Am Mi 17. September 2008 schrieb Andy Green: > Somebody in the thread at some point said: > | Actually Andy explained the pin3/pin5 issue. > | From what I understand, with removed receptacle and 3-5 short, your buzz > | actually vanished, no? That's good news. > | > | For the suggested rework, that's exactly why I bought a Dremel couple > of days > | ago ;-) > | You described my plans to the smallest detail. > | > | Contrary to Andy I don't hope for eventual enlightenment somewhere in > future. > | Especially since no one than me is examining the whole issue, and I'm > sure > | there *is* *no* other way for existing devices. > | If you got the fox on the farm, you don't investigate how it's actually > | killing the chicken, rather you simply fix the hole in the fence. > > Our incomplete understanding does not lead to a solution for headset mic > buzz nor any security about future designs. You're sure about that?
> One way or another we need > to penetrate those mysteries a bit deeper up to WM8753. If anybody thinks he needs to learn why it's bad to route RF into a can that's designed to keep RF outside, go ahead! Those cans are used *because* not even the chip designers can predict what will happen when their chip is flooded with 1800MHz. If they could, they could change chip design in a way we wouldn't need cans anymore ;-) Basically it's always the same problem: RF hits a non-linear component (like crystal-detector back in ~1900, or any P-N-zone [aka diode] in a 2- or 3-pole (chip-)component nowadays), and there it gets rectified and introduces "DC"-current (actually audio-frequency LF-current) in parts of the circuit where we absolutely don't want to see it. You can't do anything else than just stop RF *before* it reaches this critical point. Typical points to stop RF are entrance of external "antennae" (=short or long unshielded wires) to PCB, and **entrance of traces into can**. We don't want to learn how to make RF "behave" inside a can, simply because we'll never win. RF is a beast, mostly you just can't tell what it will do until you actually tried. cheers jOERG
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