Car audio system - ground loop noise isolation


#1

I installed a after market car radio for my 2000 corolla. I used the special “adapter” so no splicing of wires were needed. The problem is that when I connect my phone to the aux-in port and charge the phone through the cigarette lighter at the same time…there is high pitched noise coming out of the car speakers.

Ive read that to fix it, I would need to do a ground loop. Do i just get a wire and tape one end to the metal body of the radio and the other end to the metal body of the car?


#2

Ground loops are bad, not good. But what I think you are referring to is a better ground connection for the radio.

Tape is not usable for an electrical connection. You have to put it under a screw or perhaps there is a ground post on the rear of the radio that you can use.

But try just touching a #12 wire to the radio and the car ground to see if that helps before you search for a more secure connection. For the car ground, look for the cable from the battery negative terminal to the car chassis.


#3

The radio should have a mounting bolt somewhere on the back. It’s designed to secure the rear of the radio so it doesn’t shake up and down and destroy the front plate. That bolt is also normally the grounding bolt. If you’ve mounted it to plastic, use a wire and ring adapter on one or both ends, and ground it properly. If that’s all you need is a single ground, you should be good. Be prepared for this not to fix it entirely.

A ground loop is the problem, not the solution.


#4

Ground loop isolater"s do exist and can in some cases fix this problem, i’ve been chasing a ground loop in a church audio system and filtering out the electrical noise has worked so far.


#5

Ideally all the ground connections for the audio gadgets located in the passenger compartment would connect at the same point on the chassis or at the same ground feed wire from the battery.


#6

If the problem only manifests itself when you plug in the charger for the phone, it’s not a ground loop problem. Is this a charger from a reputable manufacturer or some cheap unit? It sounds like they omitted any type of line filtering and the high frequency switcher is back flushing into the car’s electrical system or radiating a heck of a lot of noise.

Naturally, grounding of both the new radio and the antenna feeding it is important. This allows the radio’s internal filtering to bypass any noise conducted on the power supply input lines into the chassis ground. Likewise, an ungrounded antenna will pick up the slightest radiated noise and feed that right into the radio.

Personally, if I new the grounding was correct, I’d try a different charger first.

Barring that, you could install a line choke filter on the power supply for the radio to augment its own filtering. This common mode filter will block any conducted, high frequency noise from entering the radio power supply. They used to be more commonly used years ago but most electronics now has to meet Class A or B emissions and be tested to not interfere with other electronics (i.e. EMC standards). Most stores that sell radios will have these line chokes near the installation parts. Crutchfield also sells them…


#7

@TwinTurbo said:

Personally, if I new the grounding was correct, I’d try a different charger first.

That. I’ll never understand why everyone insists on putting a $600 phone on a $2 charger and $1 cable. It’s not the best thing to do. Sure, the manufacturer’s equipment may cost more, and the higher quality stuff will cost more, but in the end, you get what you pay for.