A Q about isolated ground outlet & humming amp

Every day around 7 or 8pm my power amp (Pass X250)starts humming.I suspect that somebody gets home from work in my building and turns some kind of appliance on that leaks DC in AC line.The hum stops somewhere very late at night,2 or 3 am (i never had a chance to stay that late to find out)In the morning at 8am and till 7 pm it is dead quiet then it starts all over again.I had a heavy duty hospital grade outlet.Yesterday i installed a heavy duty Isolated Ground outlet in hope to defeat the hum.The sound really improved due to a 20 amp outlet contact tightness with the power cord but the hum appeared in the evening as usual.
My question is:
What is the purpose of isolated ground outlet ?Nelson Pass warns in the manual never to float the ground.Am i floating the ground by having IG outlet?
I connected the outlet the usual way like all regular outlets are connected.There is a ground screw on the side but i have nothing to attach to it.Please,help me in understanding the whole thing.Thank You.
Isolated ground outlets simply have the screw (green) for the ground wire separated from the metal body of the outlet, the ground is not floated (ie disconnected) its just separate. The bottom line is that in many houses the wiring is in metal conduit and uses metal outlet boxes, so when a standard outlet is installed there are two ground paths...the ground wire and through the metal box the outlet is screwed into. This can lead to noise since you now have a shared ground in all you house and this can lead to hum. If you have plastic outlet boxes it is my understanding that you already have isolated grounds.

Your situation is different though. Forget the isolated ground outlet, you don't have a ground wire. No Ground wire means floating ground and in general not advisable with equipment that is designed to be grounded (3 prong plug). You may have a house that grounds through the outlets, in which case the isolated ground outlet used without a ground wire is not the way to go.

Are all the outlets in your apartment 3 prong or 2 prong?

I would go to home depot and get an AC Outlet Circuit Tester plug ($5). You plug it into a socket and a set of lights tells you if the outlet is wired correctly and whether there is proper grounding.

PS audio makes a humbuster outlet to remove DC, which is probably your problem. Proper wiring is more important at this point though.


I had a hum in my Creek 4240SE integrated amp. it was so loud that it kept me awake at night. The PS Audio Humbuster completely eliminated it.

Good night....zzzzzzzzz

Brad Day
Atlanta, GA