Engine noise/high Freq. after stereo upgrade

[Gronk]

A little background.

I have the 9-speaker Shaker system. I started out replacing all the speakers with JBL GTO638's in rear deck, GTO628's in front doors, and GTO329's for the mids. I disconnected the A-pillar tweeters since the 329's are two-way, and wanted to avoid impedance mismatch by paralleling the two.

Next, I added a JL Audio XD600/6V2 amp. I ran the power lead through the passenger side grommet, and power ground to the rear seat bolt.

I'm using Molex connectors to grab the front/rear low level input signals at the factory amp connector (black) and running the signals with NVX 4-channel RCA
cables to the amp along driver side door sill trim. I ran two speed wire cables, one using 8-conductors for the front/rear speakers and the other using 5-conductors for the mids and turn on signal (NVX remote trigger relay) from the amp to the grey and brown Molex connectors.

I'm using two NVX RCA splitters to feed the two front signal to channels 1&2 for the 329's (set to HP at 300Hz) and channels 3&4 for the 628's (set to full range).

And the remaining two RCA's are connected to 5&6 for the rear deck speakers (set to full range). I set the gains with voltmeter at no load with Vol set to 24 using 0dB test tones of 50 Hz, 1khz and 2.5khz.
Everything sounds great and for improved bass will add a sub later.

When I start the car I get faint high freq tone that varies with RPM's coming from the 329/mids. These speakers come with capacitors which I installed in series with + connection per JBL instructions.

Also get some popping when doors open or pushing clutch pedal. I'm pretty sure my ground is good at the seat bolt.
I can eliminate the noise by disconnecting the brown Molex connector for the mids.

Thoughts?

Gronk

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[assclown]

double check the ground point, and sand the area down to create a good connection. the shorter the ground wire is preferred.

for running the signals from the black harness, I did the same initially but to get a good pre-amp signal used a line converter with a ground loop built in

I would always get noise if I just hooked the black harness to RCAs and into an amp.

 

[stang1971]

never....never use a seat belt bolt.... ive been doing car audio since 1995 and ALWAYS make my own ground point.... in a buddy's 2016 mustang i put the 5 channel amp in where the spare tire would go. used that factory bracket that has a nut welded on it as my ground point... i ground it down to bare metal... used a bolt with a star washer..... ZERO engine noise..... sounds like it came factory.

 

[Gronk]

I'm measuring over 2 ohms from both the rear middle seat bolt and the bolt hole threads on the bracket in the spare tire well to battery (-) terminal. I have a calibrated Fluke 87 multimeter with quality test leads. Hard to find a good ground on these unibody vehicles!

 

[Gronk]

I relocated the power ground cable to the bracket in the spare tire well, and sanded down to bare metal, now reading 1 ohm to battery (-) terminal, still have the high freq whine with engine running. Maybe try ground loop isolators next?

 

[BigEasyGT]

I had the same issue with my Rockford 400.4 amp. I'm now using a buddy's pioneer 4 channel and there's no noise whatsoever. I moved my ground about 3 times and triple checked all the usual suspects. I've been doing audio for over ten years now and just could not figure it out.

 

[wildcatgoal]

Sometimes it's the amp, most of the time it's your grounding point. Your resistance should be <1 ohm, closer to 0. Point is really to have same/similar resistance as the source itself. Additionally, it's often worth it to check the quality of the ground that goes from chassis/body to battery. Can't tell you how many times I've just sanded down metal and replaced a bolt while even retaining the same stock ground wire (which is often undersized to accommodate much more than a small amplifier added to the system) to eliminate a number of issues with aftermarket audio equipment.

http://www.the12volt.com/installbay/forum_posts.asp?tid=49445

 

[OEMRadio]

I always recommend running a ground from the source to the amp.. it does make a difference

 

[Keith_PDX]

I have the same issue. I have about 2ohms from the ground cable connection point to battery negative terminal. I too thought it was a bad ground, even though 2ohms should be acceptable, so I ran a temporary jumper using 8awg from the amp directly to the negative battery post. Same exact faint alternator wine. Perplexed. Any other advice before I buy a filter?

 

[wildcatgoal]

Sometimes this is caused by a noisy regulator in the alternator.

 

[Keith_PDX]

Sometimes this is caused by a noisy regulator in the alternator.

I am assuming the filter will take care of this.

No noise at all when the car isn't running. No surprise there but just stating the situational facts.

 

[Keith_PDX]

I fixed it by grounding out the stock head unit. It appears there was a ground potential difference between the amp and stock head unit that caused some type of ground loop on the high level signals. Noise is now gone. This does explain why grounding out the amplifier itself directly to the battery made no difference, it was a signal problem. Keep in mind it appears the stock radio chassis is not grounded. Crystal clean sound now! Hope this helps someone else.
Cheers

 

[mumbles]

I fixed it by grounding out the stock head unit. It appears there was a ground potential difference between the amp and stock head unit that caused some type of ground loop on the high level signals. Noise is now gone. This does explain why grounding out the amplifier itself directly to the battery made no difference, it was a signal problem. Keep in mid it appears the stock radio chassis is not grounded. Crystal clean sound now! Hope this helps someone else.
Cheers

Thanks for circling back and telling us what fixed the issue! Could you give some more detail as to how you grounded the head unit?

 

[Keith_PDX]

There's a ground screw on the rear of the OEM case. For whatever reason on the base stereo Ford doesn't utilize it. Probably because the OEM system doesn't have an external amp so there's no external devices that can cause a ground loop or feedback problem. I just ran a wire from the amplifier ground point (under passenger seat) up to that ground screw. Effectively ensuring everything was at the same ground potential.

I got the idea off of the Crutchfield "troubleshooting noise" article and their included flow chart.

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