Review Request: 3W PAM8403 amplifier
Hey! i recently picked up a cheap speaker from a flea market. It was using two 8002A chips, but there was a constant background noise and a horrible turn-on pop every time I tried to listen to something. So, instead of fixing that speaker, I decided to design my own custom board using the PAM8403. I've finalized the schematic and would really appreciate a quick check before I finish routing and send it to production.
I am planning to power this thing from a dedicated wall charger rather than a computer's USB port, so I added a USB-C receptacle. I went for heavy decoupling on both PVDD pins because I really don't want any noise, and I used a 1000uF bulk cap on the main 5V line to handle bass transients. However, I'm honestly second-guessing if that 1000uF is going to pull way too much inrush current and cause any damage or trip OCP.
For the most part, I followed the typical application circuit from the PAM8403 datasheet. I used a stereo pot with an integrated switch for volume control, and I tied the MUTE pin to the switch using a soft-start circuit. This should create about a 1-second turn-on delay so there will be no pop when I close/open the switch. When the switch is opened, the capacitor dumps its charge via the bleed resistor. However, I am worried that the LL4148 might actually leave the MUTE pin floating. The PAM8403 requires the MUTE pin to drop below 0.4V to register a valid logic low, but the LL4148's forward voltage is around 0.6V-0.7V, which could leave the pin floating at 0.6V. Because of this, I am thinking about switching to a Schottky diode instead.
Also, the soft-start circuit is completely optional. I will first just solder a 10k resistor to R5 to test if there is any pop, and only solder the soft-start components if there actually is one. I also included the LC output filter as shown in the datasheet, but I'm starting to think it might be overkill. I will probably just solder bridge the ferrites if there are no EMI issues with the output.
I've started the layout, but I'm struggling a bit with the initial component placement and analog routing. Also, I was planning to solder the audio wires directly to the pads, but now I'm thinking if I should just place a 3.5mm female jack instead. Does soldering the wires directly actually improve sound quality or reduce noise compared to using a mechanical jack?
Any general tips or layout feedback would be appreciated:)
Datasheets:
PAM8403: https://www.diodes.com/datasheet/download/PAM8403H.pdf
LL4148: https://www.onsemi.com/pdf/datasheet/ll4148-d.pdf
Let me know if you want more detailed photos of the circuit or datasheet of other components!
