FM3 Ground loop plugged into a Voodoo Labs Pedal Power 2 Plus

make sure your power2 is grounded and the outlet of the unit is grounded, if its working fine without it then I'd say the problem is with VLPP2, personally I use Furman AC-215A on the AX8 and have the VLPP2 is connected to that.
 
Ground loops exist between multiple pieces of equipment. Look at everything in your signal chain, including power amps, speakers, and other stuff that may be way downstream. Try to tie everything back to a single ground via a common power source.
 
Divide and conquer! Start with a known source that is free of noise and add the other pieces until you hear the problem. I would also make sure the outlet(s) are wired correctly. A receptacle tester is a handy tool to have! Any home improvement store should have them for a few bucks.
 
Ground loop exists with or without input from guitar or anything else attached. FM3 power to VoodooLabs PP2 outlet, PP2 to wall outlet. Amp and FM3 on same circuit. several cables tested from unit to amp, including high end evidence cable. RJM PCM same setup, dead quiet.
 
It also might be something else causing RFI or a hum. The PP2 is a good power supply, and I'd be surprised if the internal transformer is inducing a hum, but it's possible. Assuming your gear is all using 3 prong cables, a ground loop would be caused by voltage differential between the respective ground points. So, start by making sure the power cables are good, and that everything is plugged into the same circuit (same outlet if possible). As suggested above, divide and conquer by doing the following:
  1. Eliminate the PP2 from the equation. Try plugging in the amp and the FM3 directly into the same outlet, with no instrument input. Noise / hum at this point is coming from something in the power line, or perhaps a transformer / dimmer.
  2. Plug in the instrument. If you're getting noise that wasn't there before, it's something happening in the guitar or the cable.
  3. Then try with the FM3 plugged into the PP2, with no instrument input, and unplug everything else that is connected to the PP2. Any noise / hum coming at that point is in the power supply, or some kind of RFI.
  4. Plug in the instrument. If you're getting noise that wasn't there before, it's something happening in the guitar or the cable.
  5. If you have any effect pedals that were previously attached to the PP2, power up one at a time, and add it to the signal chain. You may find that one of the pedals is inducing hum or noise, or that you have a bad cable.
 
Ground loop exists with or without input from guitar or anything else attached. FM3 power to VoodooLabs PP2 outlet, PP2 to wall outlet. Amp and FM3 on same circuit. several cables tested from unit to amp, including high end evidence cable. RJM PCM same setup, dead quiet.
Are you getting a ground loop with the FM3 plugged directly into the wall power? If you're getting a hum / buzz with the FM3 and amp plugged directly into the same outlet WITHOUT A GUITAR INPUT, then it's either (1) a bad AC cable (2) something inducing a hum (transformer / dimmer / appliance / RFI) or (3) something is wrong with the FM3 or amp. Make sure there isn't a ground lift activated on anything.

EDIT: also, try different AC cables for the amp and FM3. One of the cables might have a bad ground. When you reintroduce the PP2, make sure to do the same thing.
 
What kind of amp? A power amp or an amp head/combo?

Assuming you have a headphone FM3 can you see if there's a hum in headphones when not connected to the amp?

For use with an guitar amp it is recommended to use Humbuster cables to avoid hum.
 
Are you getting a ground loop with the FM3 plugged directly into the wall power? If you're getting a hum / buzz with the FM3 and amp plugged directly into the same outlet WITHOUT A GUITAR INPUT, then it's either (1) a bad AC cable (2) something inducing a hum (transformer / dimmer / appliance / RFI) or (3) something is wrong with the FM3 or amp. Make sure there isn't a ground lift activated on anything.

EDIT: also, try different AC cables for the amp and FM3. One of the cables might have a bad ground. When you reintroduce the PP2, make sure to do the same thing.
yes, ground loop still there when FM3 directly plugged into wall. Tried several cables, all same. using Fender Blues Jr. Not the amp, as loop isn't there when guitar just plugged in. might need to try a humbuster cable
 
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