You're shopping for stereo equipment and all the terms have gotten confusing. Pre-amplifier, amplifier, tuner, receiver; what's what, and more importantly what do you need? While the terminology can be confusing at first, it's important to identify your options and make an informed purchase.
General Information
A pre-amplifier or preamp is one of the main components of a stereo system. It is connected between the audio sources and the amplifier. A pre-amplifier can be part of an integrated amplifier or receiver or can be a separate component in the system.
Function
The pre-amplifier serves several key functions. The primary function is to receive the audio input signal from a source component, such as a CD player, read and process the signal, amplify sub line level signals to line level and then send the signal on to the amplifier where significant power is added. In addition, the pre-amplifier is the command center of the stereo and contains controls such as input switching, program modes and volume.
Misconceptions
In the purest sense of the term, the preamplifier is a device used to increase low level source signals to line level, necessary for further amplification by a power amplifier. Such sources like microphones are common in musical and recording applications. In home audio, only older sources like record players send out weak low level signals. Most modern inputs such as CD players transmit a line level signal. In this case, the pre-amplifier simply serves to switch between various input sources and control basic stereo functions like volume and balance.
Connection
In a basic configuration, the audio sources are connected to the inputs on the back of the pre-amplifier with digital or analog audio cable. The pre-amp's line out jacks are then connected to the amp or amps with RCA cable. Some pre-amplifiers may have a "Sub Out" or extra line out jack that can be connected directly to a powered sub-woofer. Powered sub-woofers have internal amplification.
Audio Signal
To demonstrate what a pre-amplifier does, here's an example of the path of an audio signal. Audio is read from a CD and transformed into electrical current by a CD player. The signal is sent from the CD player to the pre-amplifier (which is in "CD" mode). The pre-amplifier reads the signal, which is already line level (no extra power is needed) and then sends it out to the amplifier. The amplifier powers the signal so that it can properly drive the speakers and then sends to the left and right speakers. Each speaker uses a series of drivers for different frequencies and a crossover network to transform the audio into sound.
Significance
Though a receiver or integrated amp actually contains a built-in pre-amp, the most common home audio configuration with which a pre-amp is associated is a component stereo system. A pre-amplifier is used in conjunction with a separate power amplifier to provide the best system performance and audio quality. A separate radio tuner can be added for radio reception. Separate components also make it easier to upgrade aspects of the system and repair breakages. Pre-amplifiers are more common in 2-channel stereo applications than in home theater/surround sound, which often use a home theater receiver.
Tags: line level, audio sources, home audio, home theater, level signals