A vital component of any amplified guitar is the pickup (or pickups - many guitars have more than just one). These are responsible for taking the movement of the strings and converting it to an electrical signal which can be sent to the amplifier.
For this tutorial, we'll concentrate on the magnetic pickups found on electric and semi-acoustic guitars. There are other types of pickups, but more about those later.
In some respects, the construction of pickups is fairly straight forward. They comprise a magnetic core with 'pole pieces' which rise up to bring the magnetic field closer to the strings. This core is wrapped many thousands of times with fine electrical wire.
When the strings vibrate, being steel they disrupt the magnetic field from the pickups. This induces an electrical current in the pickps and ultimately gives the guitar its electrical 'voice'.
Whereas the principles and construction of a magnetic pickup may be fairly straight forward (the physics behind this is the sort of thing taught in first year of High School), the art of pickup design is the subtle and not-so-subtle variations on the basic concept. The material used for the core can have a fundamental influence on the sound. Not just any old magnet is used. A common type of magnetic core is a compound of aluminium, nickel and cobalt (known as alnico) - and there are variations on this basic compound with different amounts of each material being used. Alternatively, you may also find pickups with a ceramic magnet at their core.
The way in which the pickup is wound can also have an influence on the way it sounds. The type of wire, the number of turns, etc. all have a part to play in forming the overall sound. Indeed, there are specialist rewinders who will rewind the wire around a pickup to alter or improve its sound.
An important manufacturing stage of pickups is 'potting', whereby the pickup coils are encased in wax. This prevents any movement within the coils, such as disturbance by sound vibration, which can cause unwanted microphonic feedback. Potting is not always done on cheaper pickups, but it can be done as an after-market operation although this is best left to a professional as the job is not as easy as it sounds.
The first pickups were based around a single magnetic coil, and this is a design which continues to be used on guitars to the present day. Single coil pickups produce a relatively bright sound, but this clarity of tone can at a slight premium in that they have a certain amount of signal noise.
In order to alleviate the signal noise problem, pickups featuring two coils were developed. These coils are wired out of phase in order to cancel out (or 'buck') any hum from the coils - hence the name of humbucker. The sound from a humbucking pickup tends to be more mid-range biased than a single coil and not quite so bright. Also, humbuckers are inherently louder and so more useful for driving an amp into distortion (important: a pickup will not produce a distorted signal - you still need an overdrive channel on your amp or an effects pedal like a fuzz-box - but the higher output can cause a dirty channel on amp to break up more easily than a single coil pickup).
Some manufacturers produce a type of humbucker which is stacked so that it is the same width as a single coil pickup. This retains the hum-cancelling benefits of a humbucker but brings back some of the brightness of a single coil pickup.
To hear the differences between the two basic types of pickup, listen to the following examples:
A simple clean sound, played first using a humbucker and then with a single coil
Clean, funky chords. First with the humbucker and then with a single coil
Power chords through a distorted channel. Again humbucker, followed by single coil
The position of a pickup on a guitar can have an influence on the sound. This is because the strings vibrate less closer to the bridge and more towards the neck, and so any disruption of a pickup's magnetic field is different.
Even with identical pickups in the bridge and neck position, each will sound different. The bridge pickup will produce a more trebley sound whereas a neck pickup will produce a fuller, more rounded sound. Also, a neck pickup will be louder than a bridge pickup, but a good set up pickups will be balanced to compensate for this.
As an example, listen to these sound-bytes of a Les Paul guitar with two humbuckers:
A clean sound first with the bridge pickup, then the neck pickup, and finally both pickups together
A distorted sound. Again, the bridge pickup, then the neck pickup, and finally both pickups together
A number of switching mechanisms can be employed on a guitar to control the sound produced. The most basic configuration is a guitar with more than one pickup where it is possible to toggle between either of both pickup at a time, as in the last set of examples.
Another popular switching mechanism is to allow a humbucking pickup to be split so that only one coil is in use. This is a useful way of providing two sounds out of one pickup, but a split humbucker rarely sounds like a true single coil pickup. The larger magnetic 'footprint' affects the sound differently to that of a true single coil. Take a listen to the following sound-byte of a humbucker using both coils and then coil-tapped as a single coil pickup.
Something played with a full humbucker, and then with the one coil switched off
Something which you may encounter less frequently is the practise of phase switching. For this, when two pickups are being used at once the phase of one of them is reversed. This only works with single coil pickups or in coil-tapped humbuckers - in a humbucker one of the coils is out of phase already. This produces an interesting sound, variously described as 'nasal' or 'smokey'.
This example is 2 single coil pickups first in phase, and then out of phase
A toally different type of pickup is the piezo pickup. This is made from a piezo crystal which is in contact with the strings and pickups up sound by direct vibration. As it is not magnetic in nature it is commonly used on acoustic guitars which are to be amplified.
More recently, some manufacturers have included both conventional magnetic pickups and a piezo pickup on an electic guitar. This allows the player to select a 'normal' electric guitar tone or a more natural or acoustic sounding tone.
This tutorial is meant to give a bit of backround information on how pickups work, and the main things to look for. If you are choosing an electric guitar the best rule is to let your ears guide you and pick an instrument that sounds right for you. Hopefully, however, this backgound knowledge will help you know where to start looking (and listening).
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