i built a small VU meter with a lm3915, and i assume it is what is causing the strange subtle vvvmmmm... vvvmmmmm... noises when i use my trackball to scroll up and down pages... it's not a wireless trackball, it's an old trackman marble fx ps2. the vu meter circuit is sitting in between the mouse and my pc, is that why? the circuit's power is coming from the pc's psu too.... i don't know if that would have anything at all to do with it either....
The noises happen to a lot of people. It isn't to do with your little circuit. Some reasons discussed here. Using the search always helps before posting a question If you're worried about your VU meter interfering, make sure you have a suitable DC blocking capacitor between your output from your soundcard and the input to your circuit (unless you already remembered to include one).
Both my laptop and desktop computers do this, my friend sugested muting the cd audio input (because it worked on his computer), and this works on both my computers. The only thing the cd audio does is amplify audio played by the cd drive, playing music cd's through a program like windows media player, is not affected. To turn this off, go to the volume settings at start->Programs->Accessories->Enterainment->volume controll and click the mute box under cd audio. If the cd audio volume slider is not there, go to options->properties to turn it on.
i read through that article, and one mentioned problem was interference between poorly isolated audio cables and mouse cable. this may very well be the problem. i am using a y splitter audio cable. it starts at my subwoofer, then splits into one of the speakers and the VU Meter. The VU Meter is positioned in the front of my case, incidentally right beside me and my trackball mouse. Is there a better way to connect the VU Meter? Will a DC blocking cap help although the circuit is not connected directly to the soundcard? Blue Raven- I have never had the internal audio cable between my mobo and cdrom drive.... but i did mute it just to see if it would help.... no luck.
It may not help, but I noticed the 3915 circuit you posted a couple of days ago has no filter caps. Adding a couple may reduce any broadcast noise.