So where do you think the Wooaudio headphone and amps are made ?
In NY ? Your joking, right...?!
Of course they are made in China! ...and BTW very well made, but sorry mate, IMO not worthing 600 dollars.
I have a friend that have some amps made in Hong Kong ( China is too big, and Hong Kong has an heritage of British tradition and manufacturing that you don't find in other parts of China) and they are beautiful handmade aswell.
About the hummin', coulb be a faulty tube...?! or - the main reason imo - troubles with the ground wires.
Only in one amp he had hum problems, and he's made some mods in the caps and gounded the chassis and other parts and that's it, a beautiful sound without no hum, like the pics shows



Anyway, have fun.