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Old 19th March 2010, 10:30 PM   #1
KThug is offline KThug  United States
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Question First Post - Stumped on a Car Audio Problem

If anyone knows the solution to this, that would be GREAT. Anyways, I just registered on here and I'm looking for some help. I previously had 2 subs and an amp hooked up working fine in my car. I decided to upgrade and went with a JBL GTO1214D subwoofer and a JBL GTO3501 amplifier. Well I recently installed them and found that when I turn up the input level, there is just a constant rumble from the sub, not hitting with the beat at all and will still rumble even if no music is playing. I found that it only happens when the RCA's are plugged in. My previous setup worked fine with the same wiring and everything. So I'm stumped on this one and hoping one of you guys can help me out.

This is all I've done to try to fix the problem with no luck:
Replaced RCA's
Replaced Ground Wires
New Ground Location for Headunit and Amp
Double checked everything was wired correctly
Tried a Ground Loop Isolator
------------------------------------
All of these things didn't work for me.

The only other bit of info I have is that when I tried the Ground Loop Isolator it stopped the rumbling but then there was no hitting at all...



Thanks for the help.
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Old 20th March 2010, 12:02 AM   #2
m4ick is offline m4ick  United States
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Location: Gainesville, FL
Ground loop issue, problem in the head unit or problem in the amp. I've had bad amps and shorted speakers scew up some head units before.

Is this JBL equipment new or used?

Do not loop ground wire from one amp to the next, each one should go directly to chassis. Do not ground to side panels or other braces, they are tack welded offering little continuity. Ground to the floor (seat belt bolts are great) being careful to avoid the fuel tank and lines. Run a drill bit or file to shave away paint and primer at the ground point, make that metal SHINE!

It sounds like you've eliminated most of the possibilities. If all else fails, borrow an amplifier and install it. If the amp fixes it then there is a problem in the amp itself like a broken trace on the RCA shielding. If no change, switch head units with the same (borrowed) amp installed.

If that fixes it there is a problem in the CD player but this new amp may have caused it especially if it is used or "refurbished". You will need to check for voltage on the RCA inputs of the new amp before re-installing the amp with a new deck (to avoid messing up another). If you power up your new amp and find voltage on the RCA inputs (RCAs unplugged, of course) then the amp may need some help. I've had bad amps that could SHOCK THE CRAP OUT OF YOU on the RCA inputs.

Hope this helps, ground loop issues can be a real wrestling match if you avoid checking for bad equipment.
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Old 20th March 2010, 12:15 AM   #3
KThug is offline KThug  United States
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The JBL equipment is brand new out of the box.

I think I have everything grounded good.

I'm pretty sure the new equipment is all working properly because I took it down to an audio shop and they tested with a MP3 player with an RCA connection. The sub appeared to work fine then so wouldn't that narrow it down to something before the amp? I replaced the RCA's so I don't know what else it could be. The Ground Loop Isolator stopped the rumbling, but now there is no hitting at all.

RCA's-Amp = Rumbling
RCA's-Ground Loop Isolator-Amp = No hitting at all

I know it can vary from system to system but keep in mind that my previous setup worked fine with all of the wiring how it is.
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Old 20th March 2010, 12:29 AM   #4
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By any chance do you have a pioneer headunit? When uninstalling your old amps did u unplug the rca jacks before diconnecting the ground wire to the amp?
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Old 20th March 2010, 12:35 AM   #5
KThug is offline KThug  United States
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Quote:
Originally Posted by mike49504 View Post
By any chance do you have a pioneer headunit? When uninstalling your old amps did u unplug the rca jacks before diconnecting the ground wire to the amp?
I do have a pioneer headunit.. I only had/have 1 amp and I'm not too sure about the uninstalling of the old one.
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Old 20th March 2010, 01:04 AM   #6
m4ick is offline m4ick  United States
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wow, best guess is that head unit has been damaged during install/uninstall of amplifiers.

if it worked great through a portable MP3 player while it was installed in your car and the RCAs are new then I would assume the HU is bad.

i've remedied noisy head units by grounding the RCA shield behind the HU to the HU ground. not sure if this is kosher with most people but it has worked for me after testing a blown amp and messing up my deck (when i was a noob). that fix left me with a BARELY audible ground loop problem.

I just jammed a small wire into the shield before connecting it to the output on the deck then connected it to the ground connection. you only need to do this on one RCA, they are connected inside the RCA post.

Last edited by m4ick; 20th March 2010 at 01:10 AM.
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Old 20th March 2010, 01:13 AM   #7
KThug is offline KThug  United States
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Quote:
Originally Posted by m4ick View Post
wow, best guess is that head unit has been damaged during install/uninstall of amplifiers. if you have another head unit, try it. if not, try any other signal source like a portable MP3 player but not your expensive IPOD touch. If it goes away, the HU is likely the culperit.

i've remedied noisy head units by grounding the RCA shield behind the HU to the HU ground. not sure if this is kosher with most people but it has worked for me after testing a blown amp and messing up my deck (when i was a noob). that fix left me with a BARELY audible ground loop problem.
The audio store did try the MP3 player thing and it did work that way.. is there anyway the HU isn't damaged then? I remember awhile back I swapped amps with someone for a day and I think it did the same thing, but my memory could be bad because that was over a year ago. I don't have a HU to swap, or any other equipment to swap. I just have what I'm trying to get to work now.

The rumbling starts when I turn the input level up on the amp.. it doesn't rumble when the input is low enough but it doesn't hit loud enough to really tell I have a sub when the input is so low.

Anyone know why the Ground Loop Indicator makes it so there is no hitting at all no matter how high the input level?

Last edited by KThug; 20th March 2010 at 01:34 AM. Reason: More Information
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Old 20th March 2010, 01:37 AM   #8
m4ick is offline m4ick  United States
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only 2 things before this amp, RCAs and head unit.

the only way the head unit isn't bad is if it is not grounded properly.

this has worked for head units that have noise on the RCAs for me. insert a small piece of wire into the RCA itself (do not touch the center lead on the RCA, just the outer shield) and plug it in (now the wire should be between the shield and the RCA post). then ground the other side of the wire to the head unit ground.

you may be left with small pops that occur between tracks and when you turn the volume from 0 to 1 but it should be a big difference from what you have now.

i assume the isolator isn't working because there is NO ground on the head unit side (cause of noise). the ground loop isolator REQUIRES a ground on both sides in order for the transformers inside to work.

Last edited by m4ick; 20th March 2010 at 01:45 AM.
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Old 20th March 2010, 01:38 AM   #9
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Sounds like the fuse blew for the rca shield ( inside the head unit.) You must always unplug the rca jacks from the amp before you unhook the ground wire from the amp.

If you dont unplug the rca's from the amp before unhooking the ground wire The amp looks for another ground (head unit which burns out a fuse inside the unit.

Your Pioneer head unit is likely the source of the problem.

Ground a wire to the case of the head unit and touch the ground shield on the rca jacks' outer part And see it you still get the same problem

But its very likely the cause of your problem

Theres another thread that tells you on how to fix this problem

Last edited by mike49504; 20th March 2010 at 01:41 AM.
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Old 20th March 2010, 01:57 AM   #10
m4ick is offline m4ick  United States
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good point mike, never had that happen to me but makes perfect sense.

should be a rare occurance because RCA shield ground is generally the secondary center tap of the power transformer (isolated from chassis ground by a high ohm resistor) but not all amps are created equal. Above all, why chance it?

learned something new today.
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