On Tue, 8 Jun 2021 13:52:59 -0500 "Chris Caudle" <6807.chris@xxxxxxxxxxxxxx> wrote: >On Tue, June 8, 2021 6:43 am, Bill Purvis wrote: >> Stagg dual DI box. > >Is it this device? >https://staggmusic.com/en/products/view/SDIST-2-channel-passive-di-box-with-monostereo-switch/ > >I don't see any specifications, so I'll just guess that it is a pair of >low cost transformers inside the case. > >David Kastrup's advice about verifying the adapters cables is probably the >first place to start. > >> to get a lot of hum pickup on that, which I think is down to the >> proximity to the laptops. > >The only mains frequency noise around a laptop would be the power supply, >which you should be able to move farther away since it is on a cord, and >probably the LCD screen refresh rate is running at 60Hz. >If it is a proximity problem because the DI transformer is not shielded, >you should be able to tell by using a longer cable between the laptop and >the DI box and just moving the box farther away. Put the AC power supply >farther away, or just remove it temporarily and run on battery, and if >that is not the problem put the box farther away from the laptop screen >(or change the power settings to only power off the screen when you close >the laptop, not put the entire laptop to sleep, and just close the lid). > >> keyboard and bass and I've had no problems with that. > >Bass should be easy because it does not have a connection to AC power >supply, and most keyboards are low enough power that they have an isolated >power supply with only two pin power entry, no third earth pin, so they >are effectively floating sources and so pretty easy as well. Computers >are almost all high enough power that they have a connection to safety >earth, which you can get rid of temporarily for troubleshooting by running >on battery power. > >> raise the ground lift switch on the DI box, which reduces the hum >> somewhat but still get enough hum to be noticeable when nothing >> else is playing. > >Have you made sure that the volume controls on the laptop are at maximum >so you can optimize the gain structure? If you have not, you may be able >to make the hum less noticeable by turning down the gain at the mixer and >turning up the output from the laptop. > >> I wondered if the matching transformers in the DI box >> are acting as pickups for the RF noise generated by the laptops. > >If you are seeing mostly 60Hz noise probably not RF, but could still be >magnetically coupled from the laptop or the laptop power supply. > A while ago I was surprised to find that some very cheap USB modules (mic in phones out) to my great surprise *totally* isolated the audio from the USB. I don't use the mic, just the stereo out (at 48k) Even though it's on a 3.5 TRS the quality is good enough for all but the most demanding purposes. They go by the name ugreen. -- Will J Godfrey https://willgodfrey.bandcamp.com/ http://yoshimi.github.io Say you have a poem and I have a tune. Exchange them and we can both have a poem, a tune, and a song. _______________________________________________ Linux-audio-user mailing list Linux-audio-user@xxxxxxxxxxxxxxxxxxxx https://lists.linuxaudio.org/listinfo/linux-audio-user
