Whether they are inside of our amplifiers or as standalone units on our pedalboards, preamps are as essential to live music as electricity! It's history is also as rich as that of electric music itself!
The first stages of an amplifier, the preamp prepares a small electrical signal for further amplification or processing during the power amplifier stage.
During the advent of the guitar amplifier, preamps only came with a few controls relegated for clean sounds such as your run of the mill treble, bass and tone settings. As music itself progressed, so did the preamplifier. As players began to further explore the sounds capable with their amplifiers, such as pushing the preamps farther than the power amps could bear, causing that well known overdrive/distortion effect, more sophisticated preamplifiers were being built.
Marshall gave the rock and roll world amplifiers with preamps made specifically towards crafting that loud overdriven sound that conquered much of rock during the ‘60s and ‘70s, but even that wasn’t hard enough by the time heavy metal was in full swing.
Although getting a guitar to sound loud wasn’t the issue (as you could always add more cabinets), high gain control was. In came the active pickup system and with that, the onboard preamp. The use of an onboard preamp along with active pickups gave players – specifically the hard rock heavy distortion minded players – the ability to work with a boosted signal (thanks to the active pickups) and then have the built in preamp directly shape it before it even leaves the guitar, giving the player a much more concentrated sound that holds up and retains its tone much better than the signal given off by a standard passive pickup, even when used with several effects pedals or high gain settings, as is the norm in metal. Not only that, but onboard preamps can even give passive pickups some of the benifits of active pickups, such as Duncan's BMP-1 preamp.
Making our way to the ‘90s and we are finally able to fully realize much of the potential of the digital revolution as they are applied to music. One such innovations was the creation of amp modelers which are essentially preamps made specifically to copy the sound of popular amps by digital means (although some come with their own crazy, non-cloned effects). It should also be noted that most standalone preamp units aren’t strictly amp modelers but similar to effects pedals in that they are made to give you a bit more tone shaping ability and not just sound cloning.