question: How do guitar pickups make sound and send it to the amp?
comment: They are electric coils, basically a lot of wire wrapped around an "iron" core. Imagine a electric magnet. When you move something else that is magnetic, the guitar string) in the vicinity of the coil an electric current is induced into the coil. This tiny electric signal is then amplified by the guitar amp.
passages: BULLET::::- H-H-S (Mayones Legend “22” Anders Nyström signature, some ESP Stephen Carpenter Models, and Alembic Jerry Garcia Models)
  
  BULLET::::- H-S-S-H (Music Man Steve Morse Signature)
  
  BULLET::::- S-H (some Telecasters, Music Man “Valentine” James Valentine signature)
  
  BULLET::::- S-H-H (some early seven-string ESP Horizons)
  
  BULLET::::- S-H-S (Fender Wayne Kramer Signature)
  
  Section::::Piezoelectric pickups.
  
  Section::::Piezoelectric pickups.:Sensors.
   The pickup is connected with a patch cable to an amplifier, which amplifies the signal to a sufficient magnitude of power to drive a loudspeaker. A pickup can also be connected to recording equipment via a patch cable.
  
  The pickup is most often mounted on the body of the instrument, but can be attached to the bridge, neck or pickguard. 
  
  Section::::Magnetic pickups.:Construction.
   BULLET::::4. Electrostatic pickups. Another way is to use the changing capacitance between the string and a pickup plate. These electronic pickups produce much higher dynamics than conventional pickups, so the difference between a soft and a loud pick strike is more pronounced than with other types of pickups.
   The final stages of on-board sound-shaping circuitry are the volume control (potentiometer) and tone control (a low-pass filter which "rolls off" the treble frequencies). Where there are individual volume controls for different pickups, and where pickup signals can be combined, they would affect the timbre of the final sound by adjusting the balance between pickups from a straight 50:50.
  
  Section::::Sound and effects.:Guitar amplifier.
  
  The solid-body electric guitar does not produce enough sound for an audience to hear it in a performance setting unless it's electronically amplified—plugged into an amplifier, mixing console, or PA.
   Gibson created the HD.6X Pro guitar that captures a separate signal for each individual string and sends them to an onboard analog/digital converter, then out of the guitar via Cat 5 Ethernet Cable.
  
  Section::::See also.
  
  BULLET::::- Contact microphone
  
  BULLET::::- Electric lamellophone
  
  BULLET::::- Electric sitar
  
  BULLET::::- Humbucker
  
  BULLET::::- Instrument amplifier
  
  BULLET::::- Lipstick pickup
  
  BULLET::::- List of electronics topics
  
  BULLET::::- Magnetic circuit
  
  BULLET::::- Nominal impedance
  
  BULLET::::- Preamplifier
  
  BULLET::::- Reverberation
  
  BULLET::::- Single coil
  
  BULLET::::- Transformer
  
  Section::::References.
  
  BULLET::::- Tillman, Donald (2002). Response Effects of Guitar Pickup Position and Width
  
  BULLET::::- Wheeler, Tom (1992). "American Guitars: an illustrated history". Harper. New York
  
  Section::::External links.
   Most pickup-equipped guitars feature onboard controls, such as volume or tone, or pickup selection. At their simplest, these consist of passive components, such as potentiometers and capacitors, but may also include specialized integrated circuits or other active components requiring batteries for power, for preamplification and signal processing, or even for electronic tuning. In many cases, the electronics have some sort of shielding to prevent pickup of external interference and noise.
   A humbucking pickup is composed of two coils, with each coil wound reverse to the other. Each set of six magnetic poles is also opposite in polarity. Since ambient hum from electrical devices reaches the coils as common-mode noise, it induces an equal voltage in each coil, but with opposite amplitudes. These effectively cancel each other, while the signal from the guitar string is doubled.
   The neck and fretboard (2.1) extend from the body. At the neck joint (2.4), the neck is either glued or bolted to the body. The body (3) is typically made of wood with a hard, polymerized finish. Strings vibrating in the magnetic field of the pickups (3.1, 3.2) produce an electric current in the pickup winding that passes through the tone and volume controls (3.8) to the output jack. Some guitars have piezo pickups, in addition to or instead of magnetic pickups.
   BULLET::::3. Magnetic pickups. Magnetic pickups, as applied in electric guitars, register the vibrations of nickel or steel strings in a magnetic field. They have the advantage that they can be connected directly to an (electric guitar) amplifier, but in combination with a steel-string acoustic guitar the sound tends to be electric. This is why acoustic guitarists typically choose a piezoelectric pickup, built in microphone, or both.
   Pickup (music technology)
  
