Alright I have 3 guitars (2 with humbuckers) and all 3 hum when plugged into my Amplifire and also when plugged in via irig hd to my iphone. I am sure it is not a cable or stomp box issue as I have tested many times.

Now, the problem is either with all 3 guitars or with the output not getting grounded.

Guitars: when I touch the jack, maybe 95% of the hum goes away. When I touch strings or bridge, 75% goes away. turning guitar vol off completely eleminates noise. Btw the hum doesn't change when I change guitar direction.

Amplifire: touching the metal casing has the same effect as touching the guitar jack - 95% elimated. Now, the Amplifire comes with a 2-prong psu. Same problem with a onespot psu (2 prong). It is not grounded.

With headphones, hum is present. With speakers it is present. Now, the speakers have 3 prongs but they are plugged into ground in a way where I can unground them (I live in Japan where I have to use an adapter for 3 prongs which has a regular wire to ground which can be removed). When I unground it, the hum is present. When I ground it, there is a 20% hum reduction. My theory is the guitar is getting grounded by going to the amplifire and out to the speakers which are grounded, but there are so many stops in that, that it is not a proper ground.

My theory is if the Amplifire psu was grounded that I could eliminate hum coming from the guitars. The sad thing is the only things that I can find that would do this are the expensive big psus like voodoo labs. It would be quite an expensive gamble to buy one to try out. What do you think?
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21GunSalute There can be more reasons of it, I saw somewhere thread, where the reason of hum was tube. I suppose you need to talk to technician to define a problem.
I doubt highly that it's the PSU. Amplifires can take AC or DC of either polarity. That indicates quite a bit of circuitry, most likely with a floating PS earth.
The earthing is probably at the audio cable. So the question is, how's the earth on the input of the amp that the Amplifire is plugged into? That's where I'd be looking first.
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