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In electrical engineering or audio, the nominal impedance of an input or output is the equivalent impedance of all of the output or input circuitry of a device lumped into one (imaginary) component. An impedance is a combination of resistance, capacitance, and inductance. It can be thought of as a resistor that changes values at different ( sine wave) frequencies.

(This article is intended to be a layman's introduction, and focuses on audio frequencies at which cable impedance is not significant. See impedance for a more technical discussion. See also impedance matching, cable impedance.)

1 Voltage divider

Explain voltage divider
Examples with resistors

2 Source and load impedance

Any electronic source device (electric guitar, microphone, amplifier output, battery, generator, turbine, etc.) can be simplified to two imaginary electronics components, to simplify analysis. This simplified model is only valid under certain conditions, but it is valid nonetheless. These two components are a source and a source impedance. These are usually connected to a load (loudspeaker, amplifier input, motor, space heater, etc.) which can be simplified to only one component, the load impedance. This diagram shows the three components:

These three components form a voltage divider, one of the basic electric circuit configurations. The voltage across the load will be proportional to the ratio of the two impedances.

For instance, an electric guitar can be modeled as a voltage source (V_source) in series with a general impedance (Z_source). The impedance will probably be mostly resistive and inductive, because the pickups of the guitar are a coil, which is an inductor. There may be some capacitive impedance from tone controls or the like that will cancel out some of the inductance. All of these properties are lumped together into one value. The value of this impedance and of the voltage source depend on the properties of the coil, tone circuitry, the position of the knobs, etc.

Most signal-processing equipment is designed to operate with the internal impedance of a signal source much smaller than the load impedance of the input to which it is connected. This provides the most efficient voltage coupling, and is best in most, but not all, situations. The nominal impedance is the assumed impedance for the purpose of deciding whether two pieces of equipment are compatible for connection, and is normally, but not always, similar to the actual impedance.

If impedance is mismatched between inputs and outputs that are connected together:

Power is wasted or signal level is reduced.
Frequency response is no longer as linear.
DistortionIn telecommunication and signal processing, the term distortion has the following meanings: #In a system or device, any departure of the output signal waveform from that which should result from the input signal waveform's being operated on by the system' may result.
Damage to both units is a distinct possibility.

3 Signal level impedance

Three common nominal impedances for low-level signals are:

High impedance.
Low impedance.
Line impedance.

3.1 High impedance

Guitar amplifiers normally have a nominal input impedance of about 50K ohms, both to suit the original guitar pickupThis article is about pickups for musical instruments. For a small truck used by both business and consumers, see pickup truck. For a scene which is filmed after the main production of a film has finished and which will be edited into the rest (commonly cs and because this was a convenient impedance for circuits based on valves such as the 12AX712AX7 is a miniature dual triode vacuum tube of high gain. It was believed to be originally developed in 1946 by RCA engineers in Harrison, New Jersey under developmental number A-4522. Release date for public sale under the 12AX7 identifier was September. The actual impedance of the output of a guitar with magnetic pickups and no inbuilt preamplifierA preamplifier is an electronic amplifier designed to prepare an electrical signal for further amplification. Preamplifiers may be: in a separate housing. incorporated into the housing or chasis of the amplifier they feed. mounted in other items of equipm is typically about 250K ohms.

The first solid-state amplifiers had relatively low actual input impedance, which was one possible cause of the disappointment some guitarists expressed with their tone. Since the invention of the FET, solid state amplifiers have had actual input impedances up to about 500K ohms.

Higher impedance means a relatively small current flows but a relatively large voltage is present. It creates greater noise problems, and this factor and the eventual loss of high frequencies limit the length of the cables that can be used.

The most common high impedance input connector is the 6.5mm (quarter inch) jack plug, which is also used for many other purposes.

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Topics: Nominal Impedance Input Output Ohms Common Voltage Low High...

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