Amp trouble. Please help

mjd616 · 12-09-2008, 07:55 PM

I just installed a new system in my car. Head unit, speakers, amp, sub, the whole shabang. I got the infinity 5 channel 5350a. I had it before but it got ripped off in my old car. I liked it so I got another. sooo..... we got everything installed and the all the wires ran. We started it up and the music started playing. It was very clear and completely free of any hissing, then my cousin folded the seat down.... when he did this he disconnected and broke the metal piece on the ground. It went into protect mode or whatever that is and we turned it off. Ever since that the speakers have been making these terrible sounds. We're pretty sure its the amp.We got a new terminal for the ground and sanded the ground spot. Didn't help. Then we started messing with the rca's and we found that if you disconnected either the right or left rca and just touched it to the input jack, but not actually put it in, a considerable amount of the hissing went away, but the second we plugged it back in, HISSSSSSS. It doesn't make any sense. My cousin also tried setting the ground not while the car was on, but while the battery was still connected. I don't know if that makes a difference. he thinks the amp is messed up. No fuses blew or anything like that. Replacing the amp if need be isn't the issue, but does this sound like the sort of thing that could do this to an amp? I'd really appreciate any help, as I'd had a very disappointing two days.

Also if it matters the amp is 50wx4 and 150x1 rms. I had a 4 guage kit that came with a fuse block with a 100a fuse, but it was messed up so we got one real quick at best buy. Its a rockford with a 60a fuse but I doubt that would have anything to do with it, as I'm not running that much power anyway

Bugbyte · 12-09-2008, 09:02 PM

If it stopped hissing when you disconnected an alternate path to ground, you've found a ground loop. As good as you may think your ground spot is, the ground path through the speakers and HU is better, thus a ground loop.

You can try to continue to solve the ground problem or use a ground loop isolator. Here's a post from a thread that may help.

mjd616 · 12-09-2008, 09:17 PM

how would I got about disconnecting an alternate path to ground to test this?

AudioXtreme · 12-10-2008, 05:17 AM

Does it still hiss when the vehicle is turned off and the sound system is only running off the battery? If so, it could be that your amp is bad. Try disconnecting the rca line inputs into your amp with the speakers still hooked up and see if you still get hissing sound. If you do, it's your amp. If not, reconnect your cables and disconnect them from the back of your head unit. If it stops hissing, it's the cable running to your HU. Also, is the hissing coming from all your speakers including the subs, or just one, two or some of the speakers? Make sure the system is shut down before disconnecting or reconnecting any cables. Good luck...