This post is intended to be a place for people to learn a little bit about the mumbojumbo that some of the more knowledgeable around here constantly seem to argue about. Please try to keep your comments of the question/answer type... there are a hundred other threads already in which you can argue about what you like or don't like, or the merits of different types of amps.
I came across this article today while at work and thought that it would be a good primer for folks who know a little bit about electronics but don't know much about amplifier topology (myself included). The following is quoted from the article, and the link to it is included at the end of the quote.
"The development of analog power amplifiers has been focused on improving fidelity while at the same time improving amplifier efficiency. Amplifiers are classified by the letters A, B, AB, or C based upon their operating or bias point, and the percentage of the input signal cycle over which they conduct.
This article will explain the difference between the various types of audio amplifiers, detail the theory of operation of Class D amplifiers, and show how they increase efficiency and reduce power requirements and size.
Audio circuits [...] demand the vital characteristics of low power, small size, and low heat dissipation. However, audio amplifiers are often inefficient heat generators that require bulky heatsinks. To reduce size and power requirements, Class D, or digital amplifiers, offer a good solution.
What the switched mode power supply brought to power sources, the Class D amplifier brings to audio playback. With Class D amplifiers, audio inputs are encoded as pulse width modulated (PWM) signals that drive the power devices between on and off levels, with power only being dissipated during the transitions.
These “digital” amplifiers greatly increase the efficiency of audio amps, resulting in lower heat dissipation and smaller physical size. Also, recent developments have changed the modulation schemes so that low-pass filters are no longer required at the outputs, further reducing size and complexity."
(Class D Amplifiers Offer Significant Advantages | DigiKey)
This article speaks about PWM & Duty Cycles:
Pulse Width Modulation (PWM) uses digital signals to control power applications, as well as being fairly easy to convert back to analog with a minimum of hardware. Uses for PWM vary widely. It is the heart of Class D audio amplifiers, by increasing the voltages you increase the maximum output, and by selecting a frequency beyond human hearing (typically 44Khz) PWM can be used. The speakers do not respond to the high frequency but duplicate the low frequency, which is the audio signal. Higher sampling rates can be used for even better fidelity, and 100Khz or much higher is not unheard of.
(Pulse Width Modulation | DC Motor Drives | Electronics Textbook)
Glossary:
Duty Cycle is the ratio of time a load or circuit is ON compared to the time the load or circuit is OFF. It is expressed as a percentage of ON time. A 60% duty cycle is a signal that is ON 60% of the time and OFF the other 40%.
Pulse Width is a measure of the actual ON time, measured in milliseconds. The OFF time does not affect signal pulse width. The only value being measured is how long the signal is ON (ground-controlled).
Bi-Polar Power Supply: A bipolar supply is a power supply with 2 rails - one positive with respect to ground, and one negative with respect to ground. A bipolar supply also must have 3 terminals for audio use.
Voltage Rails: A PSU (Power Supply Unit) supplies voltage to the system. These voltages are often called rails, referring to the fact that although there are multiple wires carrying a specific voltage, they are normally tied to a single rail (or tap) in the PSU. You can think of each rail as a separate power circuit, kind of like a power supply within the power supply. (Voltage Rails - Power Supply 101: A Reference Of Specifications)
I came across this article today while at work and thought that it would be a good primer for folks who know a little bit about electronics but don't know much about amplifier topology (myself included). The following is quoted from the article, and the link to it is included at the end of the quote.
"The development of analog power amplifiers has been focused on improving fidelity while at the same time improving amplifier efficiency. Amplifiers are classified by the letters A, B, AB, or C based upon their operating or bias point, and the percentage of the input signal cycle over which they conduct.
This article will explain the difference between the various types of audio amplifiers, detail the theory of operation of Class D amplifiers, and show how they increase efficiency and reduce power requirements and size.
Audio circuits [...] demand the vital characteristics of low power, small size, and low heat dissipation. However, audio amplifiers are often inefficient heat generators that require bulky heatsinks. To reduce size and power requirements, Class D, or digital amplifiers, offer a good solution.
What the switched mode power supply brought to power sources, the Class D amplifier brings to audio playback. With Class D amplifiers, audio inputs are encoded as pulse width modulated (PWM) signals that drive the power devices between on and off levels, with power only being dissipated during the transitions.
These “digital” amplifiers greatly increase the efficiency of audio amps, resulting in lower heat dissipation and smaller physical size. Also, recent developments have changed the modulation schemes so that low-pass filters are no longer required at the outputs, further reducing size and complexity."
(Class D Amplifiers Offer Significant Advantages | DigiKey)
This article speaks about PWM & Duty Cycles:
Pulse Width Modulation (PWM) uses digital signals to control power applications, as well as being fairly easy to convert back to analog with a minimum of hardware. Uses for PWM vary widely. It is the heart of Class D audio amplifiers, by increasing the voltages you increase the maximum output, and by selecting a frequency beyond human hearing (typically 44Khz) PWM can be used. The speakers do not respond to the high frequency but duplicate the low frequency, which is the audio signal. Higher sampling rates can be used for even better fidelity, and 100Khz or much higher is not unheard of.
(Pulse Width Modulation | DC Motor Drives | Electronics Textbook)
Glossary:
Duty Cycle is the ratio of time a load or circuit is ON compared to the time the load or circuit is OFF. It is expressed as a percentage of ON time. A 60% duty cycle is a signal that is ON 60% of the time and OFF the other 40%.
Pulse Width is a measure of the actual ON time, measured in milliseconds. The OFF time does not affect signal pulse width. The only value being measured is how long the signal is ON (ground-controlled).
Bi-Polar Power Supply: A bipolar supply is a power supply with 2 rails - one positive with respect to ground, and one negative with respect to ground. A bipolar supply also must have 3 terminals for audio use.
Voltage Rails: A PSU (Power Supply Unit) supplies voltage to the system. These voltages are often called rails, referring to the fact that although there are multiple wires carrying a specific voltage, they are normally tied to a single rail (or tap) in the PSU. You can think of each rail as a separate power circuit, kind of like a power supply within the power supply. (Voltage Rails - Power Supply 101: A Reference Of Specifications)
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