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Old 12-04-2006, 09:12 PM   #1
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Electrical noise problem

OK, here goes...

We travel with a laptop that houses our entire music collection (~80 gb - ripped using iTunes)

I have changed out both my truck and AS stereo with a JVC head unit (12v, of course) that has a front aux input that I feed from the laptop audio out (standard run-of-the-mill analog output - 1/8" stereo mini to 1/8" stereo mini)

In the AS, if I power the laptop using the 110v adapter, I get nothing but noise. If I use the 12 volt adapter, everything is fine, the music sounds great. OK, I can live with using my 12v adapter.

(Noise also happens if I use the 110v adapter plugged into a small portable inverter that is plugged into the 12v in the truck - using the actual 12v laptop adapter works fine - no noise)

[I know what you're thinking - why I would use the 110 v adapter in an inverter if I have a 12v adapter to begin with...well, let's just say it's the whole "which came first, the chicken or the egg?" scenario!!]

Anyway, I decided on our last trip I would like to run the stereo output from the standalone dvd player through the AS stereo speakers instead of the putzy TV speakers. The audio output from the dvd player (110v) going to the JVC (12v) aux input results in, you guessed it, nothing but noise.

I'm certain that a straight 12v dvd player will solve the problem (haven't tried yet - I'm assuming success based on the laptop experience), but I'm curious to know if there is a way to filter the noise.

The AS is a 2003 Safari and it looks like from the schematic that both 110v and 12v systems are grounded at the same point, so I would guess that it is not a ground loop issue.

Can anyone shed some light? - Is it just not possible to "interconnect" 110v and 12v components together sucessfully? Obviously, this is the first time I have ever tried "mixing and matching", so to speak.

Thanks in advance.
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Old 12-04-2006, 09:23 PM   #2
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Noise

Let me get this straight, you are plugging a 110v inverter into a cigarette lighter receptacle /power port, then plugging the 110 v adapter into the inverter to run the appliance(computer DVD player) and you get electrical noise through the speakers?
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Old 12-04-2006, 09:44 PM   #3
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In the AS, no. The DVD player is a 110v unit plugged in to shore power with the audio output going into the input of the AS stereo, which is a 12v automotive head unit - that produces nothing but noise. That's the problem I am wondering about. My laptop acts the same way in the AS when using it's 110v adapter versus it's 12v adapter. No portable inverter involved at all in the AS.

Didn't mean to confuse the issue - In the truck, I initially had the laptop's 110v adapter plugged into a portable inverter with the laptop audio going to the 12v stereo - that produced nothing but noise. When I switched the laptop over to a 12v adapter, the noise stopped. I threw in the truck scenario since it also involved some similar 110v and 12v interconnect problems.
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Old 12-04-2006, 10:11 PM   #4
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Scott, you've confused me. "nothing but noise" isn't too descriptive. Is this noise a loud hum, or is it a hissing noise? Is the noise at the same volume level setting as when you get the good stuff from the adapter?
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Old 12-04-2006, 10:34 PM   #5
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I would call it a humming noise. It is a steady, higher pitched sound - it is at the same volume as the music plays when using a straight 12v adapter and it does increase/decrease in volume as you change the volume on the stereo receiver.
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Old 12-04-2006, 10:49 PM   #6
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Scott,

I don't know if I got quite a clear picture of your problem. But a couple more questions.

Do you have a built in inverter on your air stream? Some come with a that option. If so, you might try turning that unit off when you run the computer audio into your stereo, just to see what happens.

You mentioned that you heard the hum/noise on the stereo. Did you try a pair of headphone plugged into the computer and listen for noise while plugged into the 110V inverter and 12 adapter?

Sam
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Old 12-05-2006, 09:24 AM   #7
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humming is the 60 hertz frequency of shore power leaking through - somewhere something isn't grounded or you've got a bad filter capacitor.
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Old 12-07-2006, 07:47 PM   #8
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Ground loop hum. I get the same thing in my B-van when I try to hook my laptop up to play movies or music through the stereo system. One solution I've found is to run the laptop off batteries. Another is to use the 12-volt adaptor I bought for it.

And, sometimes...this is really annoying... it just doesn't happen. It should, but doesn't. I haven't figured out why, although I did discover that the ground on the 120volt line into the camper wasn't connected, and I'm not sure I've tested it since I fixed that. It also seemed to matter which outlet I used - the one in the cabinet by the entrance was better than the one in the back wall, for example.
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Old 12-07-2006, 11:23 PM   #9
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Ground loop hum. That would make total sense. The 12V system probably shares the same ground with 110.

I wonder, if a person could eliminate the problem using an isolation transformer between the 120V outlet and the AC adapter for the computer. I've seen them for about 60 dollars at electronic supply houses.

Sam
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