Adapted from the book Guitar Effects Pedals: The Practical Handbook (Backbeat Books/Hal Leonard)

Having opened up the wonderful world of overdrive-type devices in the first installment of this series, let’s start breaking down this category to the individual effects that fit this description. All of these increase the gain of your guitar signal, but they do it in very different ways. Since this is a big category, we’ll take these in two bites in order to have enough space to go into some detail. We’ll also work from those that affect our tone least to those that affect it most. This time, boosters, and compressors; next time, Overdrives, Distortions, and Fuzzes.

Boosters

Transistor booster preamp stages are often billed as “linear,” “clean,” or “distortion-free” boosters, and are intended to boost the guitar signal before it reaches the amplifier, without adding any artifacts like fuzz or distortion. The “linear” bandied about in the names or literature of many means, in basic terms, that the guitar’s frequency range—and therefore its tone—should be unchanged as it passes through them, only the signal level should be increased.

If this is the essence of the unit in itself, the intended use and, therefore, the resultant sound of the majority of boosters is anything but an entirely clean, transparent level increase. In actual fact, many do fatten the guitar sound slightly or enhance the treble, but more significantly, most players use boosters to drive their amps harder (tube amps, mainly) in order to produce some distortion. Plenty use them for a supposedly “clean” volume lift for undistorted lead lines, certainly, but this perceived clean tone is always thickened by a degree of distortion anyway. And the best way to get nothing but an unadulterated volume lift would be to tweak the level at the amp’s output stage, not stack another gain-boosting stage in front of the amplifiers own preamp stage. “Clean” boosters they may be, but the good ones are extremely effective at coaxing a good tube amp into coughing up its luscious distortion sounds at slightly lower volume settings, say your blackface Fender Super Reverb on four rather than seven.

The booster circuit can be one of the simplest out there, though many are extremely clever, verging on the complex. The fact that most other pedals in this genre—many fuzzes, overdrives, distortions, and compressors—contain a booster stage in addition to their other sound-shaping circuitry hints that the booster pedal itself is a lesser engineering task than any of these. But the effort of keeping it transparent?that is, altering the timbre and tonality of the raw guitar sound as little as possible?is an art in itself.

At about the same time that fuzz pedals were becoming big stuff in the rock world, plenty of other guitarists wanted a means of boosting their attack and sustain but without adding the artificiality of the fuzz sound—ostensibly retaining their natural, clean guitar tone.

LPB-1Considering its simplicity, it’s surprising that Electro-Harmonix’s LPB-1, the first widely available commercially produced booster, arrived a few years after fuzz boxes had already flooded the market. E-H’s Mike Matthews had marketed a fuzz box previously, and even sold a great number of them to Guild, but he founded his now-famous company in 1968 on the back of the LPB-1 (the name stands for Linear Power Booster model 1). Where even the more basic fuzzes used a pair of transistors and a handful of other components, the LPB-1 used a single transistor for its gain boost. It was an enormous success.
Dan Armstrong Red Ranger
Other boosters followed, such as MXR’s popular, upmarket Micro Amp, and Dan Armstrong’s Red Ranger. For plenty of early-1970s guitarists, one of these was all that need come between guitar and 100W stack for rock heaven to prevail.

The format is equally popular today, if not more so, and 21st century guitarists use boosters individually to overdrive amps or offer clean level increases for soloing; at the front of a long chain of effects to act as a buffer and line driver; or at the end of a similar chain to boost levels again after the signal drain of six or ten pedals.

There’s a myriad of boost pedals available today, sSuper Hard Onome relatively straightforward units like Fulltone’s two-jfet-driven Fat Boost, Roger Mayer’s Voodoo Boost, or Carl Martin’s Boost Kick, and some more unusual, such as Z.Vex’s simple but clever Super Hard On, which uses a single BS-170 mosfet transistor and has a unique negative-feedback control for a volume knob (labeled “Crackle Okay” because of the crackle inherent in such controls when turned while in circuit).

