Currently Being ModeratedJan 14, 2013 7:25 PM (in response to jimsreynolds)Re: Ground lift cables fixes hum in a 4CM setup
Thanks a lot Jim !
I just tried your "ground lift cables" with my M13 and it fixed the hum. But I don't understant why it worked. Do you know why ?
Currently Being ModeratedJan 15, 2013 1:21 AM (in response to marc937)Re: Ground lift cables fixes hum in a 4CM setup
For Info: I eventually permanently disconnected the grounds on cables 2 and 3 of my 4CM and have lived happily ever after.
Why does this help? Well as I understand it, the noise is caused by the signal ground connection at the input and in the amp loop being at different voltages.
Ground is not Zero volts throughout a whole rig and there can be significant voltage differences between two points in the rig .... in this case between the amp input and the amp loop connections. Current will therefore flow via the ground connection between the amp Input and Loop, via the POD itself. This current is effectively modulated by (generally unavoidable) noise within the system and therefore creates a noise signal.
The modulated current interacts within the internal resistance within the POD circuitry and cable to create a noise voltage in the signal ground path, .... which gets overlaid onto the signal that you wanted to keep! The higher the voltage and/orresistance in the signal ground path betwen input and loop, the higher the degree of noise.
By removing the ground connections in the Loop cables (#3 and #4) , you eliminate the current flow via the ground path between amp loop and Input. You still have the connection you need to ground via the amp input so everything is rosy.
Fantastic link by Space below! Cleared up a bunch of stuff for me.
Currently Being ModeratedJan 14, 2013 8:36 PM (in response to jimsreynolds)Re: Ground lift cables fixes hum in a 4CM setup
here is a great little paper on the subject of eliminating ground loops.