DiyMobileAudio.com Car Stereo Forum banner

1 - 16 of 16 Posts

·
Registered
Joined
·
5 Posts
Discussion Starter #1
Hi all,

I'm the new guy and am seeking some help. I have a '69 Chevelle daily driver that I've restored. Its pretty much all buttoned up, but has a strange audio issue. When the engine is running, I get a static noise coming through the speakers, but mostly from the rear two 6x9s. Best way I could describe it is like an electric bug zapper noise. The strange part is that when I rev it up, it stops and the sound is clear. There doesn't seem to be a specific RPM where it breaks off. It could be anything from 1500 to 3000. It will just suddenly stop. But its always there at idle.

Of course, let me describe my system to you. First of all, most everything is brand new. The head unit is a RetroSound Model 1 which is hooked up to a US Amps brand 4 channel amp (sorry I don't know the # off hand) with Monster red RCA cable. There are four Infinity Kappa speakers in the car, two 6.5s in the front kick panels and two 6x9s in the rear deck. Again, I used Monster red cable to hook em up from the amp. The amp is mounted in the trunk to the underside of the rear deck. I'm powering the amp through an 8ga stranded wire directly off the battery. This wire runs under the car and up through the trunk, but is on the other side of the car (not running alongside the RCAs). I grounded the amp directly to the trunk sheetmetal with a piece of the same 8ga wire. Also, in an effort to diagnose this problem, I installed ground straps from the engine to body and to frame. That didn't fix it.

Another thing I tried was disconnecting the alternator, but the static was still there while running.

Any ideas?
 

·
Registered
Joined
·
413 Posts
Ignition noise prob spark plug wires or points with bad capacitor if you still have points or non resister plugs.
 

·
Registered
Joined
·
5 Posts
Discussion Starter #3
Thanks for the reply. I just replaced the spark plug wires with a nice MSD 8.5mm set. Its got an HEI on it too, so no points to speak of...

I will say that I really thought the new plug wires would fix the issue since the old ones had cracks in the rubber.
 

·
Registered
Joined
·
238 Posts
Could be a ground loop caused by the head unit touching ground up front and the amp being grounded in the back. If your cables are long enough at the head unit, remove the head unit from its mount sleeve up front and play the system with the engine running and see ifhe noise is gone.

Also try in-plugging the RCA cables that feed the amp (at the amp) and see if there is noise...if there is NOT...plug the RCA's back in and unplug them at the head unit...see if you have noise.

Bottom line: we are trying to isolate the noise...is it an electrical ground loop or is it radiated noise being picked up by the RCA cables.
 

·
Registered
Joined
·
5 Posts
Discussion Starter #6
Thanks DiMora. I tried unplugging the RCA cable at both ends. When I unplugged it at the head unit only, the crackling was still there. But when I unplugged it at the amp end only, the crackling was gone! So is it safe to assume that the RCA cable is causing the crackling, whether it be due to its vicinity to other wires or damaged insulation? By the way, this is the exact cable I'm running: http://www.amazon.com/Monster-MPC-I304-4C-6M-4-Channel/dp/B000BMQR54
 

·
Registered
Joined
·
238 Posts
Thanks DiMora. I tried unplugging the RCA cable at both ends. When I unplugged it at the head unit only, the crackling was still there. But when I unplugged it at the amp end only, the crackling was gone! So is it safe to assume that the RCA cable is causing the crackling, whether it be due to its vicinity to other wires or damaged insulation? By the way, this is the exact cable I'm running: Amazon.com: Monster MPC I304 4C-6M Extra Low Noise 4-Channel Car Stereo RCA Cables (6 meters): Car Electronics
Alright, now we are getting somewhere.

So...what I would do now is try a couple of different things.

To answer your question, yes...the RCA cable *may* well be picking up the noise you are hearing - acting as an antenna if you will - but we need to give it a music source to be sure.

You could also just be hearing a ground loop, but usually ground loop noise is still present when RCA's are disconnected if the loop is caused by the electrical power connections, but in devices that don't having floating grounds, the RCA cables can complete the ground loop.

I proceed simple to difficult in these things, so the first thing I would try is a different RCA cable. Don't install a different one under the carpet, rather just hook it up to the head unit and to the amps, and keep it up high over the seats - away from the vehicles electrical wiring.

