Help needed with Ground loop problems.

I have had my stereo installed for a while now and i have the whining noise that pass through to my speakers from my 4 channel amp. This is the first time i have encountered the whining noise on any of my installs. The noise only comes when i start the truck, and i can only hear it if my radio is turned down really low, almost to the point of no music passing though, but it does whine with engine acceleration. My first initial fix was trying a ground loop isolator, but i still had the noise. The only thing that made the noise go away was lowering the gain, but by doing that the output voltage of the head unit is not matching up with the amp and my mids and highs volume is not where i want it. I am not trying to use the gain as a volume, but i am trying to match the output signal voltage of the head unit. The volume is also out of sync with my mono amp. I don't have any issues with the mono amp giving off noise at all.

I am using a different route of tuning my installs with a multimeter and testing the output voltage of the amp to the speakers. I wanted to tune it like this because it matches your output voltage of the headunit with the amp without any additional enhancements turned on, and everything should sounds more in sync. Now for my mids and highs they run at 80watts rms and when tuning with everything on the head unit set at flat with all enhancements off my output voltage of the amp is 17.88v per channel which puts my gain for my 4 channel amp in between quarter and half and i am getting noise. Used the same route for my mono amp and i am not getting any noise.

Stereo Components:
Headunit: Pioneer DV 4000

Mono Amp: Alpine MP850 Running 4 gauge from battery, and 4 gauge ground wire

4 Channel Amp: MB Quartz ONX 4.80 Running 8 gauge from battery, and 8 gauge ground wire with speakers wires ran individually to each speaker.

RCA: Schoshe Scosche-EFX ReVo for both mono and 4 channel amp ran on opposite side of power wires.

Ground: For the ground i attached it for both amps on that back bar on the double cabs. Usually the plastic bins bolt onto it. I sanded down the paint before grounding, and my ground wires are about 1' long. The mono amp gets no noise at all, but i cant figure out why i am getting this noise with the 4 channel amp with gain set under half way. If i disconnect the RCA's from the 4 channel amp i don't get the noise.

Is having the gain not even set half way too high, or is lowering it just masking the problem? From what i understand is that the noise will still be in the system with the gain turned down even if i cant hear it, and raising the gain just amplifies the sounds to where i can hear it. I really want the noise gone and not just using filters to band aide fix it. Any help would be appreciated and any recommendation on better ground locations.

 

You say you don't get the sound when you disconnect the rca's, have you tried using different rca cables, could be a defective set?

i don't think it's a band aid fix turning down the gain if the sound goes away to the point you can't hear it anymore. If the speakers have enough power going to them you shouldn't need the gain that much.

Maybe it's running the power cables together thats causing the noise.

just some suggestions,

Good luck

 

Try a different pair of RCA's to the 4-channel amp. I just switched from some cheap ass BOSS ones that came with my wiring kit, to some kicker RCA's and it made a hell of a difference. But that was with my mono amp, I dont have a speaker amp

 

I actually switched the RCA's around already, but still getting the noise. I posted on "the12volt.com" and one of the guys on there said its the head unit. The pioneer head units have something called a pisco fuse in them that grounds the shields of the RCA's. The fuse is supposedly very small and soldered directly on the board. Going to look into it some more and see if I am going to try and fix it or get a new head unit since I have had this one since 07.

 

I know what you mean by lowering the gain wouldn't really be considered a band aid fix, but I rather just get rid of the noise all together. Gain being slightly over 1/4 shouldn't be giving me noise to begin with.

 

run a set of RCA's just across carpet direct to amp. see if noise. If yes then its a deck issue, If no then route these new RCAs an opposite route then current ones.

If you had noise with new RCAs, one installer i knew tried grounding the deck to the amp location as well. Creating a common ground for both. might be worth a try.

Back when i sold Car Audio (5yrs ago) some decks didn't play well with some amps. you swap the deck out to another brand, and instant noise fix.

Just some ideas i thought i would throw out.

 

Thanks, probably going to try creating a common ground as you suggested before ditching the unit for a new one.