Audio & Power in car: Electrical Noise

kd5ftn · Mar 18, 2008

I've got a problem when I plug my phone into my car stereo as well as cigarette adapter.

I'm also got a kind of custom setup.

Audio
Honda Civic Stock Stereo -> CD Changer to Aux Input Adapter -> 3.5mm to 2.5mm adapter -> 2.5mm input on HTC Y adapter.

Power
Belkin Cig. Lighter to USB Female Port (From old iPaq) -> HTC Stock Sync/Charge USB cable -> MiniUSB input on HTC Y adapter.

So, when both the power and audio are plugged in, I hear a horrible hiss on my car stereo, not to mention a sound that varies in pitch to my throttle. When I unplug the power, the audio is completely clean. To me this seems like some kind of a grounding issue - to say that the Audio and Power both have seperate grounds, and bridging the two creates a potential difference in the form of noise on my Sound. Also to note: I only hear the noise when the Y adapter is plugged into the phone. With the audio and power plugged into the Y adapter, but the Y adapter not plugged into the phone, It's perfectly clean. I'm kind of baffeled.

The only solution I can think of is to gut the Belkin Power->USB adapter, and providing it from 12VDC elsewhere. I've got a tap directly below my passenger seat where I have a big power inverter tied to my battery. I don't know if I'd hear the same sound by grabbing my power from there.

Anyone with an engineering mindset have an idea? I'm open to suggestions.

Asphyx · Mar 18, 2008

If it was a grounding issue I would expect a buzz not a hiss...

Does it go away when you unplug the power and just leave the audio?

Go away or stay when the phone is unplugged?

It could be a bad adapter so maybe try another...

kd5ftn · Mar 20, 2008

It goes away when I unplug the power, or unplug the phone. It's only present with audio+power both plugged into the phone.

I've tried powering it using the AC adapter and a power inverter - that sounds clean.

devoe · Apr 10, 2008

Fix?

I have the same problem and went out and bought a ground loop isolator from Radio Shack. It ran about 12.00 and it definitely got rid of the noise but unfortunately it noticeably affected the sound quality of my music and made it sound high pitched.

Perhaps buying a higher quality one will solve the problem. In the meantime, I've returned the isolator and just run on battery when listening to music. Perhaps I'll hit Ebay and see if there's a higher quality ground loop isolator.

worwig · Apr 23, 2008

Definitely a ground loop problem.
As devoe said, you can get a ground isolator and put in the audio line, but those are typically a simple transformer, and they often don't pass low frequencies very well.
You may be able to simply cut the ground going to the audio jack input. Not a perfect solution, but it sometimes works. But it usually requires a blocking cap in each channel. An experiment for sure.
A different power adapter might help. Or not.
You may also be able to add in a power plug that is wired directly to the radios ground and power. Then your power adapter plugged into that might have a ground that is close enough to the radio ground to not have a problem.

Me, I would open up the power adapter, and if it is a switcher supply with a transformer, see if I could isolate the ground.

meccanoble · Apr 26, 2008

I had the exact same issue. I believe it is called alternator noise.

01 Nissan Maxima with Eclipse AVN 5435 RCA hook up. When cigarette lighter and audio are both on, it makes the noise. I dont think it happened in the beginning but definitely happens now....

Luckily my Kicker 12L7 overwhelms the noise and allows me to tolerate it...somewhat.

Carty · Apr 26, 2008

When the audio wire and power wire are close to each other, this problem happens. Intead of using an isolator for audio wire reducing quality, try shielding your power wire instead. Might work but not very sure..

J Shed · May 16, 2008

worwig said:
Definitely a ground loop problem.
As devoe said, you can get a ground isolator and put in the audio line, but those are typically a simple transformer, and they often don't pass low frequencies very well.
You may be able to simply cut the ground going to the audio jack input. Not a perfect solution, but it sometimes works. But it usually requires a blocking cap in each channel. An experiment for sure.
A different power adapter might help. Or not.
You may also be able to add in a power plug that is wired directly to the radios ground and power. Then your power adapter plugged into that might have a ground that is close enough to the radio ground to not have a problem.

Me, I would open up the power adapter, and if it is a switcher supply with a transformer, see if I could isolate the ground.

What he said. The fact it alters in pitch with engine speed says it's alternator wine, which is related to grounding issues. I have a similar problem, but it's not a wine that follows RPMs, just a static like hiss. I need to dink around with the ground and see if I can get it.

studentjunk · May 21, 2008

I had a similar problem. I hadn't used my car audio for a while and when I started it up again, it was making horrible noises. I bought a new charger and had significant improvements. I'd recommend buying a charger from radio shack. If that doesn't fix it (or if you find it cheaper online), then you can return it.

nttdemented · Sep 24, 2008

If you can, verify the grounding cable on your cigarette lighter. Best thing you could do it to cut it and look for the nearest solid metal ground point in the lighter's general vicinity and ground it to that. Could be the stock ground on the plug.

I'm a car audio buff and my previous car, a 01' Camry had that issue when I charged my Creative Zen touch and played audio through it as well... Fixed it by re-grounding my lighter plug directly to the chassy, its just a matter of finding the right spot nearby to ground it with a good sized gauge wire, like 12 or 14 AWG.

Xorgeo · Dec 12, 2008

I had a similar problem. I discovered that my problem was that the Mogul's CPU noise was conducting out the USB DC power cable and then coupling back through to my FM transmitter on it's DC power cable. I never was able to completely get ride of the noise. However, I was able to reduce it substantially by using a different USB 12VDC power source. USB hubs normally contain low pass filters on the USB power lines, so your mileage may vary.

The tick to solving your problem is to try different configurations by moving and disconnect wires. Often you can here noise variations that will indicate whether the noise is external to your system.

EMI is either conducted (ground loops) or radiated. Since audio is below 1MHz it is best if there is only a single ground point. Since you normally have multiple wires, ground loops are common, so keep your wires short and your devices close together.

ultradj83 · May 31, 2010

Same trouble here, but on a Touch Pro...

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Audio & Power in car: Electrical Noise

kd5ftn

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Asphyx

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kd5ftn

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devoe

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worwig

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meccanoble

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Carty

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J Shed

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studentjunk

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nttdemented

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Xorgeo

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ultradj83

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