What to Consider When Buying an Amplifier

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What to Consider When Buying an Amplifier

Amplifiers are used to increase the power of a signal from a stereo system, a musical instrument, a home theater or any sound-playing device, by using an external energy source. Basically, common amplifiers can make sound more powerful and louder, while not losing quality.

As an amplifier is an intermediary between a sound-playing device and a set of speakers, so the type of speakers usually has to be taken into consideration when buying amplifiers. While people generally want the most possible power from amplifiers, those with a preference for acoustic music should look for different types of amplifiers than those who frequently listen to music with a lot of distortion and high volume peaks.

There are many considerations to take into account when selecting amplifiers. First of all, one needs to acquire a basic knowledge about the items’ most common features and specifications. With a little research, and following some basic tips, buyers can also avoid the most common mistakes that people make when selecting amplifiers.

Although some people may think that the best way to choose an amplifier is simply by listening to its actual sound output, it is also possible for buyers to tell whether an amplifier can deliver excellent sound based on its specifications’ sheets.

Finding the Right Type of Amplifier

There are many amplifier classifications, but the most important things to consider when buying these items are whether they use transistors or valves, whether they are integrated or not, and finally, which “class” they belong to.

Transistors or Valves

Amplifiers can use two different kinds of technology. Valve amplifiers have been around the longest. In fact, when transistor amplifiers first appeared on the market, they had some serious limitations. Today, the choice between valve and transistor amplifiers is mainly a matter of taste, as the modern transistor models do not have the limitations of their earlier versions. 

As a general rule, transistor amplifiers, are better suited for people who want to play their music extremely loud, while valve amplifiers are generally preferred by those who enjoy mainly acoustic music. There are also hybrid amplifiers, which combine both technologies.

Valve amplifiers, also called tubes, are said to produce more fluid and lifelike sounds, while transistor amplifiers, also known as solid state, are considered to have more power and slam. There are mixed opinions about hybrid amplifiers; some expert claim that by trying to get the best of both worlds, they have also ended up with the limitations of both types. As all-valve amplifiers are usually more expensive, hybrids can be a way to get a bit of the lifelike texture of valves without splurging on an all-valve amp.

Integrated vs Pre plus Power Amplifiers

An amplifier has two functions, processing the input and powering it up to send it to the speakers. Originally, amplifiers only came in different blocks, each holding the pre-amplifier and the power amplifier sections. Today, there are integrated amplifiers that can perform both functions in one single device. Generally speaking, it can be good to separate the delicate signals in a pre-amp from the radiations of power amps. In fact, it is even possible to purchase amplifiers where each channel has its own separate block. All that said, the modern integrated amplifiers have many advantages, and some of them can offer as much power and fidelity as the best combinations of pre and power amplifiers.

Moreover, the modern integrated amplifiers have been designed to adapt to the digital age, often including USB-input and iPod-ready digital-to-analog converters, which allow users to simply connect them to their portable music players or computers.

Integrated amplifiers also offer cool features such as gain offset, which allows users to attenuate the level of different inputs individually, in order to avoid annoying volume jumps when switching sources. While state-of-the-art integrated amplifiers are not cheap, the best among them offer sound quality that can be compared to that of excellent pre-amp and power-amp combinations. However, when the two functions are carried out by different devices, it is possible to upgrade one’s power amplifier, for example, in the case of buying less powerful speakers, whereas with integrated amps, one would have to buy a whole new system

Class A, B, AB, and D Amplifiers

Amplifier class has to do with harmonic distortion, as it is connected to the output stage, when distortions occur. This stage has two sub-stages: the amplification of negative voltage signals and that of their positive counterparts.

Class A

Both stages are on at all times. It delivers the best sound quality. Power efficiency rate is 10 to 20 percent, and it is the type that produces the most heat, regardless of audio signal levels.

Class B

When one stage is on, the other one is off. Also called “pull and push” because of this. Power efficiency rate is 50 to 75 percent. Higher level of harmonic distortion due to the continuous pull and push process.

Class AB

Hybrid in which both stages are on (A) for low level signals and they alternate (B) for higher level signals. Higher power efficiency than A and less distortion than B. Usually considered a very good compromise between the fidelity of A and the power efficiency of B.

Class D

The input signal undergoes a conversion into a sequence of output pulses of higher voltage. Often wrongly called digital amplifiers for this reason. The output pulses go through a filter before being sent to the speaker, which removes any unwanted components in the frequency. Power efficiency rate is 90 percent, beating all the other classes. However, in terms of sound quality, they are at the bottom of the scale.

A power efficiency of 100 percent would mean that all the power that comes in would be coming out of the amplifier, with no loss in the form of heat. This is not possible, and amplifiers are thus classified according to how much power actually comes out after processing input signals.

