The actual output of the amplifier can be measured using this audio power meter. This circuit schematic can be put in a box as a measurement instrument or integrate it inside the power amplifier to get real power display.


audio power meter circuit diagram

For an audio engineer, this circuit seems to be very helpful, especially for checking of sound system installation and field testing. Due to its logarithmic scale, the wide range of audio output with only ten scales can also be measured. If you take an attention to the pin number 5 of the LM3915, you will see that the input is not yet rectified. At this input pin, the negative swing will present. However, it is harmless since the current is limited by R1, therefore the LM3915 will respond only to positive cycle.

Peak detector is not available in this circuit. The absence of it is going to give the circuit a fast reading of instantenous power. This will gives us insight of both peak and average condition. [source : national semiconductor application notes]

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