This circuit shows the clipping of an output signal coming out of a preamp or a final amplifier through a short lighting of a LED.
The supply voltage of the circuit is not critical - it can be either symmetrical or unsymmetrical. This circuit is normally connected as
part of the amplifier circuit and uses, therefore, the existing supply lines of the amplifier. The monitored output signal is sampled at
the point before the electrolytic output coupling capacitor as shown in the diagram 4.1. The LED lights up at clipping levels in both
positive and negative swings of the signal.
The transistor T1 must be selected according to the supply voltage level. If the supply voltage is lower than 40 Volts, use one of the
ff: transistor types: 2SA970, 2SA1136, 2SA1137. If the supply voltage is between 40 and 65 Volts, use either 2SC1285 or 2SC1285A.
Select the value of R4 to let a current of around 12 mA flow through it.
It is also important to maintain a constant threshold level for the monoflop.
To do this, select the the value of resistor R9 so that the current flowing through the zener diode D4 is between 20...24 mA
The calibration of the circuit can be done quickly and accurately by using an oscilloscope. To calibrate: First, connect the oscilloscope at the junction of resistors R1 and R2. Then, inject a positive signal strong enough to cause clipping of the positive peak and adjust P2 until the LED lights up. Conversely, inject a negative signal and adjust P1 until the LED lights up.
Printed Circuit Layout
Parts Placement Layout
Electronic Circuits volume 1.0 - Circuit Nr. 4
The complete data of the electronic circuit described above can be found in the following book and is available from Amazon.com.
Click on the image to view the book.