ground loop noise
Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=119692
Printed Date: May 17, 2025 at 11:42 PM
Topic: ground loop noise
Posted By: kbirtch
Subject: ground loop noise
Date Posted: January 27, 2010 at 3:52 PM
hey guys, having a funny ground loop problem.
just installed a clarion vz409 7" flip out lcd in a 2006 pontiac g6 coupe. client has a nice monoblock amp running an avg 10" ground thumper. sub works fine, system sounds great.
allow me to describe the problem,
1) while pausing the audio on vz409, at low volume levels there is audible static. resembles fm static somewhat.
2) again with dac (digi-analog conv.) paused, (stopped or switching modes has 0 static) rolling up the volume increases static until audible ground loop can be heard. for clarification, this is a 'whining' sound that correlates to engine rpm and sounds like a penny-whistle.
the ground loop happens only through the speakers in the car, the sub appears exempt. (or inaudible) i initially faulted this to a head unit ground cable, which was coming from the factory harness. i've since swapped that out for a solid ground from inside the dash to no avail. the noise is fairly quiet or completely inaudible under normal listening conditions, only on a paused dac with high volume does it become noticeable.
i believe this car to be factory amplified, could this have anything to do with my problem??
extremely frustrating, and i have limited experience with ground loop isolation, mainly when an aftermarket amp is used with crappy signal cable. any ideas?
Replies:
Posted By: DYohn
Date Posted: January 27, 2010 at 6:04 PM
If it has factory amps, how did you interface the Clarion to them? ------------- Support the12volt.com
Posted By: kbirtch
Date Posted: January 27, 2010 at 6:33 PM
tldr to your question; i just wired the harnesses together. got the metra kit 99-3303, in it is a harness labled 'factory amp interface' which took oem plugs, converted the driver info center into it's own native lcd in the pocket location and gave me traditional 11-wire harness for aftermarket head unit. i'm assuming the factory amps are running from speaker level inputs. if my assumption is incorrect, that would mean the oem head unit uses signal level output on speaker level (looking) harness, and i've plugged speaker level output to that. either way the output is clean, not distorted or squaring in any way, so i've assumed the former option.
Posted By: i am an idiot
Date Posted: January 27, 2010 at 8:20 PM
How loud can you turn the volume of the radio before you reach a level that you consider loud? If you can only turn the radio to 8 or 10, the amp may be looking for Preamp level. If you can turn the volume up a good way before it is loud, the following may help you. Cut the negative speaker wire connections. Insulate the negative speaker wires that are coming from the radio. It is very impoortant that they not touch anything. Now ground the negative wires that go to the vehicle. This will cut the input signal going to the amp in half. This should eliminate your noise. Make sure you do not ground the speaker wires that come from the radio. Only ground the negative speaker wires that connect to the harness you purchased.
Posted By: kbirtch
Date Posted: January 27, 2010 at 8:41 PM
so in the 99-3303 harness which interfaces oem plugs to traditional aftermarket HU 11-wire, you want me to cut all (-) speaker wires and splice to ground? as soon as i performed the install i noted that roughly 50% up the volume control and the system is already quite loud. by quite i mean by 70% up the volume knob you had best be wearing earplugs, its really that loud. about 8-10 on a scale of 30 is average listening volume.
Posted By: i am an idiot
Date Posted: January 27, 2010 at 10:09 PM
Cut the negative wires and ground only the wires that lead to the vehicle. Insulate the negative wires that are coming from the radio.
Posted By: poonamt93
Date Posted: January 28, 2010 at 3:09 AM
I have the same problems and check everything , change all the wires i day spend all day and nothing later i change the amplifier and the noise was still there.
The problem was the pioneer radio was sending the noise for some reason it when bad that day a radio that was install for 3 months.
Check your radio.Good luck as i know how irritating this can be.
Posted By: DYohn
Date Posted: January 28, 2010 at 11:11 AM
Most factory amps do NOT use speaker level inputs, they use line-level inputs, which is why I asked the question. Your symptom is common if you overdrive the OEM amps by sending them a speaker level signal. I suggest bypassing the amps. Is this a Monsoon system? ------------- Support the12volt.com
Posted By: kbirtch
Date Posted: January 28, 2010 at 8:35 PM
it is a monsoon system, yes bypassing the amps is something i would like to avoid if at all possible, rather try to swap my speaker level outputs for line using a LOC or similar, seems like a simpler / easier solution given that the amps are in fine working order and are probably higher / cleaner output than the amp in the clarion HU. at some point client would like to swap for a 4ch amp and do door speaker conversions to aftermarket, which imo is a good time to look into amp bypass. granted i'm a newb, but ground loop being a common problem from overdriven factory amps?... find that hard to believe being that a ground loop is a specific problem and shouldnt be related to strength of an input signal... am i wrong?
Posted By: kbirtch
Date Posted: January 28, 2010 at 8:38 PM
i am an idiot wrote:
Cut the negative wires and ground only the wires that lead to the vehicle. Insulate the negative wires that are coming from the radio.
grand idea if it works, if it doesent i'm just making more work for myself in having to undo these spk connections. assuming this is a troubleshooting step rather than a solution, is there any way i can perform the same troubleshoot with a non-destructive means?
Posted By: i am an idiot
Date Posted: January 28, 2010 at 8:55 PM
I did not know that cutting 4 wire connections was a destructive method. You could do only one speaker, you will have to stick your ear to each speaker to see if the one you did is less noisy than the other 3 channels.
Posted By: kbirtch
Date Posted: January 29, 2010 at 12:31 AM
lol gotcha =)
thanks for the tips, will try them all in one by one tomorrow + post the results
Posted By: kbirtch
Date Posted: February 08, 2010 at 7:04 PM
alright, took a little longer than expected to try some solutions, but here is the update:
[quote]1) cut the grounds for the speakers, shorted them to a good ground.
2) insulated the ends from radio.[/quote]
this fixed the problem upon initial inspection. ground loop noise is completely gone, although the interference near the top of the volume knob is still clearly audible. for clarification sake, this isint a high pitched whine like before (correlating to engine rpm) but rather just plain old static.
the noise at normal listening level is inaudible, and thus client is satisfied with this solution.
HOWEVER.
upon plugging the antenna back into the clarion HU, i find that the ground loop has not only returned, but has actually gotten significantly louder.
what might cause a ground loop when antenna is plugged in?
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