I’ve Got a Great Amp, Why Do I Need an Overdrive?

Ever since the advent of the electric guitar and amplifier in the 1930s, people have looked for ways to a) make it sound louder and b) make it sound “better.” Better is of course a subjective term, but in this case it usually incorporates some combination of:

• Louder
• More Sustain
• Fatter/Fuller
• Less Harsh
• Tighter Bass

One of the stories about Eddie Van Halen’s famous Frankenstein strat, one of the world’s most famous partscasters (in the company of Clapton’s Blackie and Gilmour’s Black Strat. And Hendrix’s favorite…black strat. See a trend here?) is that when young Eddie put in a rewound Gibson PAF from his ES-335, he couldn’t figure out how to wire the tone control in the circuit, so he only had the volume potentiometer active, and stuck the knob labeled TONE on it. There is a lot of truth to the idea that turning up a guitar and amp makes it sound better, so let’s understand why that is.

When you turn knobs on most guitars and tube amps, it’s vital to remember that all of those controls are subtractive, not additive. That means that at 10 on the volume knob, for example, you are getting the maximum signal possible from the guitar’s passive circuitry. The guitar isn’t adding any extra volume. Same thing for the tone knob, it can only reduce brightness from a maximum level, it can’t add any. That’s true for all of the amp controls as well, usually, unless you have one of the not very many amps that use active EQ circuitry. When the controls are all dimed, that is the maximum potential of your guitar and amp combination. If your pickups are lower output, you will get more dynamics but less volume than a guitar with high output pickups. If your amp is designed to have a big, loose bass at top volume, then there’s nothing you can really do about it. And heavens forbid if you love the tone of your guitar and amp when its cranked but you have to play a gig where you can’t crank it.

That’s where drive pedals come in. When Keef first hit the Maestro or Clapton first hit the Dallas Rangemaster, they were suddenly able to get more sustain, fatter tones, and ones that sounded like the amps were really cooking, even if they weren’t. That, in a nutshell, is what drive pedals do.

Drive pedals can be understood in four basic categories:

1. Boost pedals. Boost pedals are some of the simplest circuits, because they simply increase level. Some boosts increase level at specific frequencies more than others, even as they increase the total overall level, these are generally referred to as color boosts, or, they can be specifically refer to the boosted frequencies, aka treble boosts or mid boosts. These pedals increase level and not gain, so in front of a clean amp, they just make everything louder. In front of a dirty amp, they will push the preamp into clipping faster, so you can get more of your amp’s natural overdrive sounds at a lower volume level.

2. Overdrive pedals. These are pedals that increase both level and gain, so they can do what a colored boost pedal does, and for some pedals, they can even be close to a clean boost. Normally they don’t really do truly clean boost though, because the circuit is built to an EQ profile that will sound good with the gain control. The difference between gain and volume is crucial here. In an overdrive pedal, volume is the final level of the effect that goes out after processing. Gain is the level that goes in to be processed by the effect. Do you see the difference? Gain is like your guitar’s volume knob, and Volume is like the amp’s volume knob. The more gain, usually the more saturation, bass, and treble attenuation, as well as making things louder. Volume is just loudness. So an overdrive pedal basically puts a preamp in front of your amp, and many manufacturers actually just make preamp pedals that can be used as overdrives. What this means practically is that overdrive pedals give you one more level of tone shaping over a boost pedal. Overdrives, even the so-called transparent ones, usually have a mid-hump EQ, i.e. they cut some bass and treble while emphasizing mids. The Tubescreamer is the most well known example of this, but the Klon and the Bluesbreaker also cut lows, round highs, and push mids, just to different degrees and in different frequency ranges. This is really because otherwise drive circuits would produce an ugly, fartily large bass and harsh, ear-splitting treble when they increased the gain. Increasing mids is part of what makes overdrives sound smooth and pleasant.

3. Distortion pedals. Distortions operate in some ways very similarly to overdrives, but the clipping is different. Clipping describes how the signal behaves when it gets bigger than the circuit can cleanly handle. A soundwave looks like a squiggly line inside a box. But when you add gain and volume, the wave gets squished up against the top and bottom of the box, and how the wave handles that is called clipping.

What an overdrive does is typically soft clipping, as you can see from the image above, when the waveform approaches its limits, it rounds out, creating a smoother type of sound. Distortions generally use hard clipping, which starts approaching a more trapezoid-shaped wave. That means that distortions often sound a bit edgier and more aggressive, even as they also push mids. The difference in most distortions is really in which they push and by how much over the range of the circuit. Think of the venerable ProCo Rat as opposed to the Tubescreamer, and you can imagine how with the different things they do, why they are such a potent combination.

4. Fuzz pedals. Fuzz pedals are the square wave, mid-scooped distortion. Keef used it to substitute for horns in “(I Can’t Get No) Satisfaction”, but Hendrix really started showing the range of the fuzz as his main tone shaper. With a germanium Fuzz Face, Hendrix was able to create thick slabs of massive, fat, in-your-face sustain, but he also rolled back the guitar’s volume knob to change gain levels and get a uniquely wiry clean-ish tone. Gilmour used his Fuzz Face for those regal, buttery tones on Dark Side of the Moon, showing the versatility of the effect in a mix compared to Hendrix.

All of these four options give you different ways to control gain levels going into your amplifier, and as a result, they create different kinds of tones. This brings us back to the original question, why do you need an overdrive?

In Part II, we will continue to explore the enormously rewarding world of drive pedals!