Ok, power in most consoles is ran down the bus... wether ribbons or cards.
So , for instance, top to bottom, trace/lead to trace/lead, youd have something similar:
+48v
+5v
0v
0v
0v
-5v
+12v
-12v
+15v
+18v
aux1
aux2
aux3
aux4
aux5
aux6
L
R
sub1
sub2
sub3
sub4
sub5
sub6
sub7
sub8
etc etc
some of them, power is on the same card/cable... others they are seperate.
The problem is that you will bleed from one to the next in close proximity, level dependant on quality of pcb or cable shield, connector quality, ribbon length, distance from point of distribution (Where power comes in), grows as you get further down the bus adding channels, etc.
lots of factors.
Typically, your power and ground comes in where the cable plugs into the back of the console (Drrr) and branches out down the board.
Usually this goes into one channel, then the next, then the next, and so on. one to the next, all the way down the board.
STAR GROUNDING is a method of separating the ground from this scheme. As easy as clipping the ground where it comes in the console... and separating it between channels.... so that it doesn't extend to the channels and down the 'bus'
Then, take a nice heavy gauge, (You can bench each input module / channel, measure it's needs, multiply by the number of channels and buses, and get your gauge)..... run it to say midway down the board to a terminal block. Then branch off the block to each individual channel.
That is a star ground. It does three things.
1) It provides an adequate gauge ground to support it's load. 99% of consoles, even high end, can suffer from use of insufficient ground. believe it.
2) it provides even distribution of the ground, rather than pulling thru all previous channels to ground, each channel grounds straight to ground.
3) It isolates your ground from close proximity to what may be audio signal or + voltage causing bleed. In the case of mackies with ribbon busses andd power, you have a + voltage directly against your ground.... booooo....
You can do this with your power as well.
Clean power, and isolating it from your audio paths, will make that joker seem like a different console.
Seriously.... google this ish.
Even big name manufacturers boards suffer from this and can be improved on.
So why dont they do it out the box? Time ... and time is money, and extra wire is money.... but it's mostly the time.
WAY WAY faster to and cheaper to just slap a ribbon cable in. Cost of manufacturing a harness is dirt with ribbons cause it's all on a machine, verses hand trimming, tieing and crimping/soldering a custom harness.
The difference on my board, just with the ground, was night and day. I swear. Unreal. From hearing the nopise floor in the monitors, to NOT. You can barely even SEE it now in PT when zooming the waveform height on 'silence' .... and you can't hear it. you'll get more digital ripple trying to amp and hear it, than you will get actual recorded noise....
Trust me

Grubs... I'll be at studio around 5 if you wanna jump thru for a bit. Or I can come to you. Where you at?
Gimme a call. PRIMARY number on my websites