What to Look for in Amplifier Specifications

Reading an amplifier’s specifications’ sheet can be challenging without some basic knowledge about power efficiency, distortion levels, signal to noise ratios and general sound quality indicators. Whether looking at high-end, multi-channel variations or a more affordable integrated version, it is very important to give these aspects some thoughtful consideration.

Amplifier Power

Although most buyers look for the highest power capability in amplifiers, sound quality must not be overlooked. Although power is generally expressed in watts, audio amplifiers’ power specifications are a bit more complex. They generally include power per channel in Watts followed by frequency in Hz, speaker load in Ohms and total harmonic distortion expressed as a percentage.

An amplifier’s power rating specifications might thus look something like this: 90W/Ch RMS 20Hz-20kHz, 7 Ohms 0.08% THD. As buyers are usually looking for the highest power, manufacturers tend to offer some potentially misleading reports, for example, quoting peak power, instead of average power. which is generally a more reliable figure.

Dynamic headroom

Dynamic headroom is expressed in dB. It represents an amplifier’s ability to output power at a much higher level for brief periods, in order to accommodate peaking music or sound effects. An amplifier that can double its power output in these cases is said to have a dynamic headroom of 3dB, if it can multiply it by four, the dynamic headroom becomes 6dB, and so on.

Amplifiers with low dynamic headroom imply a diminished impact, as they compress all high peaks to fit within the levels of their headroom. 

Amplifier Sound Quality

Better sound quality is always preferable to more power. Moreover, amplifier power does not directly result in perceived loudness. For example, it takes 10 times as much amp power for the human ear to perceive sound twice as loud.

The most important things to consider in terms of sound quality are total harmonic distortion, or THD, and signal-to-noise ratio, or S/N level.

As a rule, distortion levels under one percent are fine, and human perception can’t really tell the difference between, for example, 0.03 percent and one percent THD. As a reference, an amplifier with a 10 percent THD would yield very poor quality sound at both high and low volume levels. 

Harmonics can be described as tones that accompany the original note. As THD numbers do not provide information about the nature of the harmonics present, some manufacturers do offer more detailed information, but experts claim that this is no substitute to actually listening to the sound.

Noise Levels

The signal-to-noise ratio expresses the correlation between sound signal and background noise levels. Background noise is unwanted noise produced by the amplifier itself. For example, an 90dB is a very good S/N ratio; in this case, background noise would only be perceptible at very low level signals.  

Matching Amplifiers and Speakers

There is a widespread myth that powerful amplifiers can damage speakers. However, high-end speakers are designed to manage high power levels. In fact, even in the case of low quality speakers, it is much more common to cause them to overheat by driving underpowered amplifiers into clipping distortion than by feeding them excessive power. 

The question about matching amplifiers and speakers has to do with providing the necessary power and, as a rule, more power is usually better. When selecting an amplifier for a typical two-speaker system, one should focus on its rated power at 8 Ohms, which should be more than 50 percent higher than the speakers’ RMS power rating.

How to Buy Amplifiers on eBay

The rule of thumb for buying amplifiers online is not to look at any of their specifications in isolation. There is a wide variety of amplifiers available from eBay sellers, and you must try to take different variables into consideration when selecting the one you want. The idea is to make sure that sound quality will be good under varying conditions.

eBay offers thousands of amp and pre-amp listings that you can look through by entering the relevant keywords into the search box found on every page. Sellers usually include detailed specifications for each item, and you can always ask questions when in doubt. If you absolutely must listen before you buy, well-known manufacturers often offer sound samples you may check out on their official websites. 

If you are looking for a more vintage sound, there are many great deals available on used valve amplifiers. While buying new amps may be safer, a top brand-name device with little use can be a very convenient deal.

Some amplifiers can be bulky and heavy, and it is always a good idea to double-check shipping costs and times. Once you have selected an amplifier that fits your needs, you can type in the brand and model into eBay’s search panel, in order to make sure that you are getting the best deal and lowest shipping costs for each particular item.


When buying amplifiers, the focus should be on finding the perfect balance between power and sonic integrity. Whether one prefers solid state or tubes, integrated or non-integrated amps, all variables must be taken into consideration. Extreme power will be of no use if distortion levels are high, and excessive background noise can ruin even the nicest sound quality.

On the other hand, while Class A amplifiers may sound like heaven, they heat up easily and consume a lot of power. Finding the perfect balance between power efficiency and distortion levels is one of the keys to finding the perfect amplifier.

Finally, the greatest amplifier can be of no use if it is not suitable for the speakers that are going to be used with it, and it is also important to make sure amps have the right connectors and docking stations for each user’s preferred digital devices.

Amplifier specifications may appear a little challenging at first, but considering the main aspects mentioned in this guide can help anyone succeed at purchasing excellent amplifiers for a variety of uses.

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