"gndloops"

[Rene Schmitz]

At 09:33 08.04.1998 +0200, you wrote:

>I want to propose some idea and let me precisely say: it is about ONE
>(big) modular system. I'm not talking about different separate machines
>tied together, just ONE (in the case of a large distributed system,
>with different power supplys etc etc. you won't get away without
>balanced connections). The case is connected to power-gnd, but the jacks
>are isolated, power-gnd may be connected only at the star point to signal gnd.
<SNIP>
>Any comments ? Experiences ?
>
>
>m.c.

Hm, I'm not sure if thats what you propose, 
but when every GND reference goes to the central star ground,
and one would NOT connect the modules GND to the grounds of the jacks,
and one just connects the frontpanel to the jacks GND, and one makes ONE 
connection from the grounded front panel (and all the jacks) to the star 
ground, ground loops are avoided for the signals, and shielding is maintained. 
If you patch a chord into two jacks there is still a loop, but the magnetic 
induced voltage cannot change the voltage at your reference
point. 
I've thought that this would be perfect within a single supply system.
(Something like a banana-jack system with maintained shield)

Maybe this is just the opposite approach, focusing on the magnetic fields 
and not on the ground connection resistances. 

in an ascii matic it looks like this:

+---+   shield     +---+
| A |--O--------O--| B |
+---+  |        |  +---+
  |    |        |    | 
===star=ground=point======

The loop that is formed by the shield of the cable and the connection to 
the star point cannot influence the reference voltage.
(Or did I miss something?)

Of course the current that flows from the modules to ground, changes the 
reference levels of that module (and of the connected) now, but the only
modules 
that can "poison" the ground are VCOs and LFOs, I decoupled the discharge
switches 
in my VCOs and don't notice any crosscoupling. And I didn't even use
extrordinary 
thick wires for the supply.

The next level could be to use "reference" and "power" ground connections, 
all the ground references of the opamps would go to "reference"
and e.g. all the ICs (LEDs ...) 0V power connections go to "power".

And even this all isn't necessary thoughout the whole system, just where it 
is usefull.
 
Bye
-René if-everything-else-fails-use-optical-links!






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