Need help with achieving efficient noise filtering!

[Rattanee]

Hey guys! Could anyone help me out with noise filtering and how it's done?

Case in point, I need to power an amplifier from a PC PSU. The amplifier is working fine, and near completely silent when signal is disconnected. The only noise I'm getting is from mouse activity this way. As soon as I plug the jack into the back of the (same) PC, I can hear everything from HDD spinup to cd-head-servo-farts.

So my question is, how to go about filtering out this noise? Why don't the cheap-ass PC speakers pick these noises up? From what I've seen cracking some open, they have even shittier power filtering then my own design.

What I have running is the reference design for a TDA2003A doubled up for stereo use. I'm pretty sure this noise would be present even if I didn't power it from the PC PSU. So what is the solution?

Thanks for any help guys!

 

[OLIVE2222]

Hi,

It will be usefull to confirm you feeling by testing the amplifier on an external (not switched mode type) power supply.

Doe's the amplifier work well with an external audio source like an MP3 player?

The idea is to find out if it's power supply problem or an input stage problem.

regards,
Olivier

 

[Rattanee]

It's definitely a powersupply problem. Running it from the PC PSU with my phone as an audio source, aside from distortion at higher volume levels (need to lower the gain) I get no background noise. I ended up putting a 6.8mH inductor on both the ground and 12v rails at the input to my pcb along with a 4700uF cap, and that pretty much solved my issues. Ground loop from the audio jack is gone completely. There was some mild noise from the sound card when the mouse was moving or somesuch, but that was apparently a soundcard problem, installing the latest drvers fixed that.

Cheers