Electrical issue: Feedback

[brad77]

I recently installed a new headunit in my X that accepts a 1/8" stereo line in on the face. I hook my MP3 player to this connection. When running the player on batteries I have no problems, but when it is plugged into a power point (DC) I get feedback. The MP3 player has a hard drive, and whenever it spins up I hear the clicking of the drive access through my speakers. When I turn the unit off, it gives the speakers a good pop (kind of like the sound when a sub gets flipped on/off).

Since this sound only happens when the player is hooked up to vehicle power, I'm thinking it's a bad ground connection somewhere. I spoke to a local stereo installer and he suggested hooking the player to an RCA input on the back of the deck, which I may try eventually. He said that 1/8" stereo connections are prone to noise and interference.

Any ideas? I'm about to do a few experiments to try to isolate the problem, but wondered if anyone had any input.

Thanks for any help,
Brad

[Schludwiller]

I got a lot of noise when using my portable CB with the power point. I think this was very common for people. I wonder if you could run a clean line from your battery?

Maybe Chuck or Coolerman have some ideas. They're more familiar with the electrical systems.

P.S. You said it had a hard drive. Are you using an iPod?

[brad77]

Originally posted by Schludwiller
P.S. You said it had a hard drive. Are you using an iPod?

Nope. I'm using a Nomad Jukebox upgraded with a 30 GB hard drive. I just made a cradle for it (first experience with shaping ABS plastic) and want to attach it to my center console. Kind of a home project to see if I can pull it off. Ideally, the line and power connections will be built into the cradle. I will probably be tapping into the console power point, but I'm starting to reconsider due to the noise.

Wouldn't I need some sort of step-down thingimajig if I ran a line from the battery?

[superjens]

The device you plug into your cigarette lighter looks like it's doing the job of stepping it down from 12 volts. If you run a power feed from the battery you still need to go through the adapter, in this case you could just snip the end off and hack it together. One of the wires on the adapter cable is a ground (negative) which should definitely be as short as possible to avoid any noise.

Another option is to get an in-car fast recharger for those NiMH batteries your Nomad came with. Unless your 1/8" jack/cable is really really crappy I'm more prone to thinking it's the power source causing the noise you hear. 1/8" are prone to noise, but I'm running two 25-foot ones together to get my sound card pumping into my home stereo with zero problems. In any case, since you say it sounds fine with the batteries you have your answer -- it's the external power causing this noise. It could also be the adapter that's doing this. Try it with another device if you can (make sure the power ratings are the same).

[hobbes69]

One of the most common reasons for getting "noise" from a car stereo is the alternater. All good head units have some kind of inline filter because the alternater produces AC power. Maybe you could find one a Radio Shack and add it inline with your MP3 players power cord.

Richard

[brad77]

Thanks for all the input. I've got plenty of experiments to keep me busy for now. I hope to use vehicle power rather than batteries, because the HD upgrade sucks a bit more juice than before. I think I'll avoid trying to run a line directly to the battery for now, but if filters fail it may be inevitable. I'll let you know. If I hack the plug off the DC adapter, I'm assuming I'll need to add an inline fuse to protect my player. If so, what gauge wire could I use without risking meltdown?

If anyone else has any ideas, let me know.

Thanks!
Brad

[coolerman]

Before you go hacking the plug off make SURE the plug does not contain the voltage dropping circuitry! Measure the voltage on the output side of the plug, if it's less than 12 volts then the plug is the dropping device. If you feed 12 volts to a 6-9 volt device, well, smoke is the usual result !

Your noise problem is most likely caused by a difference in grounds(commonly known as ground loops) used in the audio system. Experiment with grounding the components together with a jumper wire. Example: Ground the frame of the head unit and the frame of the Nomad to a common ground. If that doesn't work you might try an isolator between the head unit input and the Nomad output to break the ground loop. Any good stereo shop carries these. They can also help you solve the problem for a fee .

Alternator noise is a whine that increases in volume and frequency when the RPM's go up. In line filters can help cure this but don't count on it completely disappearing! A constant hum is usually a ground loop issue or a poor ground. I think the isolator would cure your problem since it doesn't happen on battery power.

[Schludwiller]

Hey Brad77, nice posing on a rock picture! You should add it to this old thread and maybe we can revive an oldie but a goodie with your 2002 (bummer some of those pic links are gone now)

[brad77]

Coolerman:

Too late! I did it the old fashioned way. I didn't have a voltmeter, so I just took the plug apart. The only thing I found was a fuse, so I'm using an inline fuse. The step-down circuitry is in a little box between the power plug (now hacked off) and the output to the Nomad. I've installed it (details in another thread, soon to come) and it's working fine.

I'm still running into some noise issues, though. I'm using an inline filter to no avail. I'll probably end up trying some of your suggestions. The isolator sounds like it may work. One question: How am I supposed to ground the Nomad as it's plastic? There's no "frame" to speak of.

Thanks for your help.

Schlud:

Thanks for the suggestion. I've tried to upload a pic to the thread several times, but it hasn't worked. The image is <100 Kb. Is AF still allowing uploads? I'll figure it out soon, I'm sure.