[sdiy] Shielding

harry harrybissell at prodigy.net
Sat Dec 1 19:58:16 CET 2001


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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