  A pickup is a transducer that captures or senses mechanical vibrations produced by musical instruments, particularly stringed instruments such as the electric guitar, and converts these to an electrical signal that is amplified using an instrument amplifier to produce musical sounds through a loudspeaker in a speaker enclosure. The signal from a pickup can also be recorded directly. 
  
  Most electric guitars and electric basses use magnetic pickups. Acoustic guitars, upright basses and fiddles often use a piezoelectric pickup.
  
  Section::::Magnetic pickups.
   Many semi-acoustic and acoustic guitars, and some electric guitars and basses, have been fitted with piezoelectric pickups instead of, or in addition to, magnetic pickups. These have a very different sound, and also have the advantage of not picking up any other magnetic fields, such as mains hum and feedback from monitoring loops. In hybrid guitars, this system allows switching between magnetic pickup and piezo sounds, or simultaneously blending the output. Solid bodied guitars with only a piezo pickup are known as silent guitars, which are usually used for practicing by acoustic guitarists. Piezo pickups can also be built into electric guitar bridges for conversion of existing instruments.
   BULLET::::- Piezoelectric (or "piezo") pickups (also called "piezo" pickups) use a transducer to convert vibrations in the instrument's body or bridge into an electrical signal. They are typically mounted under the bridge saddle or near the bridge and produce a different tone from magnetic pickups, often similar to that of an acoustic bass. Piezo pickups are often used in acoustic bass guitars to allow for amplification without a microphone.
   Pickups are transducers attached to a guitar that detect (or "pick up") string vibrations and convert the mechanical energy of the string into electrical energy. The resultant electrical signal can then be electronically amplified. The most common type of pickup is electromagnetic in design. These contain magnets that are within a coil, or coils, of copper wire. Such pickups are usually placed directly underneath the guitar strings. Electromagnetic pickups work on the same principles and in a similar manner to an electric generator. The vibration of the strings creates a small electric current in the coils surrounding the magnets. This signal current is carried to a guitar amplifier that drives a loudspeaker.
   Early EUBs used magnetic pickups similar to those in electric guitars, or percussive magnetic diaphragm pickups (e.g., the Ampeg Baby Bass). Many modern EUBs use piezoelectric pickups located in the bridge or a combination of pickup types. The signal from the pickup is usually preamplified and equalized with a preamplifier and then sent to a bass amplifier or a PA system. For practice in a hotel room or apartment, an EUB can also be connected to headphones.
   An electric guitarist records a dry, unprocessed, unaffected track in a recording studio. This is often achieved by connecting the guitar into a DI unit (a Direct Input or Direct Inject buffer box) that is fed to a recording console or, alternatively, bypassing the console by using an outboard preamplifier. Often, the guitarist's signal is sent to both recorder and guitar amp simultaneously, providing the guitarist with a proper amplifier "feel" while she/he is playing while also tracking (recording) a dry (un-effects processed) signal.
   For early pickup devices using the piezoelectric effect, see phonograph.
  
  Section::::Other transducers.
  
  Some pickup products are installed and used similarly to piezoelectric pickups, but use different underlying technology, for instance electret or condenser microphone technology.
  
  Section::::Double systems pickups.
  
