What to Consider When Buying a Digital Amplifier

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What to Consider When Buying a Digital Amplifier

An amplifier is a vital component of any home audio or cinema system, whether using an integrated amplifier or a pre-amp and power amp configuration. An amplifier receives the audio signal from a source component, such as a turntable, radio, or DVD player, and increases the power of the signal before sending it on to the speakers. In a loudspeaker, the electrical current is converted to sound waves through the movement of a cone.

Digital amplifiers are designed to work with digital input signals from their source components. Because they use microchips to handle the amplification process, digital amplifiers can be much smaller than analogue amplifiers. When shopping for a digital amplifier, it is important to have a basic understanding of how the device works, significant technical specifications, and optional features. Informed consumers can compare models within their price range and find the right digital amplifier to power all their digital audio.   

How Digital Amplifiers Work

Digital amplifiers receive a digital signal from a source component, such as an iPod, CD player, or DVD player. This digital input is usually in linear pulse code format. The amplifier then converts the signal to pulse width modulation (PWM) format. An output filter removes the high-frequency part of the PWM signal, restoring the original audio signal. The timing and alignment of the signal must be kept constant throughout the process for it to be successful.

Advantages of Digital Amplifiers

The main advantage of digital amplifiers is their compactness. Some quality digital amps weigh just a few kilograms, and can fit nearly anywhere in a car or home audio system. And thanks to technological developments, only a few microprocessor chips are needed in a digital amplifier, which means that production and retail costs are much more affordable than in the past.

Identifying True Digital Amplifiers

Digital amplifiers are meant to process digital, rather than analogue, input. Some amplifiers claiming to be digital are in fact digital-to-analogue converters. These can be identified by one or more inputs labeled “analogue”. Digital amplifiers have inputs for optical TOSLINK cables, digital coaxial cables, USB connectors, and/or HDMI cables. 

Digital-to-Analogue Converters, Power Amplifiers, and Integrated Amplifiers

Amplifiers can be divided into three categories, depending on their function. These classifications are pre-amplifier, power amplifier, and integrated amplifier.

Pre-Amplifiers and Digital-to-Analogue Converters

A pre-amplifier’s function is to select an input source and adjust volume levels, which are then sent to the power amp. A digital-to-analogue converter (DAC) converts the digital signal to analogue, which is required by the speakers. DACs also select input sources, and those that allow volume control replace the need for a pre-amp.

Power Amplifier

A power amplifier increases the volume of the signal and passes it along to the speakers. A power amplifier must work in conjunction with a pre-amp or DAC.

Integrated Amplifier

An integrated amplifier contains both a pre-amp and a power amp in the same chassis. The advantage with integrated amplifiers is that they tend to cost less than separate DACs and power amplifiers; however, some audiophiles insist on keeping the units separate.

Important Specifications

Technical specifications for digital amplifiers can be disorienting. Before shopping, consumers should get a grounding in the most important product specifications and what they mean in practical terms.

Power Rating

An amplifier’s power rating may be expressed in a few different ways. The most important specification is the average or continuous output, which is the amount of energy, expressed in watts (W), that it produces over a long duration. RMS (root-mean-square) is another accurate measurement of average power. Peak power is sometimes cited by manufacturers as a marketing device, although it only expresses the power that can be used temporarily, such as during a particularly loud moment in a piece of music.

It is crucial to match an amplifier’s power output to the speakers’ power output. Speakers need to be able to handle the continuous power output of the amplifier to prevent overheating and damage. However, if an amplifier’s power output is too low, this may result in distortion. Buyers should check with experts if they have a question about what power rating is right for their system.


Another important specification connected to the system’s speakers is impedance. Measured in ohms (Ω), impedance is the speaker’s resistance to an electric current running through it. Typical speaker impedance ratings are 4, 8, or 16 ohms, with a higher rating meaning more resistance. An amplifier should indicate which impedance ratings it is compatible with.

Impedance is related to power output, since higher resistance means is the speaker draws less power from the amplifier. This is why an amp’s power rating is often expressed according to speaker impedance. For example, if an amplifier’s power output reads “75W x 2 (4 ohm), 50W x 2 (8 ohm)”, this means that it runs at 75W on each channel if the speakers have an impedance of 4 ohms, and if the speakers have an impedance of 8 ohms, each channel runs at 50W.

Frequency Response

Frequency response is the range of frequencies, or pitches, that the amplifier can produce. The human ear can generally detect frequencies between 20 Hz and 20,000 Hz (20 kHz).

Total Harmonic Distortion

Total harmonic distortion (THD) gives the buyer an idea of how much an amplifier may degrade signal quality. There are various opinions about THD: some feel a THD of under 0.1 percent is ideal; others do not consider this a critical specification, since a THD of under 1 percent is inaudible to most human ears. Although some manufacturers boast very low THD, this is not necessarily an indication of the amplifier’s quality. In fact, the suppression of distortion also results in suppressed tone and musicality, meaning poorer performance. It is advisable to look for a receiver with a THD between 0.1 and 1 percent.

