Audio levels can be monitored using a small panel meter with this circuit built from discrete components.
Notes
The circuit has a flat frequency response from about 20Hz to well over
50Khz. Input sensitivity is 100mV for a full scale deflection on a 100uA
meter.
Built on two common emitter amplifiers, the first stage has a preset
resistor which may be adjusted for a FSD. The last stage is biased to
operate at roughly half the supply voltage for maximum ac voltage
swing. Audio frequencies are passed through the 10u dc blocking
capacitor and
the full wave bridge rectifier converts the signal to a varying dc
voltage. Note that the meter reading is instantaneous and will not
provide
a "peak" reading.
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