Grounds ran to frame, swapped RCA cables, etc. Still noisy.

[longbedbob]

Good evening, folks.

I have a 2016 F150 that came with a base, factory stereo. I've installed a PAC dash kit and converted it to accept a double DIN with GPS.

I have also installed new speakers all around, two amps, and a sub.

Gear:

New head unit - Kenwood DNX693S

Primary Amp -Infinity Reference 704 A

Sub amp - Sound Ordnance 350-1 (hey, it's a truck. There's not much room behind the rear seat for a monster sub)

Despite my best efforts I have a few problems.

1. I have static through the door and dash speakers when the truck is turned off. No unusual sounds from the sub, though.

2. When the truck is running, I have alternator whine. Again, no whine heard through the sub.

Both sounds are base level noises that don't seem to get louder, only the pitch of the whine changes with RPM.

Prior to joining and writing this post, I have performed the following:

1. All wire to wire connections are soldered with heat shrink applied.

2. Power is running to both amps from the battery via 4 gauge wire, to a junction box under the hood, then through two 6 gauge wires- one for each amp. These wires are ran down the driver's side.

3. Moved grounds at both the head unit and amps. Finally routed 8 gauge wire for the rear amp and 10 gauge wiring for the head unit both through the front fire wall and rear of the cab directly to the frame. The frame was sanded prior to bolting the terminals. Both terminals were soldered and heat shrink applied to cover the terminal lugs and promote long term durability.

4. Resistance from the negative battery terminal to the head unit ground is .04 ohms. To the amp ground in the rear of the truck is .06 ohm. It's a long bed, supercab so there's a little more steel involved.

5. Voltage was 12.67 both at the rear of the head unit and at the amp.

6. Disconnecting the JL Audio RCA cables at the amp caused the sounds to disappear with no self induced noise. Disconnecting at the head unit did likewise. However, if I touch the head unit side of the disconnected RCA cables, I can get "body noise" which I guess is my body's electrical signal being amplified. They will also make a sound if the ends touch one another. Also, relocating and swapping out RCA cables doesn't eliminate the noises. RCA cables have been ran both down the passenger side or through the center of the cab.

7. Disconnecting the RCA cables from the amp and then connecting a classic iPod with mini RCA adapter provides clean output. No unusual noises and music is normal, either with the truck on or off.

8. Connecting temporary speakers to the speaker wire output of the head unit yields static.

So, at this point I'm thinking the problem is with the head unit or supplied power. The only inputs to the head unit are: constant 12V, switched, 12V, antenna, GPS (aftermarket), USB, PAC steering wheel control unit, reverse signal, and back up camera.

9. I've removed the CANBUS inputs and antenna one a time with no change.

10. Removing the constant 12 volt signal to the head unit and connecting it to the accessory power didn't produce any changes.

11. However, and this is the important bit....reconnecting the constant 12V to the factory harness but connecting the 12V switch power directly to the battery eliminated the static. The alternator whine was still there, but there was no noise whatsoever with the radio on and truck not running.

So, it seems that one of my noises is on the accessory power side of the head unit. I have two PAC 12V noise filters on the way and hope to install them tomorrow. I will connect one each to the constant 12V and switched power.

Anyway, I'm open to suggestions as to if I'm on the right track or if I should try something else.

FWIW, as a last resort I'm considering running a constant 12V from the battery and installing a relay to likewise get clean accessory power. I'm also open to swapping out the Infinity amp for a JL Audio RD line, which can handle unbalanced inputs.

Any feedback or ideas appreciated.

Thanks!

Click to read more...

 

[BOOMINGRANDPA 5,000+ posts]

yeah it maybe a connection but u ever try just running rca from hu over seats to amp see if u still have noise? could be rca or a pinched or cut rca or messed up end..

 

[longbedbob]

yeah it maybe a connection but u ever try just running rca from hu over seats to amp see if u still have noise? could be rca or a pinched or cut rca or messed up end..

Thanks.

Yes, this is where I'm at now. The dash is apart and the RCAs are ran from the head unit and draped over the seats running to the amp.

Something else that occurred to me is that my power wires are running through a firewall grommet that it also shares with the truck's primary wiring harness. I'm wondering if perhaps there's some EMF or something induced into that primary harness. That might explain why getting my 12V directly from the battery cures some of my noise.

 

[Papermaker85 5,000+ posts]

probably the h/u ground.

 

[longbedbob]

probably the h/u ground.

The head unit has been ground directly to the frame. .04 ohms resistance back to the negative battery terminal. Amps are grounded directly to the frame. .06 ohms back to the negative battery terminal.

 

[hispls 5,000+ posts]

Often times factory HU is the weak link. They're basically built just well enough to have inaudible noise with the 8W or whatever they produce, once you start doubling that a few times with aftermarket amps what was inaudible becomes irritating.

