When using an amplifier at vir­tually its full output power there is a risk of “clipping” occurring. The amplifier is overdriven to the point where output peaks are flattened because the amplifier simply can­not provide a high enough output voltage. The distortion caused by clipping is often quite severe and readily apparent, but this is not .always the case. It is not uncom­mon for the tweeters in loud­speakers to burn out due to overloading caused by clipping producing strong high frequency signals!

Circuit in lines (Click to enlarge)

The circuit relies on the fact that with less than about 2V applied to a LED it will not pass any significant current and will fail to light up. If the voltage applied to the LED is only marginally increased above 2V, the LED avalanches, a heavy current flows and it glows brightly.

R1 is adjusted so that the voltage applied to LED1 via cur­rent limiting resistor R2 is just suf­ficient to cause D1 to glow quite brightly when the amplifier is dri­ven into clipping.

With the ampli­fier driven just below the clipping threshold there is just enough voltage applied to the circuit to cause LED1 to visibly glow, al­though it does so at less than full brightness.

If the amplifier is dri­ven significantly below the clip­ping level there will be insufficient voltage fed to D1 to cause it to conduct and it will not light up.

Regards

Team Coreelectronics