Simple board for THS6012 (TPA6120)

[misterstarshine]

This project has served me for about a year now.

http://www.carmi.se/misterstarshine/Projects/9

I'm almost completely satisfied with it except for a weird behaviour that has occured maybe once a month. A background hum appears similar to when there is no grounding and it increases in strength until it disappears with a load plop sound. The device is only grounded through the signal cables since the built in psu board is designed to accept an ac wall wart. I like to avoid having mains hooked to my projects directly. I can shake the box and knock on it but there is no way I can provoke this weird behaviour. It just happens whenever it wants to.

[peranders]

Bad solder joint maybe?

[misterstarshine]

It's probably the most intresting idea so far. Today I tried banging the box as hard as I could but it still works flawlessly. I've not been able to provoke the behaviour one single time. The intresting thing is that it seems to do this for a certain amount of time and then pops away like if there were some capacitor involved in this event. Since this event occurs so rarely it is probably nothing to worry about in practice but being a perfectionist I really don't like faults like this. The most important thing is that there should be no flaw in my design so it must be some poor solder joint or something like that.

[goldkenn]

Have you painted something on the PCB to protect the bare copper trace?

[peranders]

It looks like fresh copper.