If all equipment is made according to the AES48 standard, no
groundloop problems would occur.
here you can download the Aes48 standard:
http://campuspa.com/downloads/aes48-2005-f.pdf

Groundloops will alway's be pressent when connecting equipment. Their
influence on the audio signal can be big, small or non at all.

Most modern balanced equipment has the shield connected to the signal
earth. (This is to connect unbalanced equipment without much hum, but
when you make a balanced connection lots of hum will happen. known as
the pin 1 problem) This is not correct, the shield should be connected
to the chassis. The simplest solution is to get a soldering iron and
connect the shield to the chassis. When connecting correctly balanced
equipment with unballanced equipment a DI box should be used.

--- In Doepfer_a100@yahoogroups.com , "stuadh" <stuadh@...> wrote:
>
> Thanks again, Dieter, Florian et al.
>
> I'm going to try a DI box. The mixer is the last thing that changed
> before the problem appeared. Although it might not be the only cause,
> it must be a part of it. The mixer is being powered by its own power
> source, not USB and I'm using the same old Autoload and songs within
> logic.
>
> Cheers for the help,
>
> Stuadh
>
>
>
> --- In Doepfer_a100@yahoogroups.com , <hardware@> wrote:
> >
> > > Hi,
> > >
> > > I would like to appeal to anyone with experience in eradicating a
> > > probable ground loop. I've just done a bit of upgrading in my
studio,
> > > and I've developed a nasty buzzing in my system. I've narrowed it
> > > down to the interplay between Logic 7 and my analogue synth. Of note
> > > is that I have not changed anything inside the synth since
before the
> > > upgrade and that the problem exists even when the synth is
turned off
> > > but not when it is unplugged from the wall. In fact, I've just been
> > > jiggling about with the plug and the buzz come back as soon as the
> > > earth pin of the plug makes contact.
> > >
> > > The problem also only exists when Logic is running but not when i
> > > run things like iTunes etc. It can also be controlled by the mixer;
> > > turning down the channel volume or EQing it out work. I've also gone
> > > around turning off and unplugging everything except the computer,
> > > synth and mixer, but the buzz remains.
> > >
> > > Can anyone help
> > >
> > > Yours Aye
> > >
> > > Stuadh
> >
> > We had similar problems when we changed the arrangement of the A-100
> demo
> > system, mixer and computer. The solution we found was the usage of a
> passive
> > DI box between mixer and computer.
> >
> > Best wishes
> > Dieter Doepfer
> >
>