Signal-To-Noise Ratio

Amplifiers can produce background noise for a number of reasons, including noise from the power supply, the movement of electrons, and more. The signal-to-noise ratio gives buyers an idea of the loudness of the audio signal compared to noise. The higher the ratio, the better. For example, an S/N ratio of 90 dB is excellent, whereas if it is 65 dB, noise may be distracting at high volume settings.

Number of Channels

An amplifier has one channel dedicated for each speaker. Amplifiers labeled “Stereo Output” have two channels, one for the left and right speaker, respectively. Some amplifiers feature multiple channels.

Power output is sometimes expressed as watts per channel, with the total output as the combined sum of each channel. 

Sample Rate and Sample Format (Size)

The sample rate of a digital audio input is the rate at which digital samples are captured per second, expressed in Hertz (Hz). The sample rate of audio CDs is 44,100 Hz, often shortened to 44 kHz. Sample format, or sample size, refers to the number of number of digits in each digital representation of a sound wave. This is measured in bits; an audio CD has a sample format of 16 bits, and 24-bit is also commonly used in digital recording.

A higher sample rate means a digital recording is capable of greater frequencies (high pitches), while higher sample size better dynamics of loud and soft sounds.

An amplifier should specify what sample rate and size it is capable of handling.

Inputs and Outputs

Digital amplifiers vary in the inputs and outputs, which affects which kinds of components they can connect with. The most common are optical TOSLINK, digital coaxial, and USB connections. Verify the inputs and outputs are compatible with the devices to be used with the amplifier.

Dimensions and Weight

After poring over an amplifier’s technical details, buyers should not forget to note the product’s dimensions and weight. This is particularly important when space is limited. The amplifier should fit comfortably into a home audio or cinema system.

Optional Features

There are several features that can increase a digital amplifier’s versatility and convenience. These include a built-in radio receiver, multi-channel capability, a graphic equaliser, and a remote control.

Radio Receiver

Some digital amplifiers have a radio receiver built in. Buyers should verify what kind of signals it receives, whether DAB, FM, AM, or some combination thereof.

Surround Sound, Multi-Channel, and Subwoofer Output

As noted above, amplifiers have one channel for each speaker. Some amplifiers are equipped to work with surround sound systems; if the channel mode is indicated as 5.1, for example, there are five channels for side, front, and center speakers, plus one channel dedicated to the subwoofer, which is a speaker that plays low-frequency bass sounds.

Amplifiers may have flexible channel modes, such as 2.1, 3.1, or 5.1. The “.1” indicates the subwoofer output, which is in addition to the other channels.

Graphic Equaliser

Built-in graphic equalisers allow users to control the volume levels of different frequencies. This means they can adjust the sound for optimal playback.

Remote Control

Amplifiers that include a remote control offer the ultimate in listening convenience. Users can control volume and inputs from the ease of their armchair.

Where to Find a Digital Amplifier

Digital amplifiers are available for purchase through electronics supply stores, and online through Internet merchants and auction websites like eBay. Buyers should compare different models in their price range, and research customer and expert product reviews online if possible.

How to Buy a Digital Amplifier on eBay

If you’ve decided to buy your digital amplifier on eBay, you’ll find a wide array of new and used items at competitive prices on the auction website. Start on eBay’s home page, and enter keywords like “new digital amplifier” into the search bar. You can then narrow your search results by price, seller location, and more. You can also browse eBay Shops for digital amplifiers and other related equipment.

Check Product and Seller Information

Once you’ve found an item you’re interested in, read the product description carefully, noting specifications, condition, and the seller’s return policy. Also note postage fees, and you can ask the seller a question, if you’d like more information.

Lastly, it helps to have an idea of how reliable the seller is. Have a look at their feedback rating and comments posted by past customers, particularly those who have purchased audio equipment. Top-rated sellers have a strong record of excellent customer service.


Digital amplifiers process a digital audio signal from a source device, and increase its power before sending it to speakers. With their compactness and affordability, digital amplifiers are an excellent way to increase the power of a home audio or cinema system. When shopping for a digital amplifier, there are several product specifications to keep in mind, as well as different optional features.

Two of the most important specifications are power output and impedance, or resistance to the flow of electrical current. An amplifier’s power output is optimised for speakers of certain impedance ratings, so these should always be compared with the existing set of speakers. Specifications like frequency response, sound-to-noise ratio, total harmonic distortion, and sample rate give the buyer a sense of how well an amplifier can perform. The number of channels indicates what kinds of speaker setup the amplifier can accommodate. Extra features such as a remote control or built-in graphic equaliser enhance the versatility, control, and convenience an amplifier can offer.

Taking all of these factors into consideration is vital when shopping for a digital amplifier. With the right preparation, buyers can find a digital amplifier that will help their sound system perform its best.

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