transformer Hum

Try transfering the vibration away from the audio path. If you give the resonance frequency a place to go other than the audio path it will. The most effective unit out there deigned to do this is a Sistrum stand anybody that has heard one will agree. Look it up on the audiopoints website @www.audiopoints.com. However you should still fix the source of the problem. Most times lifting the ground is a simple solution and cheaper than a power conditioner. Still try the rack even if to fix the hum.

Flying, Sndsel has hit it on the head! It is simply loose core laminations in your power transformer. This is a very common problem so don't feel alone. Placing sorbathane pads under the transformer will most likely do the trick. Your problem has nothing to do with a bad power supply or bad AC power. Please do not run out and purchase an expensive line conditioner as it will not fix your problem.

Thanks everyone for the help. I won't go and by a conditioner becuase after placing the sorbathane...it decreased. I can still hear it, but only if my ear is within 12" or so of the preamp. I guess it is ok now ?

Where do you purchase sorbahane and what form/shapes does it come in? I have seen it mentioned in other threads, but only recall seeing some little half sphere footers of sort that I think were made out of this substance. I would like to try it out on the power supply of a tube amp that I have and would like it in washer form if possible for a rack that I am planning.

I echo Dekay's inquiry: where does one get sorbathane washers?