Here is my situation. Pair of tube monoblocks. The monoblocks have 2 separate AC wall plugs separated by about 10 feet of 12gauge wire that reside on the same mains circuit.
When only monoblock A is powered (filaments and B+), the Vac at speaker A measures 0.8mV.
Then, while monoblock A is still powered, monoblock B is powered (filaments and B+). The Vac at speaker A connected to monoblock A increases to 1.2mV from 0.8mV.
This same increase of 0.4mV occurs if I reverse the process with monoblock A and B. So, it appears to me that there is a ground differential? Would it help if I added a 1ohm ground lift resistor between the chassis and earth ground. Other ideas?
When only monoblock A is powered (filaments and B+), the Vac at speaker A measures 0.8mV.
Then, while monoblock A is still powered, monoblock B is powered (filaments and B+). The Vac at speaker A connected to monoblock A increases to 1.2mV from 0.8mV.
This same increase of 0.4mV occurs if I reverse the process with monoblock A and B. So, it appears to me that there is a ground differential? Would it help if I added a 1ohm ground lift resistor between the chassis and earth ground. Other ideas?
Try plugging both into the same wall outlet to reduce any ground differential.
Connect both with a 3-pronged mains cable and with the wall outlet that has a correct protective ground connection.
I plugged both monoblocks into a garage duty power strip. I helped. So, now I need to either put in a wall outlet that can be shared by both monoblocks or build a DIY audio grade power strip. Thanks everyone for helping.
While you are doing that, run a dedicated line for audio power directly back to the panel.
I bet the preamp and/or signal source and one monoblock was powered off of one outlet.
Of course the other monoblock was powered off the 2nd outlet.
You ought to check both of your outlets.
I think one of them is wired incorrectly, using the Safety Ground as the return wire for the Hot wire (and then using the Neutral wire as the Safety Ground.
That is a no no.
Ground and Neutral are only the same voltage all the way back at the Mains Breaker / Fuse Panel.
In certain situations, I have seen as much as 8 VAC between the Ground and Neutral wires at a single user 3-wire power wall outlet.
Mis-wire power outlets, and you can get very large ground loops, and Hum will be your result.
Hmm.
Of course the other monoblock was powered off the 2nd outlet.
You ought to check both of your outlets.
I think one of them is wired incorrectly, using the Safety Ground as the return wire for the Hot wire (and then using the Neutral wire as the Safety Ground.
That is a no no.
Ground and Neutral are only the same voltage all the way back at the Mains Breaker / Fuse Panel.
In certain situations, I have seen as much as 8 VAC between the Ground and Neutral wires at a single user 3-wire power wall outlet.
Mis-wire power outlets, and you can get very large ground loops, and Hum will be your result.
Hmm.