Re: [LAU] Realtek ALC882D

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On Sat, Jul 28, 2007 at 03:07:44PM -0700, Thomas Vecchione wrote:
> Sorry Sampo mentioned this thread elsewhere and I came back to it...
>
> I will STRONGLY reiterate what Sampo has said. Even beyond that I will add
> a few things...
>
> Re:19 VDC
>
> It is still strong enough to penetrate the skin (Approx 10V give or take
> some, less when water is involved, thus why licking a 9V battery can give
> you a nice tingle on your tounge, and that is much lower amperage) and it
> doesn't take much electricity to screw with internal organs(Measured in
> miliamps). Admittedly it is DC which is safer than AC through organs such
> as the heart, but it is still NOT A GOOD THING!
>
> Re: 3 Prong Power Supplies and when they showed up
>
> They have existed, especially in the US, for quite some time. The reason
> you didn't see them as much on older laptops is the older laptops did not
> draw quite as much power in general if memory serves. You now have laptops
> drawing 300W in some cases, it is freaking ridiculous. So yes, as power
> requirements go up, danger increases and as a result safeties are put in
> place, aka ground wires in case a short happens so that that increased power
> goes to ground and NOT through your body.
>
> Lifting the AC ground is a common solution, and is VERY WRONG!. It is a
> common solution not only in laptops, and desktops, but also on the live
> stage, where people die from it quite often unfortunatly because someone
> lifted an AC ground on a guitar amp.
>
> Best solution is to isolate the audio grounds as Sampo mentioned. There are
> a couple of different ways of doing this, including 1:1 transformers,
> removing the ground wire on balanced connections on one end, etc. The
> transformer solution is prefered. There are rackmount units such as the ART
> T8 that will do this on multiple channels all at once.
>
> You can, also as Sampo mentioned, institute a star wiring scheme in your
> studio where everything is fed from a single grounded outlet. If your
> studio is small enough to do this, it is a good idea if you are low on
> money. Keep in mind the power draw of your equipment vs what that outlet
> can give of course.
>

This is frustrating. The buzz is still present even if all the devices are connected to the same AC ground, i.e. the laptop and the amp both plugged into the same outlet or power strip. It does not make the buzz any softer.

I have captured a sample of the buzz (normalized; it's nowhere near this loud) if that helps:
http://www.restivo.org/misc/buzz.ogg

I have been told that this is probably caused by the power distribution circuitry within the laptop: it does not separate earth ground from "signal" (I'm assuming USB signal since my audio interface is USB) ground. The buzz certainly sounds more like "computer" noise than 60 cycle hum.

So far the only thing that works is to lift the ground on the power supply. Luckily my audio interface has balanced outs, so I'll try lifting the ground on the balanced output instead, as soon as I can build or locate an adatper which does that.

For most gigs I'm going from a balanced out (USB audio interface) into an unbalanced in (my little Roland keyboard amp). Next Sunday I'll be plugging into a proper pro PA on a real stage at an actual club (not just a bar), so I'll assume I'll be plugging into a DI box, and maybe I can go TRS directly into that, dunno.

- -ken
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Received on Mon Jul 30 08:15:01 2007