Need help with DIY car audio noise
 

I have a hobby in electrical engineering so I built my own car audio system given the fact that it didn't have any before. It's basically two pairs of PC speakers adapted with some resistors and regulators to work on DC 11-15V from my car. In order to eliminate any ripple and noise I have added a 4700 uF capacitor in parallel with the power wires. Like this (excuse the paint drawing)
http://i.stack.imgur.com/jwOkL.png
They are low power enough (around 30W max) to work without any noise when the car is running (noise induced by the alternator) as well as when it's on battery only (of course, no noise).

My problem is when the device i'm using is charging from the SAME power lines, all the noise-filtering the capacitor is doing suddenly vanishes.

This is when my problem occurs:
http://i.stack.imgur.com/oRr8O.png
My skills aren't advanced enough to figure out what's going on, so I'm asking here after 1 month of research: How do i eliminate the ripple from when my device is charging and plugged into the audio system at the same time?

What you are observing is a ground loop. You need a ground loop eliminator to isolate the audio feed to the speakers. Something like this should do the job.

https://www.prohavit.com/products/hv...loop-isolator/

Simon

Your phone charger probably has a PWM circuit or likewise that alternately draws current and doesn't. This creates spikes on the feed.
Your capacitor cannot filter out high frequency signals like said spikes.

Maybe you can put a RFC choke on the feed to the speakers, ahead of the capacitor. You'd filter out spikes from any source.

Or maybe try ferrite cores? They are cheap. My only experience with this is on an instrument signal line of 4-20mA 24VDC that would spike when a walkie talkie transmits close by 1m.

http://images.monoprice.com/productl...ages/41552.jpg

Here's another Industrial best practice; shielded cables. It's like a mesh of wire surrounding the conductors and supposed to 'shield' from electromagnetic interference. Ground shield at only one end, not the other. But if persist, try ground both.

Transistors are noisy. Maybe try a better quality adapter?