Just as the name implies, an amplifier speaker turn-on delay circuit is a circuit added to the amplifier that adds a brief delay before the speakers are connected to the amplifier output.
When the amplifier is initially turned on, there may be an unwelcome loud ‘thump’ sound from the speakers, this delay helps avoid this unwanted sound.
Circuit Working:
Parts List:
| Component Type | Description | Quantity | Notes |
|---|---|---|---|
| Resistors | All 1/4 watt unless specified | ||
| 33k | 2 | ||
| 1k | 1 | ||
| Capacitors | |||
| Electrolytic | 100μF 25V | 2 | |
| Semiconductors | |||
| Transistor | BC547 | 1 | |
| Diode | 1N4007 | 2 | |
| LEDs | |||
| Any 5mm 20mA | 1 | ||
| Miscellaneous | |||
| Relay | 12V DPDT | 1 | |
| Speakers | 8Ω | 2 |
Let us start with a switch, a unique switch known as a ’12V DC DPDT relay’ will be utilized to regulate the connection between the amplifiers output and the speakers.
This relay functions similarly to a conventional switch except electricity is used to turn it on and off rather than a human flip.
Because 12V relays are so widely available we decided to utilize one.
Relay coil resistance varies with coil size, ours is around 180 ohms.
This indicates that in order to turn it on, we just need a little current roughly 0.067 amps.
We will utilize a 12V power source that can generate at least 300 milliamperes to supply this current.
An additional electronic component known as a ‘transistor’ is required in order to operate the relay.
An BC547 NPN transistor is what we are employing in this instance.
It has enough power to provide the relay coils required current.
Our circuit diagram above is a basic illustration that illustrates how these components are linked.
The transistor is wired in what is known as a ‘common emitter’ arrangement.
It can function with incredibly faint control signals because to its architecture.
The use of a diode across the relay coil is a crucial safety precaution.
By doing this, the transistor is shielded from a voltage spike that results from the relay turning off.
In order to demonstrate if the relay and transistor are operating properly, we have also included an LED light that has a resistance.
A capacitor and an additional diode improve the circuits efficiency and guard against unintentionally connecting the power supply backward.
You can utilize two single contact relays linked together if a DPDT relay is not available.
By doing this, the overall resistance will be reduced by half which will facilitate the transistors ability to switch them on.
The transistor may be worn out and unable to magnify the weak control signal if the circuit is not operating.
The problem could be resolved by replacing the transistor.
Try adjusting the values of various components if replacing the transistor is not a possibility.
Sometimes it helps to increase the size of the capacitor C1 and decrease the resistance R2.
Finally, you may use a larger capacitor C1 to alter the delay if the 3 second duration is not long enough.
Formulas:
The following formulas are used to create an amplifier speaker turn-on delay circuit using a transistor-based RC delay circuit:
The Delay Calculation Formula:
The RC circuits time constant (τ), which establishes the delay, is provided by:
τ = R × C
where,
- From resistor R1, the resistance is expressed in ohms as R.
- The capacitance in farads from the capacitor C is represented as C.
The estimated value of the delay time tdelay in seconds is:
tdelay = 1.1 × τ
where,
- You may rewrite the formula to get a desired delay time:
R = tdelay / 1.1 × C
In order to ensure correct sequencing in your audio system, this circuit offers a basic delay mechanism that controls the turn-on delay for an amplifier or speaker utilizing an RC network and a transistor switch.
Modify component values according to desired delay characteristics and particular requirements.
How to Build:
To build a Amplifier Speaker Turn-On Delay Circuit follow the below mentioned steps:
- Gather all the required components as mentioned in the diagram above.
- Connect collector of transistor Q1 to positive supply through resistor R3 and LED1, connect base of transistor Q1 to resistor R2, connect emitter of transistor Q1 to ground.
- Connect resistor R1 and capacitor C1 from positive supply to ground.
- Connect capacitor C2 from positive supply to ground.
- Connect the 12V relay coil terminals between collector of Q1 and positive supply.
- Connect poles of 12V relay to the left and right audio outputs of the power amplifier.
- Connect the corresponding NO contacts of the relay to the left and right speakers.
- Connect diode D1 to the coil terminals of the 12V relay.
- Connect a diode D2 to positive supply of +12V.
Safety Notes:
- Keep in mind that electronics can use dangerous currents and voltages.
- Prioritizing safety is crucial while designing or constructing circuits.
- See an electronics expert if you have any questions concerning any part of the circuit.
Conclusion:
To conclude, this amplifier speaker turn-on delay circuit protects your speakers by delaying speaker connection during amplifier starting and avoiding the irksome ‘thump’ sound.
Building using common components is simple but when working with electronics, safety precautions should always come first.