Glossary of Electronic Terms

Electronic: The use of active electronic components (integrated circuits, transistors, valves etc) which require a power supply to function. Such "active" components will always be used in conjunction with passive components

Earth (1): also known as ground - commonly used to describe the chassis and other materials that provide a return path for power supplies and signals within any electronic device

Earth (2): also known as ground - a protective connection from wall outlet to equipment chassis to conduct fault currents away from human contact

Electromagnetic Interference (EMI): an unwanted (possibly interfering) signal emitted by any electronic apparatus. The emission of EMI is heavily regulated in most countries.

Electromagnetic Radiation (EMR): a transmission medium that includes radio waves and light waves.

Farad: the base unit of capacitance - equal to the capacitance of a capacitor having an equal and opposite charge of 1 coulomb on each plate and a potential difference of 1 volt between the plates (Abbreviation - F). The Farad is a very large value, and is more commonly referred to as the pico-Farad (pF, 1 x 10-12 Farad), nano-Farad (nF, 1 x 10-9 Farad), micro-Farad (uF, 1 x 10-6 Farad), and (less common) milli-Farad (mF, 1 x 10-3 Farad)

Filter: a circuit which is frequency dependent. The "pass band" is the range of frequencies allowed through, and the "stop band" is that range of frequencies which are blocked

Filtering: a process used to remove or accentuate specific frequencies or frequency ranges of a signal

Frequency: The rate at which an alternating current changes in a cyclic manner from positive to negative and back again (one cycle). The basic unit of measurement is the Hertz (Hz), which equates to one cycle per second

Frequency Modulation (FM): a modulation technique that records changes in an information signal by modifying the frequency of the carrier signal according to changes in the amplitude of the information signal.

Henry: The basic unit of inductance in which an induced electromotive force of one volt is produced when the current is varied at the rate of one ampere per second (Abbreviation - H)

High-pass: A filter which allows high frequencies to pass while blocking low frequencies

Hertz (Hz): the measurement of frequency. Hertz represents the number of cycles of an electrical signal measured in one second

Impedance: A load applied to an amplifier (or other source) which is not a pure resistance. This is to say that its loading characteristics are frequency dependent. Impedance consists of some value of resistance in conjunction with capacitance and/or inductance. The equivalent circuits can vary from two components to hundreds.

In-Phase: a condition of two waveforms when they cross the reference line at the same time and in the same direction.

Inductor: A coil of wire which exhibits a resistance to any change of amplitude or direction of current flow through itself. Inductance is inherent in any conductor, but is "concentrated" by winding into a coil. An inductor tends to pass low frequencies more readily than high frequencies. Electrically it is the opposite of a capacitor. Basic unit of measurement is the Henry (H), in crossover networks it will typically be measured in milli-henrys (mH = 1 x 10-3H) and for RF micro-henrys (uH) are common

Insulator: A material that prevents the passage of electricity, heat or sound. The plastic coating on wires is an insulator, preventing the wires from coming into electrical contact with each other. Insulators are extensively used in electronics. Most good electrical insulators are also good thermal insulators

Integrated Circuit (IC): A collection of active and passive devices (e.g. transistors and resistors) mounted on a single slice of silicon and packaged as a single component. Examples include operational amplifiers, Central Processing Units (CPUs), random access memory (RAM), etc.

Intermodulation Distortion (IMD): the intermixing of two frequencies. It is often caused by non-linear distortion within an amplifier or loudspeaker system

Laser: Light Amplification by Stimulated Emission of Radiation. Originally, lasers were either gas or precious stone (e.g. ruby), but are now made using semiconductors. Laser light is coherent, meaning that the emitted light waves are in phase, which gives the light a strange appearance since our eyes were never designed to observe coherent light

Low-pass: A filter which allows low frequencies to pass while blocking high frequencies

Octave: Musical terminology, meaning the doubling (or halving) of frequency. For example, one octave above "Concert pitch" A440 Hz is 880Hz, and one below is 220Hz. Musically, each of these frequencies is "A"

Oscilloscope: An electronic measurement tool which allows one to view a waveform. The vertical axis shows amplitude and the horizontal axis shows time

Passive: Containing no devices which require a power supply. Passive devices include resistors, capacitors and inductors

