Audio Systems: car audio engine interfrence, ground loop isolator, toyota corrola

Question
Hey, i have wired up an amp in my toyota corrola 1997.
its a 4 channel amp and i was running two subs of it and it ran fine, But then i decided to attach my two speakers also to the amp.
They go fine when my car engine is turned off, But as soon as i turn the engine on the two speakers get interfence from the engine. while the subs still run perfectly fine
any idea's?

thanks Ben

Answer
I would guess that the subs have the noise as well but perhaps you cannot hear it due to a crossover setting.

1) Unhook the RCA cables from the amp.
If the noise persists:
The noise in entering at the amp and you should focus on getting a good ground for the amp.
If the noise goes away:
Go to 2)

2) Plug RCA's back in to the amp and unhook them at the headunit.
If the noise persists:
The noise is entering the RCA somewhere between the headunit and the amp. BE certain that the power wire for the amp is not ran next to the RCA's.  The RCA's might be damaged. Try a new set as a test.
If the noise goes away:
The noise is entering the audio chain at the headunit.
Check its' ground and the vehicle grounding location.  
*Oftentimes in such cases it is better to simply run the headunit ground to the vehicle chassis and NOT the factory radio harness.


Did I mention checking the grounds?  ^^

If all else fails (rare) you can get a 'line level ground loop isolator' from PAC.
http://www.gdielectronics.com/sni-1.html


Good luck and thanks for the question!

JM