The Amplifier Is Part of the Instrument

An acoustic guitar is finished when it leaves the workshop. An electric is not. What comes out of the output jack is a fraction of a volt of alternating current, and on its own it is inaudible. The amplifier is not an accessory to an electric guitar in the way a case is — it is the part of the instrument that does the third job from the first lesson.

Inside, the signal passes through three stages. The preamp raises that tiny voltage to a useful level. The tone stack — the knobs marked bass, middle and treble — filters it. The power amp raises it enough to physically move a loudspeaker cone, which moves the air, which finally is a sound.

Then there is the accident that defined electric guitar music. Early amplifiers were built with vacuum tubes, or valves, because in the 1930s and 40s there was nothing else to build them with. A valve amplifies cleanly up to a point, and then it runs out of headroom and starts clipping the peaks off the waveform. Engineers considered this a defect. Guitarists heard a sound that sustained, sang and growled, and spent the next seventy years chasing it deliberately.

This is why an amp's volume control is not just a loudness knob. Pushing the preamp harder changes the character of the note, not just its level — which is why amps grew separate gain and master volume controls, so you could get the distortion without deafening the room.

Solid-state amps, built with transistors, arrived in the 1960s and are cheaper, lighter and more reliable. They clip too, but more abruptly, which many players find harsher. Modern modelling amps use digital processing to imitate specific valve amps, and they have got convincingly good. The speaker matters as well, and for an unglamorous reason: a guitar speaker rolls off almost everything above about five kilohertz, and that filtering is a large part of why heavy distortion sounds like a guitar rather than like static.

One consequence worth taking away. If you are unhappy with your electric sound, the amp and its settings are usually a bigger lever than the guitar. New strings and a better amp setting will change more than a new instrument will.

A slow, spacious rock track in G minor — the kind of setting where sustain and amp character do the work. Hold long notes and listen to how they decay.