Vintage Deluxe Electric Mistress HUM!


Hi, I posted this before but didn't had good luck, but now I know that the filter caps were good, since the problem persists...

"I just bought a 1979 green Deluxe Electric Mistress, I have two questions:

- Hum is a problem with this unit: I tried just guitar, cables, DEM and amp and it hums a lot, especially when bypassed, with the effect on seems less prominent...maybe the "swoosh" is louder and I cannot hear, but I think it hums only when bypassed.
In a true bypass looper the hum goes away even with the effect bypassed, if you don't select that loop clearly. But if I power the DEM from the auxiliary AC outlet on my Pedal Power Mondo it hums a lot with every loop or everything bypassed...I think this is a ground loop, 'cause the problem goes away if I plug the DEM elsewhere.
I tried to exclude the ground connection on the 3-prong cable but the problem persists when powered from the "wall" outlet, I didn't try with the Pedal Power, maybe this can help, but I don't want to play without a safe ground...
So, what is left? Maybe the filter caps are gone? Should I try to replace them?

- The second problem is that the guy in the shop didn't know a thing about pedals, so he told me what the private seller said to him: the pedal was modded for True Bypass and Volume Drop issue. Now, since the pedal IS NOT true bypass (just hardwire bypass) I doubt even of the volume drop mod: the pedal is at the same volume to my ears when activated, but can I check some particular component in the circuit to be sure about this mod? To me it looks stock, if they touched it they have done a good job, but I'd like to know if it's stock or not. Then, if you increase the volume, does the sound change? On certain effects it happens (vintage Vox Wah, Small Stone...), how is it with a DEM?

It is a fantastic sounding flanger, a great chorus\doubler\filter too! I'd like to have it working properly...

Thank you all and sorry for eventually bad english, I'm italian, let me know if something isn't clear! ;)"

Does every DEM with the internal transformer hums like this? They weren't working properly from the beginning?

If someone has a solution let me know please, if not I'll remove the transformer and try with an external (18v?) power supply, but I'd really prefer to leave the pedal as stock as possible...

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