So, I've recently "attempted" an O2 amp build and seemed to screwup somewhere along the way. I skipped the resister tests due to finding out that my DMM kicked the bucket, and I only anticipated using 9 volt throw aways (since I have a ton of them) I skipped the other tests. I know, pretty dumb...

I'm primarily using an old set Shure E4G's that I want to get better audio out of using my Galaxy S5. And, I would be listening for about 2 hours at a time. Can I run a small DAC/Amp that runs off of USB OTG power and adequately run the Shures? And if I do that, how much quicker will my phone's...