We’ve all been there. You get your rig just the way you want it, your amp sounds killer, the guitar is perfectly in tune, and all your pedals are dialed in. Then, you go to take a face-melting solo, and you… disappear. You’re not cutting through the band. So where do you go from here? A seemingly simple solution is a boost pedal. But, as dozens of models are available, which one is best for your needs and your style?
These are pedals that don’t alter the tone of the original signal much, if at all. The idea is that you want to maintain your tone, but just give it extra volume. A historic example of a clean boost is the MXR Micro Amp—think Andy Summers of the Police—which can provide around 20dB of boost. At higher settings, a clean boost can make your amp’s preamp tubes work a little harder, resulting in a natural overdrive tone.
There are three viable applications of a transparent boost:  Place the boost after your dirt pedals to boost your signal without any tone change;  place the boost before all of your pedals to either add more saturation to your signal by hitting your dirt pedals harder on the input, or to compensate for varying output levels of different instruments without having to change the levels on your other pedals;  place the boost in your amp’s effects loop—before your time-based effects—to drive the power amp harder. This a trick that L.A. session ace Tim Pierce often uses to get natural clipping from an amp without using an overdrive pedal in front of the preamp section.
A mid boost offers exactly what it says—a boost to the midrange frequencies. Compared to a transparent boost, a mid boost has a more obvious “effect” on the signal, as it adds midrange (the frequency range when guitars typically live) to the overall EQ of your tone. This is often described as adding more “honk” to the sound, or making the notes sound more forward and present. This can be very effective with a clean amp that might have a scooped EQ personality—meaning the midrange frequencies are less apparent—such as blackface Fender-style amps. Here, the mid boost not only boosts the signal level, it adds the “missing” midrange frequencies. Some sonic examples are Eric Clapton’s Journeyman album (his guitars were equipped with a +25dB mid-boost circuit), or Van Halen I and II (where Eddie Van Halen used a Boss GE-10 EQ pedal to boost mids into his Marshall amps).
There are two schools of thought on signal-chain placement of a mid boost:  Put it before your overdrive/distortion devices to add gain (saturation) to your already distorted signal with a less prominent level increase, and  put it after your overdrive/distortion devices to increase output level without necessarily adding more saturation. If you want to do more of the Clapton-style mid-boost thing, put the pedal as close to your guitar in the chain as possible. EVH was boosting mids into a distorted amp, so placing your mid boost before any drive pedals would be closest to that sound.
Treble boosts are generally considered to be the vintage-style applications of volume boosts. The most famous treble booster—the Dallas Rangemaster—was famously used by Eric Clapton, Brian May, and Ritchie Blackmore. In these cases, the idea was to hit the front end of the amp harder to force earlier breakup, while adding treble frequencies to help players cut through the mix.
Vintage treble boosters are equipped with transistors that make them sensitive to other pedals. For the best results, place a treble booster first in your chain. Also, make sure you aren’t using any buffers—or even a tuner with a buffer in it—before the treble booster.
Mason Marangella runs Vertex Effects.