AW: [sdiy] Seperate Grounds

[Ingo Debus]

harry wrote:
> > 2. If a signal is transmitted from one module to another, a direct
> > ground connection between the two modules that does not share any other
> > current. Otherwise the voltage drop caused by these "other currents"
> > will add to the signal.
> 
> Maybe yes..maybe no. You pointed out that this means there are now two
> ground paths...  If both grounds are at the same potential, this would be good...
> If not... this would be bad.  If these are patch cords (with shields) it might be
> best
> to connect the shield at only one end... and let the signals use the other ground
> as a reference...

If both grounds are at the same potential then the problem is solved...
we don't need to worry about ground connections any more :-)
I think, cutting a shield of a (unbalanced) cable at one end often will
make things worse.

Funny, just after I wrote my first mail, I experienced a hum/noise
problem :-/. I haven't sorted it out yet, but I think it is a ground
loop between my computer and my DAT tape deck and my mixing console. One
ground connection is the shield of the audio cables and the other one is
the shield of the S/PDIF cables between computer and DAT. If this is the
case, and if I cut the shields of the audio cables then, this would
leave the only return path for the audio signal via the shield of the
S/PDIF cable. Certainly not a good thing.

> > 3. No ground loops.
> > (I'm using the term "modules" here, these can be modules of a modular
> > synth or anything else)
> 
> A ground "loop" means that there are two grounds at different potentials...
> ground loops are always bad.  

Ah, here's the misconception. With "ground loop" I meant just duplicate
ground connection. I like the latter term much better than "ground
loop", BTW.

Ingo