On Wednesday 11 January 2006 22:18, [EMAIL PROTECTED] wrote: > > Date: Wed, 11 Jan 2006 21:11:05 -0500 > > From: Steve Adeff <[EMAIL PROTECTED]> > > > > you've obvously not deallt much with audio equipment ground problems. > > ...except, perhaps, in my days doing live audio work for theaters. :) > [Aha! I think you said this because I was careless in my phrasing; > see a few paragraphs below. No hard feelings. :) ] > > [I note that going into excruciatingly correct theory on audio signal > handling is -way- beyond the scope of this list. So I'm simplifying. > (Ditto for how to design the grounds on sub-microvolt lab instruments.) > There are actually some interestingly controversial theories about it > in the audio field, too, some of which seem like total voodoo, and a > lot of religious arguments over it; I prefer the lab-instrument people, > who tend to be less argumentative as a rule. And I'm especially glad > that I no longer have to nail other peoples' hum problems, particularly > during live events.] > > > A > ground > > loop hum/buzz will work its way from the input ground to the output > > ground to the amp ground, etc, etc. causing hum in the output. > > Usually the hum will increase in volume as the preamp volume is > > turned up, depending on the topology, and can be a good way to tell > > if its a ground hum or powerline hum. > > I never said it wouldn't. ---oh wait, I see (now) how you read my > reply. I was answering the coax-bit-flipping case for the "shield > missing" hypothesis, and you were thinking along the lines of "intact > coax shield enables ground loops" hypothesis, which I didn't get into > until the -next- paragraph about tying grounds together. But I got > careless and typed "ground hum" there instead of "signal hum". Oops. > Total change in meaning due to a braino on my part. Sorry for the > confusion. > > But my suspicion (as I said before) is that all this talk of ground > loops is probably bogus. I think he's got a bad signal shield > somewhere, or a bad cap, or a bad design. > > > All good home theatre equipment will have at least 1 screw that is an > > external ground point for helping to solve ground loop problems, > > though really they are (or "were") there to ground record player arms > > back when people knew what vinyl was. > > Yeah, but I'll bet his TV and his computer don't, unfortunately. > And frankly, they shouldn't need it---the vast majority of stereos > get along just fine with no more attention to grounding than "make > sure you plug all the cables in all the way". > > > Yes, connecting both peices of equipment to a good filtered power > > strip (Panamax, Belkin PureAV, NOT Monster) will be the best way to > > solve the > > Maybe if it's powerline-induced ground hum, which I doubt. I've > typically found that concentrating on (and chasing) loops in powerline > grounds is counterproductive; it's usually some screwup in the signal > paths. Everybody instantly leaps to "oh, it's a ground loop!" but it > turns out to be pretty difficult to really get nailed by that sort of > thing in audio work. (I could tell you stories of truly bizarre > all-analog line-level (thank god, not mic-level) whole-building > distribution systems that, amazingly enough, functioned despite > looking like the entire thing would be one giant hairball of loops, > but nonetheless were fine if signal grounds were done right. But > I digress... :) > > > problem, but may not always work, if the hum is coming from, say, a > > cable line, or failing capacitor... > > My current theories. (Or just a crappy soundcard that -always- hums, > but was only noticed because he's suddenly turning things up really > load to hear unexpectedly faint output---it'd be good to know if he's > really maxed out his soundcard outputs and mixers all along the way. > Sure, they may distort, but he can back off from that and then see > if he still has to turn up the amp so far that he hears hum.) > > I really think that the most productive next step in this discussion > is not to have either one of us keep talking, but to have him start > swapping cables (first), then soundcards (second), then maybe what > outlets things are plugged into (distant third), but I think that > without some experimental evidence, we've reached the end of what > anyone can sensibly say might be wrong. So I'll bow out now. :)
and thats how flame wars start... in the end we agree, we just don't type the same langauge ;-) I've actually seen ground loops with modern 2prong televisions. I never was able to figure out the problem exactly, but I got a case of beer for fixing the overall issue, so I was happy... I've also had ground hum through coax digital on my own stereo before I purchased a line filter power strip. I could not connect a peice of equipment to my receiver in any fashion, the coax digital cable as well. in the end it was due to a mismatch in ground potential due to a bad powerstrip, go figure... oh, I like the lab geek method of solving ground hum over the audiophile geek version as well. They can postulate a theory as to why their idea works, the audiophile geek can't, they're just happy it does, and then charge way too much money for it... -- Steve _______________________________________________ mythtv-users mailing list mythtv-users@mythtv.org http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users