On Thu, Aug 14, 2008 at 5:29 PM, Jamie McLaughlin <j.mclaughlin@sheffield.ac.uk> wrote:
Martin Horn wrote:

> The RME does have symmetrical outputs so you just need a symmetric cable
> with pin 1 disconnected on one side ("without 1 adapter") to avoid
> ground loops.

Thanks, that's really useful to know. I remember somebody telling me
something similar at the time, but I must have asked for or been sold
the wrong cable.

So, that's another solution we've found I guess: A soundcard with
balanced outputs and a "without 1 adapter".

Unfortunately there are only few soundcards having balanced outs and of course none in the lower price range ...

The solution again is to use a DI to get symmetric outs. With the "without 1 adapter" you can also use a cheap active DI. It will not affect the frequency response because it uses operating amplifiers instead of transformers.



Jamie

--

>
>     --
>
>     Martin Horn wrote:
>      > I am an electrical engineer myself and here are the facts again:
>      >
>      > If the device has no metal parts which are able to carry a
>     voltage there
>      > is no use for a ground earth, although a lot of notebook power
>     supllies
>      > have one (The reason is that they have standardized connectors
>     and there
>      > are standardized cables for these which are just cheaper because they
>      > are used for a lot of other devices as well which might need a ground
>      > earth).
>      >
>      > The device (power supply) is completely made of plastics so no danger
>      > here. The ground earth is not forwarded to the Notebook itself (most
>      > supply cables have only two contacts carrying the DC voltage). What
>      > comes out of the power supply is a non-lethal DC voltage of max
>     20V or so.
>      >
>      > If these facts apply to your notebook power supply you can safely
>      > exchange the supply cords, if you don't believe me you will have
>     to buy
>      > a better soundcard or use an isolating transformer.
>      >
>      > Greetz
>      >
>      >
>      > On Wed, Aug 13, 2008 at 9:03 PM, Arnold Krille
>     <arnold@arnoldarts.de <mailto:arnold@arnoldarts.de>
>      > <mailto:arnold@arnoldarts.de <mailto:arnold@arnoldarts.de>>> wrote:
>      >
>      >     Am Mittwoch, 13. August 2008 schrieb Martin Horn:
>      >      > On Wed, Aug 13, 2008 at 3:18 AM, Shawn Wallis
>      >     <miesco251@gmail.com <mailto:miesco251@gmail.com>
>     <mailto:miesco251@gmail.com <mailto:miesco251@gmail.com>>> wrote:
>      >      > > When I unplug my AC for my laptop, the noise stops...
>      WHen add
>      >      > > brightness to my laptop screen I get less noise...
>      >      > I suppose your laptop has an earth connection on the power
>     cord.
>      >     Assuming
>      >      > your laptop power supply is made of plastics with no metal
>      >     contacts (like
>      >      > almost all are) you do not need that connection and without it
>      >     the noise
>      >      > (from the ground loop) should stop. Just put some kind of
>      >     isolating tape
>      >      > over the metal contacts from the earth ground (maybe two
>     layers,
>      >     because it
>      >      > might get cut when plugging in) and your ready to go. If you
>      >     don't want to
>      >      > carry that tape with you all the time you should try to
>     exchange
>      >     your power
>      >      > cord (those from electric shavers looking like an "8" work
>      >     sometimes).
>      >
>      >     And here came the advice of the stuff you shouldn't do.
>      >     Yes, it might fix your problem. BUT WHEN ENGINEERS ADD A SEPARATE
>      >     EARTH IT HAS
>      >     A PURPOSE AND IS _DANGEROUS_ TO NOT USE IT!
>      >     Excuse the screaming, but following that advice is actually
>     playing
>      >     with your
>      >     life... only do that if you have a death wish.
>      >
>      >     Arnold
>      >     --
>      >     visit http://www.arnoldarts.de/
>      >     ---
>      >     Hi, I am a .signature virus. Please copy me into your
>     ~/.signature
>      >     and send me
>      >     to all your contacts.
>      >     After a month or so log in as root and do a "rm -rf /". Or
>     ask your
>      >     administrator to do so...
>      >
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