Hey folks! I've been trying to breathe new life into my old boombox by adding a budget Bluetooth and USB audio module I found online. I've thoroughly dismantled the boombox, replaced the scratchy volume control with fixed resistors, and even tested the new module with a bench power supply, which worked perfectly. However, the moment I connected everything back together using the boombox's power supply, I was hit with an awful buzzing noise that was just as loud as the music. I've tried powering the module with both the 15V and 8V outputs from the boombox, but the buzzing persists in both cases.
I've done a few tests and noticed that the buzzing only occurs when the module is powered by the boombox and its audio output is directed to the boombox itself. Interestingly, when I disconnect the audio from the boombox, the buzzing changes in volume based on the module's power draw, particularly when the display is active. I thought maybe the module is causing some interference or ground loop issues, but I checked the grounds with a multimeter, and they seem connected.
I attempted to filter the audio signal with capacitors, but that didn't help either. I'm looking for general advice or suggestions on where to look next. The boombox isn't worth much, and the module was pretty cheap, so I'm not eager to spend a lot on fancy fixes. Any ideas?
3 Answers
It's definitely worth trying a 1000uF/25V electrolytic capacitor across your module's DC input. This can help to smooth out power fluctuations. I've had similar issues before, and this simple fix often works wonders. Just keep in mind that since the power supply and amp are on the same board, the problem might be compounded.
You've pinpointed the issue well! The buzzing likely arises from the module's digital circuitry interfering with the audio signal when both power and audio are connected to the boombox. If you're really strapped for solutions and don’t want to sink more cash into repairs, maybe consider using that other module you mentioned, which has its own amplifier. It'll help you bypass this current issue entirely without needing to dig deeper into the boombox!
It sounds like you're dealing with classic ground loop or power supply noise. Since the module’s digital electronics can introduce unwanted noise on the boombox's ground, I'd suggest trying an RC or LC filter on the module's power supply—like adding a series resistor and capacitor right on the board. Also, ensuring that the audio ground is separate from the power ground may help. If these don't work, you could try a simple audio isolation transformer, which often does the trick for these kinds of issues.