|
I installed a phone in my car but I am having a problem with noisy audio (humming/buzzing at erratically changing frequencies, popping, crackling) that I can't seem to track down. The noise mostly disappears when there's audio playing, but it's really bad when the phone is idle. I made a billion flow charts to help myself figure out what the problem is but it's just left me even more confused. Here is my setup, the headphone amp is there because I get insufficient volume with just the phone. The power adapter is using the same ground and switched 12v the stock radio used.  The noise disappears entirely if the phone is not plugged in.  It also disappears if the headphone amp is not plugged in.  Since sharing a power adapter seemed like the problem, I tried plugging one of them into a second power adapter going into my cigarette lighter socket, but the noise remained.  Then I tried connecting one of them at a time to a portable power source that was completely isolated from my car, and the noise disappeared.   To rule out a load related issue, I tried plugging the power adapter into a different phone, then plugging in the headphone amp but isolating it from the audio signal. The noise went away.   To rule out the car amp and its ground, I plugged headphones directly into the headphone amp. The noise remained.  At this point it looked like it was some kind of ground loop issue, so I bought a ground loop isolator. I placed it after the headphone amp, which didn't do anything for the noise, but it did entirely remove the alternator whine.  Then I placed it before the amp; the volume of the noise decreased by half but it was still audible, and its character remained the same. The alternator whine came back.  This seemed to support the ground loop theory, but I couldn't make sense of how the ground loop was happening, so I tried testing it by connecting only the ground to the phone, no power. The noise disappeared!  Powering the phone externally with only the ground connected to the power adapter resulted in the same.  So that's where I am as of today. I am far from an expert, but don't my last two tests rule out a ground loop problem? I was also under the impression ground loop noise was a steady hum/whine, not the crackling, popping, buzzing mess I'm getting. Aside from the alternator whine there's also no correlation between the noise and what the car is doing. If so, what could it be? I have swapped out every component aside from the car itself, even wires, with no change. I verified the ground and connected the power adapter directly to the chassis with no change.
|
#
¿
Sep 6, 2015 21:39
|
|
|
|
| # ¿ Apr 28, 2024 03:20 |
|
|
MikeyTsi posted:Another thing to consider is your source, have you tried using another source to see if the problem goes away? You could have a combination of a ground loop plus a poor quality source and/or crappy amp. Yeah, sadly it didn't change anything. Taking the amp out of the equation didn't do anything either. Thanks for the explanation. The part I don't get is, are ground loops unavoidable if you have two pieces of grounded equipment connected to one another? From what I could find you just need a sufficient ground to prevent the electrons from using that path, but it seems unlikely there would be enough resistance at that connection to prevent that. And no matter how much I beef up my ground I can't seem to get rid of the noise. It's odd to think my setup is fundamentally impossible without creating a ground loop. ...can I just put some very tiny resistors on the connection between the two?
|
|
#
¿
Sep 10, 2015 03:11
|
|
|
After spending way too much time trying to fix this properly, I decided to call it and settled for the bodgiest bodge job I've ever done: one ground loop isolater upstream to filter the alternator whine, another ground loop isolator to filter out half the buzzing, and a third in series with the second one to filter out the rest. I can still hear a faint hum, so I'm seriously considering adding a fourth one. Amazingly I don't hear any degradation in the sound quality, which I am taking as a sign from the audio gods to continue throwing isolators at the problem. Needless to say I am deeply ashamed, though I am hoping to make up for it somewhat by properly fixing the alternator whine soon, which I think is due to a bad diode.
|
|
#
¿
Sep 13, 2015 01:07
|
|
|
MikeyTsi posted:No. It's unavoidable if you have two pieces of grounded equipment USING DIFFERENT GROUND POINTS, and it decides to use the loop path instead of using the ground like a good boy. It's most common when you end up using the cigarette lighter/power port to power something that also does audio, since for some reason those have the shittiest grounding on earth an you'll pretty much always get noise. You might have some luck by running your own power port; run it to the battery, fuse it properly, and then run the ground for it to the same place as your amplifier ground. You could even just run some temporary wiring to test and see if that makes the noise go away before you do it permanently. You aren't kidding, I measured a shitton of resistance between the cig lighter's ground spade connector and its body, they're bridged very poorly. I ended up soldering a wire between the two, and while that fixed the lovely ground, it didn't solve the noise problem. I also don't know how great the ground springs on the power adapters are, I guess I should take one apart and connect the ground directly to the PCB, and connect the positive directly to the battery like you said. MikeyTsi posted:What are you grounding your amp to, by the way? In my setups I've grounded my amps to one of the rear seat bolts, since they're nice and big and you typically get a really good chassis ground out of them without having to drill holes or anything. I'm not sure actually, it's the stock amp buried inside the trunk somewhere. However the noise is still there even if I'm using headphones and nothing is connected to the car aside from the power--in this scenario, there should be no ground loop since there is only one ground point, right? Unless I have an actual bad ground.
|
|
#
¿
Sep 15, 2015 07:29
|
|
|
The noise is consistent regardless of what setup I use, and is a mix of a static hiss in the background combined with a dial up modem type screech that changes pitch every so often for no reason I can discern. If I unplug any one device both types of noise disappear entirely. You might be right that it's the power supply, I'm not sure how to find a 'good' non noisy one though; the adapters I've tried all had great reviews, but the noise is the same.
|
|
#
¿
Sep 15, 2015 08:01
|
|