hissing coming noise from all speakers

Hi, Im new here and sorry this is kinda long, but Ive got a problem with my car and thought itd be best solved here. I have a 1997 Isuzu Bighorn(/Trooper) UBS69 3.1DTi with a Fusion headdeck running 4" JVCs off the headdeck in the rear pillar, the three sets of RCA from the headdeck go to a JVC 800w mono block (in back) to power a 12W4-D4 JL Audio sub and the other two RCA go to a Response 4x50w amp (under passenger seat) that powers fusion performance serries 6x9 in the rear doors and JBL 5.25" components in the front. I havent upgraded the earth from the headdeck (told this may be a problem by a friend but after my tests im not sure how this would affect this?) and am running the stock loom into it but I have pretty good earths on both the other amps.. however I am getting a hissing noise in all speakers (and even the sub). I only just upgraded from a 2CH presicion power amp (for 6x9 and run the comonents off the headdeck) to the response amp but the hissing was still present before this swap so Im sure it isnt the amp, although amping the signal seems to have made it more pronounced through the tweeters especially. The hiss doesnt seem to change with the colume so even with the vol. set to 0 I get the same hissing

So heres what I've tried and found...
With the ignition off and head deck running there is a hiss on all the speakers (incl. sub). I tried unplugging the RCA from the JVC (sub) amp and the noise was quieter on the sub but still there. Also tried unplugging the RCA from the 4CH but the noise was still completely there in both the front and rear speakers.
After this test of the 4CH I tried to run some speakers wired out of the amp with another set of cables that came form the amp right onto the back seat (less than 1m) away from all power cables (try not have it near power cables incase the interferance was the problem) but the hiss was still the same.
I then thought that while I had a speaker out of the door I could listen carefully when I turned the engine to see what happened, so I did this and heard the hiss and another fluttery kind of sound that increased a lot when I reved the engine.

Also, I am running seperate 8G each to the two amps and the RCA, Audio and Power are all together (I know this shouldnt be done but my two RCA into the 4CH amp are supposidly highly shielded and after testing the amp iteself with an auxilery imput and seperate speakers away from the power it didnt seem to make the difference so I thought id ask here before re-wiring the entire car...)

Anyone got any ideas on what this could be? Im hoping its simple but its completely baffled me as I wired my last car with a similar setup and didnt have any of these problems

Thanks in advance

If your unplugging the rcas and still have his it is not coming forming the head unit unless there is feedback on the remote turn on wire. This could honestly be quite a few things but personally I would start with checking all the grounds and make sure they are good clean bare metal grounds. Even a little resistance can cause hiss and noise. Also make sure the gains are set properly. If there are no shorts in the system wiring this usually fixes all noise issues but to me this sounds like a poor ground or ground loop.

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Gary Sather

tonanzith wrote:

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If your unplugging the rcas and still have his it is not coming forming the head unit unless there is feedback on the remote turn on wire. This could honestly be quite a few things but personally I would start with checking all the grounds and make sure they are good clean bare metal grounds. Even a little resistance can cause hiss and noise. Also make sure the gains are set properly. If there are no shorts in the system wiring this usually fixes all noise issues but to me this sounds like a poor ground or ground loop.

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How likely would it be that the remote power could cause an issue? Anyways, I will try check all the grounds again (best to ground both amps to the same location?), hopefully tonight I'll have the time..

tonanzith wrote:

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If your unplugging the rcas and still have his it is not coming forming the head unit unless there is feedback on the remote turn on wire. This could honestly be quite a few things but personally I would start with checking all the grounds and make sure they are good clean bare metal grounds. Even a little resistance can cause hiss and noise. Also make sure the gains are set properly. If there are no shorts in the system wiring this usually fixes all noise issues but to me this sounds like a poor ground or ground loop.

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Ok so I just sanded the metal to bare where the grounds are (didnt have enough time to check the headdeck ground, maybe tonight) and tried again but hissing was the same. Also how should I set the gains? the 4CH is on almost 0 as otherwise the hissing is hugely amplified.

Imaged didnt look like they worked before so here they are..

Ok, well I was able to do a lot of testing tonight and have found added a better ground from the headdeck to the same spot as the 4CH amp is (no difference in noise). I then tried to ground the battery better so I added another ground the battery (yes I sanded and got it to bare) but that didnt seem to do much other than make it worse... however when I started the engine the noise got really loud and on revving the engine it got louder again with the revs... I disconected that extra ground and tried again, still hissing when car off but not increasing with revs when on.
I kinda gave up on the hissing for tonight but as a last check I disconected the fuse on the power to the subs amp (so only the 4CH and headdeck were running and both grounded to a common ground) but that didnt make any differnece either (all speakers still hissed incl. the ones directly plugged to the head deck)

All of this testing was done with the head deck out of the car and on the seat.

At what number on the volume do you listen to it?   Pause a disk and turn the volume all the way up, at what number does it stop?

if you turn the gains down on both amps does the hiss go away? you should move your grounds to a spot that is not a factory ground for other equipment in the car, you could be getting interference from your factory electronic devices being grounded all in the same spot. try to find a spot close to each amp, they dont necessarily have to be grounded in the same spot because if each ground has to be 3 feet (1 meter) away from the amp then this can also make your noise worse.

find a spot less than 12 to 18 inches (closer is even better)away from each amp and sand the paint off of each spot and screw it down with one or two self tapping screws each. does it make a difference?

how exactly did you "upgrade" your battery ground? where did you try to screw your new ground to? upgrading the battery's ground should be done by screwing a larger gauge wire than the stock wire straight from battery to the steel chassis frame, and the spot should be sanded down to bare shiny metal.

i am an idiot wrote:

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At what number on the volume do you listen to it?   Pause a disk and turn the volume all the way up, at what number does it stop?

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normaly listening between 10-20 and I think it goes all the way up to 50

soundnsecurity wrote:

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if you turn the gains down on both amps does the hiss go away? you should move your grounds to a spot that is not a factory ground for other equipment in the car, you could be getting interference from your factory electronic devices being grounded all in the same spot. try to find a spot close to each amp, they dont necessarily have to be grounded in the same spot because if each ground has to be 3 feet (1 meter) away from the amp then this can also make your noise worse.

find a spot less than 12 to 18 inches (closer is even better)away from each amp and sand the paint off of each spot and screw it down with one or two self tapping screws each. does it make a difference?

how exactly did you "upgrade" your battery ground? where did you try to screw your new ground to? upgrading the battery's ground should be done by screwing a larger gauge wire than the stock wire straight from battery to the steel chassis frame, and the spot should be sanded down to bare shiny metal.

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I will try to find a spot between them both, I have the subs amp grounded to under the rear seat so I could try run the 4CH ground back (less than 1m) but I havent got the time to try this right now... hopefully this weekend Ill have the time.. and I ran a cable around the same size from the battery straight down to the body, sanded bare and screwed down (I heard something about grounding on the engine block being bad for audio and thought another bettery ground would be better but it was far worse..)

Turn the gains all the way down on both of your amplifiers. Does the hissing go away? Can you reach your desired listening level? If not, turn the gains up till the noise is back then back them down till it is quiet again. Can you reach your desired listening level?

How did you run your power wire. Make sure your power wire is away from all the factory wiring.   Your RCA cables should be ran down the opposite side from your power wire and they should also be away from from any factory wire harness.   hope that helps.