Audio power amplifier

An audio amplifier is a broadband and low-distortion amplifier as possible for alternating voltages in the audible low frequency range of 20 Hz to 20,000 Hz or higher. Audio Amplifier include an electronic circuit, small audio signals like a pickup, tuner or CD player amplified in order to play them with higher power with the most infinitely adjustable volume control on a speaker can.

• 4.1 single-ended amplifier
• 4.2 push-pull amplifier

• 5.1 Transistor Amplifier 5.1.1 Integrated Circuits
• 5.1.2 Hybrid Circuits

Basics

Audio Amplifier power amplifier are. They are part of an electrical transmission chain, at the beginning and end of a converted sound event is. The signal sources usually provide relatively small voltages with large internal resistance, while the speakers present a very low impedance load. Therefore, audio amplifiers amplify the input voltage first before any frequency response corrections (eg tone controls ) are made and the volume is adjusted. In the subsequent power amplification of the current is mainly reinforced to drive the low impedance of the load ( speaker) can.

An audio - amplifier can be considered as electric quadrupole whose output voltage Vout is greater than the control voltage at the input Vin. An operating voltage source ( AC or battery ), the energy available.

Usually there is a linear relationship between the output and input voltage (level and current value ). Wherein the voltage gain v, the relationship between input and output voltage is expressed as a factor.

Usually, however, the gain is expressed as a gain level. So with the unit Bel. Since the values ​​in Bel be too small, the gain level is multiplied by "10". ( DB )

Derived from:

Breakdown by function

Audio amplifier can be distinguished according to their function in an electro- acoustic transmission chain:

• Preamplifier prepare a very small input signal so that its further processing or propagation is facilitated or made ​​possible due to a higher voltage level and / or a lower output impedance.

• Distortion / equalizer amplifier with targeted are deviations from the linear frequency response (eg, Emphasis, so pre-emphasis and de-emphasis, RIAA equalizer ) or linearity ( distortion ). In the field of musical instruments can also be an effect unit desirably produce nonlinear distortion.

• Mixers consist of a number of preamplifiers with adjustable gain and adjustable frequency response for multiple audio signals whose output signals are combined additively. The sum signal can also be affected in its level, and is used for example for supplying a power amplifier or a recording apparatus.

• Repeaters increase by a lowered conduction level or are used to adjust the level or impedance between various elements of the transmission chain.

• Control amplifiers contain control elements, which can be adjusted so the level, frequency response, the stereo balance or regulate. Mostly these are funktioniell identical to the preamplifier.

• Cutting amplifier, recording amplifier, modulation amplifier and the like. are the intermediate end member of a transmission chain before recording or transmission. Depending on the requirements they have properties of amplifiers (eg modulation amplifier for anode modulation in the medium-wave transmitters).

• Power amplifier or amplifiers are amplifiers, which often require a relatively high input level for modulation and in turn have little or no control members. Provide you with the lowest possible output impedance of the voltage for speakers, cutting equipment (for the record recording ) or the modulation path ready ( for transmitter).

Mixed forms are, for example, the mixing amplifier and the amplifier.

Breakdown by application areas

Home Electronics

The aim is the reproduction of the transmitted or stored audio signals. The focus is on economic production, design, and often the highest freedom from distortion. Audio amplifier for home use have a few settings, for example, source selection, volume, balance, frequency response.

Studio equipment

In recording studios are reliability, durability, general robustness, insensitivity to electrical and magnetic interference, low noise, low distortion, a large transmission bandwidth and signal fidelity in the foreground. Furthermore, much more extensive control options are common towards the home electronics.

Modulation amplifier

For transmitting audio signals as electromagnetic wave high-frequency transmitter is used which has to be modulated signal to be transmitted. For this modulation amplifiers are used, which amplify the voltage of the audio signal so that they can influence the high frequency level of the transmitter clock signal in the case of amplitude modulation. Often, this modulation is performed at the end of the high- frequency signal, so that substantial achievements can be required. Modulation amplifiers are reliable, distortion, protected against electrical interference and have a defined bandwidth.

Amplifier for musicians and stage

In musicians audio amplifier are used to amplify the sound of the musical instruments. They often have characteristic features (such as guitar amps, partly as a tube amp ) or are part of a feedback loop that alters the original sound of the instrument specifically. Such amplifiers are often connected instead of a microphone to a pickup.

