I have an after-market navigation/audio receiver wired to my cars 12v system, with audio connected to my cars built-in AUX jack. When no audio is playing, I can hear a high-pitched whine, which changes with engine speed. I know this is a common issue with car audio, and that one can build a filter to eliminate it. I'm wondering what that filter should consist of, so I can build a good one to insert into system (I assume into the power line going to the receiver?)
Preamp level?
Is the preamp ground for the nav directly connected to the chassis ground of the nav?
Is the preamp ground for the nav directly connected to the chassis ground of the nav?
The whine is caused by the alternator. If the whine is entering through the power supply you might be able to filter it. But if it enters through the wiring to the AUX jack you may be out of luck.
Tom
Tom
Is that because the whine would be entering the circuit downstream of the AUX jack, so I wouldn't be able to insert the filter after the whine is induced? I presume I could test this by connecting the AUX jack directly to a phone or other device decoupled from the cars electrical circuit?
The problem is likely a ground loop. A Ground loop isolator may solve the problem.
Unless the nav is connected to an isolated battery, there is a chassis ground.
Unless the nav is connected to an isolated battery, there is a chassis ground.
How would a ground loop isolator connect here? The only connections to the aftermarket NAV unit are 12v +/- and audio L/R/G
It's a preamp level device that's two transformers (1/channel). It typically has RCA connectors. You'd adapt to fit your connections if you use one.
https://www.bcae1.com/glisoltr.htm
https://www.bcae1.com/glisoltr.htm
I found when this happened it was radiated noise from the alternator, and that a choke on the power wire was all that was needed.
I put the choke out near the battery.
I put the choke out near the battery.
Usually there is a capacitor on the B+ terminal of the alternator to prevent the whine, those were deleted years ago by many manufacturers as cost cutting measures. You can buy aftermarket alternator suppressor kits, it's best to filter the noise at the alternator B+ terminal.
Interesting, I'd never heard of a filter cap on the alternator. I drive a 2003 Mercedes, not sure if it has one or not. If I were to add one, what sort of specs would I want on the cap?
Manufacturers during the 70's up to the 90's used a capacitor as a filter on the back of alternators, Bosch, who probably made your alternator, had a black rectangle plastic cover over their filter. I'm hesitant to recommend a spec. since modern alternators are in the 50 - 150 amp outputs to power all the electronics. I bet if you google Bosch alternator filter(s), they probably have the spec's for your vehicle.
BEWARE! The B+ terminal on the back of alternators MUST have the nut tight for the B+ terminal, I recommend never reusing the split washer for the B+ terminal. Failing to tighten to the correct torque, can and will cause very expensive damage, starting with the B+ terminal welding the nut/washer/terminal to the output stud. This will substantially degrade the metal the stud/bolt/washer is made of, once this happens BAD things happen to all the ECU/ECM's in the vehicle.
The best place to mount the capacitor/filter is the B+ terminal on the alternator, you want to stop the noise before it enters the electrical architecture of the vehicle.
Of course, all this work MUST be performed with the battery negative terminal disconnected. You will maybe lose, radio presets, clock, seat/steering wheel settings, auto up/down windows, god only knows what the TCM and ECM settings will end up when you reconnect the negative cable.
Your NAVI system may send you to the HOME DEPOT in Death Valley the next time you want a light bulb.
Your NAVI system may send you to the HOME DEPOT in Death Valley the next time you want a light bulb.
My thinking is that if the noise is being induced into the AUX wiring you'll have a hard time filtering it out because it's in the audio band. So if you filter it out you'll filter out some audio as well. That's probably not what you want. In that case you'll either have to prevent the interference from radiating into the AUX wiring or prevent the interference from radiating in the first place (so attack it at the source).
Tom
Few years ago I also have the same problem, i have try many approach from using power filter to rca ground loop isolator. Rca ground loop isolator degrade the system quality, so i ditch it. What I found is the alternator noise is coming from ignition wire to the head unit.
I solve it by attaching 5 pin 12v relay, the ignition goes to one of relay coil where the other pin connected to ground. The relay NO pin connected to battery(from head unit battery input wire) and the middle pin connected to the head unit.
So now car ignition trigger the relay and connect the head unit ignition straight from the battery. You might also use this relay output as your remote amplifier triggger just in case. You also might need a fuse between battery and the relay NO pin, a 0.5-1a fuse will do.
I solve it by attaching 5 pin 12v relay, the ignition goes to one of relay coil where the other pin connected to ground. The relay NO pin connected to battery(from head unit battery input wire) and the middle pin connected to the head unit.
So now car ignition trigger the relay and connect the head unit ignition straight from the battery. You might also use this relay output as your remote amplifier triggger just in case. You also might need a fuse between battery and the relay NO pin, a 0.5-1a fuse will do.
Hi SoaDMTGguy
The whine noise is a GROUND LOOP PROBLEM as referenced in #6
Buy a "Two Channel ground loop isolator" it is a 2 transformer 1:1 ratio. it will break a common ground connection. Amazon has a number of this type of isolators. $10-25 ea. They are usally RCA type connectors input & output. When you install the isolator you may want to tape over any metal part so it won't contact any other contact with the chassis.
Duke
The whine noise is a GROUND LOOP PROBLEM as referenced in #6
Buy a "Two Channel ground loop isolator" it is a 2 transformer 1:1 ratio. it will break a common ground connection. Amazon has a number of this type of isolators. $10-25 ea. They are usally RCA type connectors input & output. When you install the isolator you may want to tape over any metal part so it won't contact any other contact with the chassis.
Duke