Simple DIY Bluetooth Speaker Using PAM8403

I had an old Philips 5.1 home theater system collecting dust. Since it lacked Bluetooth and had damaged wires, I decided to repurpose one of its speakers to create a compact, mono Bluetooth speaker for my PC. My goal was to make a plug-in speaker powered directly from my PC's USB 3.0 port. Using the low-powered PAM8403 amplifier and a 5W speaker driver from the 5.1 system, I successfully built a reliable and compact Bluetooth speaker with readily available components.

For this project, I used a 5W, 4Ω mid-range speaker driver from my old Philips 5.1 home theater. However, a 3W to 5W full-range speaker driver is also a good choice. Ensure the speaker impedance is 4Ω for optimal performance with the PAM8403 amplifier.

You can use a Bluetooth AUX adapter or a dedicated Bluetooth audio receiver like the MH-M18. If you're using an AUX adapter, ensure the AUX output is correctly connected to the PAM8403 inputs. However, with a dedicated audio receiver, you also have the option to transfer audio via data lines in wired mode, allowing playback without Bluetooth.

The main challenge is converting the stereo output from the Bluetooth module to mono. This can be done in two ways:

1. Active Summing – Uses a low-noise op-amp like the TL072 for better audio quality.
2. Passive Summing – A simpler method using resistors.

I used the passive summing method by combining the left and right audio channels with resistors and feeding the summed mono signal into the left input of the PAM8403 amplifier. The right input channel was connected to the ground using a 10kΩ resistor to prevent interference.

For power, I directly connected the circuit to my PC’s USB 3.0 port via a Type-C cable. The USB 3.0 port provides at least 1A of current, which is sufficient for the PAM8403.

To assemble the circuit, I used a piece of perf-board, but you could also design a custom PCB. Ensure proper wiring to minimize distortion, interference, and latency.

I secured the amplifier circuit inside the speaker enclosure using hot glue. To reduce unwanted resonances within the speaker encloser due to internal sound reflection, I placed cotton wool inside the enclosure as an insulating material.

To protect the speaker driver, I attached a mesh dust filter (originally from my PC fans). This prevents damage when carrying the speaker around.