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  • Automatic Volume Control Circuit

  • Created: May 26, 2016

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Summary

In acoustics, volume refers to amplitude, sound pressure and dynamics. This circuit controls a volume line automatically. It delivers an output voltage of approximately 4Vpp. This voltage remains relatively constant by input voltages ranging from several hundred millivolts to several volts. This electronic circuit is not highly recommended for Hi-Fi applications because its noise factor is way above the accepted level. However, it is very useful in tape recording of computer programs. The constant amplitude is desirable in such application.

The MCP6002 is a dual general-purpose op amp offering rail-to-rail input and output over the 1.8 to 6V operating range supply voltage. This amplifier has a typical Gain Bandwidth Product (GBWP) of 1 MHz with typical quiescent current of 100uA. The MCP6002 is available in 8-lead PDIP, SOIC and MSOP packages. It works as an input signal buffer and its DC bias is done over R4 and C5. This allows the op-amp B to limit the DC level at its input to a maximum amplification of 100 times. The offset bias is relatively constant. The amplified signal is fed to the regulator diodes D1 and D2 over the transistor Q1 and Q2 while the trimmer RP1 controls this sample signal. The higher this signal is, the higher is the current flowing through the diodes. These regulator diodes have a non-linear curve where resistance decreases with increasing current. The input signal gets grounded more or less through the diodes. The diodes work as an attenuator with increasing effect by increasing the current through the diodes.


The automatic volume control (AVC) adjusts the volume or loudness of an audio signal. It primarily enhances intelligibility of speech to create an audible sound that suits the taste of the user. The AVC has potential applications in any audio devices such as in handheld audio devices, headsets, personal media players, car radios and sound systems.

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