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Old 14th March 2006, 02:49 PM   #1
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Location: Flint, MI
Default Vehicle AV Equipment question

Hi all, I have been searching the web for the answer to my problem, and thought that I'd see if anyone here could help out a bit.

Basically I have a Chevy Astro Conversion van that came with a TV and VCR pre-installed. What I am trying to do is add a DVD player to the van and run all of the audio (DVD & VCR) through my headunit so that it comes out of all of the stereo speakers. I have a Panasonic CQ-DFX701U that has RCA inputs on the back. I have used these inputs before with an MP3 player, using it's headphone jack, and everything worked beautifully. The problem that I am having now is when I connect either the VCR or the DVD player, I can barely hear a thing. I have to turn the volume on the radio all the way up to max and I can faintly hear the audio coming out of the speakers. As far as I can determine, the RCA line audio coming out of the video devices is not strong enough. I am looking for an inexpensive way to boost the RCA power before it goes into the headunit. I am looking to either find a schematic and build some sort of pre amp or purchase one. Which would work best? Any help would be greatly appreciated!
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Old 15th March 2006, 12:41 PM   #2
lndm is offline lndm  Australia
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Does your headunit have a high/low level switch/knob? I don't know about your headunit but you'd think line level was line level wouldn't you?

Have you checked your cable for continuity (or tried another)?
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Old 15th March 2006, 12:45 PM   #3
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The headunit does not have any settings for the aux input other than on or off. I have tried using both a mobile DVD player and mobile VCR with 2 different sets of cables. I get the same results every time.
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Old 15th March 2006, 01:05 PM   #4
lndm is offline lndm  Australia
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Sounds like your headunit wants a higher level signal. This may not be as elegant, but could you feed it from the TV headphone jack (being sure not to overdrive the inputs)?
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Old 15th March 2006, 04:12 PM   #5
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Yes this is the same conclusion that I have come to. When I use my MP3 player's headphone jack it works fine through the stereo. The problem is I am bringing the audio directly out of the VCR and out of the DVD player into the headunit so I need to amplify the line level signal before it goes into the radio. Is there an easy way to do this?
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Old 15th March 2006, 05:47 PM   #6
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I'm not sure what the standard output level is for home equipment but the CD/DVD player I have here produces 2 volts AC (RMS) when a 0dBfs (maximum possible level) track is played. Even if the output is lower than this, it should be at least 1 volt. That should be more than enough.

Use a multimeter set to AC volts and measure the output of your VCR and DVD player when playing a disc/tape with a relatively high level of output (don't try to measure the level when the movie/video is on a quiet scene). If you read anything more than ~1/2 volt, the signal source is likely good enough.

If you try to amplify it, you're likely to run into noise problems. Car amplifiers and preamps have special input circuitry to cancel noise/isolate the signal ground. If you build an amplifier for the signal, you will need to build in a special input circuit, run it from batteries (no ground connection to the vehicle) or use an isolation transformer.

Was your MP3 player powered from the vehicle or from batteries?

If you set your meter to ohms, what is the reading if you place the black lead on a known good ground and the red lead on the shield ground of the VCR or DVD player? Unplug all RCA cables from the VCR/DVD player before measuring the resistance.
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Old 15th March 2006, 07:41 PM   #7
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Location: Flint, MI
I'll check the output voltages of both the DVD player and VCP later today. They are both 12v mobile devices powered off of the vehicle's system. The only thing I come up with is that my headunit needs a lot of power on the aux input RCA's. I'll post my results later tonight or tomorrow. Thank you!
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Old 16th March 2006, 03:33 AM   #8
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Location: Flint, MI
Ok, I figured out that I had a short in the RCA cables coming out of the radio. A quick soldering fix with a new set of cables and the audio from all of my devices are coming through loud and clear. Thank you for all of the suggestions!
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