Chiming in on the 'cheap-usb-audio-interface' conversation

[Ralf Mardorf]

On Sun, 2011-01-09 at 16:35 +0100, Ralf Mardorf wrote:
> On Sat, 2011-01-08 at 22:28 +0100, Thomas Orgis wrote:
> > Am Sat, 8 Jan 2011 14:47:46 -0500
> > schrieb Mike Holstein <mikeh789 at gmail.com>: 
> > 
> > > ground lift added to the plug on the laptop quieted down my firewire
> > > interface,
> > Still sad that that's necessary, isn't it?
> 
> No, ground lift is even used for professional studio equipment, e.g. the
> Brauner VM1 power supply. It's not cutting ground, but decoupling it by
> a capacitor. At home I added a ground lift to my SPX90II, without a
> capacitor, I simply cut ground if needed and I seldom need to use it,
> but it can happen that it's needed even in professional studios. This
> shouldn't be needed for equipment that durable is installed to studio
> racks, but could happen for additional equipment.

PS: I read that diodes should be the right way for a ground lift (a
resistor and capacitor could be add in addition), it's said that the
diodes need to be able to stand more but 1A, otherwise they burn, before
the fuse will do it. It's also said that usually only tube equipment
should be dangerous, when ground is completely cut, but I don't think
so.
Btw. I had potential differences for an analog mixer and my guitar -
with ground added to the strings - connected to a transistor guitar amp,
when using the same power feed. There wasn't noise, but it wasn't funny
to touch the strings and the mixer at the same time. The amp was
connected to the ground, while the mixer shipped with a european plug =
no ground, but the one on the neutral.