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Discussion Starter · #1 ·
Man I hate these.

So, when my amp (Alpine PDX-5) is hooked up to nothing at all, other than power, ground, and speaker-outs, I am getting a hiss, very audible, from the rear coaxial speakers. Also from the front tweets but not as noticeable. I have checked the ground and it is reading 0.3 ohms, same as touching the two multimeter leads to each other. So that means its good right? This is driving me nuts, is the amp bad? Or is this the noise floor, and if so, how the hell do I get rid of it? Is it possible I am bringing in some noise from the grounding point? I am grounding at the bolt by the rear passenger seatbelt tensioner.

At first I thought it was the 3sixty, but now I think its the amp..
???
 

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Remember, every ground counts. Your amp has a solid ground. But double check and make sure your HU has a solid ground as well. Also, if your power wires are running right beside your speaker wires from front to back, this can induce unwanted whine. (I don't think that's your problem though, it usually happens when the vehicle is running in that situation.) What is the quality of your RCA's going to your amplifier? What I mean is, are they 5 dollar RCA's from Radio Shack or something much higher quality?

A bit more in depth troubleshooting that you can do is disconnect your speaker wires from the amplifier and read from each lead to ground. You should have an infinite reading. Any reading to ground points to your speaker wires having a minor short to ground. If you know the nominal impedence of your drivers you can read from positive to negative on the leads and should have only the reading of your drivers impedence, your meter lead impedence plus MAYBE a .1% increase due to the length of the speaker wires.

Sometimes there is inherent noise in systems due to poor grounding practices within the equipment itself.

As an electrician, these are the basics I would look into. I'm sure some of the guys will be able to shed some light on your specific situation if this doesn't cover it.
 

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Discussion Starter · #3 ·
All good info thanks. I will check the speaker outs to ground this morning. The RCA's are Knuconceptz, but I ruled those out because the noise is present without them being attached to the amp.

My power wire us right up next to the speaker wires, all the way down the right side of the truck. I thought you had to keep it away from RCA's but speaker wires carried enough voltage to block out the noise. But now that I think of it, my speaker-outs from the stock HU are reading about 5V on the multimeter, so this may be my problem!
 

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Discussion Starter · #4 ·
Well I was wrong, only the front left speaker-outs from the amp are running next to the power wire. All the others are on the passenger side. I am trying to read the impedance on the speaker output from the amp. When I ground the black wire, then put the red wire on each lead (for the fronts), this is what I get:

FL+
0.1 ohm
FL-
3.8 ohm
FR+
3.8 ohm
FR-
-2.8??

Those readings are all over the place, am I doing this right?
Multimeter is set at 200 OHM, black lead in center "COM" port, red lead in left OHM port..

This noise is a hiss, when the engine is off, and the gains on the amp are all the way down. It sounds like if you paused a cd on your home stereo and then turned the volume all the way up, that type of hiss. It is so loud as to be distracting, not just background hiss.
 

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Discussion Starter · #5 ·
For the readings above, I am putting the red lead on the speaker wire coming out from the amp. I disconnected the output to the crossovers so it is a direct feed from the amp.
 

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Discussion Starter · #6 ·
uh oh.. Google PDX-5 and hiss. Not good.

Looking at the specs, PDX-5 SN Ratio is 77db. That is pretty bad :worry:

Kenwood Excelon XR-5S is rated at 102db!

This amp os over 18 months old and out of warranty period. I hope I don't have to buy a new amp, but it is not looking good..
 
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