[LAU] Ground lifts, TRS, etc. to PA? USB/other signal crossover to audio?
fons at linuxaudio.org
Fri May 9 11:29:21 UTC 2014
On Fri, May 09, 2014 at 11:21:32AM +0000, Kaza Kore wrote:
> Now what has confused me is laptops where I get a ground hum. IE 50/60Hz (plus possibly harmonics) hum even when using nothing but headphone plugged into onboard audio output, which is eliminated (or vastly reduced) by running off batteries or by using a PSU with no earth pin. Never quite understood why that happens when there is no connected piece of equipment for the signal to loop around... But that's not really part of this discussion ;-)
That is due to crappy PCB design. The rules for audio and for digital
electronics are very different, and most PCB designers haven't got a
clue about how ground tracks and planes for audio and just apply the
guidelines for digital boards.
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