Have you made sure the audio is working as your expect OUTSIDE of OBS?
Windows 10 is much more complex in terms of Audio settings that prior OS versions.
So, I've found that starting with Basic OS level settings/checks makes a lot of difference. Within Win10's Sounds settings, you can check Mic settings, levels, etc... make sure that is correct, then go into OBS and audio there. And there are reasons to use Global/Default Audio sources, but it may be more direct to troubleshoot by disabling an audio source in OBS [Global Audio] Settings and within a scene, add the specific Audio Input source. the results of the above should give you a better idea where your issue is