force. However, an amplifier should increase the power of the input signal without significantly distorting or changing the output sound. Electronic amplifiers are often characterised by critical output components, such as vacuum tubes or transistors. Gain, bandwidth, efficiency, linearity, and noise are few elements that vary depending on the amplifier.

Electronic amplifiers vary from power amplifiers to musical-instrument amplifiers. Power amplifiers are further divided up into various classes that differ based on the efficiency level available. Electronic amplifiers are commonly used in products such as radios, guitars, and television transmitters. Electronic amplifiers can be purchased at an electronic stores, speciality shop, or online. When browsing electronic amplifiers, consumers should be aware of what factors to consider in determining the quality of an amplifier, as well as what types of amplifiers are available for purchase.

How to Determine the Quality of an Amplifier

There are many factors that should be considered when determining if a select amplifier is a quality product. A consumer is better informed during the purchasing process if they can understand the language used when measuring the merits of an individual electronic amplifier.


Gain refers to the output power to input power ratio divided by amplitude, measured in decibels (dB). A good gain level will range depending on the type of amplifier, but as a general rule, an amplifier with higher gain settings will be more sensitive.


Bandwidth refers to a range of frequencies over which an amplifier provides a satisfactory performance level. Satisfactory performance is measured by examining the half power points, or the frequency where the power goes down by half the value when balancing frequency versus output. In other words, bandwidth is the difference between the upper and lower half points on this curve. The gain of a quality amplifier will be flat between the bandwidths of 20 Hz to 20 kHz.


Efficiency is a determination of how much power is used to create an output. In other words, a measure of power in versus power out. Efficiency will vary based on the class of amplifier, keeping in mind that no amplifier is ever 100 per cent efficient.


Linearity is important to understand because it affects the amount of distortion that will be present through the output. In an ideal world, all amplifiers would be completely linear, resulting in no distortion. Realistically, this is not the case. When the signal input is increased, the signal output is also increased until it reaches a level where it can no longer receive output, which is called saturation. This saturation results in distortion. Some amplifiers have features that help reduce the unpleasant sounds of distortion.


The amount of undesirable noise introduced into the process of amplification from electronic devices and components is measured in terms of a noise figure or noise factor. Noise figure compares the output signal to the noise ratio and thermal noise of the input signal.

Types of Electronic Amplifiers

Historically, there have been many types of amplifiers for many different uses. Today, the markets are flooded with a variety of different types of electronic amplifiers. Each type of electronic amplifier is classified according to their specific input and output properties.

Power Amplifier

The term power amplifier is a general term used to describe an amplifier that seeks to raises the power level of an input signal. A power amplifier consists of a signal pickup transducer, a small signal amplifier or amplifiers, a large signal amplifier, and an output transducer. Power amplifiers are further classified based on their mode of operation, or the amount of transistor bias and amplitude of the input signal. These classifications range from Class A to Class F with the amount of efficiency increasing respectively.

Different classes of power amplifiers are sought after for different uses. For example, a Class A power amplifier has the lowest efficiency, but produces the least distortion. A power amplifier can be used in conjunction with a variety of different electronic devices such as antennas, microwaves, and CD players, to name a few.

Valve Amplifier

The valve amplifier utilises a set of tubes to increase the amplitude of a signal. Valve amplifiers are often used in high-power equipment such as radar, countermeasure, music, and communication devices. Valve amplifiers are very linear, which means less distortion with little negative feedback. On the other hand, valve amplifiers require a heater cathode, which means an increase in heat loss and energy.

Transistor Amplifier

The transistor amplifier uses a transistor to magnify the input signal to produce a large output signal. Transistor amplifiers have various uses, ranging from in-home stereos to semiconductor equipment.

Operational Differential Amplifier

The operational amplifier is classified by its high-voltage, differential input, and single-ended output. Because the operational differential amplifier creates a voltage that is hundreds of thousands times larger than the voltage difference in its input terminals, they are used in a wide array of consumer, industrial, and scientific electronic devices.

Fully Differential Amplifier

In contrast to the operational differential amplifier, the fully differential amplifier is classified by its high-voltage, differential input and differential output. The output is controlled by two different negative feedback paths, which determines the output voltage for a select input. On the downside, the fully differential amplifier has a finite gain, as well as nonlinear imperfections.

Distributed Amplifier

The distributed amplifier is characterised by its incorporation of transmission line theory into traditional circuit design to create a larger gain-bandwidth. Distributed amplifiers are often used in radio, acousto-optic modulators, and time to digital converters.

Musical Instrument Amplifier

The musical instrument amplifier is probably an electronic amplifier that is common to the everyday consumer. The musical instrument amplifier is an audio amplifier that is used to amplify music or speech. Whether looking for guitar amplifiers or other audio amplifiers, there are a few things to consider that are unique to this type of amplifier.

Frequency Response

While other amplifiers might specify the frequency range, consumers must pay attention to the frequency response when shopping for a musical instrument amplifier. Frequency response refers to the amount of noticeable variation across the audible frequency range to the human ear. When shopping for audio amplifiers, buyers should shoot for a specification that is close to 20 Hz to 20 kHz +/- 0.5dB.

Power Output

Another thing to consider is power output, or what power level is obtainable with the least amount of distortion present. A quality audio amplifier will have a relatively loud sound pressure level from the loudspeakers with as little distortion as possible in return. Finding the right offset between these two things is key.

Low Distortion

While no audio amplifier is perfectly linear, consumers should pay attention to the harmonic content of the sound as it passes through the electronic signals. Typically, the goal is to aim for the least distortion possible, or at least find an acceptable level in relation to the desired sound.

How to Buy Amplifiers on eBay

Once you have a basic understanding of how amplifiers work and how they differ, it will be easier to choose the right amplifier based on your needs. eBay has thousands of different electronic amplifiers ranging from power amplifiers to guitar amplifiers. For example, if your are searching for a quality power amplifier, eBay can help make that process easy and affordable. Simply navigate to the eBay website portal and type power amplifier into the keyword search box. Once you hit click, a list of options matching that description will be populated for you.

In addition to laying out the different types of amplifiers available to you, eBay also helps ensure that you are only buying products from reputable sellers. Pay attention to the Top-Rated Seller identification used throughout the website. Top-Rated Sellers are the best sellers on the eBay website. These sellers earn this label based on consistent, positive buyer feedback, with ratings reviewed regularly by eBay. This is just one way that eBay helps make the buying of amplifiers worry-free.


Amplifiers cover a broad range of electronic devices used to enhance electronic performance. While it can be easy to get bogged down in the language that describes the different types of amplifiers and what they do, a basic understanding of these concepts is essential in choosing the right type of amplifier. Understanding a little about characteristics such as gain, bandwidth, efficiency, linearity, and noise can help a consumer make the most informed decision possible when purchasing any type of amplifier.

It is important to determine that a select type of amplifier will be compatible with a specific electronic device. For instance, while it may seem like common sense, an amplifier used to amplify the sound of an electronic guitar must be compatible with that type of energy input source. With a little bit of insight into what each type of amplifier does and what it is used for, it will be a lot less likely for the everyday buyer to purchase an amplifier device without asking the right questions.

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