Build a Multi-Input Audio Selector
An audio input selector allows multiple audio sources to be connected to a single amplifier. Instead of unplugging cables every time you want to change from Bluetooth to a CD player or computer, an audio selector lets you switch between sources instantly using a rotary switch, push buttons or relays. This project explains several methods of building a low-noise stereo audio selector suitable for Hi-Fi systems, home theatres and DIY amplifiers.
Project Overview
Each audio source provides left and right stereo signals.
The selector routes only one stereo input to the amplifier while isolating all other inputs.
A good selector introduces virtually no audible noise, distortion or signal loss.
Project Difficulty
| Item | Value |
|---|---|
| Difficulty | ⭐⭐ Beginner–Intermediate |
| Build Time | 1–3 Hours |
| Supply Voltage | None (Mechanical) or 5–12 V DC (Relay Version) |
| Inputs | 2–8 Stereo Inputs |
| Soldering | Minimal |
Typical Audio Sources
| Input | Example Device |
|---|---|
| Bluetooth | Bluetooth Audio Receiver |
| AUX | Mobile Phone or Tablet |
| CD Player | Home Audio System |
| Computer | Desktop or Laptop |
| FM Tuner | Radio Receiver |
| Media Player | USB or Network Player |
Methods of Switching
| Method | Advantages |
|---|---|
| Rotary Switch | Simple, inexpensive and highly reliable. |
| Push Buttons + Relays | Short audio paths and remote control capability. |
| Electronic Analog Switch IC | Compact design with electronic control. |
| Microcontroller + Relays | Remote control, display and memory functions. |
Components Required
| Quantity | Component |
|---|---|
| 1 | 2-Pole Rotary Switch (or Relay Board) |
| 2–8 | Stereo RCA or 3.5 mm Input Connectors |
| 1 | Stereo Output Connector |
| 1 | Metal Enclosure |
| Several | Shielded Audio Wires |
| Optional | Relays or Analog Switch ICs |
| Optional | Push Buttons and LEDs |
How the Circuit Works
Both the left and right audio channels are switched together.
When the selector is turned, only one stereo source is connected to the output, while all other inputs remain disconnected.
Relay-based selectors operate in exactly the same way, but the switching is performed electronically rather than mechanically.
Applications
- DIY stereo amplifiers.
- Home Hi-Fi systems.
- Bluetooth receivers.
- Audio mixers.
- Recording studios.
- Home theatre systems.
- Workshop audio systems.
- PA installations.
Testing
- Check every audio connection.
- Connect two or more audio sources.
- Connect the output to an amplifier.
- Select each input one at a time.
- Verify that only the selected source is heard.
- Check both left and right channels.
- Listen for clicks, hum or unwanted noise.
Troubleshooting
| Problem | Possible Cause |
|---|---|
| No audio | Incorrect wiring or faulty switch. |
| Only one channel works | Loose left or right channel connection. |
| Hum or buzz | Poor grounding or unshielded cables. |
| Two sources heard together | Switch wiring incorrect or contacts shorted. |
| Crackling while switching | Dirty switch contacts or switching while music is playing loudly. |
Project Improvements
- Add remote control using an infrared receiver.
- Use relays for quieter switching.
- Add OLED or LCD input display.
- Store the last selected input in memory.
- Add automatic Bluetooth input priority.
- Include input status LEDs.
- Add a mute circuit during source switching.
- Use gold-plated RCA connectors for improved reliability.
Skills Learned
- Stereo audio routing.
- Low-noise wiring techniques.
- Mechanical and relay switching.
- Signal integrity.
- Shielding and grounding.
- Audio system integration.
Safety Notes
- Keep audio cables away from mains wiring.
- Use shielded cable for all low-level audio signals.
- Connect all audio grounds to a common star ground point.
- Switch sources with the amplifier volume reduced to avoid loud clicks.
- Use a metal enclosure for improved shielding against electrical interference.
Key Points
- An audio selector allows multiple sources to share one amplifier.
- Both left and right channels must always be switched together.
- Good shielding and grounding minimise unwanted noise.
- Relay-based selectors offer premium performance and remote-control capability.
- An audio selector is a useful addition to any DIY Hi-Fi or home theatre system.