A preamp, short for preamplifier, is an electronic device used in the first stage of amplification to boost the low-level signal to about line level. Basically, the preamp takes a low-level signal from a microphone, turntable or other transducer and provides voltage gain, but no significant current gain. Then the power amplifier provides the higher current necessary.
Preamps may be:
Mounted with or near the signal source in a microphone, as in mic preamps. Mounted with or near the signal source of an instrument, as in guitar and bass preamps. Incorporated into the housing or chassis of the amplifier they feed In a separate housing, a stand alone unit for use in live music and the recording studio. Part of a stand alone channel strip or channel strip built into a sound console or audio mixing board.
Preamps often set the tone of how a device or system will sound and preamp designs often have their own signature “sound”. There are two types of preamps; vacuum tubes and transistors. Both types of preamps add coloration to the mix. The sound of tube preamps is often described by presence, warmth and clarity.
However the transistor has a better low frequency performance. It all comes down to a matter of preference, and in recent years the quality of both kinds of preamps has improved.
Preamps are very useful during recording. Since the output signals of most microphones and guitars are at levels far too low to drive the line level input, a preamp must be used to boost its signal to acceptable levels.
Preamps are needed for both analog and digital recording systems. The DAW requires a quality preamp, or set of preamps, for plugging audio signals directly into the sound card.
Whether the preamp is integrated into the amplifier, mounted near the signal source, or built into the audio mixing board, the function it performs is critical. Important considerations when choosing a preamp are:
Is it a tube or transistor style?
Is it quiet or noisy?
Is it designed with quality components?
The sonic contribution of the preamplifier in the recording process is significant and should not be ignored or left to chance.