Phase: Hmmm. Tricky..... Ah-ha! Think of a bunch of soldiers all marching happily (?) to the sergeant's cries of "Hep, rah, hep-rah-hep" - except for Pt. Johnny who is blissfully "Rah, hep, rah-hep-rah"-ing. He is 180 degrees out-of-phase with the rest (or vice-versa). So it is with musical signals, where some signals have a "phase angle" (phase is measured in degrees of rotation) which is different from other signals

Power Amp: An amplifier that is designed to drive loudspeakers or other relatively low impedance loads. Usually combines voltage and current amplification. May be integrated with the preamp (see below)

Preamp: Multiple meanings, but in hi-fi generally refers to a separate section of circuitry that includes source switching, volume and balance controls (as well as tone controls in many cases). Used to raise the level from tape decks, turntables, CD players and other music sources to a level suited to the power amplifier

Quasi: to some degree or in some manner, resembling. For example, a quasi complementary-symmetry output stage in an amplifier is not in fact complementary-symmetry, but appears to be, and acts in a similar manner

Quiescent: being still or at rest, in an inactive state. The quiescent current in an amplifier is that current drawn when the amplifier is "at rest" - i.e. not amplifying a signal, but supplied with power

Resistor: An electrical device which impedes (resists) current flow regardless of frequency. Basic unit of measurement is the Ohm

Resonance: The natural frequency at which a physical body will oscillate. An example is when you blow gently across the top of a bottle, the enclosed air resonates at a frequency determined by the internal volume. Also refers to the natural resonance of loudspeaker drivers, cabinets and ports, or the frequency where an inductance and capacitance have the same impedance (this causes maximum impedance with a parallel circuit, and minimum impedance for series circuits)

rms: Root Mean Squared. Applies to voltage and current, but is commonly (although incorrectly) applied to power. Defined as an alternating voltage (or current) which has exactly the same energy content (power) as the same value of direct current

Thermal Coefficient (1): Of expansion, describes the amount by which a material expands when heated. Commonly expressed as a percentage per degree Celcius so the exact size at various temperatures may be calculated. Knowledge of the expansion characteristics of different materials is important in high power semiconductor manufacture, since differing expansion rates may cause device failure due to temperature cycling fractures

Thermal Coefficient (2): Of resistance, describes the change in resistance at various temperatures. Most metals have a positive temperature coefficient of resistance, which means that the resistance increases with increasing temperature. Carbon and some alloys have a negative temperature coefficient of resistance, so as temperature is increased, resistance decreases

Thermal Resistance: The resistance of various materials to the passage of heat energy. Most electrical conductors are also thermal conductors, with the higher electrical conductivity materials usually having higher thermal conductivity. Important in the design of high power electronics, heatsinks, semiconductor casings, etc.

Total Harmonic Distortion (THD): the sum of all amplifier distortion components, plus system noise. THD measurements are sometimes quoted as THD+noise. Usually measured at specified frequencies and power levels

Velocity: speed of motion or rapidity. In audio and electronics, we are concerned with the speed of a signal in air and a conductor. Speed (velocity) of sound in air is approximately 345 metres per second at sea level, but it varies with temperature and humidity. Speed of an electrical signal in a wire is approximately 3 x 108 metres per second, but may be influenced by ...

Velocity Factor: a situation that occurs in conductors that are close to another conducting material. For example, a coaxial cable has an inner and outer conductor, with insulation between the two. The velocity factor of such cables varies from 0.7 to 0.9 (i.e. the signal travels slower than in free space)

Volt: The basic unit of "electromotive force". One Volt applied to a resistance of one Ohm will force a current of one Ampere to flow (Abbreviation - V)

Watt: The basic unit of power. 1 Volt across 1 Ohm (giving 1 Amp) dissipates 1 Watt (all as heat with a resistive load)

Wavelength: the length of one cycle of an AC signal. Determined by Wavelength = c / f where "c" is velocity and "f" is frequency. The wavelength of a 345Hz audio signal in air is one metre

Xenon: A gas commonly used in flash tubes, HID (High Intensity Discharge) automotive headlamps, and having an intense white light output with a colour temperature close to that of daylight