quick question...

[goon 10+ year member]

I am having alternator whine and read in a previous post while searching that if i unplugged the rcas and the whine went away then the source of the whine could be my HU? is this true? i have checked everything else excpet for re-grounding the HU or simply putting a new HU in...thanks for any help guys.

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[helotaxi 5,000+ posts]

Well I would then think that the first thing to try would be a reground of the HU. Alt whine can 99% of the time be traced to a bad ground of some sort.

 

[jrz126 10+ year member]

what HU are you running? you might have to reground your RCA's

http://www.caraudio.com/vb/showpost.php?p=1121098&postcount=39

There's a bunch of info in that thread as well. http://www.caraudio.com/vb/showthread.php?t=113520&page=3

 

[helotaxi 5,000+ posts]

Any good amp or head unit will have the signal path ground isolated. Any time that grounding RCAs is fixing the problem, you have a ground loop, meaning that you have two problems; 1) your components do not have a ground isolated signal path and 2) you have a ground loop caused by voltage differential between the grounds of the components connected by the RCA in question.

 

[jrz126 10+ year member]

Well regrounding the RCA's worked for me...and many others on this board.

 

[helotaxi 5,000+ posts]

I'm noty saying that it doesn't work, because you know from personal experience that it does, but I am saying that it shouldn't be necessary unless there is something wrong with one of the components in the signal chain or its ground. Basically what is occurring is that there is a potential difference between the grounds of the components in the chain (bad ground on one or more components) and the potential is equalizing across the signal cable and intruducing noise (AC ripple at 3 times the frequency of the alternator RPM) into the signal. Grounding the RCA jacket might cover the symptom but it doesn't address the cause of which the noise is the only readily obvious symptom.

 

[jrz126 10+ year member]

I'm not sure of the exact cause for the noise, but I think the problem is inside the HU itself.

Just curious, why is the noise 3 times the alt. RPM?

 

[helotaxi 5,000+ posts]

Actually, thinking about it, it should be 6x the alt RPM. The noise that you hear is the ripple voltage left over from the rectification process. The direct output of an alternator is 3 phase AC. The rectifier basically flips the neg swing of each phase over to the positive. The result is DC with a slight pulse six times (once each for the pos and neg of each phase) for every revolution. Check out the picture below.

The first is straight DC, basically what it coming from your battery. The last is what you get from a properly working alternator. Notice the ripple at the top. Alot of people that are getting really bad noise (especially radiated noise) have a bad winding on their alt so the resulting voltage is somewhere between the second and the third diagram with a really pronounced ripple. As long as this ripple is kept out of the signal path, you will never hear it. It doesn't really cause a pulse in the power that is seen by your audio components because they have capacitors in the power supply that effectively filter it out. If the signal section of the component is not electrically isolated from the power section, the ground differential between the various components of the system will use the path of least resistance (in many cases the shielding of the signal cable) to equalize the ground potential. Once this ripple is introduced into the signal chain, you're going to hear it.

 

[jrz126 10+ year member]

ahh, ok. I figured it had something to do with the alternator ripple, but I couldnt figure out where the 3x came from. I also didnt know that the alts were 3 phase. Makes sense though.

Are you a EE?

 

[helotaxi 5,000+ posts]

Are you a EE?

If by EE you mean "Eventually Economics," then yes.

I've been dabbling in this stuff for about 15yrs now and have managed to learn a lot in the process about how stuff really works as opposed to buying off on the large quantity of marketing BS that is out there that manages to keep a lot of the myths alive.

 

[goon 10+ year member]

I am using a Pioneer 6500mp...I will try re grouding the HU..I think this is the same as groudning the RCAs? I'll let you all know how it turns out, i can't take much more of this whine. thanks guys

 

[jrz126 10+ year member]

regrounding the HU isnt the same as regrounding the RCAs.

This is a common problem with the pioneer HU.

helotaxi, I kinda figured you were going for electrical engineering (or already were one). I'm also into learning stuff like this on my own. (and I'm going for a double major in computer and electrical engineering).

 

[goon 10+ year member]

Ok, so how do i reground the RCAs? I havn't gotten a chance to get to the HU...what exactly is the common problem with pioneers?

 

[jrz126 10+ year member]

there is an internal ground problem inside the HU. Someone said its from disconnecting the RCAs when the unit is turned on.

Take a look at those links that i posted above. (3rd post in this thread)

 

[helotaxi 5,000+ posts]

helotaxi, I kinda figured you were going for electrical engineering (or already were one).

Actually graduated from college 8+ years ago with a major in Econ. Originally wanted to be a EE but the math dept at my school and I didn't see eye to eye. Got a C- in differential calc and a C- in diff eq. and decided that if I had to take more classes with these guys I wasn't going to graduate (the math dept was known for their awful instructors though there was one who was excellent and a 20 something hottie to boot, but that's beside the point). I switched to Econ and had a lot more fun and free time and a lot less stress.