Isolated Ground causes ground hum.

I'm not an electrician, but I have two ground rods installed to my house.
  There is an earth ground attached to your service panel (circuit box) which is the ground for all circuits in your house. 
  If you have a dedicated AC line, it is also grounded to your house. You may attach a ground rod to this line which has an isolated hot and neutral to your system. 

There can only be one ground for the entire house and your components must share this ground.

I stand under correction but i Have found that if all are common ground with good rca cables that should sort it unless one of your devices has a switch mode power supply, that can cause chaos!

colin, assuming there is a common ground, in theory there should be no grounding issues using RCA cables. But not all components use the same grounding scheme, so there may be a difference in ground potential which cause ground faults. Also some RCA cables use a ground connection, some don’t. In these situations there may be hum or noise introduced.

With a SMPS the issue is noise. These power supplies can bleed noise or interference back down their power cord into the mains thus contaminating the entire system.
Some modern components are using high quality internal SMPS’s. It’s the wall-warts that add noise and are not as effective as a linear power supply.

Hi Experienced Goner.
I am adding the isolated ground into my music system and when I connected the ground wire into my existing system and it hums badly.
Did I do st wrong?
Thanks
Calvin
dangcaonguyen12-19-2018 7:34pm

dangcaonguyen OP113 posts12-19-2018 9:43pm

I hammered three copper rods under the ground then linked them together with a solid 4 awg copper wire and through the exterior wall into my music room.

dangcaonguyen OP113 posts12-19-2018 9:45pm

When i touched that wire to the ground post on the preamp, hum occurred. Thanks

You got the hum because there is a difference of potential, voltage, between the new isolated earth connection and your homes main electrical service earth connection.

An isolated earth connection is great for lightning frying your audio equipment. A high voltage lightning transient could enter on your new earth ground connection, travel through your audio equipment, travel out through the equipment grounding conductor at the wall outlet through the equipment grounding conductor of the branch circuit wiring, back to the main electrical panel main service neutral/equipment ground, and then back to earth through the earth ground connection for the electrical service.... Oh and in less than a blink of an eye the event takes place. The lightning high voltage transient may jump across to other branch circuit wiring and fry other equipment and appliances on it way back to mother earth.

An isolated earth connection does nothing for improving the sound of an audio system. Mother earth does no possess some mystical magical power that sucks nasties from an audio system. If anything in your case it adds noise.

dangcaonguyen OP113 posts12-19-2018 11:29pm

I figured out where the problem is. It is on the Conrad Johnson amplifier. When I plugged it into the outlet out of my dedicated line network, or when I used the cheat plug, the hum was gone.
Now, anyone has any idea of how to fix it will be much appreciated.
Thanks

Yeah, ditch the isolated ground electrode. ( New ground rods).If you think you need a lower resistance earth connection then connect your 3 new ground rods to the main earth grounding system of the electrical service. A minimum #6awg copper wire is required by code. Use Approved grounding clamps.

Here is some great reading material on grounding.
https://centralindianaaes.files.wordpress.com/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdf

Jim

@jea48 
Thank you for the paper, it helps a lot. 
What do you think about the use of Isolated Ground Receptacle in this case.
Thanks