Hi Guys, I recently installed a mono block amp and connected to the factory line level outs since the amp didn't have high level inputs. Here's the problem... When the car is running I get a humming noise out of my rear 6x9's. As I drive it sounds like the cars engine is being picked up. This is the weird thing, when I disconnect the amps inputs the noise from the engine goes away. I used the rear inputs as the low level inputs to the amp. Is it possible that the amp is somehow feeding the noises it's picking up back into the factory BOSE amp? If so how can I fix it?

 

Nothing weird about this at all - it's pretty common. There is a ground loop between the new amp and the old amp and the deck (three things - should say "among"). Ground loops aren't really "injections' of noise.

Best way to avoid this is get an LOC and tap the by-nine wires. (Or upgrade the Bose amp).

You COULD try to find the right place to insert a ground loop isolator. But I suspect it's on the way to the OEM amp.

 

Elduderino. Thanks for the confirmation. I am going to pickup some grouploup isolators from the Source tomorrow and put it in line with the amp. I suspect it's that new amp that is doing this because when I disconnect the RCA's it stops. So I'll start by putting it there and see what happens. I'll post my results as soon as I can.

 

Okay just picked up a $20 Ground Loop Isolator. I also did lot's of reading about it and that did the trick. I guess the aftermarket amp was feeding ground to the factory BOSE amp and that amp was amplifing the Ground noises.

In case anyone is interested a ground loop isolator is basically a 1:1 ratio of coils around a ferrite carbon material similar to a transformer. It basically works on the concept that sound is A/C and the noises are D/C. A/C can pass from one coil to the other whereas D/C cannot hence the D/C signal is eliminated altogether. I may not have everything here exactly right but that's what I got from another source.

 

Thanks, Anderson Cooper.

Uh, if the noises are heard, how can they be DC?

I know how it works, but that's not really the explanation...