I had trouble with the volume on my MacBook Pro when using the Zoom platform for the Group Classes. Some of the others told me they couldn’t hear me very well. The next time I logged in, I noticed it asking if I wanted to join meeting by computer audio or microphone. Before selecting the Green Button to join by computer audio, I clicked the blue link underneath that says “Test computer mic/speakers”. Then I was able to adjust the input volume to 100%. The default was set to about 20%! I haven’t had any trouble since!
If you are already logged into the meeting, you can click the little arrow next to the video on/off button to access the Video Settings where you can also adjust the audio settings.
Hope this helps. Let me know if you have any questions!! I really don’t think you will need a microphone if you are able to find these settings. You could join one of the Violin Hangouts to test these settings. They happen daily at 10am EST, 8pm EST, and 11:30pm EST.