Ruby Headphone Amp w/Line-In?

[mydementia]

Hi guys.
I've got a few builds under my belt now and am starting a nice collection of spare parts.  I'd like to use some of these parts to make a simple headphone amp that I can run my guitar AND MP3 player into.  I'm not really interested in outputting the signal to an amp...but if it works in headphones, I assume I could patch it to a powered stereo/PA (I'm looking for a quiet practice tool here...not performance gear).  Does anyone have an end-to-end schematic/component layout for this configuration?  I see many of the pieces on the internet but am unsure how to put them all together.  I'm thinking a mini pot for driving the opamp and an overall volume pot so I don't blast out my ears when I want to play overdrive...just thinking... 

Thanks in advance.
Mike