Wierd car grounding issue (I think).

[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]

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.

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. 

[Howard_Casto]

Yeah I'm sure. 

As I've noted above it's currently already attached to the chassis. 

A ground to the battery wouldn't make any difference... unless the ground locations I've already tried are bad... that's what I'm trying to rule out. 

[dkersten]

I read it as you had grounded the 5v adapter to chassis ground, not the common side of the input you created in the factory unit.

[Howard_Casto]

No the chassis of the stereo. 

The old delco units don't have a common ground wire internally if that's what you mean.  There is a ground wire on the stereo harness, but that leads to the metal housing (chassis) of the stereo. 

[dkersten]

But the common wire on the input itself, is it grounded to the chassis of the stereo?  or is it floating (only connected to the pre-amp circuit in the delco)?

[Howard_Casto]

Yes, that's the ONLY ground for the stereo.  It wouldn't make any sense to ground it to anything else except to troubleshoot. 

[lilshawn]

just to add 2 cents,

the 12 volt line in cars is dirty as all hell in old cars. couple that with questionable ignition wires and you are looking at a bad day.

look at applying a noise filter for the power for your stereo (usually a common mode choke coil or two and some  caps.) this will eliminate a bunch of noise.

check your alternator output and see if you have a pile of AC coming out (indicating a failing bridge rectifier) this is often a common source of noise.

also look at resistor plugs and wires to reduce noise from the ignition system. NKG has a pile of OEM compatible conversions.

[BadMouth]

Or just avoid powering the Bluetooth device from the car's noisy electrical system and deal with the inconvenience of having to recharge it every few weeks.   

You could get crazy and make a charging circuit for the Bluetooth module battery that only lets current flow when the car is turned off.
It will run off battery power when the car is running (no noise) and recharge when the car is off. 

[dkersten]

just to add 2 cents,

the 12 volt line in cars is dirty as all hell in old cars. couple that with questionable ignition wires and you are looking at a bad day.

look at applying a noise filter for the power for your stereo (usually a common mode choke coil or two and some  caps.) this will eliminate a bunch of noise.

check your alternator output and see if you have a pile of AC coming out (indicating a failing bridge rectifier) this is often a common source of noise.

also look at resistor plugs and wires to reduce noise from the ignition system. NKG has a pile of OEM compatible conversions.

except this is happening without the engine running.. so none of that applies.  DC voltage from a battery is steady and even if your input ground is directly tied to it, will not change the signal in the slightest.  With the alternator charging the battery, it will get bumpy and that, along with spikes from relay coils discharging and other noise will cause some issues when the path for the signal is not isolated from the electrical system. 

Furthermore, a chassis is one big wire, but it is also a ground plane and a positive wire running through the car becomes an antenna to pick up noise from the spark plug wires and any other devices that emit EMF. 

So while you are right that a car's electrical system is noisy, a ground loop will only be an issue while the engine is running.

In this case I think we have a voltage differential due to a common ground in the BT device that is feeding back through the makeshift input.  Usually this would just cause a pop as the input was plugged in and the voltage spiked, but my guess is it is big enough that once the loop is completed the DA converter or PA circuit in the Delco is going crazy due to the voltage and causing the feedback.

Other things that come to mind that would cause this would be the input polarity being backwards (so the ground from the BT is feeding the voltage differential into the positive input on the Delco and causing a loop), or possibly just a straight up lack of ground on the DA circuit so it is getting it's power through the ground on the input wire.  But either isolating the input common lead with an isolator circuit or just grounding it to chassis should stop it.. if the polarity is backwards on the input then an isolator would result in no sound at all (incomplete circuit). 

@Howard, I'm not sure we are on the same page.  The Delco unit is grounded through its chassis to the chassis of the vehicle (most likely), and this is to power the unit.  But I am not talking about unit power here, I'm talking about the line level input.  Take either the outside of the RCA jacks or in the case of a 3.5mm plug, the shield wire in the cable itself (the bottom part of the jack), and tie it to ground (the radio chassis) after the connection between the BT and Delco is made.  This is an old stereo trick we used to use when there was a voltage differential between the source and the amplifier circuit.  If you are already grounding the line level input common side to chassis, then this is not the cause (obviously).  In fact, it might be that the BT unit has a floating ground (not the same ground as the power input uses) and this is why the unit freaks out and sends crazy feedback.  In that case I would add a ground loop isolator to the input to prevent the ground on the Delco from affecting the output of the BT.  The power side of both units is seldom a factor, regardless of where you ground.  As long as 10-15 volts goes in, you will get ~5 volts out on the adapter and the unit will power up.  If you had noise while the alternator is going, I might say to play with different ground sources.  If the unit was cutting out (motorboating) when you turned it up, I would say the ground is the issue (low voltage due to bad chassis ground at the battery).  But getting feedback while just on battery power indicates some kind of incompatibility between the output of the BT and the input of the Delco.  Hope that makes sense.  Not saying there is a solution here, just a couple things to try.  Good luck!

[pbj]

How about getting an AC/DC inverter and then powering your bluetooth adapter with a wall wart?

[Howard_Casto]

I got it sorted. 

I tested the wiring three times..... but I didn't test the cable that came with the adaptor.  I cut one end of the plug and soldered it directly.  It's got three wires, white, red, and green, so like any sane person I assumed green was ground, white was left, and red was right.  I forgot this came from china.... yup the wires are just in a random order.  What I don't get is why my phone and my mp3 player ect didn't behave the same way.  I can only assume it was because they are battery powered and therefore don't ground to the system.

Anyway, that was embarrassing.  Sorry for wasting everyone's time. 

Anyway, it works great now... virtually no interference, even with the car running.  Cleaning all of my grounds (radio, car body, battery and wiring) during the process of troubleshooting was probably worth the effort just for that.  I highly recommend the mod assuming you don't screw it up like me. 

[dkersten]

I tested the wiring three times..... but I didn't test the cable that came with the adaptor.  I cut one end of the plug and soldered it directly.  It's got three wires, white, red, and green, so like any sane person I assumed green was ground, white was left, and red was right.  I forgot this came from china.... yup the wires are just in a random order.  What I don't get is why my phone and my mp3 player ect didn't behave the same way.  I can only assume it was because they are battery powered and therefore don't ground to the system.

Yeah that would create a big feedback loop, lol.  Glad you got it sorted out.