Noise, but only when using multiple RCAs

I've got a bit of an odd problem.  I'm getting engine noise when hookuping up more than 1 set of RCA's to my HU.   I have tested each cable individually and everything seems fine with no noise but as soon as I add a second set noise is a problem.   The headunit has 3 RCA out's (Front/Rear/Sub) and there is no noise on the first RCA regardless of which HU RCA out I'm using.    Any ideas what might be causing this?  

For refrence - my amp is grounded directly to the battery (in the truck in my Ion anyhow, I figured I might as well ground directly since it's right there.   I measured for both reistance and voltage between battery and HU ground and all seems ok there as well.   

Since each RCA works indepentandly of the others with no problems, I'm guessing this may be a problem with my HU but I'm looking for any other thoughts before I do a HU swap.

Thanks.

James 

without any other info, I might suggest taping your rca connections at the deck as they can sometimes touch each other inside the dash...  

Sounds like the deck then, because the rear outs and the front and sub outs are on seperate sides of the deck, so shouldn't be an issue there.   It's a Pioneer DEH550MP deck.  Frustrating, but I'll try pulling the Alpine from my wife's van and see if that clears it up.   She only needs one set of outputs in her van anyhow :)

James

bullman96 wrote:

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i would either agree with you that it is the deck or is some freak incident, where 1 pair of rcas doesnt pick up the engine noise, but when you add the extra rcas it does. try putting space in between each pair of rcas. if its not that, than its the deck. sucks, what kind is it?

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Nope, never posted anything about this before.   Also, I tried using my wifes deck this afternoon and had the same problem - I even tried making sure there was no interferance by running new RCA's directly back without putting them under the carpet just to be sure there was no onboard power source causing the problem.  I guess it's looking more and more like a fault in the amp; Either that or I have the worlds worst luck with two fault head units.   The odd thing being, I'd think it was something in the amp the noise would increase with volume, but it doesn't so at the moment I'm stumped as to where else to check.

DYohn] wrote:

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idn't you post this question before and the general consensus was a faulty or poorly constructed head unit?

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Another update -  the noise goes away if I turn the gains down to around 25% on the amp.  Unfortunatly I don't seem to be getting nearly the SPL expected at those levels however.   No clipped or distortion problems at higher gains, just engine noise.

James

I'm running 4 gauge power and ground directly to battery.   All connections are solid and reconnected.  I have tried both twisted and untwisted RCA's, both giving me the same issue.   As I said, it's bizzare.

James

bullman96 wrote:

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try running a new power wire to the deck and ground. if that doesnt work, seriously, try spreading your rca's about 6 inches apart each. and if that doesnt work, get some unshielded twisted rcas.

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Sorry, it must have been someone else who also had this problem.

The size of power cables will have nothing to do with this kind of problem.

How did you set your input levels (gain)?  How did you determine that "25%" was the correct setting for your setup?  Too high a gain setting will introduce all sorts of problems, including noise.

Well, the 25% was the level at which the noise is unnoticeab le - not the correct gain level needed for my setup.  I found it was best (using the 75% deck volume refrence level method) at around 50-55% - unfortunatly then I have a considerable amount of noise at low volumes.   I'm going to try running a deck external to the vehicle and test  with the car running and see if there's noise, that will elimate the amp as the source of the problem is the noise isn't there I would think.   

James

DYohn] wrote:

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/p>

Sorry, it must have been someone else who also had this problem.

The size of power cables will have nothing to do with this kind of problem.

How did you set your input levels (gain)?  How did you determine that "25%" was the correct setting for your setup?  Too high a gain setting will introduce all sorts of problems, including noise.

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