Perhaps better power and ground to the HU will help, and perhaps even swapping amps will help. I've had swapping amps kill noise before and not due to defective amp, just the amp is somehow more sensitive to whatever the actual culprit is.

Guess and test at this point, you're on the right track in your troubleshooting and IMO haven't isolated any problem yet. My money is on the limitations of your factory HU.

 

[Papermaker85 5,000+ posts]

The head unit has been ground directly to the frame. .04 ohms resistance back to the negative battery terminal. Amps are grounded directly to the frame. .06 ohms back to the negative battery terminal.

try regrounding your alternator..

 

[shizzzon 10+ year member]

get jumper cables and clamp the HU ground to the amplifier ground. keep the cables outside the vehicle.

Do not move the current grounding locations, just add the jumper cables to them.

See if that fixes it.

 

[longbedbob]

Often times factory HU is the weak link. They're basically built just well enough to have inaudible noise with the 8W or whatever they produce, once you start doubling that a few times with aftermarket amps what was inaudible becomes irritating.
Perhaps better power and ground to the HU will help, and perhaps even swapping amps will help. I've had swapping amps kill noise before and not due to defective amp, just the amp is somehow more sensitive to whatever the actual culprit is.

Guess and test at this point, you're on the right track in your troubleshooting and IMO haven't isolated any problem yet. My money is on the limitations of your factory HU.

The factory head unit was pulled and replaced with a Kenwood double DIN. The DNX693S. I should have stated that this was a deck in the first post rather than just list the model #.

That being said, the head unit was the last part of the upgrade. There was still noise with the factory head unit with the amps attached. Thinking the same as you, I upgraded the stereo in an attempt to take care of it. Sadly, it didn't //content.invisioncic.com/y282845/emoticons/frown.gif.a3531fa0534503350665a1e957861287.gif

 

[Papermaker85 5,000+ posts]

The factory head unit was pulled and replaced with a Kenwood double DIN. The DNX693S. I should have stated that this was a deck in the first post rather than just list the model #.
That being said, the head unit was the last part of the upgrade. There was still noise with the factory head unit with the amps attached. Thinking the same as you, I upgraded the stereo in an attempt to take care of it. Sadly, it didn't //content.invisioncic.com/y282845/emoticons/frown.gif.a3531fa0534503350665a1e957861287.gif

hog wash. you have a ground loop or emf. isolate tge rcas from every thing. regound the hu

 

[longbedbob]

hog wash. you have a ground loop or emf. isolate tge rcas from every thing. regound the hu

The RCA's are currently ran through the middle of the truck and dangling over the seats. I've also tried several pair ranging from cheap to the JL 4 ways that are currently attached. I even have some shielded sub cables that didn't make a difference.

I've relocated the ground from the factory harness, to a factory ground at the fuse box, rear of the dash, screwed to the floor, and a temporary jumper back to the negative terminal. I eventually gave up and wired it directly to the truck frame. Ditto the amp ground.

I'm thinking that maybe, just maybe, my amp power wires are interfering with the main factory harness. They both pass through the firewall in the same grommet. That's one reason that might explain why running the switch power directly to the battery causes the noise to go away.

 

[Papermaker85 5,000+ posts]

you have a ground loop. try to reground the alternator. check your connections.

 

[Papermaker85 5,000+ posts]

as far as inductive signal in the factory wiring its very possible. not very likely but possible.

 

[hispls 5,000+ posts]

Have you tried grounding the outside ring of your RCA cables? Internal fault in the head unit can cause noise that's fixed simply by doing that.

I'm super busy working today so perhaps someone can post pics or tutorial of what I mean sooner.

 

[longbedbob]

Have you tried grounding the outside ring of your RCA cables? Internal fault in the head unit can cause noise that's fixed simply by doing that.
I'm super busy working today so perhaps someone can post pics or tutorial of what I mean sooner.

I haven't tried that specifically, but I know what you mean.

I did measure resistance, though. The grounds of each RCA jack measured .5 ohms or less to the cage of the head unit.

On Crutchfield's advice, I also trying grounding the cage separately to the dash with no luck.

The only thing that's worked so far is running accessory power directly to the battery. I hope to install noise filters on both 12v inputs later today. If that works, I probably won't use it as a long term solution. Instead, I'll probably install another fuse panel and run power directly to the head unit for constant power and via a relay for switched power. At that point, the only connections to the factory harness would be the antenna, back up camera, the reverse signal for said back up camera and CANBUS signals used by the PAC RadioPro (included with dash kit).

At that point I'd say that my problem is under the hood. Since my truck is still under warranty, I've already spoken with the local dealer about investigating "dirty" power. Predictably they said they couldn't help since I'd installed the stereo and therefore might have caused the problem. I'd need a very convincing case to demonstrate otherwise.