rage against the ground loop

haemphyst wrote: Disconnect the RCA cables from their respective jacks - do both ends. Using an ohmmeter set on continuity, ring out the RCA jack grounds (to ground) on the amplifiers. If they show continuity, do the same on the deck. This will tell you which end is the "funky" one. If neither end shows continuity, THAT is why touching a wire between ground and the shield kills the whine. Any resistance readings you receive SHOULD be less than one ohm. With a partner, check that resistance (from the RCA jacks) to the battery ground. Also check the resistance from the alternator housing to battery ground. It should effectively be the SAME resistance as the meter leads alone.

I'm a little fuzzy on using my ohmmeter. I'm not entirely sure what you mean by ring out the RCA grounds (to ground) on the amplifiers? Can you explain the produce more simply? Thanks, -Greg

From the visible silver (or gold plated) part on the RCA jacks to the ground terminal of the amplifier or deck. "Ringing it out" is just a term that means "test for continuity", because most continuity testers have a buzzer of some sort that "rings" while in continuity mode. When you hear the buzz, you have a low resistance electrical path between those two points in the circuit. When testing for ground resistance, you need to know what your meter leads are adding to the circuit. Touch them together in "resistance" mode, and note the number that remains after about 5 seconds. (It should be about .1 to .2 ohms.) This is the number you must subtract from all resistance measurements from now on. This will get you much closer to the actual resistance that you are specifically trying to measure.It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

Thanks for the clarification. I will have to test this out next Monday as I am gone all weekend. It's going to bug me not having this resolved but nothing I can do about that for the moment. Cheers, -Greg

This is a very common problem.  What seems to be a very common cause in our shop is head unit preamp grounds have been damaged.  This happens when you connect an amplifier and have a bad ground connection on the amp.  OR if you turn on the stereo without a good ground to the amp.  What happens is the amplifier will try to ground through the RCA cables.  Often the small circuit traces inside the indash will open up like a fuse.  This will definitly cause engine noise.  Once you ground the amps correctly, the signal is now using the car chassis for the now damaged rca ground.  In some decks like Pioneer, they have fuses in the deck on the RCA connections that blow, Then there is seemingly NO rca output.  I have seen MANY Pioneer decks that have been "cobbled" by wrapping a wire around the rca connectors on the deck and grounding it to the chassis in an attempt to "undo" the damage.

While the stereo is playing and you hear the noise, Take a Jumper wire and temporarily connect the rca outer shield to ground.  If the noise lessens, or goes away, that is probably your issue.  You may have to try this with each rca connector, or with one rca connected at a time.

And hence why you do NOT fuse ground circuits. (As a general rule.) Not that I mean to hijack, but some months ago there was a poster that thought there was an advantage to fusing the ground AS WELL AS the hot side. But they finally saw the light (without the sparks) and saw how this type of problem could occur - ie, a bad ground (or blown ground fuse) means alternate ground paths will be used.    Summary - only fuse the hot side (as a general rule).

The resistance on all of the RCA's seems fine. I tested with one of the RCA's on the front speaker amp input and front speaker head unit output and it's like it "half plays". Upon ground out the head unit RCA's (the non used one's) it worked again. Or grounding out the RCA's. Resistance between the amp and the ground was 0. I wasn't able to test voltage because my multimeter doesn't seem to be capable of it... thanks radio shack. -Towels

I guess what I need is clear and concise instructions on how to test whether the pre-outs on the AMP or the pre-outs on my head unit are are not grounding properly. I believe the RCA cables are good. -Greg

I have no continuity from my RCA outer edge and the frame of the head unit leading to me to believe something went wrong and the lines are blown. Sigh. -Greg

wartowels wrote: I have no continuity from my RCA outer edge and the frame of the head unit leading to me to believe something went wrong and the lines are blown. Sigh. -Greg

Just as I suspected.  Your amps must have tried to ground through your RCA's.  This will be a problem in the headunit at this point.  You can get by by grounding the rca sheilds on the deck to the chassis of the radio, But the radio should be looked at for a proper repair.