If you don't have a spare RCA cable and don't want to buy one yet, you can also uninstall the RCA cable from below the carpet so that you can manipulate it, and see if the noise goes away when it is high in the car, say up over the seats - that can help tell you if the RCA is picking up noise.

What I usually do next is remove the head unit from the dash (but keep the power wires connected) and see if the noise goes away - if it does, the chassis of the head unit may be grounding to the chassis, making a ground loop. I've seen this on older Kenwood decks before.
 

·
Registered
Joined
·
238 Posts
Higher end head units also are usually noise-free. I had an older Clarion head unit in a car, and it was noisy, so I replaced it with an Eclipse CD7100 and the system became dead quiet with no other changes. The Eclipse has a 55 Ohm output impedance. The lower the output impedance on your head unit, the less likely it is contributing to a noise problem.

I looked in your owners manual, and it does not list the output impedance for the low level outputs, only for the amplifier section for drivers (4-8 Ohms).

Here might well be the simplest solution of all, but it will cost you $125. There will be those on here who will flame away, but if you were to add a line driver (AudioControl Overdrive) right after the head unit, you will not only gain more voltage (up to the max your US Amps amp can handle, and you could turn your USAmps gain all the way down), but the output impedance of the Overdrive is 45 Ohms, which can help prevent noise, and the grounds in the Overdrive are also switchable from isolated, to ground, to 200 Ohm, so the device can break an RCA cable induced ground loop. They are about $100-$125 shipped.
 

·
Registered
Joined
·
5 Posts
Discussion Starter #9
Wow. :eek: Just wanted to update this thread and report the solution. Replacing the distributor completely fixed the static!!! The old distributor was worn out anyway, so I unintentionally killed two birds with one stone. :D
 

·
Registered
Joined
·
238 Posts
Wow. :eek: Just wanted to update this thread and report the solution. Replacing the distributor completely fixed the static!!! The old distributor was worn out anyway, so I unintentionally killed two birds with one stone. :D
Glad you got it sorted! Asota nailed it up top!
 

·
Registered
Joined
·
8,628 Posts
Bringing back a relevant thread. I just finished a 2-way to 3-way front stage upgrade. I added a new PDX amp and stage 4 mids. I get this exact same noise when the car is running, but it stops when I turn off the motor. My voltage has been a little off lately, it used to sit at 14.2 v almost constantly, but now 13.5 is more common. It seems that the noise is also gone when the car actually reaches 14.2 v. I have new spark plugs and a good battery, so I suspect my alternator is giving up again. I have a new bosch alternator on the way, so hopefully that takes care of things. I suspect some of you will go straight to telling me to check my grounds, which I'll do this weekend, but the system is completely noise free when the motor isn't running, so I don't think that's the problem. Besides the alternator, do any of you have any other ideas, coil pack maybe? It seems obvious that the problem is caused my something that is only functioning while the car is running. If there's something I can check while waiting on the alternator to be delivered, let me hear your ideas! Thanks!
 

·
Registered
Joined
·
66 Posts
Did you have the noise before you replaced the spark plugs?
 

·
Registered
Joined
·
8,628 Posts
I've not had the noise at all until the install I finished yesterday. After paying more attention, the noise only lasts a short time after starting the car. After a mile of driving it goes away, it's also accompanied by alt whine, which also goes away after a few blocks of driving. Maybe it's related to the battery voltage recovering after cranking it? I'm just throwing out ideas. But, the noise is nonexistant without the motor running and only lasts for a short time after starting the car.
 

·
Registered
Joined
·
66 Posts
That is possible. The alternator is under a heavier load while it recharges the battery. Hopefully your new alt will be all you need. Check back after with results.
 

·
Registered
Joined
·
8,628 Posts
The cheap Autozone alternator has been a piece of junk, luckily the warranty is good, so it's been replaced for free once or twice, and it's even been disassembled to replace the voltage regulator. I fully expect the new Bosch to be an improvement, it's also provides at least 15 amps more current than the stock alternator, so that should help too. The current alternator was run pretty hard with a Zuki Eleets and Xenon amp wired up.

I may take the battery in for testing, but even in the sub zero weather it starts the car without hesitation. It might not be getting fully charged, but the car starts every time, without hesitation. It's a Die Hard Platinum that's about a year old, so if there's an issue there it's well within the warranty period.
 
1 - 16 of 16 Posts
Top