Grounding

Blackest of the black voodoos, give me the power to ground my amp and the cunning to do so safely. I summon you to smother hum beneath the multitude of your slithering sable tendrils and to untwine my ground loops as if they were the entrails of philistines. For thine is the impedance, the silence, and the Safety Earth, now and forever. 

The ground symbol in schematics is generally used for electrical ground, which I use to mean the common current return path and reference for circuit voltages. The third prong on an outlet/plug is safety earth, which may also be referred to as ground. These are slightly different things, but generally the electrical ground and the safety earth will be connected one to the other at some point. When all the “ground” connections are at the same point, this is referred to as a star ground because everything radiates outward from the center like a hub and spokes. I am lobbying to change the term to “wagon wheel ground” and attend all the local IEEE conferences to picket and generally be a nuisance. I’ll let you know how it goes.

 

sandwich board
Sandwich board was re-purposed from other events
I usually make my chassis connection where I tie the electrical ground and safety earth together and locate it as near to the power supply cap grounds as I can. The chassis connection to safety earth is essential; this is what will blow your fuse or breaker if somehow a loose wire tries to electrify the chassis. I usually use a wire nut or the metal mounting leg of a turret strip for the chassis connection and mount it securely through the top plate with a bolt and lock washer.
terminal strip ground
This makes a good wagon wheel ground point and chassis connection
I like to wire the audio grounds to a bus bar or tie them together and then run a single connection to the star ground point. In effect, I have one common point for audio grounds (input/output jacks, grid resistors, cathode resistors, etc) and one common point for power grounds (filter caps, heater reference divider, power transformer center taps). The audio ground is connected to the power ground at a single point (usually through the bus bar if you look at pictures on this site) and the power ground is tied to the chassis and safety earth. Pro Tip: grounding ‘pig tails’ and romex wire are two easy-to-find sources of low gauge solid copper wire for bus bars.

If you strung all the grounds out along a single wire, I would have the safety earth at one end and the inputs at the other end. Everything between them would be arranged in order of ascending current draw (most current nearest the safety earth). Real world wire has a resistance and the small voltage drop differences caused by return currents contribute to hum; we want all of the audio ground references to be the same, so we try to connect them where they’ll “ride” the same return current voltage drop (from the higher current power grounds) and thus have the same reference.
current timeline.png
This is not the only way to ground a project, but it usually works well enough for me. A single bus bar is not always practical either, so it’s often a mixed approach of star grounds and bus bars in most of my builds. If you run into a ground-related hum and can eliminate a ground loop as the cause, you may want to play (safely) with your grounding approach. Star grounds, multiple star grounds, bus bars, and ground planes have all worked for builders in the past. The best system for you is the one that works repeatedly.

And don’t forget to pray.