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Help me interpret some RMAA results (ground loop or no?)

Discussion in 'Computer Audio' started by overhaze, Jun 18, 2018.
  1. overhaze

    I'm looking to for help interpreting some RMAA results from an odac+O2 combo connected to one of my computers. I can't judge whether I am looking at an actual ground loop between my computer and the odac or one between the odac and my PCs line-in. Some large screenshots incoming.

    This is what I get with a direct connection to my pc Odac_direct_connection.png

    And this is what I get with a hifimediy USB ground isolator

    odac isolated.png

    Also since I had one lying around here is what a direct USB connection to the pc looks like using a Behringer HD400 Hum destroyer instead of a standard audio cable

    odac hum distroyer direct connection.png

    And here is the mess I get if I combine the Hd400 and the USB isolator

    odac hum distroyer isolated.png
  2. overhaze
    Thoughts? Does this look like a genuine ground loop between the odac+O2 and the PC or one created between the odac+O2 and the PC's line in? Also worth pointing out I get a very small spark and an audible crackle when I plug the odac in directly with any audio equipment plugged into it.
    Last edited: Jun 18, 2018
  3. castleofargh Contributor
    you should probably go ask there https://www.head-fi.org/threads/o2-amp-odac.616331/ if you want super knowledgeable dudes.
    as a very tentative interpretation not to leave you alone, but I have little confidence and no expertise:
    the results are really not that bad. do you even hear a 'hum' in your normal use?
    the default measure was done with Direct Sound, the others with MME. not sure it matters but extra variables introduce a doubt nobody likes to think about.
    all I can say is that your results with the Behringer HD400 Hum destroyer scares me a little in this setup. it's really one of those stuff I personally wouldn't touch unless I really have a big problem. while the hifimediy toy(if the change in API for the measures is irrelevant), comes closer to what I would expect the Odac RMAA to "look like". is it the original cheap hifimediy one or the 100$ ludicrous speed one? I wondered if the 200mA limit given by hyfimediy on the cheap one was enough for the odac, so if that's the one used it certainly seems fine.

    your input seems reasonably clean, that's always nice for curious minds trying to troubleshoot significant issues.
  4. overhaze
    No I don't hear a hum, I'm more worried about a weak ground loop damaging my equipment over time. And yeah its the cheap one, it works with the odac 99% of the time but plugging in other USB devices can cause it to drop connection. And thanks for the advice. I'll post it there!

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