60Hz Hum Vs EMI/RF
Hum in your guitar comes from a few different sources. We discussed how shielding can minimize RF/EMI noise
HERE.
Electromagnetic interference exists anywhere there is electricity. This is compounded by the fact that anything with a transformer in it, TVs, Fluorescent lights, Power supplies, all emit a lot of EMI because they contain coils. This means that you can have noise from devices that neither share a circuit with your guitar, or are connected in any way. This is because this interference travels through the air.
No matter how effectively you have shielded your guitar, you may still be experiencing some noise. This is because even though you may have minimized the EMI interference that travels through the air, you may still have noise coming from other places.
Ground!
We hear this term all the time when dealing with guitars. "MAKE SURE IT'S GROUNDED"....
When we have good solid grounds, we have a nice clean flow of signal. This is especially important when dealing with "unbalanced" signal like we have in a guitar. This means the ground is not isolated from the signal path. When we have a bad ground from a bad cable end, a loose fitting AC adapter, pedals that are poorly grounded, etc, we create a condition where signal leaks into the audio.... as hum. The video below will explain this in further detail.
It is important that every circuit in our rig be properly grounded. If we do this, and have a properly shielded guitar, we can minimize 60hz hum AND RF/EMI interference
http://youtu.be/ictggb7aaO4
