Audio Clipping Indicator

Detects clipping in preamp stages, mixers, amplifiers etc.

Single LED display - 9V Battery supply unit

Circuit diagram:

Audio Clipping Indicator


R1_______________1M  1/4W Resistor (See Notes)
R2,R3,R8_______100K  1/4W Resistors
R4,R6___________10K  1/4W Resistors
R5_______________5K  1/2W Trimmer Cermet or Carbon
R7_______________2K2 1/4W Resistor
R9______________22K  1/4W Resistor
R10______________1K  1/4W Resistor (See Notes)

C1,C4__________220nF  63V Polyester Capacitors
C2_______________4p7  63V Ceramic Capacitor (See Notes)
C3_____________220µF  25V Electrolytic Capacitor
C5______________10µF  25V Electrolytic Capacitor (See Notes)

D1,D2________1N4148   75V 150mA Diodes
D3______________LED  (Any dimension, shape and color)

Q1____________BC547   45V 100mA NPN Transistor

IC1___________TL062  Dual Low current BIFET Op-Amp (or TL072, TL082)

SW1____________SPST  Toggle or Slide Switch (See Text)

B1_______________9V  PP3 Battery (See Text)


This circuit was intended to be used as a separate, portable unit, to signal by means of a LED when the output wave form of a particular audio stage is "clipping" i.e. is reaching the onset of its maximum permitted peak-to-peak voltage value before an overload is occurring. This will help the operator in preventing severe, audible distortion to be generated through the audio equipment chain.
This unit is particularly useful in signaling overload of the input stages in mixers, PA or musical instruments amplification chains, but is also suited to power amplifiers.
A careful setting of Trimmer R5 will allow triggering of the LED with a wide range of peak-to-peak input voltages, in order to suit different requirements. Unfortunately, an oscilloscope and a sine wave frequency generator are required to accurately setup this circuit.
Obviously, the unit can be embedded into an existing mixer, preamp or power amplifier, and powered by the internal supply rails in the 9 - 30V range. The power supply can also be obtained from higher voltage rails provided suitable R/C cells are inserted. SW1 and B1 must obviously be omitted.

Circuit operation:

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