Timer Circuit for Amplifiers

Timer Circuit for Amplifiers

Timer Circuit for Amplifiers #2
Part List Circuit Project Description

The circuit was created for the purpose of providing timing capability to turn OFF the amplifier as it becomes idle a specified amount of time.

Terminology 7812 – 3-terminal 1A positive voltage regulator with short circuit protection, thermal overload protection, output transistor safe operating area protection, output current up to 1A, and output voltages from 5V to 24VLM358 – a dual operation amplifier consisting of two independent, high gain, internally frequency compensated op-amps which were designed specifically to operate from a single power supply over a wide range of voltages having advantages of eliminating the need for dual supplies, compatibility with all forms of logic, and power drain suitable for battery operation, and with features of low input offset voltage, large output voltage swing, and very low supply current drain4060 – a 14-bit ripple counter with internal oscillator that has glitches which may occur in any logic gate systems connected to its outputs due to the slight delay before the later counter outputs respond to a clock pulseBC557 – PNP general purpose transistors used for amplification and switching due to its low current and low voltage Circuit Explanation

Based on the values used in the circuit, it can cause an amplifier or any other device connected to this circuit to be turned OFF after a minimum of 15 minutes of non-occurrence of even a low level audio signal from its input. The device can be turned ON by pushing the SPST switch P1 to allow feeding on any equipment connected to the female mains socket SK1. The combination of IC2A and IC2B produces square audio input while amplifying and boosting the input signal. This process is being monitored by the yellow LED D4.

The ripple counter and oscillator IC3 restarts and resets its counting when LED D4 illuminates for a very short peak value. During this stage, the 10.5 V relay with SPST switch starts to operate while the two transistors Q1 & Q2 are turned ON. Simultaneously, the Pin 2 of IC3 will remain in the low state. When no signal emerges from the input after 15 minutes of idle time, the counting is ended by IC3 and the Pin 2 goes high.

During the turning OFF stage, the relay RL1 will also switch OFF and the transistors Q1 and Q2 will stop conducting. As the device completely turns OFF, it also brings the same effect to the equipments and appliances connected to SK1. The device can be powered ON by resetting the IC3 through capacitor C5 and resistor R9. The presence of SPST push button P2 allows the switching OFF of the circuit at any preferred time.

The left and right tape output of the amplifier will be connected to J1 and for picking up audio signals from both stereo channels is made possible by employing two RCA input sockets. Altering the values of R13 and/or C6 will change the delay time. A double pole relay switch can be used where the second pole switch is connected in series to the device supply, if there is a need to operate a device that is not supplied by the power mains.


This time circuit is mainly applied in amplifiers to conserve mechanical energy and power consumption especially when using batteries. This can also prevent the electronic components from heating up even during the idle time, which can prolong the life of the circuit and the appliance connected. 

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