I found this box completely unusable. No matter what I did I could not get rid of a severe hum whenever the unit was switched on. I tried everything I could think of to get rid of the problem: I tried it in three different amplifiers, two solid state and one tube. I tried different guitars with it. I tried different cords thinking one might be defective - not so. I tried plugging the unit straight into the amp with no guitar - same thing. I replaced the tubes with tubes I know to be good thinking that may be it. Nothing worked. Whenever the unit is plugged in and switched on there is severe and unacceptable hum that almost obliterates the signal.
So I figured it must be a defective unit and I returned it (to Amazon). They sent me another one and it had exactly the same problem. I looked on the Web and found out that many people have had the same problem while others did not. Clearly there is either something wrong with Electro Harmonix’s quality control or it is a very poor design to begin with. I returned the second unit for a refund. It’s too bad as the rich vibrato that I could hear under all of that hum sounds nice and I would have liked to have it.