A power amplifier cannot deliver an output wave wider than its power supply voltage. When you reach the limit, increasing gain may sound louder but sound will be distorted and can even damage speakers .This simple clipping indicator circuit will announce with an LED that you have reached that limit.
Step 1: Circuit Diagram & Main Components
Q1 BC547NPN transistor
Q2 BC557PNP transistor
note: If your amp V+ voltage is higher than 45v use BC546/BC556(up to 65v) or other higher voltage ones.
also increase R4 for a led current of 30mA. ( R=v/a )
Step 2: Q1: Emitter Follower
Step 3: Q2: Led Driver
Step 4: C1: Peak Hold
For longer "peak hold" time increase R3 up to 100K