Ground loop hum

milgo

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Hi there,

I recently bought an rdac kw, which introduced a loud hum into my setup. I have a rega rp1 turntable, TV and DAC all connected via RCA leads to my audiolab 8000a amplifier.

All of these have twin wire power cables. I replaced the interconnects with new ones, which has helped. Without the TV connected the hum is rather loud. Once the RCA leads were hooked up to my TV it calmed down significantly. It would seem that my only ground is the coax aerial in the TV.

I would like to isolate that and provide the system with a new earth. What is the best way to go about this?

I would appreciate any advice.
 
It sounds like it's the very common TV coax earth loop. To confirm, just disconnect it. If the hum goes disappears, it is.

If the coax is for a cable TV or standard terrestrial aerial, you just need a simple coax ground loop isolator, such as this or this, depending on the connector type.

If the coax is for a satellite (including SKY) aerial, you cannot use this isolator as it won't pass DC, so you'll get no signal. Instead call in the satellite (SKY) installer and get him to do his job properly - the installation is supposed to be correctly earthed at the consumer side, so it's clearly faulty. Unfortunately, this corner-cutting seems to be fairly common, judging from the number of posts we get here.

I strongly recommend not trying to solve this by altering the earthing elsewhere in the system, unless of course you're a suicidal pyromaniac.
 
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Thanks for the reply Mark.

If I disconnect the coax with the TV off the hum is worse, if is disconnect it with the TV on the hum is worse. If I pull it out after just switching the TV on to standby it is lovely and quiet for about 20 seconds. Then a relay or something clicks in the TV and "hummmmm".

If I don't have the TV connected by RCA the hummm changes by touching the amp chassis and dials etc.

I will order an isolator incase, cheers for the links.
 
Just been mucking about with everything. It would appear my amp is faulty. After pressing the tone switch in everything is quiet. When releasing it I get a pop through the speakers and the hum is back.

Looks like I will be sending it off for repair.

Appreciate the help Mark.
 
Just been mucking about with everything. It would appear my amp is faulty. After pressing the tone switch in everything is quiet. When releasing it I get a pop through the speakers and the hum is back.

Looks like I will be sending it off for repair.
As you said in post 3, it wasn't a coax ground loop.
 

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