RCA induced noise....but never did before

MacLeod

Ran across something weird today and it took me 3 days to track it down so I thought Id pass the experience on to you guys just FYI.

Last weekend at my first show with my beloved new amps I got docked for noise. A weird humming noise that changed in pitch but wasnt affected by the volume control and you couldnt hear it with the engine on - just with the engine off and listening to SQ tracks. It was especially noticeable when switching between tracks or at the quiet part when a track starts. Pausing the CD made the noise less but it was still there.

So I first thought it was the HU. So I pulled the optical output - didnt work. I pulled the Ai-Net cable - noise still there. Then I pulled the RCA cables not from the amps but from the processor - noise still there. So I figure that it has to be from the amps back so I start checking all the grounds.

Spent the last hour or so coming up with, sanding down and putting together a new ground spot for the amps. Fire em up - noise still there. At this point Im thinking the amp is bad. DAMMIT! My brand new Polk amp was bad. But on a whim I stick my ear up to the sub - NOISE! So both amps are bad?!?! What are the odds?

So I pull the amps and all the wiring out and start checking. Spot on. Damn could both amps really be bad? Am I that lucky? So I hook up my old Crossfire amp and there is the noise! I ran that thing for 3 years and it was quiet as a mouse. Good new is my amps are fine - bad news is I dont have a f**king clue what it could be.

The only thing I hadnt done is replaced the RCA's. I knew that couldnt be the problem because I used them all last year in this very car and they were clean as a whistle. But I figure Ive got nothing to lose so I grab my set of 18' JL cables from my old Ram's system and slap em in there. Quiet as a mouse. Yup, no noise anywhere! So just to make sure it wasnt something under the amp rack running by the Streetwires RCA's that was causing the noise, I pulled them out and ran them on top of the amps. There's the noise again.

So Ive got 18' long RCA's running the 1.5' distance from my processor to my amps right now, but I have no noise. My question is, how can a set of RCA's that ran for a year with no noise, all of a sudden induce noise?!? I sat out there and listened for 15 minutes and never heard anything. Ill know for sure after I drive around today for a few hours. If all is well I know for sure that was the fix. And shame on me for doubting the quality of Polk amps.

Oh well, at least Im noise free now. But let this be a lesson. Just because you know for a fact that something could never be the problem, doesnt mean it isnt.

MacLeod

Lasareath wrote: »

Could it be a loose connection in the rca connector, maybe there's some fraying and neg is touching the pos in the cable some place.

Is this cable a pair of rca's?, or just a single?, If it's a pair maybe it's only one cable at fault

Thats whats the weirdest part. Its individual pairs or RCA's running to 2 separate amps. BOTH the 4 channel amp and the sub amp were putting out the noise even tho they each had their own individual pair of RCA's.

It may be something with the processor that the higher quality JL Audio cables are able to filter out. Thats the only thing I can think of but again, I ran these same cables with the same processor all last year with no issue.

candaddy

I JUST figured out a noise problem of my own, so I feel your pain. I'd suggest that possibly a ground connection on one of the RCA's is bad and it's causing a back-feeding situation with all of them. Usually the outside (0 volt reference in most cases) is connected to all the outlets. Just take a dvm to check continuity to all the outside connection points on your processor and I bet they are all common. If that's the case, one bad connection could cause them all to suffer. That's essentially what happened to me over the last two days of hair pulling excitement!

I'd get ahold of streetwires and see if they'll do something to fix it for you. I don't know about the company currently, but they used to be pretty supportive when they were still in GA.

MacLeod

candaddy wrote: »

I JUST figured out a noise problem of my own, so I feel your pain. I'd suggest that possibly a ground connection on one of the RCA's is bad and it's causing a back-feeding situation with all of them. Usually the outside (0 volt reference in most cases) is connected to all the outlets. Just take a dvm to check continuity to all the outside connection points on your processor and I bet they are all common. If that's the case, one bad connection could cause them all to suffer. That's essentially what happened to me over the last two days of hair pulling excitement!

I'd get ahold of streetwires and see if they'll do something to fix it for you. I don't know about the company currently, but they used to be pretty supportive when they were still in GA.

That makes a lot of sense; I never thought of that. Ill bet youre right on the money. Thinking back, I remembered that when I had them in my old install I had to stretch and crank on one of the RCA's pretty good in order to get them to fit. Ill betcha I pulled something to near the breaking point and then when I was swapping them out to the new location, they finally gave up the ghost.

Im not real worried about Streetwires fixing the problem. Theyre only .5 meter cables that I got for like $25 for all 3 on sale at Cardomain last year. I got a state championship and a 2nd place at finals with them and considering I probably did it myself I figure I got my moneys worth out of them. Besides, my JL's are getting the job done even if 16.5 feet of them are coiled up and stuffed under my amp trim pieces! Ill eventually get some new cables. Im always looking for an excuse to upgrade and RCA's are cheap. Im using Knuconceptz power wire, fuses and such - may get some of their RCA's too. Good thing about the processor being only a foot away from the amps - 18" RCA's are awful cheap!!