Unwanted noise (thumps and alternator whine)

[swargolet 10+ year member]

I have some pretty bad alternator whine and some thumps (when turning car on and headlights on) but the thumps aren't too bad.

Here is some common answers to questions you guys would probably ask.

- The power wire is ran along driver side of car, remote middle of car, and signals on passenger side.

- Sub amp is a Fosgate T1001bd, speaker amp is JL HD 600/4, and deck is a Pioneer deh-p980bt

- Amplifier ground is to a well grounded (verified with ohmmeter) spot in the trunk. Both amps go to a dist block first then to the ground bolt in the trunk.

- Head unit ground goes out to engine bay where battery grounds to chassis.

- All noises go away when RCAs are unplugged which I assume means the head unit is the culprit.

- Running a wire from the ground to the RCA shield doesn't change anything.

- I havent yet ran a dedicated power and ground from deck straight to the battery (next on my list) but does it even matter?

- The 3 RCAs (front, rear, sub) are new and pretty solid. American International (a division of BML Industries, Camarillo, CA) Part# HPC-20 CL

So any ideas or any other questions for me? I'm thinking about taking apart the deck as I heard there is an internal 'fuse' (essentially a thin piece of wire which burns up) that when blown it can cause issues like this. Is this true about the internal fuse?

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[akheathen Premium Member]

pico fuse... and you should be able to jump a ground from the rca shield to the h/u body/ground wire and make it go away if it blows. how is your engine ground? i really want to say to check your amp ground again. did you try grounding the shield to the body ground 2 the amp, too?

 

[swargolet 10+ year member]

Like I said above "- Running a wire from the ground to the RCA shield doesn't change anything.".

I am unsure how the engine ground is but I know that the battery to chassis ground is good. I'm 90% sure the amp ground is good but I can recheck it. The shield should be grounded at the amp just from the contact where it plugs in but it is easy enough to run a wire to the ground at the amp. Someone else suggested a ground loop which I'll check tonight be running the deck ground to the amp ground.

 

[takeaswag]

first off, either get a ground loop isolator, or just disconnec the ground from ONE SIDE of the phono cable (normally shields should only be grounded at one end as grounding both ends causes ground loops). Second is noise oming in from the power supply. A quick easy check is to run a capacitor from the power line to ground (check the polarity of the capacitor, or use the "tap-a-filter" at electronicnoisefilters.com). If the capacitor fixes it, you're done. If it makes it better but not good enough, get an actual inline power filter with three wires (line, load, and ground) with a current rating compatible with the power amp.

 

[Worlddre 5,000+ posts]

Make sure the voltages match at each one of your components...by definition a ground loop is a difference in potential(voltage) between two components. Not always caused by a ground. So make sure that every component in your system is sitting at the same voltage as the battery when under load.

 

[takeaswag]

Just to expand on what worlddre said about ground loops, that truly is the definition, but when a shield becomes the conductor that is constanly trying to equalize that different potential, that current in the sheild is induced into the signal wire as a voltage causing noise. The cure is to prevent the sheild from being the equalizer. you can either isolate it using an isolator which runs everything through a capacitor or a transformer, or just unhook the sheild at one end or the other. Actually, you can disconnect the shield anywherre along the line, it is usually easier to do it at the ends though.