Audio signal Indicator

Posted on Aug 27, 2012

This circuit can be used to remotely monitor a loudspeaker, alarm, or audio source for presence of an audio waveform. It can also be directly connected across loudspeaker terminals used as a peak indicator. If you need to monitor some audio signal at a location that is either soundproof are too far away to actually hear the signal then you can use a circuit similar to this one. A remote indication that the audio source is active is provided visually, here in the form of a LED. Referring to the above circuit, the 10k preset is a level control which should be adjusted so that when the source ( audio signal or alarm ) is producing the desired amount of noise, the LED lights.

Audio signal Indicator
Click here to download the full size of the above Circuit.

The input stage is an inverting x100 amplifier made with a 741 op-amp. The output of the 741 is capacitively coupled into a 10k load resistor, thus removing any dc component from the signal and the offset null voltage of the op-amp. As only the amplified

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