I have 104 db Klipshorn/Altec speakers, and I can hear hum on them without the grounds lifted. I have studied this problem for 5 years and unless you use isolation transformers (which are not cheap and may compromise other parts of your system) lifting the ground is the ONLY way to totally eliminate the problem. If there was a cheaper more effective way to completely eliminate ground loop hum, I would have done it long ago. Other than using a passive pre-amp (which I own, but doesn't sound as good)
The other bottom line is an Electrical Inspector will tell you that a circuit with GFCI protection and a 3 prong device with the ground lifted is a safer situation than a non GFCI circuit with a 3 prong plug intact. So before you chastise a lifted ground with GFCI protection, please lobby everyone to install GFCI protection on their stereo circuits. I am not sure why lifting the ground raises hackles on people like it does, but it certainly does!
If we really wanted to be completely safe we wouldn't want to use electricity at all. Or even think about driving a car! Let's keep lifting a ground in perspective.
