What is An Amplifier?
Amplifiers, often referred to as amps, are the reason your speakers deliver much louder sound compared to phones and computers. Their primary role is to elevate the power of an audio signal.
Upon the use of an amplifier, it elevates the smaller input signal, like the headphone jack on your phone, producing a much stronger output signal. This uses electrical energy from a power source to amplify either the voltage or current of the input signal, leading to a much greater level of output.
The disparity between the amplified output signal and the initial input signal is termed gain. Gain measures the extent to which an amplifier enhances the input signal.
It’s quantified as the ratio of the output voltage, current, or power to their corresponding inputs. For instance, if the input signal is 1 volt and the output is 30 volts, the amplifier’s gain is “30” volts, signifying a thirtyfold increase in the input signal.
Although amplifiers essentially function by strengthening weaker signals, their designs and applications vary among different types. A simple online search reveals an array of amplifiers, ranging from high-powered units used in concerts to minuscule, single transistors employed in hearing aids. However, the distinctions among these will be explored in another post.
Microphone Level And Preamplifiers
Microphone level signifies the voltage generated by a microphone upon capturing sound, usually transmitted as a signal to a mixing console. However, this voltage isn’t robust enough to be directly transformed into line level, which is necessary for audio production at the speaker level.
To elevate the microphone level signal to line level, a preamplifier is required. Embedded within the mixing console, the preamplifier augments the gain or magnitude of the microphone level signal, transforming it into a line level signal.
Line Level And Amplifiers
Line level denotes a particular amplitude or potency of an audio signal generated via mixers, signal-processing tools, and additional audio equipment. It’s potent enough to be manipulated but lacks the strength to drive a speaker directly.
This is the juncture where amplifiers step in. They’re employed to elevate the line level to speaker level, providing adequate power to generate a magnetic field capable of moving the magnet within a speaker driver.
The speaker driver, situated within the speaker, acts as a loudspeaker transducer, transforming electrical audio signals into the audible sound waves that constitute your music or audio experience.
Introduction to the Amplifier of Power Amplifiers
The Small Signal Amplifier, often termed a “Voltage” amplifier, specializes in transforming a small input voltage into a notably larger output voltage. In scenarios requiring the driving of a motor or powering a loudspeaker, Power Amplifiers come into play, particularly for applications necessitating high switching currents.
Contrary to Voltage amplifiers, Power Amplifiers—also known as large signal amplifiers—focus on delivering power to the load. As indicated earlier, power is the product of voltage and current applied to the load, resulting in the output signal power surpassing the input signal power. This amplification of power makes these amplifier circuits ideal for driving loudspeakers in audio amplifier output stages.
The fundamental principle of the power amplifier involves converting DC power derived from the power supply into an AC voltage signal directed to the load. Despite its significant amplification capability, this process often exhibits poor efficiency in converting DC input power to AC voltage signal output.
In an ideal scenario, an amplifier would operate with 100% efficiency or at least ensure that the input power equals the output power. However, reality diverges from this perfection due to power loss in the form of heat and the amplifier’s consumption of power during the amplification process. Achieving a state where all input power converts perfectly into output power remains an unattainable feat.
Electronic Amplifier Classes
Amplifiers are categorized as voltage or power amplifiers based on comparing input and output signal characteristics, particularly measuring the time during which current flows in the output circuit in relation to the input signal.
In the realm of transistor operations, we learned from the Common Emitter Transistor tutorial that enabling the transistor to function within its “Active Region” necessitates some form of “Base Biasing.” This additional Base Bias voltage, when added to the input signal, enables the transistor to faithfully reproduce the complete input waveform at its output, preserving the signal integrity.
By manipulating the positioning of this Base bias voltage, an amplifier can operate in modes other than full waveform reproduction. Introduction of a Base bias voltage introduces different operating ranges and modes, classified into Amplifier Classes. These classifications denote various modes of operation, organized alphabetically, such as class “A,” class “B,” class “C,” class “AB,” and so forth.
In audio power amplifiers, these classes are distinguished by circuit configurations and operation modes. Each class exhibits distinct characteristics, ranging from near-linear output with low efficiency to non-linear output with high efficiency.
The superiority of one class over another is subjective and dependent on the specific application of the amplifying circuit. Each class has typical maximum conversion efficiencies:
- Class A Amplifier: Exhibits low efficiency (below 40%) but excels in signal reproduction and linearity.
- Class B Amplifier: Twice as efficient as Class A, with a theoretical maximum efficiency of about 70% due to the amplifying device conducting power for only half of the input signal.
- Class AB Amplifier: Sits between Class A and Class B in terms of efficiency, compromising on signal reproduction compared to Class A.
- Class C Amplifier: Boasts the highest efficiency but suffers from severe distortion as it amplifies only a fraction of the input signal, resulting in poor signal reproduction.
