The level at which the limiter kicks in audio can be adjusted with the selector knob LIMIT LEVEL. When this level is exceeded, the output of the half-LIMITING detector of the op-amp (used as a comparator) turns the LED causes the resistance of the photoresistor to decline rapidly. It is in tum causes the gain of Ie half LIMITED op-amp to decrease.
When the signal falls below the desired limit, the light goes out, the resistance of the photocell increases and the gain of the op-amp back to its normal level LIMITED one set by the combination of resistors RI and R2 . A dual polarity power supply (Â± 12 volts is desirable) is required for the op-amp.