This series is made to indicate that the amplifier has been given the maximum signal, the amplifier has the ability to be at its peak. if the lights do not mean the signal-plus volume. the way it works is the LED lights will light up when given a signal that more than 1.8 volts, the average amplifier will be saturated (maximum) if the signal was given more than this.
The circuit is very simple to the point that we forget that making a series of peak signal can in this way. circuit is mounted on the output tone control IC, master mixer output, or input power amplifier. This series does not impose on other circuits. survived the experiment!