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'11 Outback 2.5i CVT - '06 Forester X 5MT
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Discussion Starter #1
I recently installed an FM Modulator in my '06 Forester and I have been getting a bad whine from it. I am in the process of diagnosing the cause and wanted some help.

At first I was thinking a Ground Loop Isolotor might solve the problem but the more I read, I think part of the problem is from how I wired it in. I tapped into the power and ground from the acessory plug. It was cold and I just wanted it done, so that was easy and accesible.

ONce warmer weather comes I'm going to take it all out and reinstall it. I was looking for a few pointers.

1st what is the best place to pull power? I want switched power, so I am still considering hooking + to the cig lighter. I'd rather not run an independant power wire. Would the stereo be better? I intend of finding a good, close body ground.

2nd how can I diagnose whether a Ground Loop or Nois Surpressor is needed? I am fairly certain that, as of now, the noise is there even when I unplug the audio cable.

I know FM modulators are not ideal, but I am sure I can do something to remove the hiss I am hearing. For $12 I could just put both in, and I still might. Just looking for some knowledge on which to use and why.
 

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2015 2.5i Limited Carbide Gray
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832 Posts
The best way to work on whine is to try to power the signal components from the same power supply. I try to but sometimes its not as convenient. A proper install with quality components won't need additional parts to get rid of noise. I have seen a few times when the modulator was bad and causing the noise regardless of what else was installed in the signal chain. A ground loop isolator will be what I would try first since the noise suppressor will tend to get rid of some of the good as well as some of the bad.

I would try a more solid connection of where you started, then try behind the radio and then the ground loop isolator then to the noise suppressor. I would also look into when the noise is present and if there is anything that seems to cause it before I start buying anything else that is a band aid.
 

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I installed a VHF ham radio directly connected to the battery and I have a high pitched whine on the speaker which relates directly in frequency to the engine speed. So either I've got a bad capacitor in the radio or a signal superimposed on power feed cables.

Thinking a noise suppressor would help didn't and I still have the whine. It's not very noticeable, but it's there when I transmit and receive.

Having said all the above, I'm thinking the OP's issue might be a bad capacitor or other component in the radio. Try wiring directly to the battery terminals and see if there's a change. Perhaps there really is a waveform superimposed on the 12VDC from the alternator. Before you shell out money for something to hide the problem be sure the issue wasn't there before you installed the new equipment.
 

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'11 Outback 2.5i CVT - '06 Forester X 5MT
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Discussion Starter #5
I would try a more solid connection of where you started, then try behind the radio and then the ground loop isolator then to the noise suppressor. I would also look into when the noise is present and if there is anything that seems to cause it before I start buying anything else that is a band aid.
Thanks for the advice.

I am going to start here. Right now I just have the wires shoved into the rear of the plug on the outlet. Not the most secure, but again, it was cold and it was easy.

The noise comes on when the FM modulator is on, regardless of the input source. Right now I have it hooked to my XM and I hear the whine before the XM loads and starts feeding it audio. That is why I am not sure if a ground loop isolator would help.

I use the XM in my OB too with the Aux In and hear nothing, so I don't think that is the problem. I do have them tied to the same power source, but it's not the most solid connection.

I'm going to take it all apart when it warms up and splice directly inline to the Stereo switch power for a solid, and hopefully clean power source. I'll then find a good solid ground behind the stereo too. Lots of bare metal so that should be easy.

In hindsight and after researching a little more, I think the bulk of the problem is just that I installed everything hastily and not as clean as I normally do because of the cold weather. I should have known better.

The noise doesn't seem to be related to engine speed, I've tried to listen for that and see nothing. If anything it seems more related to temperature. When it's really cold it's alot worse and gets better as the car warms up, and I don't notice it as much when I get in the car on a sunny afternoon.
 

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2015 2.5i Limited Carbide Gray
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I would work on the install before I get around to buying anything, unless you can buy it and have it there when you re-install the equipment just in case the problem still exists. Noise issues have many sources and it's hard to diagnose. It's good that you use the XM unit in the OB since that should remove it from the equation. Now it's up to you to find some time to start digging.
 

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'11 Outback 2.5i CVT - '06 Forester X 5MT
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Discussion Starter #8
Thanks everyone for the advice.

I had some time (and the weather) this weekend to clean up the install. I added an OEM sub, so I used the wiring harness for that to solder in a nice clean power feed and used the shared ground off it to ground to the metal stereo surround. Hooked it back up and everything works MUCH better.

The modulator is still a little muffled for lack of a better term, but I think that's just the modulator itself. The whine is completely gone, at low volume or with the XM off there is no background noise.

So to summarize, I shouldn't have been lazy to begin with lol.
 

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2013 Legacy Lim CVT Car: 2011 OB Prem 6MT Car: 2006 Miata GT 6MT mc: 2003 Honda GL1800A * Reunite Gondwanaland *
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... how can I diagnose whether a Ground Loop or Noise Surpressor is needed?
Temporarily, power it from a 12V battery -- NOT the car battery,
but a separate DC power source not connected to chassis ground.

- if that kills the unwanted noise, a ground loop isolator is needed

- otherwise, a combination of noise suppressor (a.k.a. noise filter)
- and signal cable re-routing and/or shielding is your best bet

.
 

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'11 Outback 2.5i CVT - '06 Forester X 5MT
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Discussion Starter #10
Thanks looby for the answer. It looks like I got it sorted out now, but I'll keep that in mind for any future wiring projects.
 
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