Many types of grounds exist. For example the instrument may
have two grounds. One that is the negative side of signal or
power. The other that is the instrument body. Both may
eventually connect to a common point. But they remain
electrically different grounds. Why? Wire is an electronic
component - not just a conductor.
A building has two ground systems that share some common
wires. One is safety ground primarily installed for human
safety. Safety grounds are also often routed so that noise is
carried away. Safety ground must also connect to earth
ground. A wall receptacle is safety ground. It may connect
via electronic components (wires) through circuit breaker box
to earth ground. But safety ground and earth ground are two
different concepts.
Many make a mistake of assuming wire is a perfect
conductor. Therefore they assume earth ground and safety
ground (sometimes called equipment ground) are same. They are
not, just as DC ground inside that amp is not same as earth
ground or safety ground. Yes that DC ground eventually
connects to safety ground. But again, is is a different
ground often connected to safety ground at only one point.
For eliminating noise, the same concept: single point
grounding. It gets complex when other electronic conductors
such as humans get into the circuit. We try to eliminate the
human (and other) created problems by using single point
grounding and better conductive paths (wires). For example,
guitar and mic might use same single point ground at the amp.
Then the amp shares a single point ground with all other
equipment at the power distribution strip. That power strip,
in turn, shares a single point ground at the wall receptacle
OR where all safety grounds meet back at circuit breakers.
Then that circuit breaker box shares a common earthing ground
with concrete under your feet.
Yes, even concrete is a conductor of electricity. How
conductive determines how much it affects your ground
network. More specifically, what type of electric currents
might be passing through it. To a mic signal, concrete is not
a conductor. To AC mains electricity, concrete might be a
conductor. To static electricity, concrete is a good
conductor.
Try to keep things simpler - using single point grounding on
the most conductive electronic components - the wires. Good
conductors sharing single point ground techniques make less
conductive paths less relevant - ie. eliminates hum and ground
loops.
