On Mon, Apr 06, 2015 at 03:47:25PM +1000, Patrick Shirkey wrote: > Now that has been resolved, here's some suggestions for resolving the issue. :-) You're trying very hard to get Behringer in the clear, but most of you argumentation is wrong or irrelevant. > (1) The mixer and the Linux box both use switching power supplies. They > are plugged into the same outlet strip. This will occur with most > switching power supply audio devices and most laptops. Much less of a > problem with workstations with large well filtered motherboards and power > supplies. * Switching PS have their problems - they can generate nasty wideband interference etc. - but w.r.t. ground loops there is no reason why they are no better or worse than linear PS. * The linux workstation in this case was not a laptop, it did have a 'large well filtered' PS. * Connecting it via coax madi (wich creates a ground connection) to an RME ADI648 and a battery of assorted DA converters (some using very cheap switching PS as does the ADI648) does not create any problem at all. Not even with 20m cables to a different room. > Less of a problem if the devices are on separate power circuits. Usually having separate circuits makes things worse, not better. > Not a problem if the audio device is powered from a linear supply or battery. A linear power supply wouldn't make any difference. Using battery power at one end of course breaks any ground loop, but is not always an option, certainly not in this case. > Often goes away even if just the laptop gets powered off its battery. No laptops were involved. > (2) If Fons had audio cables from his workstation plugged into the mixer > (even if the faders are all down) with the USB plugged into same, then the > odds are he had a "ground loop" as the "digital ground" and "analog > ground" of the workstation do not reference the same points (i.e. are not > the same "ground"). There were no other connections. Just the USB cable. Even if there had been external analog connections and massive 50 Hz signals at the inputs due to ground loops, with all faders down the input to the headphone amp should be silence. Unless there are *internal* ground related problems, which seems to be the case. > This will happen with ALL gear that does not have audio isolation > transformers on the inputs and outputs. Simply not true. Not if that gear is properly designed and wired. Here at home I have an analog mixer wired to the sound card in my PC and a all sorts of consumer gear using unbalanced connections. There is no trace of hum. Well there is, but you need Jaaa to detect it at -140 dB or so. > If his Linux audio workstation is a full-out desktop workstation with > a big high-end power supply and the motherboard has a premium audio > chipset, then the above "ground loop" is almost certainly the problem. The on-board audio interface was not involved at all. It's even disabled in the BIOS. > Both of these, are not really Behringer problems. This is definitely a problem with the mixer and nothing else. > It is nearly impossible to sell new audio gear with linear supplies > due to regulations about power efficiency in many countries. Not true. Manufacturers use switched power supplies because they are small and cheap. They use wall warts to bypass safety regulations which apply when a PS is built-in. But none of that should matter much w.r.t. ground loops. Tschuss, -- FA A world of exhaustive, reliable metadata would be an utopia. It's also a pipe-dream, founded on self-delusion, nerd hubris and hysterically inflated market opportunities. (Cory Doctorow) _______________________________________________ Linux-audio-user mailing list Linux-audio-user@xxxxxxxxxxxxxxxxxxxx http://lists.linuxaudio.org/listinfo/linux-audio-user
