This circuit is intended to indicate the power output level of any audio amplifier. It is simple, portable, and displays three power levels that can be set to any desired value. IC1A is the input buffer, feeding 3 voltage comparators and LEDs drivers by means of a variable dc voltage obtained by R5 and C4 smoothing action. The simplest way to connect this circuit to the amplifier output is to use a twisted pair cable terminated with two insulated crocodile clips.
Setup is best accomplished with an oscilloscope or an audio millivoltmeter like the one described in these pages. Precision Audio Millivoltmeter
A 1KHz sine wave generator with variable output is also required (see a suitable circuit in this website als