TV Audio Delay Circuit using CD4066 & NE555 to Stop Pop Noise

This is a delay circuit for the TV’s audio output. The sound from the TV’s headphone output is too low, so we connect it to a power amplifier. However, when the system starts, a pop noise comes from the speakers. This circuit helps prevent that noise.

Here’s a simple circuit I built to explore bottom-up learning. It uses only basic components and is easy to put together on a breadboard. Great for beginners, homeschoolers, or anyone who enjoys DIY projects.

Circuit Features:

• Simple turn-on delay circuit
• Adjustable delay time: 0.1 to 11 seconds
• Runs on USB 5V power (draws less than 10 mA)
• No relay or moving parts — completely silent operation
• Built with common parts: CD4066, NE555, and a few passives
• Compact, low-cost, and easy to build on a breadboard

Inspiration & Real-World Use

I received an email from a friend with this message:

I connected the headphone output to a quite powerful Kenwood KA990 amplifier.  And now comes the problem: the headphone output is poorly designed and as soon as the tv starts, there’s a short very loud ‘plop’ sound coming through the speakers. This hasn’t been a problem with our previous TV, which was obviously of higher quality and didn’t simply switch on the headphone output instantly.

 Now I had this crazy idea! The TV also has USB ports, which don’t supply a voltage if the TV is in standby, so I thought about a RC Delay Circuit like the one you’ve outlined at: https://www.eleccircuit.com/simple-delay-speakers/
If the TV turns on, the USB ports get power which would in turn power on the circuitry and activate the headphone jack after some seconds…..

We thought his problem was really interesting. Let’s begin by making a quick summary of what we had to work with:

• A great power amplifier (Kenwood KA-990) with high efficiency, a strong protection system, and very good sound quality
• A USB port from the TV that provides a stable 5V at around 100mA
• A headphone output with very low power — no more than 1 watt

We begin by looking at the complete circuit, and then we will explain the reason behind each component and what function it serves.

The Complete TV Audio Delay Circuit

Here is our simple time delay solution to solve the problem of pop noise during startup. The circuit schematic below shows the complete and functional audio delay circuit.

You may think that there are a lot of parts, but in fact, this circuit is easier than it looks.

The full experimental process and schematics are documented in the extended notes.

How This Circuit Works

Now that we have seen the complete circuit, we may wonder what each part does. So, without further ado, let’s see how this circuit works.

Block Diagram Overview

From the full circuit above, we can simplify it by breaking it down into smaller parts. The easiest way is to replace each part with a block diagram.

Each block is connected and works with the others, as shown below.

This helps us greatly in understanding the current or signal path of the circuit.

Finding the Right Circuit for Each Block

We usually begin with the main section we are most interested in, then gradually build and connect each part until the full circuit is complete.

Logic-Controlled Audio Switch

Earlier, he wanted to use a simple RC delay circuit, which requires a 12V relay. As a result, the USB power is unable to sustain it. We found two ways to solve this problem, each with its own drawback:

• Increase the USB port voltage to 12V using a DC boost converter circuit. However, this method is quite complicated.
• Replace the relay with a 5V version instead. This method is more practical because it matches the voltage level of the USB port.

We measured the current through the 5V relay coil and found it to be about 50 mA. The USB port can supply around 100 mA, so it should be enough.

However, we think using a relay is not a good idea. Relays are designed for switching high-current loads. But in this case, the headphone output has very low current, so it is better to use a component that is suitable for low-power signals.

A few days ago, we learned how to use the CD4066 Analog Switch in a digital circuit. It works like a relay, but it consumes less power, making it suitable for small signals.

Furthermore, since it is a CMOS IC, it can work with a 5V power supply, such as from a USB. So, we decided on using the CD4066 to switch the audio signal instead of a relay.

Time Delay Circuit

He needed an RC time delay circuit using a transistor that could adjust the delay from 0.1 to 10 seconds.

However, this approach is usually inaccurate and difficult to fine-tune, especially with a basic transistor circuit like this one.

So instead, we decided to use an NE555 timer. It is easier to use and gives more precise time delay results. The schematic below shows a basic time delay circuit using the NE555.

 

🔁 Logic Inverter Circuit

At this point, if we were to connect the Time Delay Circuit to the control input of the Logic-Controlled Audio Switch, we would hear TV audio only for the duration of the delay (e.g., 10 seconds). Why is that? The answer is:

• The Time Delay Circuit outputs a “high” logic during the delay duration.
• The Logic-Controlled Audio Switch allows the audio signal to pass through when it receives “high” logic.

In other words, during the delay duration after powering on, the analog switch receives “high” logic, which closes the switch inside and allows the audio signal to pass through.

After the delay, the timer ceased the “high” logic, and the analog switch opened again, disallowing the audio signal from passing.

The solution is awfully simple: We need to invert the signal that comes from the Time Delay Circuit before it goes into the Logic-Controlled Audio Switch.

We call this part of the circuit a Logic Inverter Circuit. It works by flipping the signal logic — when the Time Delay output is “low”, the inverter output is “high”, and vice versa.

This prevents the audio signal from reaching the amplifier for the first 10 seconds (when noise may happen), and only passes on the audio signal afterward.

Final Summary

We did not test this exact circuit in a real-world setup (i.e., hooking it up to a real TV and amplifier), so we cannot fully guarantee that it will work perfectly in every case.

However, from my testing, the circuit operates as expected and follows the design process. If you spot any mistakes, feel free to let us know. We’re always happy to improve.

More importantly, we have learned some valuable electronics concepts through this project, including:

• Logic-Controlled Audio Switch Circuit using CD4066
• Time Delay Circuit using NE555
• Logic Inverter Circuit using a Transistor

I hope you found this project useful and enjoyable. Thank you for following along!

Even if you do not build this exact circuit, the ideas and methods here can help you in future projects. Keep learning and exploring!

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