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So last night I was working on the jeep. I discovered something I never noticed about my sound system. When I have the key in the accessory position and turn the volume down low the system performs as expected and no background noise is heard. But if I turn the key to the “run” position and turn the volume down very low I can hear some kind of background static. I have an alpine head unit and a PDX-5 amp. I ran heavy power wire right to the battery and used all new audio wiring for the head unit and speakers. Soldered everything.

Anyone know why? Or what the background noise is?

Once the engine is started and the volume is turned up you can’t hear anything unusual but I am sure the noise is still in the system.

Rocken the Jeep Creep this weekend ---------
 

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Is the noise there if you bypass the amp? Make sure the ground wire on the amp is short and to BARE METAL. I would also run a ground wire from firewall to the head unit to see it that helps.
 

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Oh man...I HATE chasing stuff like that down. First place I'd check is along the wiring you did to your amp and from the amp to the speakers. Look for anywhere where it's crossing (or running parallel with, but real close) other wires it could be getting errant signal from and move the wiring away and see if the noise goes away or changes. If it does, give it some extra shielding (electrical tape) in those areas. If not...well, we'll cross that bridge later. Hopefully one of the audio guys will chime in...this is just what I'd do-and I'm sure it's rudimentary, but it's all I got.
 

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cole_slaww said:
You ran the power wire for the amp on the separate side of the rca cables correct? If not it could cause static
Exactly what I was thinking. Make are you ran them on opposite sides to avoid interference.
 

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Discussion Starter #6
thanks for the ideas on what to look for. I will have to check tonight how i ran the power wire. I installed this a year ago, I used a skinny pedal mount and ran the power straight out the firewall and the rca wires run horizatal and up to the head unit. what i dont get is what is "on" with the key in the run position that makes the back ground noise. The engine isnt running so what can it be?
 

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McDaniel said:
thanks for the ideas on what to look for. I will have to check tonight how i ran the power wire. I installed this a year ago, I used a skinny pedal mount and ran the power straight out the firewall and the rca wires run horizatal and up to the head unit. what i dont get is what is "on" with the key in the run position that makes the back ground noise. The engine isnt running so what can it be?
Probably just feedback from the amp or radio. You can test it by unplugging the power to your amp then see if the sound is there.
 

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Do you by any chance have a convoluted set of ground connections run helter-skelter around your TJ? Sometimes having a poorly executed ground system can cause what is called a "ground loop" condition which can cause nearly impossible to diagnose problems. When I was a field engineer for a large computer company, many years ago, strange problems were sometimes found to be ground loops caused during the installation.
 

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Sounds like a bad ground to me.

Well it doesn't help that you have a pdx amp either. They use ICE chips and you hear distortion with them. It's just a crappy design. That particular chip is used because its cheap and they can sell a lot of those amps with them and the average listener would never know or notice.

Check your ground and consider a better amp.
 

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Discussion Starter #10
Jerry my father was an IBM guy and I was never allowed to run convoluted wires for anything! I will check the ground tonight see if I can make some improvements.
 

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It sounds like a ground loop. Check your gain levels - if you have an aftermarket radio with 4v preouts, the gains should be set to less than 1/4 way up. If you have 2v pre-outs, it should be closer to the half-way up mark. Where did you ground the amp? I would try grounding it to the same place as the radio is grounded. If you used the factory grounding strap to ground the radio, I believe it terminates right behind the gauge cluster; try running the amp's ground up to here and terminating them together on the same bolt.
 

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eboven said:
It sounds like a ground loop. Check your gain levels - if you have an aftermarket radio with 4v preouts, the gains should be set to less than 1/4 way up. If you have 2v pre-outs, it should be closer to the half-way up mark. Where did you ground the amp? I would try grounding it to the same place as the radio is grounded. If you used the factory grounding strap to ground the radio, I believe it terminates right behind the gauge cluster; try running the amp's ground up to here and terminating them together on the same bolt.
In fact those low voltage outs should be converted in most cases to a high level pre out, If he doesn't have a converter and is running low level inputs into the hi level amp terminals this could be his issue.

Some would say its a glorfied volume knob and that's true up to a point but its an incorrect way of viewing the gain setting.

He may have the gain too high.
 

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In fact those low voltage outs should be converted in most cases to a high level pre out, If he doesn't have a converter and is running low level inputs into the hi level amp terminals this could be his issue.

Some would say its a glorfied volume knob and that's true up to a point but its an incorrect way of viewing the gain setting.

He may have the gain too high.
The alpine PDX amp he has actually does have low-level inputs, so the deck's pre-outs should be fine, the difference in signal voltages between "low-level" pre-outs is what the gains are meant to take into account. The lower the voltage pre-out on the deck, the higher the gain on the amp must be set to compensate for the low voltage signal. If you have 4 volt pre-outs as most mid range to high end Alpine radio's will, the gains on the amp should be almost all the way down. If they are too high, you get a low signal to noise ratio, which will give you whine, especially when the ignition is on. Saying the gain is a volume control couldn't be further from the truth, they are just there to make up for the different signal levels that different decks put out. They should be set and never changed unless a component changes in the system.

The only time you need a converter is when you have a deck without low-level outputs, like a factory stereo. All aftermarket amps want a low-level signal for the most part, so you need a converter to change the radio's amplified signal and turn it into a low-level pre-out.
 
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