A pickup gets its name from the fact that it picks up your guitar’s sound and sends it to an amplifier. Back in the 1930s, ’40s, and ’50s, pickups were sometimes referred to as microphones or guitar mics, which makes sense, but pickup is pretty much the universal term for these units today.
Pickups are electromagnetic devices, meaning they use a coil and magnets to produce an electrical signal, and the vast majority of them are passive, meaning they require no electrical input from a battery or wall socket to function. Some other popular types are active, requiring power that’s usually supplied by a 9-volt battery.
Pickups do their job by sensing the vibrations of the guitar’s steel strings and translating that movement into an electrical signal that can be reproduced by an amplifier. They’re pretty simple devices really, but quite miraculous when you think about it:
Just as different notes on the guitar are created by strings vibrating at different frequencies (determined by factors of length, tension, and thickness), these same vibrations produce notes of the same pitch after the electrical signal they generate comes out the other end of an amp’s circuitry and speaker.
The precise way in which the pickup performs this simple yet amazing job, however, is utterly crucial to the sound of any guitar. Although these electromagnetic devices are pretty basic — crude, almost, and truly a technology from a bygone age — they are extremely sensitive.
Even minute changes in the way two different pickups are constructed alter how they sound, even when fitted in the exact same guitar. In fact, small differences in the way two of the same type of pickup are manufactured even result in noticeable differences in their sound, so a deep understanding of different pickups can get to be pretty “under the microscope” stuff!
The result of all these variables in pickup design and construction is that, although the vast majority of pickups used on electric guitars function in exactly the same way, the many different types sound quite different — or, to put it more accurately, result in your guitar sounding very different when you swap from one type of pickup to another.
An invisible power in an electromagnetic pickup
Anyone who has ever pushed two magnets together with their positive or negative poles toward each other knows that there’s a power at work in these simple chunks of hard material, even if you can’t see it. That strange, invisible barrier that pushes two magnets apart when they’re turned the wrong way around is direct evidence of a magnetic field, a power that guitarists harness every day to make music.
The magnet in an electromagnetic pickup is truly the power that enables you to plug in this plank of wood and wire. It (or they, when more than one is used) creates a magnetic field above the pickup itself through which the strings pass, and when the strings vibrate, they produce a disturbance in this magnetic field that is picked up by the coil of wire wrapped around and beneath it.
For this reason, as you might guess, several variables in a pickup’s magnet(s) and in the way your guitar strings interact with them raise significant variables in the way any pickup performs and, therefore, in the way your guitar sounds. Among these differences are
Magnets and magnet structures: The magnetic field exhibited by one type of pickup is affected by the type of magnet and magnet structure.
String gauges or types: The strings’ vibrating steel — and the amount of it — is primarily what induces a signal in the pickup.
Pickup shapes and sizes: The shape and size of the magnetic field is affected by the structure of the pickup.
Truly electric tone
When the guitar’s vibrating strings disrupt a pickup’s magnetic field, the disruption is sensed by the coil, which is made of several thousand wraps of extremely fine wire in one long, unbroken piece. The coil translates it as a small, low-voltage electrical signal, which is the start of your electric guitar tone.
The shape, condition, and strength of that low-voltage electrical signal all play a part in determining what your guitar sounds like when it comes out of the amplifier, as do several aspects of the way the guitar itself is made. Many players give little thought to their guitar sound as an electrical signal, but if you consider this yourself, you’ll be ahead of the game.
The fact that signals of different strengths and frequency induce different reactions within your guitar amp is the reason for the following phenomena:
If you strum your strings lightly, your sound will stay cleaner (less distorted). The strings’ reduced vibrations from lighter strumming or picking react less with the pickup’s magnetic field and induce a lower-voltage signal in the coil.
Whack the strings hard, and your guitar is likely to sing, or distort, more. Intensive string vibration produces the maximum potential signal from the pickup, which can often be just enough to induce a little overdrive in a tube amp set just on the edge of distortion.
Your guitar’s volume control is really a clean/dirty control. Often, even more than affecting raw volume, turning down your guitar’s volume control(s) just a little reduces the pickups’ electrical signal and makes your guitar sound cleaner when it comes out through your amp.