  There are basically four principles used to convert sound into an alternating current, each with their pros and cons:
  
  BULLET::::1. A microphone registers the vibrations of the air caused by the instrument. In general this technique guarantees a good sound quality, but with two limitations: feedback and crosstalk.
   A typical magnetic pickup is a transducer (specifically a variable reluctance sensor) that consists of one or more permanent magnets (usually alnico or ferrite) wrapped with a coil of several thousand turns of fine enameled copper wire. The magnet creates a magnetic field which is focused by the pickup's pole piece or pieces. The permanent magnet in the pickup magnetises the guitar string above it. So the string is, in essence, a magnet itself and its magnetic field is in alignment with that of the permanent magnet that magnetized it. When the string is plucked, the magnetic field around it moves up and down with the string. This moving magnetic field induces a current in the coil of the pickup.
   Compared to an acoustic guitar, which has a hollow body, electric guitars make much less audible sound when their strings are plucked, so electric guitars are normally plugged into a guitar amplifier and speaker. When an electric guitar is played, string movement produces a signal by generating (i.e., inducing) a small electric current in the magnetic pickups, which are magnets wound with coils of very fine wire. 
   Pickups can be either active or passive. Pickups, apart from optical types, are inherently passive transducers. "Passive" pickups are usually wire wound around a magnet, and are the most common type used. They can generate electric potential without need for external power, though their output is relatively low, and the harmonic content of output depends greatly on the winding.
   Other high-output pickups have more turns of wire to increase the voltage generated by the string's movement. However, this also increases the pickup's output resistance/impedance, which can affect high frequencies if the pickup is not isolated by a buffer amplifier or a DI unit.
  
  Section::::Magnetic pickups.:Pickup sound.
   The last type of guitar is commonly called an "acoustic-electric" or "electro-acoustic" guitar, as it can be played either "unplugged" as an acoustic, or plugged in as an electric. The most common type is a piezoelectric pickup, which is composed of a thin sandwich of quartz crystal. When compressed, the crystal produces a small electric current, so when placed under the bridge saddle, the vibrations of the strings through the saddle, and of the body of the instrument, are converted to a weak electrical signal. This signal is often sent to a pre-amplifier, which increases the signal strength and normally incorporates an equalizer. The output of the preamplifier then goes to a separate amplifier system similar to that for an electric guitar.
   BULLET::::2. Contact pickups register the vibrations of the instrument itself. They have the advantage of producing little feedback and no crosstalk at all. In spite of their lesser sound quality and thanks to their low price, contact pickups (and especially the piezoelectric pickup) have become the most popular transducer.
   A lot of electric bass guitars use magnetic pickups. The vibrations of the instrument's ferrous metal strings within the magnetic field of the permanent magnets in magnetic pickups produce small variations in the magnetic flux threading the coils of the pickups. This in turn produces small electrical voltages in the coils. Many bass players connect the signal from the bass guitar's pickups to a bass amplifier and loudspeaker using a 1/4" patch cord. These low-level signals are then strengthened by the bass amp's preamplifier electronic circuits, and then amplified with the bass amp's power amplifier and played through one or more speaker(s) in a cabinet.
   Most pickups for bowed string instruments, such as cello, violin, and double bass, are piezoelectric. These may be inlaid into the bridge, laid between the bridge feet and the top of the instrument, or, less frequently, wedged under a wing of the bridge. Some pickups are fastened to the top of the instrument with removable putty.
  
  Section::::Piezoelectric pickups.:Preamps.
  
  Piezoelectric pickups have a very high output impedance and appear as a capacitance in series with a voltage source. They therefore often have an instrument-mounted buffer amplifier fitted to maximize frequency response.
   A way to increase the usability of the sound acquired this way is to wire a capacitor in series with the pickup that has its electric polarity reversed. This filters out that pickup's lower frequencies and thus preserves the corresponding frequencies from the other pickup. The resulting sound is fuller and stronger, yet still different from the standard in-phase combinations, resembling the sound of a "cocked wah" (a wah-wah pedal set in a fixed position). The capacitor used for this is usually in the 20–100 nF range.
  