Audio Amplifier Switch Timing to Prevent Speaker Pop Noise
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Solution Overview
Problem
Conventional electronic devices with audio amplifiers experience pop noise when the power supply is turned on/off, causing discomfort due to instantaneous changes in voltage levels, which result in noise being outputted through connected speakers.
Innovation Solution
A circuit comprising a switch, power supply, controller, and signal delay circuit is used to delay the changes in the operating states of the switch and power supply, preventing pop noise by ensuring the switch is in an open state when the power is on/off, using RC and propagation delay circuits with transistors and diodes to manage control signals and power transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the power supply is turned on/off instantaneously, then the power supply efficiency is improved, but pop noise is generated in the audio amplifier
Solution Approach 1:
The switch is activated in advance before the power supply is turned on, or deactivated in advance before the power supply is turned off. This preliminary action ensures that the audio amplifier output is disconnected from the speaker before voltage changes occur, preventing pop noise while maintaining efficient power supply switching
Solution Approach 2:
A switch is introduced as an intermediary component between the audio amplifier and the speaker. This switch acts as a mediator that can isolate the speaker from the amplifier output during power transitions, thereby preventing the transmission of pop noise while allowing normal audio signal transmission during operation
2Device complexity
If the switch and power supply states change simultaneously, then the device complexity is reduced, but the control precision is insufficient to prevent pop noise
Solution Approach 1:
The controller is designed to output control signals that activate or deactivate the switch at different times relative to the power supply state changes. This time-differentiated control ensures precise timing coordination without requiring complex control circuits, as it uses simple sequential signal generation
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The circuit effectively prevents pop noise from being outputted through speakers by ensuring the switch is in an open state during power transitions, thus eliminating the discomfort caused by instantaneous voltage changes in audio amplifiers.
Implementation Method 1
the signal delay circuit may comprise a RC delay circuit delaying the change of the operating state of the power supply
Implementation Method 2
a propagation delay circuit delaying the change of the switch into the closed state in accordance with the output of the first control signal
Data Source
AI summary
Disclosed is a circuit for preventing an output of a pop noise, which occurs from an audio amplifier when a power switch of an electronic device loading the amplifier is turned on/off. The circuit may comprises an analog switch for switching an electrical connection between an audio amplifier and a speaker, and a signal delay circuit capable of respectively delaying times that the operating states of the analog switch and the power supply are changed when the power switch is turned on/off, and it is structured such that the analog switch is already opened state at the time that the power supply is on/off. Accordingly, it is possible to prevent the pop noise from being outputted through a speaker connected to the amplifier. The circuit of the invention can be applied to a variety of electronic devices having an audio amplifier.