Ground Loops Explained

[frederic]

A picture is worth 1000 words :-D

NEVER lift grounds off AC cords, its dangerous to you and your equipment.

Another neat trick is to make a patch cord with a small resistor in series with the shielding, and the ground leg on the 1/4" phone jack. You'd have to experiment with the value, but often its good enough in a pinch.

 

[Giganova]

Can ground loops be a problem for audio recording?? I spent years working in a physics lab and ground loops were our worst enimies. If we hadn't hooked up each of our equipment to a central ground (like forming a "star" pattern) we had ground frequencies all over the place.

 

[frederic]

Can ground loops be a problem for audio recording?? I spent years working in a physics lab and ground loops were our worst enimies. If we hadn't hooked up each of our equipment to a central ground (like forming a "star" pattern) we had ground frequencies all over the place.

Same thing for audio gear. Though not all audio gear, its been my experience that I got ground loops when I mix older, and newer gear for whatever reason.

 

[Jblount]

What is accomplished by adding a resitor in series with the shield?

 

[frederic]

What is accomplished by adding a resitor in series with the shield?

The resistor in the shield is more of a debugging tool, which by increasing the resistance between the two signal grounds, if you are close to the resistance of the earth rounds (or the third prong on your outlets), your hum will be reduced.

Its not something you leave there forever, of course

 

[Jblount]

Yes, but you have defeated the purpose in the grounded wire, which is to offer a path of least resistance to ground for leak voltage. In a surge, you could really damage equipment, it is the same as not even having a ground!