[sdiy] Shielding

[Theo]

Moho Disco said the noise was not there when the laptop ran of batteries.
Think that rules out the sound card
and points a heavy finger to wards a ground loop.

Theo

From: harry <harrybissell at prodigy.net>

> Hi Ingo....
>
> I'd be more suspicious of the card itself. A lot of cheapie sound cards
were
> not designed for high quality audio use.  Maybe 50dB signal to noise is OK
> for a video game, but not an album !
>
> It would be easy to cheat the ground on the computer (2 to 3 wire plug
adapter)
> and find out.  If it goes away, its ground loop and you can buy the
isolation
> transformer (I paid $50 new for a stereo unit from ebtech). I bet the
noise remains.
>
> H^) harry
>
> Ingo Debus wrote:
>
> > Moho Disco wrote:
> > > Currently I'm just using the laptop's crappy internal soundcard, which
> > > is wired directly into my Mackie 1604vlz.  A laptop adapter for my
> > > Layla24 sound card should be arriving Monday, and I'm *praying* that
> > > it does not exhibit the same symptoms.
> > >
> > > >If you remove all the wires, does the noise stop ?  (the idea is if
the noise
> > > >stops... it is being conducted by some wiring, not through the
air...)
> > >
> > > Yep, the noise stops when I disconnect the cables from the computer
> > > to the mixer.  It is most definitely being conducted through a wire...
> > > But it doesn't matter what wire I use, they all transmit it.
> >
> > Like Theo obviously suspects too, this is most likely a ground loop
> > problem. A friend of mine had that prob too with a Mackie mixer. It's
> > difficult to disconnect signal ground from protective earth in these
> > mixers without affecting electrical safety. All jacks are connected
> > directly to the case as well as the power transformer, power switch and
> > so on. An option is re-building the mixer's power supply into an
> > external case (larger DIY project). Another option is using DI boxes or
> > isolation transformers in the audio pathes between mixer and computer.
> > I don't know the Layla card, if it has assymetrical (unbalanced)
> > ins/outs the problem most likely won't go away :-(
> >
> > Ingo
>
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