I was sitting around today and I though to myself, "Gee, I wonder what a ground loop is?" I've read a lot of people having problems with them, and I believe this is the cause of my problem also. I was hoping someone would be able to provide a somewhat technical explanation of what it is, why it causes noise in electronics, and how ground loop filters actually filter them out of a signal.

Thanks,
Chris

 

http://www.epanorama.net/documents/g...oop/index.html

check that page out.. good info. not necessarily about a car, but gives a general idea of what it is.

 

This is the infamous ground loop, avoid it at all cost! :D



:reddevil

 

This is an old posting of mine. Read it and ask questions.


To cure a ground loop problem, you must first identify what path is being used to inject noise into the system. Typically, the low level audio connection between the HU and an external power amp is weak link in a system. In systems without an external power amp, then high levels of noise from the alternator and ignition system fed up the power cable would be the source.

Noise can be picked up in a system many ways. The direct path is by leakage currents flowing through the various conductors in a system. Radiation is also a large problem. When a plug fires or a distributor rotates, an RF signal is radiated. Both the AM radio in a system and a low level audio input will pick up this noise impulse. When you place two wires next to each, they will have capacitive and inductive coupling between them. You never want to route low level audio signal with power cables. The noise currents flowing up and down the power cable will couple into the audio cables.

There are many sources for noise in a system with an external power amp. First is the alternator itself. It is a big noise generator due to it's internal brushes. If the noise suppression capacitors in the alternator are bad, the noise will be worse than normal. Next is the cars ignition system. Having a distributor and coil producing sparks is not good for low noise. Finally the DC to DC power supply in the power amp can also be a large noise generator. All these noise sources have one thing in common. They cause noise currents to flow in ALL wires in a system. These noise currents will follow every path possible from the source of the noise through the audio system and then back to the noise source. Think of it as having many wires of various resistance running from one point to another. The noise will be divided up between all the wires before returning back to the source. The goal is to minimize the amount of noise in a power cable that will return through an audio cable. You cannot eliminate this noise, only minimize it. How you hook up the power to a stereo system is critical.

One quick check for ground loops would be unplug the HU pre-amp outputs. If the noise dissapears, then short the center to the shield on all cables with a bare piece of wire. Connect the big shorted mess to the HU RCA pre-amp outputs shield only. If the noise comes back, then the noise currents are coming down the shields of the low level audio cables. You need to then stop power amp supply current from sending leakage current down the audio returns. If the noise dissapears, then the noise is actually riding on the audio signal. You need to look at the HU power feed to find out the problem. Many aftermarket HU's have poor power feed noise rejection compared to a stock HU.
he power amp input cables together where they would connect to the HU.connect the

 

Cool, makes a lot more sense now.

Thanks guys,
Chris