ASL Head Amp

I recently bought a headphone amp (Antique Sound Lab MG-Head DT) off of here. But I'm thinking about selling it. I have had an annoying, loud level of hum out of every one of my headphone (Grado SR-60, AKG 271, Audio Technica ATH-AD700). I've changed the Tubes, added Herbie's Tube Dampers, changed the inputs I use and the type of power cable (grounded to ungrounded) and most everything I can think of. Which is admittedly limited. So before I relegate this thing to the closet or the pawn shop, is there anything else I can do?

Any help would be appreciated.

Sounds like a loose wire. As much as I love my ASL headphone amp I think the quality control is suspect. Check the soldered connections inside. You might find a loose solder or wire.
I have one of these and never had a single issue. Does the amp produce any audible noise directly from the unit or is the noise just heard through headphones?

Also, have you hooked up the amp to run directly into a power amp and through your speakers? If so, did you experience the same noise through the speakers that you are experiencing through your headphones?

The unit I have is the OTL version and can be switched to play OTL or with the transformer. I point this out simply for the possibility that it could be the transpormer (in addition to a loose wire as stated above), and if your's has the OTL option to try that. I obviously don't know details about their different amps, hence the above comments on the OTL aspects.

I have had great success with mine and the tube rolling is very productive.