Other designs add a clean-boost function to an overdrive pedal—sometimes independently switchable, sometimes not—resulting in products like Carl Martin’s Hot Drive’n Boost, Fulltone’s Full-Drive, or Voodoo Lab’s Sparkle Drive.
Vox Treble/Bass Booster
Other boosters are deliberately designed to enhance certain frequencies. Vox offered a Treble Booster and Treble/Bass Booster way back in the mid-1960s, and Electro-Harmonix followed its LPB-1 with the Screaming Bird and more powerful Screaming Tree treble boosters. Though these certainly emphasized high frequencies, as desired by countless guitarists at the time trying to cut through the mix as bands got louder and louder (and often, as a result, muddier), they also offered a general signal boost that had a similar amp-overdriving effect on an amp as the more linear boosters.

Compressors

These generally contain a boosting stage as well, but are designed as compact versions of the large studio compressors—leveling devices that smooth the attack and decay of a signal by softening the front edge of the note and amplifying its tail, to put it simply.

Part of the compressor’s original appeal to guitarists was its ability to replicate the natural compression, or sag, of a tube amp run at medium to high levels. Whether induced by a pedal or by the amp itself, compression is often as much a “feel” thing as a tonal element, making the guitar feel more tactile, touch-sensitive and playable. Many favor compressors as sustainers, and some players also use them as booster pedals, by turning down the “compression” or “sustain” control and winding up the “gain” or “volume.”

Ross CompressorMore than just the intended squashing and sustaining effect, however, certain comps have been attributed with magical tonal properties, especially the gray Ross Compressor, MXR’s Dyna Comp, and Dan Armstrong’s little Orange Squeezer. The first two in particular are frequently copied, and sometimes even improved upon, by boutique builders and hobbyists alike. In addition to softening the attack of the note and sustaining its decay, each of these adds its own characteristic thickening of the tone, often with a little appealing grit thrown in as a bonus. Plenty of players go their entire careers without using a compressor pedal; others give one a try, and like its appealing swell and fatness so much that they rarely switch it off from that day forward.

Trey AnastasioThe compressor has long been considered an essential weapon in the Nashville session-player’s arsenal. It helps to smooth out snappy chicken pickin’ runs or to thicken up otherwise thin, clean rhythm and lead parts. But the effect can be heard in the work of players from all genres—from LA session player Jay Graydon to British Strat-picker Mark Knopfler to alt-rocker Trey Anastasio, formerly of Phish. And while even a good compressor’s range of settings is far narrower than those of, say, a fuzz (which might go from mild distortion to freakish buzz) or a chorus (which can shift from gentle swirl to nauseating wobble), great players manage to make very much their own individual sounds with the units. In fact, guitarists with no first-hand experience of a compressor’s sound and function can often hear a great part played through one and attribute the results to “just great tone”—some magical combination of guitar and amp and touch.

While a compressor pedal’s function is somewhat like that of a large studio compressor/limiter, but in miniature, many guitarists use the effect for rather different reasons than would a recording engineer—although these do cross over in certain respects. Compression as a studio tool is usually intended to be transparent, a means of keeping sonic peaks from overloading the desk or the tape or causing digital distortion, while boosting quieter passages to give an overall impression of greater loudness and presence to a part or an entire mix. Guitarists turn to compressors more for sustain, for punch, for thickening up thin sounds and, as described above, to increase the “touch” and dynamic feel of their set-up. While compression applied too heavily in the recording environment can kill off dynamics in a song or part, guitarists, conversely, often think of compressor pedals as a tool that increases the dynamics in their playing and tone. In the truest sense, however, over-used compression from a guitar pedal will of course level out the peaks and troughs of a part, too, and therefore will literally decrease its dynamic range.

The big rack-mounted or stand-alone studio units were made with fairly complex tube circuits in the early days, or used equally intricate solid-state circuit based around an opto-cell as in many classic designs of the 1960s and right up to today. Most pedals for guitar use far simpler circuits based around fairly basic opamps, or sometimes slightly more complex ICs, and the usual handful of transistors, resistors and capacitors that enables them to function in the desired manner. The original models of the little Dan Armstrong Orange Squeezer used a single JRC4558 dual opamp just like that in the most revered versions of the Ibanez Tube Screamer (detailed next installment), and a couple of jfet transistors. One of the more advanced compact compressor pedals, Demeter’s Opto Compulator, is an exception to the rule, and is built around an opto-cell like many revered studio units. The more complex units often boast about their “transparency”—that is, their ability to color the signal very little, or not at all—while other desirable but more basic models make a virtue of the way they liven up and enrich the guitar’s straight sound.

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