Tube Distortion: Your Amp's Dirty Little Secret

Written by
Dave Hunter
Published on
January 21, 2021 at 2:32:21 PM PST January 21, 2021 at 2:32:21 PM PSTst, January 21, 2021 at 2:32:21 PM PST
Anyone who has spent some time grooving on the glorious interaction between electric guitar and amplifier, will know that the former part of that equation really isn’t a complete musical instrument without help from the latter. Any electric guitar requires a good amp to fully express its potential, and without it, it’s just kind of a quiet, heavy acoustic guitar. Delving further into that realization, it’s important to understand that a truly good guitar amp isn’t just beloved for its ability to amplify the guitar’s sound—that is, to make it louder—but is also valued for its propensity to shape and enrich the guitar’s tone. Following on from that, probe further into any all-tube guitar amp and you’ll find the same applies to those glowing glass bottles that make it all happen. Tubes are indeed the essential amplification devices within our amps, but they are also the most important tone generators within any circuit, and the way they distort constitutes the most significant characteristic of their function.

Antiques Toneshow


Tubes are imperfect amplification devices, and that’s why we love ’em. It’s been nearly 85 years since guitar met amp, and while the tubes that drove those amps have been replaced in nearly every other type of electronic device and appliance over the intervening years, they remain the component of choice in guitar amps. Crazy, eh?
These devices—vacuum tubes, to give them their full name, or thermionic valves in the UK (tubes or valves for short)—have enjoyed such longevity in the realm of guitar amplification not simply because they are capable of making an audio signal louder, but because of the way in which they make that signal louder. Most good electric guitar tones, and that includes virtually all of the legendary sounds recorded by a myriad of guitar heroes over the past six decades, rely to some extent on tube distortion to give them body and texture.
Even amid guitar tones which we consider “clean,” there’s usually an element of natural tube distortion that adds thickness and increases the harmonic richness of each note. To hear an electric guitar played truly clean, plug it into a very powerful amplifier—a PA amp, a large hi-fi amp, or a studio or PA mixer—and play at a relatively low volume, monitoring yourself on large hi-fi speakers or headphones. That thin, clinical sound your beloved instrument produces is the sound of a truly clean electric guitar. In order to give it the punch, sweetness, juiciness, and dynamic range we all love, you need to process it with some distortion. And nothing distorts more sweetly, juicily, and dynamically than tubes—and the beautiful part is, they do it naturally.

Dirty Hairy

The reason we love tube distortion—whether used very lightly, moderately, or piled on thick—is because of the way these devices distort the audio signal when pushed into clipping. “Clipping” is a term used to describe how an amplifier responds when pushed beyond its ability to produce a clean signal. All clipping is a form of distortion, but the way in which different types of amplifiers clip defines the character, and thus the appeal (or lack thereof) of that distortion. When pushed past their limits, solid-state devices (at least those without a lot of extra circuitry to compensate) clip a signal suddenly; this results in a harsh, jagged distortion that is usually not very pleasant to the ear. Tubes, on the other hand, clip relatively smoothly and gradually when pushed further and further toward their operational limits. The result is a rounder, warmer, fuller-bodied distortion which is also smoother and more “musical” than that produced by a solid-state device. View two different sound waves on a scope as they clip, one from a solid-state amplifier and one from a tube amp, and you can actually see the “squareness” and “roundness” of the respective signals. Also, in the process of distorting--even when distorting just a little--a tube adds harmonics to the fundamental note or notes in the signal, which gives the guitar tone added texture and dimension.

Thick ‘n’ Rich

When you’re playing through a tube amp with anything from a little to a lot of distortion, the extra harmonics added to each note layer up to build a sonic picture that is significantly bigger than the original, fundamental note. This is the enticing “ear candy” that any truly great guitar tone presents; the kind of sound that sucks you in and makes you beg for more. And we owe it all to the way in which tubes distort. Many guitarists today play through modern solid-state amps or digital “modeling” amps, many of which are capable of creating some powerful tones, while displaying impressive improvements on the sound of such technology when it was born (a couple decades ago in the case of modeling amps, and a good five decades ago in the case of solid-state). When you dial up a juicy tone through one of these tubeless amps, however, you’re still benefiting—in a second-hand manner—from tube distortion. Digital amps come right out and say it in the amp selections on their preset menus, but analog solid-state amps have long “modeled” tube amps. In order to replicate the desirable characteristics of tube-amp distortion, solid-state guitar amps incorporate a lot of extra processing to shape, smooth, texturize and round off the signal… in short, to help them sound less transistorized, and more tube-like. Digital amps, on the other hand, directly model the characteristics of tube distortion in several classic amps and seek to replicate them precisely. Many of the good ones do an excellent job of it, too, but by and large they are still chasing a tone that tube amps produce simply and naturally, and usually with far fewer components. Bless their hairy little hearts.