[slinkelist] Two sound cards and hum

[Colby Boles]

I really think the best approach is to just use digital sound cards with
either optical (inherently isolated) or transformer-coupled coaxial outputs.
I like the RME Digi96 line of sound cards. They are PCI card with great
drivers that support multiple cards

Benefits:

* ground loops solved
* sound quality issues solved
* quality cabling cheap (can use RG-6 for coax runs)

Drawbacks:

* more expensive sound card ($80-$1000)
* need digital input on your stereo or an external DAC

Colby



> -----Original Message-----
> From: slinkelist-admin@nirvis.com [mailto:slinkelist-admin@nirvis.com]On
> Behalf Of Mike Macgirvin
> Sent: Saturday, November 04, 2000 10:56 PM
> To: Shawn Boyle
> Cc: slinkeList@nirvis.com
> Subject: Re: [slinkelist] Two sound cards and hum
>
>
> > Another solution for the ground loop problem that I've heard
> [from this list I think] is to connect the chassis of your
> > computer to the chassis of your amp. I haven't tried this yet
> but I think someone else on this list has. It'd certainly be
> > worth a try, and would be cheaper than buying an isolator from
> RS. Although if your computer is far from you amp it might not
> > be worth it if you have to run another wire.
> >
> > -Shawn
>
> With all due respects, this is essentially what has been done by
> connecting the stereo lines between the systems. This is not a cure for
> a ground loop, it is the cause. The computer is *generally* grounded
> through the three-prong plug to the electrical box in your house and
> presumably, eventually to a water line or fixed ground stake or such.
> The stereo is *generally* grounded through the cable line (which must be
> grounded at the inlet box) using a path of slightly or dramatically
> different length; since most stereos still use 2-prong power mains. If
> the ground paths on these systems are different lengths
> (impedance/resistance to earth ground), and you connect the stereo
> input/output lines together, you have created a ground loop. Same as if
> you connect the frames together. You must break the link between the
> systems *or* ensure that both are exactly the same electrical distance
> to earth reference ground. The former is relatively easy with isolation
> transformers, the latter could be very hard and possibly extremely
> expensive, as it means that you would have to re-wire the house to make
> sure that all "ground prongs" on electrical outlets and cable-TV outlets
> are exactly the same electrical length to earth.
>
> The only way this solution (tie-together) works is if your stereo can be
> lifted from ground completely ("floated") and does not have any ties to
> ground except through the computer. This generally rules out having a
> cable-TV connection in the system unless you isolate it. Cable-TV
> isolators are available as well, but most folks prefer to use stereo
> audio line isolators instead because isolators always have a wee bit of
> loss and this generally affects high-frequency video signals much more
> than audio signals.
>
> The absolute cheapest solution you can try is to plug the computer in
> via a "widow-maker" power line which has the ground wire disconnected
> (cut off the ground prong). This assumes the computer isn't pulling in a
> ground reference somewhere else through one of your peripherals. If this
> removes the hum, great but it's called a "widow-maker" for a reason.
> Your computer would now be floating and you could possibly be subject to
> deadly shock. Rare, but not impossible. If you're reading between the
> lines here, the isolator is really the best way out.
>
>
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