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| Wierd car grounding issue (I think). |
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| Howard_Casto:
Ok so I realize this is more of a car forum question, but I believe it's an electronics issue, so I'll ask here. Just finished up my aux input hack for the original delco stereo in the Camaro. Everything works great except for the cheap Bluetooth module I have wired in. The audio coming out of it sounds like a banshee and a especially vocal cat got in a fight and fell into a wood chipper. I've ruled out the audio lines I ran.... I can plug my phone into the same audio plug I made for the bt module and it sounds just fine. So that leaves power and probably points to a ground loop issue right? Well probably, but I can't figure it out. The bt receiver is one of those deals where one end has a usb plug for power and the other has a headphone jack. I'm powering it via a usb cigarette socket adaptor. The adaptor is gounded to the stereo chassis to avoid ground loops, but in the course of trouble shooting I've also plugged it directly in the ground wire of the stereo, the car frame, and plugged another adaptor into my car's real cigarette socket and powered it from there.... the issue persists. Now I should point out that the adaptor itself works fine if I plug it into a power source in the house, so it does work, but it's got to have some ground issues. So I'm open to suggestions and would appreciate any help. It's not a huge deal, I can plug stuff in directly and that works, but bt would make things a lot cleaner. |
| BadMouth:
Definitely a ground loop issue. A ground loop isolator may lessen it, but I doubt you'll find anything that gets rid of it completely. The cheap little Bluetooth adapter just isn't built to reject noise. Probably best off installing a headphone jack in the dash and then using a rechargeable Bluetooth adapter. I used this one with my old CD player: I think I paid around 12 or 13 bucks for it. Not sure how long the battery lasts if used continuously. IIRC, it would need recharged after a week and a half or two weeks of 20 minute commutes each way. It will still have noise while it's plugged in charging, but the rest of the time it's quiet. |
| dkersten:
--- Quote from: Howard_Casto on December 16, 2015, 03:26:38 pm ---Ok so I realize this is more of a car forum question, but I believe it's an electronics issue, so I'll ask here. Just finished up my aux input hack for the original delco stereo in the Camaro. Everything works great except for the cheap Bluetooth module I have wired in. The audio coming out of it sounds like a banshee and a especially vocal cat got in a fight and fell into a wood chipper. I've ruled out the audio lines I ran.... I can plug my phone into the same audio plug I made for the bt module and it sounds just fine. So that leaves power and probably points to a ground loop issue right? Well probably, but I can't figure it out. The bt receiver is one of those deals where one end has a usb plug for power and the other has a headphone jack. I'm powering it via a usb cigarette socket adaptor. The adaptor is gounded to the stereo chassis to avoid ground loops, but in the course of trouble shooting I've also plugged it directly in the ground wire of the stereo, the car frame, and plugged another adaptor into my car's real cigarette socket and powered it from there.... the issue persists. Now I should point out that the adaptor itself works fine if I plug it into a power source in the house, so it does work, but it's got to have some ground issues. So I'm open to suggestions and would appreciate any help. It's not a huge deal, I can plug stuff in directly and that works, but bt would make things a lot cleaner. --- End quote --- Just to be clear, if you run a wall wart off 110v to power it but plug it into the car input jack you rigged up, it works, right? Also, this noise happens with the engine running, right? If the engine is off then there is nothing to vary the voltage (DC battery voltage), so a ground loop would not create noise, just a pop when you first plug in (unless there is something else feeding back into that input). I will just assume the engine is running so the noise is alternator whine caused by the bridge rectifier, which makes it a power related problem. So my best guess is that the interface you made has a floating ground. When you connect a device that is independently powered this is fine, but when the device is powered by the car you create the ground loop in the input. So I would take the common wire in the jack you use to connect and try grounding that to the chassis of the stereo (assuming you use a 3.5mm jack, otherwise wrap a bare wire around the outside of the RCA connections and ground that wire). That should ground the input side and drain off the loop before it gets amplified. If that doesn't work, try a ground loop isolator (which does the same thing but adds a small 1:1 transformer to isolate the ground as well). Usually these are RCA based so you would need adapters if you are using 3.5mm. |
| Howard_Casto:
Well that's the other thing that has me confused.... it does this with the engine OFF, so it isn't your typical alternator whine. I should have mentioned that, sorry. I'm wondering if the fact that Bluetooth receivers use radio waves might have something to do with it. After some further fiddling, if I put the jack into the receiver half way, the issue goes away, so it's like the ground on the jack is doing it, but like I said, I can plug in other stuff and I don't get interference. Maybe the ground on the bt pcb needs tied in somewhere? Tomorrow just to rule things out I'm going to run a ground wire directly to the battery just for testing purposes. |
| dkersten:
Are you completely positive you got the input polarity right? I would still try to ground the common on the input to the chassis of the deck. This would take any voltage feedback and ground it. Grounding BT power to battery rather than chassis is just using a different "wire", and other than picking up noise from the bigger antenna that the positive and negative become, it won't make any real difference, maybe add a DC voltage difference of a fraction of a volt, which would cause a pop when plugged in but not much else. I think it is on the input side. But. to be 100% sure the power supply of the BT device is not creating the problem, take a red and black wire and twist them together with a drill then connect both pos and neg directly to the battery and hook it up.. that will give you a twisted pair power source that will not be an antenna for noise. If you still get feedback when plugged in without the engine running then you can rule out anything with 12v power on the BT side. From there it would be a voltage traveling over the input from one device to the other, probably causing the D/A converter in the BT device to go haywire. |
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