A capacitor is a device that stores an electrical charge on it's plates. A positive and a negative plate, are placed very close together with an insulator in between to prevent the plates from touching each other. A capacitor can carry a voltage equal to the battery or input voltage. Usually a capacitor has more than two plates depending on the capacitance or type.
The capacitor also functions as a filter, passing alternating current (AC), and blocking direct current (DC).
Capacitance is measured in farads, symbol F. However 1F is very large, so multipliers are used to show the smaller values:
* µ (micro) means 10-6 (millionth), so 1000000µF = 1F
* n (nano) means 10-9 (thousand-millionth), so 1000nF = 1µF
* p (pico) means 10-12 (million-millionth), so 1000pF = 1nF
In October 1745, Ewald Georg von Kleist of Pomerania invented the first recorded capacitor: a glass jar coated inside and out with metal. The inner coating was connected to a rod that passed through the lid and ended in a metal sphere. By having this thin layer of glass insulation (a dielectric) between two large, closely spaced plates, von Kleist found the energy density could be increased dramatically compared with the situation with no insulator.
In January 1746, before Kleist's discovery became widely known, a Dutch physicist Pieter van Musschenbroek independently invented a very similar capacitor. His capacitor was called the 'Leyden Jar' (pronounced: LY-duhn). This Leyden jar consisted of a narrow-necked glass jar coated over part of its inner and outer surfaces with a conductive metallic substance; a wire passes through as insulating stopper (cork) in the neck of the jar and contacts the inner foil layer, which is separated from the outer layer by the glass wall.
Capacitor Number Code
A number code is often used on small capacitors where printing is difficult:
- the 1st number is the 1st digit
- the 2nd number is the 2nd digit
- the 3rd number is the number of zeros to give the capacitance in pF
- Letters indicate tolerance (for example, J indicates 5% tolerance)
- a cap marked 102 means 1000 pF = 1nF (10 plus 2 zeros expressed in pF)
- a cap marked 47 means 47 pF
- a cap marked 472J means 4700 pF = 4.7nF (J indicates 5% tolerance)
- a cap marked 474 means 470,000 pF = .47 µF(47 plus 4 zeros)
- a cap marked 151 means 150 pF (15 + one zero)
- a cap marked 105 means 1,000,000 pF = 1 µF (10 + 5 zeros
Capacitors in Series
|Combined capacitance (C) of
capacitors connected in series:
- a .047 µF cap in series with a .022 µF cap would yield approximately .015 capacitance
- Show me the math:
- 1/.022 = 45.45
- 1/ .047 = 21.28
- 1/.022 + 1/.047 = 45.45 + 21.28 = 66.73
- Solve for C = 1/66.73 = .015
Capacitors in Parallel
|Combined capacitance (C) of
capacitors connected in parallel:
|C = C1 + C2 + C3 + ...|
- a .047 µF cap in parallel with a .022 µF cap would yield approximately .069 capacitance
- Show me the math (this one is simple):
- .022 + .047 = .069
Capacitors in Guitar Circuits
They are used primarily on tone controls to bleed treble to ground. Guitar tone control caps usually range from .022 µF- .047 µF. The larger cap will give you a darker tone when you roll down the tone knob. The value you choose is rather subjective. Caps are also used on "treble bleed circuits (also referred to as "volume kits" or "high pass filters") to prevent the loss of highs when rolling down a guitars volume. Usually much smaller value caps are used here, usually in the 680 pf - 1000 pF range.
Common Types of Capacitors
- Electrolytic - Constructed from two conducting aluminium foils, one of which is coated with an insulating oxide layer, and a paper spacer soaked in electrolyte. The electrolyte is usually boric acid or sodium borate. Electrolytic capacitors have a voltage polarity requirement .This means that it is very important which way round they are connected. If the capacitor is subjected to voltage exceeding its working voltage, or if it is connected with incorrect polarity, it may burst and can be extremely dangerous. Electrolytic capacitors usually have a larger capacitance per unit volume than other types, making them valuable in relatively high-current circuits such as power-supply filters.
- Tantalum - They are electrolytic capacitors but used with a material called tantalum for the electrodes. They are considered to be superior to electrolytic capacitors, possessing excellent temperature and frequency characteristics. They are also polarized.
- Polyester Film -This capacitor uses thin polyester film as the dielectric. They are not high tolerance, but they are inexpensive. Often used in guitar circuits.
- Metalized Polyester Film - Dielectric made of DuPont's trademark "Mylar" polyester. Often used in guitar circuits.
- Polypropylene - Mainly used when a higher tolerance is needed then polyester caps can offer. This polypropylene film is the dielectric. Widely used in guitar applications. The famous Hovland Musicaps and SBE Orange Drops are of this type.
- Paper in Oil Capacitors - These film capacitors use oil soaked paper as di-electric material. Widely used in audio applications. Accepted by audiophiles to be smooth and natural in sound. Starting to gain ground in guitar applications with the Allparts Vitamin-Q reproduction capacitor.
- Teflon® Film and Tin Foil - The best electrical properties of all the dielectrics. The unbelievable V-Caps are of this type. Remarkably smooth and "musical" capacitor. Available in prewired guitar harnesses by Rothstein Guitars since 2005.
- Polystyrene - Made from metallic foil interleaved with polystystyrene file. They are noted for their low losses at high frequencies, good stability and reliability.
- Ceramic - Widely used in guitar electronics as they are inexpensive and well suited for high frequency applications. Typically used to by-pass high frequency signals to ground. They are shaped like a disk, available in very small capacitance values and very small sizes.
- Silver-Mica - Mica is used as a dielectric. More expensive than ceramic, but have excellent high frequency response. Used in resonance circuits, frequency filters, and military RF applications.