Grounding/earthing systems. Which are quietest? And shielding?

[brett]

Hi.
I think this has bugged many builders at one time of another.

I was wiring up a McTube today and realised that there were several different ways that I could earth the inputs and the 2 PCboards (power supply and signal).

Usually I just use "through the box" earthing, where non-insulated sockets are earthed by the diecast box.  This seems to work quite well where there are no power supply currents that would make a noisey loop through the box, and when the circuit has low gain.

There comes a point where some circuits use enough power (e.g. CMOS and tube-based projects) or have high enough gain to warrant using a single point for earthing, because the box has too much "noise" in it.  For example, in the Real McTube, the late Fred Nachbaur recommended using insulated sockets and earthing all circuits to one location.  That sounds simple, but it still leaves a few options open.

For example, I can see at least 2 ways of achieving this:
1.  Earth the input and output sockets at the signal PCB (as hinted at by the Tonepad PCB, which shows earth connections next to the input and output pins).  Then earth the PCB to the common earth.
i.e. sockets > PCB > earth
2.  Earth the input and output sockets directly to the common earth.  Earth the PCB earth separately. 
i.e. sockets > earth and  PCB > earth

Which will be quieter?
Also, does shielding the earth line have any effect? 
>> I figure that I can easily use shielded 2 core wire for the input and output wires.  Presumably I should connect the shield to box rather than the PCboard earth.

thanks for any help.

[brett]

Any takers?

sockets > PCB > common earth
OR 
sockets > common earth and  PCB > common earth

[Joecool85]

From what I gather, #1 should be quieter.  On that same note, you could try both and see which is better.  I had to play around with my first (and second actually) chipamp to see how to get "quiet grounds."

[Transmogrifox]

#2 would typically be "better":  make everything stem from the same common point.

#1 is easier and more compact--makes the circuit a more neat installation.  If you keep all your ground connections at one spot on the circuit board, then there is essentially no difference between one or the other.

Think of a tree root when it comes to grounding.  All the far reaching "capillaries" branch from a larger vein, to a larger to a larger until they all meet at some central point.  Whether you locate that point on an edge of the PCB, or on the battery snap or power jack, or solder it directly to the enclosure doesn't matter much. 

Once you have that point established, then you may put a large-valued capacitor from the power supply positive to this point directly if you're still having grounding noise problems.

Sometimes noise is not just bad grounding, so don't be too quick to assume your grounding is inadequate just because the noise doesn't go away.  May be something else--including noise getting directly into the audio path from the guitar.

[A.S.P.]

http://www.diystompboxes.com/smfforum/index.php?topic=35849.0

[MartyMart]

I have not done very many PCB builds and mostly use stripboard, this means that I do a lot
of my own layouts, other than some from Torchy/Dragonfly so I must have 60 of my own
done by now `!
This may make no sense, but it certainly has helped avoid any ground problems :
Each and every "ground point"in  a circuit has it's own direct connection to one "strip" as
a ground plane, I try not to have any shared ground nodes, though sometimes there are
one or two.
This ground strip gets direct connections to I/O jack sockets and I use serrated washers
to get good "box" ground connections at the jacks.
It means that some builds are larger than I'd like, but I'll suffer that for a good hum free
build

MM.

[scaesic]

Any takers?

sockets > PCB > common earth
OR 
sockets > common earth and  PCB > common earth

Surely if you're "common earth" is a track on the pcb, then both of them become the same.

[A.S.P.]

a PCB-ground-trace* is not an ideal "single ground point" or "common earth".
It depends much on its width and length...

(*when multiple components are soldered to it over its length)

[brett]

Hi.
In this case my common earth is a star connection screwed to the box. 

As suggested universally, pre-amps and small signal sections should never share earth lines with power sections.