Monitor amplifiers are often integrated in monitor speakers ( powered speakers ). Musicians need such speakers during performances to listen to yourself. Partial monitor amplifier are integrated into consoles - they have a lower performance than the actual amplifier.

Amplifier for big stages and nightclubs often convert electrical outputs in the kilowatt range (ca 1 .. 6 kW). There are transistor amplifier in push-pull or full-bridge circuit ( see amplifier (Electrical ) ). In order to reduce the voltage drop in the output transistors at high current (proportional to power dissipation), one has the so-called class G or H amplifier developed ( classic AB amplifier with flagging operating voltage or Längsvorregler in the operating voltage branches ) and thus an efficiency of up to 80 reached %. Also, class - D amplifier put in the PA area slowly, although a further improvement in efficiency is connected through the D- operation with disadvantages which are mainly in the emission, intermodulation distortion and switching losses in the driver stage.

Communication / PA

The transfer of human language requires only a limited transmission range (eg, 160 Hz to 5 kHz). This concerns for example the bundle and the cellular and wireline telephony. To feed a plurality of distributed speakers in electroacoustic systems (eg in an entire building), the output signals with high impedance (eg 600 ohms ) or high voltage is transmitted (eg 100 V) and transformed down at loudspeakers.

Breakdown of connection

Single-ended amplifier

This circuit has the longest history. It is used only one power supply, and only one active component in the output stage needs. Low to medium negative feedback factors are common, so a small or medium number of amplifier stages is necessary. Is there a need balanced inputs and outputs, they are balanced or entsymmetriert with special transformers. As a power amp only tube amps are known. Single-ended power amplifiers have a low efficiency.

Push-pull amplifier

This structure is characteristic of amplifier in semiconductor technology, but also push-pull tube amplifier it will be built. Different topologies using either

• An operating voltage to a balanced output transformer ( tube technology, early transistor amplifier ) or an output coupling capacitor (modern transistor amplifiers)
• Account for two operating voltage sources of opposite polarity (only for transistor amplifiers possible) Here, the output coupling capacitor.

In modern transistor stages numerous amplifier stages are used, which are usually constructed as a differential amplifier and direct ( galvanic) are coupled. The high open loop gain allows a strong, stabilizing and linearizing feedback. Unbalanced and balanced inputs and outputs can be realized with galvanic coupling, so that a lower cut-off frequency of 0 Hz is possible (see push-pull output stage). Push-pull amplifier having a higher efficiency than single-ended amplifier.

Other types

• Class - D amplifier
• Bridge amplifier

Breakdown by active devices

It used transistors or electron tubes. Transistor amplifiers are often implemented as a monolithic integrated circuit or as a module in thick-film technology.

Transistor amplifier

Transistor amplifiers have to be able to use due to their low price, their small size, their integration, the possibility of two different polarities of transistors ( npn, pnp, n- channel, p- channel), operating with relatively low operating voltages and the elimination consuming auxiliary voltage sources a wide range of applications obtained. There are bipolar transistors and field effect transistors are used. Often both types of transistors are combined.

Integrated Circuits

Specially designed for audio applications designed monolithic integrated circuits found in particular in power amplifiers from a few watts to about 100 watts of output power. At higher powers, they are mounted on a copper cooling flange. They can be used over discrete power amplifiers, high stability of the operating point and a drastic reduction of the component expenses reach. The power IC often contain protection circuits against overheating and short circuit. They are often made ​​with two channels in order to use it as a stereo amplifier or bridge amplifier can. For small voltage amplifier ( pre-amplifier, earphone amplifier ) there are low-noise operational amplifier.

Hybrid circuits

Hybrid amplifiers comprise a plurality of transistor chips, and passive components on a ceramic substrate, which serves to dissipate the waste heat to a cooling surface.

Tube amplifier

→ Main article: tube amplifier

Due to various disadvantages electron tubes have been mostly replaced in audio amplifiers today by semiconductors. They still have some importance in guitar amplifiers and high fidelity amplifiers of the high-end class.

Because of the specific advantages and disadvantages of semiconductor and tube amp there are combinations of so-called hybrids. We used, for example low-overhead tube preamps with comparatively low operating voltage and combines them with semiconductor amplifiers.