Output Relay Delay Audio Amplifier Diagram Circuit

This is a simple circuit which I built to one of my audio amplifier projects to control the speaker output relay. The purpose of this circuit is to control the relay which turns on the speaker output relay in the audio amplifier. The idea of the circuit is wait around 5 seconds ofter the power up until the speakers are switched to the amplifier output to avoid annoying "thump" sound from the speakers. Another feature of this circuit is that is disconnects the speaker immediately when the power in the amplifier is cut off, so avoiding sometimes nasty sounds when you turn the equipments off.

Circuit diagram:

Audio Amplifier Output Relay Delay Circuit Diagram

Component list
C1 = 100 uF 40V electrolytic
C2 = 100 uF 40V electrolytic
D1 = 1N4007
D2 = 1N4148
Q1 = BC547
R1 = 33 kohm 0.25W
R2 = 2.2 kohm 0.25W
RELAY 24V DC relay, coil resistance >300 ohm

Circuit operation:

Then power is applied to the power input of the circuit, the positive phase of AC voltage charges C1. Then C2 starts to charge slowly through R1. When the voltage in C2 rises, the emitter output voltage of Q1 rises together with voltage on C2. When the output voltage of Q2 is high enough (typically around 16..20V) the relay goes to on state and the relay witches connect the speakers to the amplifier output. It takes typically around 5 seconds after power up until the relay starts to conduct (at absolute time depends on the size of C2, relay voltage and circuit input voltage). When the power is switched off, C1 will loose its energy quite quickly. Also C2 will be charged quite quickly through R2. In less than 0.5 seconds the speakers are disconnected from the amplifier output.

Notes on the circuit:
This circuit is not the most accurate and elegant design, but it has worked nicely in my small home-built PA amplifier. This circuit can be also used in many other applications where a turn on delay of few seconds is needed. The delay time can be increased by using bigger C2 and decreased by using a smaller C2 value. Note that the delay is not very accurate because of simplicity of this circuit and large tolerance of typical electrolytic capacitors (can be -20%..+50% in some capacitors).

Author: Tomi Engdahl

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Wire Break Alarm With Delay Circuits Diagram

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 The circuit uses CD4060, which is a 14-stage ripple-carry binary counter/divider and oscillator. It is wired as a timer here and does not need input pulse for trigger. CD4060 gets activated as soon as the power supply is switched on. Output O13 of CD4060 goes high after the lapse of preset delay set through VR1. Transistor SL100 (T2) is wired as a switch to power the timer section built around CD4060. When the wire loop is closed, transistor T2 does not conduct. So power to the timer circuit is not available and the piezobuzzer does not sound. 

Wire-Break Alarm With Delay Circuit Schematic

On the other hand, when the wire loop is broken by some intruder, transistor T2 conducts to power the circuit and the piezobuzzer sounds after 15 to 30 seconds. IC1 can be reset by connecting the wire loop or interrupting the supply. The circuit works off regulated 9V-12V. Assemble it on a general-purpose PCB and enclose in a metallic or plastic box of appropriate size. Connect piezobuzzer PZ1 through external wires and complete the installation. Link

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