How Do Guitar Pickups Work?
The key to understanding electric guitar signal flow begins with the pickup. While we concentrate much of our effort on how we attack and fret the strings, it is the pickup which is responsible for converting the sound into an electric signal. A guitar pickup is a type of transducer consisting of a copper wire wrapped around a series of magnets (the poles you see sticking out of the top of a pickup). These components produce an electro-magnetic field surrounding the pickup. The vibration of the magnetized steel string in the magnetic field produces an electrical current in the coil, which is converted into an electric signal mirroring the vibration of the string. This gives us a weak guitar signal, which we send to the amp. Later in the signal chain, another transducer in the speaker cone of the amp will be used to reproduce an amplified version of this original signal after it has been significantly boosted by either vacuum tubes, a transistor, or a combination of both.
Single-coil vs. Humbuckers
There are two basic types of pickups, single coil and humbucker. A single-coil pickup is the original model and utilizes a single set of magnets surrounded by copper wire. It produces a clean tone with accentuated treble but has the unfortunate side effect of picking up lots of extraneous noise and producing a faint hum. Noiseless single-coils have been produced which stack two single coils vertically, cancelling the extraneous noise without significantly compromising the clean tone of the single-coil pickup.
The humbucker was invented to combat the noise problem associated with the single coil pick-up. By placing two copper wires side-by-side and wound in opposite directions over opposite poles of a single magnet, the hum of the single-coil pickup is cancelled out. The humbucking pickup has a higher output signal as a result and can be used to overdrive a tube amplifier at lower volumes than a single coil pickup. The tone of a humbucker is warmer and darker, though there is less definition between strings. This is due to each wire being “out-of-phase” with the other, cancelling out some of the frequencies and producing a “quackier” sound.
The most important consideration for most of my students is going to be the location of the pickup on the guitar. Most guitars have two to three pick-ups, each with a different sound based on their position on the body. The pick-up closest to the neck (regardless of type) will sounded cleanest and have the most sustain. The pick-up closest to the bridge will sound more biting with less sustain. This is not because of the pickup itself, but the manner of the vibrations on that area of the string. Each electric guitar has a pick-up selector switch which allows players to toggle to the desired pick-up for whatever tone they seek. If a guitar has two pickups it will also have a setting in the middle of the pickup selector to blend both the neck and bridge pickups, giving a sound that amalgamates the tone of the two.
Some guitars (i.e. Stratocasters) have a third pickup between the neck and bridge pickup wired out-of-phase with the other two. This pickup can be selected individually to create a tonal blend of neck and bridge positions, or it can be blended with either neck or bridge pickups to not only blend tones, but also cancel extraneous noise and hum.
There will be two tone knobs on your guitar, one to control the tone of the neck pick-up and one for the bridge and middle pickups. These act as filters. Setting the knob at 10 allows all the high-end frequencies through, and as you begin to roll it towards zero, a greater section of the higher frequencies are eliminated. For the most part, it is best to leave these knobs set to 10, unless you are playing jazz, in which case you can roll them back to 5.
Pickup construction is a deep topic including such considerations as active vs. passive, P-90 vs single coil, hand vs. machine-wound, magnet type, mounting angle, series vs. parallel wiring, etc. These are unnecessary and overwhelming concepts for most beginner to intermediate players who simply wish to get a decent tone out of their current guitar. However, for those interested in further reading, I suggest checking out the book Guitar Tone by Mitch Gallagher, which includes an extensive chapter on the subject.
To begin applying this information, we can move through each pickup selector setting on your guitar from neck to bridge, identifying the type of pickup(s), playing a passage, noting the unique tonal quality of the setting, before moving on to the next. Try and imagine what style or musical expression would best suit each setting.