Thanks for the replies so far...So let me go into more detail about my ground loop.
It is only in the right channel-the left is dead quiet. I have swapped all interconnects and speaker cables and is has no effect. (well when switching interconnects from right to left to the amp, the hum changes sides as one would expect) I have tried both balanced and SE outputs from pre to amp.
I have unplugged all sources from the preamp and it goes away. As soon as I connect a source cable to any of the right channel inputs (either balanced or SE) the hum reappears. As I connect more sources to the preamp, the hum gets louder, so it appears to be a cumulative effect. However, the hum is at a constant level and does not get louder or softer with changes in the volume.
I sent the unit back to BAT after talking to Victor on an extensive phonecall and many e-mails. He gave the unit a thourough going over and could not reproduce any hum and sent it back with a clean bill of health. I brought it into my local audio dealer and had their repair guru put it on the test bench and could not reproduce any hum.
I have tried ungrounding all source components as well as preamp and amp. I have tried running a ground wire to all components. I have tried the preamp on another circuit. I have tried plugging it straight into the wall both on the same and other circuits. I have tried the Jensen ground loop isloators--both on balanced and SE between the pre and amp. Currently, all gear is running from a Furman outlet strip on a dedicated 20 amp line. I have also tried with a Monster reference 7000 power conditioner.
I have also switched the tubes from right to left channel, and swapped in a whole different set of tubes.
When I demoed another preamp from my local dealer (the Sonic Frontiers SF1) the hum dissappeared.
So, any other advice on ground loops would be greatly appreciated.
