A simple and low cost audio level meter circuit that can be used to measure the audio level of your sound source.This circuit is a valuable tool for those who are interested in audio circuits.
The circuit is designed with a flat frequency response in the range of 20Hz to 50Khz. Input sensitivity is 100mV for a FSD on a 100uA ammeter.The circuit is build based on on two common emitter amplifiers, the first stage has a preset resistor R3 (1K) which may be adjusted for a FSD. The last stage is biased to operate at about 1/2 the supply voltage for maximum AC voltage deflection. C2&C2 (10 uF) acts as a filters through which audio frequencies are passed . The full wave bridge rectifier converts
the signal to a varying dc voltage. The meter will show this voltage as the output reading which is proportional to the input voltage level.
Read more: http://www.circuitstoday.com/audio-level-meter-circuit#ixzz1DH8Cjzp3
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