Clipping is a condition where a signal is truncated by insufficient processing. The cause of clipping can be different for various case, but most of them, especially in power amplifier stage, is because the amplifier is forced to serve out-range of power when the input volume is too high. Detecting severely clipped signal is easy by listening, but a soft clipping might be hard to detect. The problem is that some people might notice and some might not. Because our perception of slightly clipped signal might be inconsistent depending on our mood and our mental focus, providing a clipping indication will be very useful for those who responsible in sound performance. This circuit will give visual indicator, the led will light, when the output reach 50Watt level (can be adjusted with R2 pot). Here is the schematic diagram of the circuit.
To hold the display (for better visibility), C1 is provided make a short overload peak light the led for longer periods. The amplifier output stage is illustrated as a pair of PNP-NPN transistors, but you can use this circuit for integrated circuit (IC) based power amp. For IC based power amplifier, connect this circuit before the DC decoupling capacitor if any.