With the popularization of digital media files for both audio and video content, computers have gradually become a primary source of entertainment. Serving as personal tools for listening to music and watching movies or serving as full-fledged home theater components, computers must have sound quality equal to the task. Since many of them have noisy and underpowered sound systems, a computer amplifier is a perfect way to get audiophile sound from your computer.
The first step in choosing a computer amplifier is to determine whether you need it to include a digital-to-analog converter (DAC). Amplifiers without a DAC depend on the computer to convert digital signals to analog and need that signal to be clean and noise-free. As most computers have suboptimal analog outputs, having a computer amplifier with a DAC is often obligatory. Unless you have already spent a substantial sum of money on an updated, musician-quality audio card, you can assume that you need a computer amplifier with a DAC. Most external cards are extremely easy to connect, however, typically just plugging into an open universal serial bus (USB) port.
Once you have decided whether your computer amplifier needs a DAC, the next step is to choose an amplifier that meets your output needs. If you will be using it to drive headphones, a small headphone amplifier will be adequate, although large and more expensive headphone amplifiers are able to amplify signals for more demanding headphones and may provide slightly better sound quality. For use with speakers, you need an amplifier that has a speaker-level output. Again, the prices of these units can vary greatly with more expensive units providing improvements in power output and fidelity.
If you plan to use your computer as a component in a full-fledged home theater system, you may not need a computer amplifier at all. Simply connect your computer's digital audio output to a digital audio input on your home theater receiver or pre-amplifier/processor. The home theater system will then convert the digital signal to analog and amplify it for output to your speakers. If your computer lacks a surround-sound digital output, look into acquiring an accessory sound card that can produce a digital signal, as opposed to an analog one. These accessory cards can be mounted internally or can be externally connected through a USB port.