Alternator Hum (System)

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A K

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I'm working out the kinks of installing a new headunit. After a relatively successful, I've run into two issues.



First, when I turn on the radio, the OEM sub pops. From searching, it appears that aftermarket decks use about a 12v power-on. So, a 12v-5v resistor from Radio Shack seems to be the easy solution. No questions here, but feel free to give an "Amen" if you've done this and have any words of wisdom--like where to mount the resistor behind the dash.



Second, I have the dreaded alternator/engine hum that reflects the RPMs from the rear sub. In addition, when the unit dims, I get an additional hum that does not change. So far, I've identified a few things I can change. First, I zip-tied the sub and deck harnesses together. I will isolate them tomorrow (so that the RCAs are away from any power and ground). Second, I will ground the headunit itself to the firewall and not to the OEM harness (I don't know where the OEM harness grounds, and it appears the longer the ground wire, the greater the chance for interference). Third, I will try to run a ground wire from the White RCA as it appears when I touch it, the hums go away (even if for a few moments). I'm hoping that I can simply wrap and tap to the firewall.



Now, for the weird part. When I twist the White RCA, the interference goes away for longer than I am holding it, but comes back. Is this due to me temporarily grounding it, or is it more likely the RCAs are shot? Crutchfield uses decent materials, so I am somewhat reluctant to immediately conclude that their cables suck.



Any comments/insight is appreciated.
 
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Maybe add and extra ground ????



How about a ground loop isolator ??? Do they even use those any more ??



Todd Z
 
From where should I run the ground? I don't mind doing a dedicated line, but I want to connect somewhere where I'll be fairly "secure" from picking up interference.
 
When I added my aftermarket deck I used a 7805 voltage regulator to drop the 12v down to 5v for the factory sub. The exact .33 and .01 caps are not cricial either, mine were close to those, and any electronic store or Radio Shack will have them.



[Broken External Image]:





The ground for my new system with the amp, is a bolt in the rear where I beleive the rear window frame is bolted to. I have zero noise.



Chad
 
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Chad:



The link below seems to be what I need. Left in, right out, and middle ground. I'll tack it likely against the rear cab wall because it apparently throws off a bit of heat and the dash interior is warm to begin with.



What are the caps--capacitors? And I essentially tap the in and outs with wire, separated by a capacitor, and run them to the ground, also?



[I can sort of follow electric diagrams, but by no means am familiar with them.]
 
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Because I'm famous for not noting resolved problems--



The problem was that one of the RCA cable plugs was bad. I picked up solder replacements at radio shack, spliced them onto the harness, and the noise is gone. (But, before I did that, I grounded the damn unit to every bolt I could find--I took a 10 foot wire, spliced it in, and was touching everything. Only after did I decide to try the cables.)



In addition, I spliced in the 7805 regulator and the pop is gone. I bolted it to the metal dash support to the right of the radio area (worked perfectly, Chad).



I'll have a complement of install photos tomorrow when it's light out. As it stands, the replacement radio is ready for simple plug and play. Woot.
 
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