Earth/Ground Loops

JohnClark · 13th November 2001, 09:26 PM

Hi

Can somebody suggest a remedy to my problem. I am running a pair of 6L6 monoblocks but I have a mains frequency hum through my speakers. The only way I can resolve it is to disconnect the earth/ground from both of the power leads, but obviuosly an unsafe situation. How can I get rid of this mains hum and still maintain my earth/ground integrity.

John

lohk · 13th November 2001, 11:04 PM

You have a ground loop (two or more different ground connections without the same impedance), what causes the hum.
Sometimes RCA cables are the cause (the principle is inherently flawed, but sometimes only the plugs are badly soldered or dirty).

The easiest and safest way to get a clean ground is to connect ALL earth lines together in ONE point and connect THIS ONE ONLY with mains earth. (Try to find out where your ground paths - visible and hidden - actually are.) The best point for that would be at the preamp power supply (this is not only my experience).

As a rule of thumb: All cases should or can be connected to mains ground for safety reasons, but the ground of each device should be connected together in one line (never a loop) or best in form of a star. This line or better the star ground point is connected with mains earth.

There are a lot more tricks to get a hum free setup, but try the best one first.
If this does not help, you will have to specify all your devices, cables, connections, etc.

best whishes
Klaus

cp642 · 14th November 2001, 12:49 AM

You might want to try wiring up a thermistor between the ground and the mains earth connection.

Keystone CL-60 ( as recomended by Nelson Pass ) or some other types of similar ratings.

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13th November 2001, 09:26 PM	#1
JohnClark diyAudio Member Join Date: Nov 2001 Location: UK	Hi Can somebody suggest a remedy to my problem. I am running a pair of 6L6 monoblocks but I have a mains frequency hum through my speakers. The only way I can resolve it is to disconnect the earth/ground from both of the power leads, but obviuosly an unsafe situation. How can I get rid of this mains hum and still maintain my earth/ground integrity. John

13th November 2001, 11:04 PM	#2
lohk diyAudio Member Join Date: Apr 2001 Location: Northern Noricum, near the Limes	You have a ground loop (two or more different ground connections without the same impedance), what causes the hum. Sometimes RCA cables are the cause (the principle is inherently flawed, but sometimes only the plugs are badly soldered or dirty). The easiest and safest way to get a clean ground is to connect ALL earth lines together in ONE point and connect THIS ONE ONLY with mains earth. (Try to find out where your ground paths - visible and hidden - actually are.) The best point for that would be at the preamp power supply (this is not only my experience). As a rule of thumb: All cases should or can be connected to mains ground for safety reasons, but the ground of each device should be connected together in one line (never a loop) or best in form of a star. This line or better the star ground point is connected with mains earth. There are a lot more tricks to get a hum free setup, but try the best one first. If this does not help, you will have to specify all your devices, cables, connections, etc. best whishes Klaus

14th November 2001, 12:49 AM	#3
cp642 diyAudio Member Join Date: Aug 2001	You might want to try wiring up a thermistor between the ground and the mains earth connection. Keystone CL-60 ( as recomended by Nelson Pass ) or some other types of similar ratings.