Audio Signal Clipping Indicator

A window comparator formed by two op-amps packaged into IC1 is the heart of the circuit below. With this technique, we can detect precisely and symmetrically either the positive or negative peak value reached by the monitored signal. The op-amps outputs are smoothed by C4, R7, and R8, mixed by D1 and D2, and feed the LED driver Q1 with positive pulse. A small output delay is added by C5 to allow detection of very short peaks.

The circuit can be easily set up to detect sine wave clipping from less than 1V to 30V peak-to-peak (i.e. 15W into 8 Ohms) using the value shown. R1 must be raised if you need to detect higher output peak to peak voltages. On the contrary, it’s convenient to lower R1 value to, say, 220K omitting C2, if the circuit will be used to detect only very low peak to peak voltages. In this way, it will be easier to adjust R5. Using a TL062 chip at 9V supply, stand-by current drawing is about 1.5mA and less than 10mA when the LED illuminates. Current drawing is about 4.5mA and 13mA respectively with TL072 or TL082 chips. The value of R10 must be raised accordingly when using power supplies higher than12V. The working voltage value of C5 must be raised to 35 or 50V when using power supplies higher than 25V. [Circuit’s diagram source:]