Mono/Stereo Headphones Output.

Hi, Ive got this question:

Quick question - I finally got around to assembling the amp. For some reason, when I plug in my headphones, there is no sound coming out of my right speaker. This happens for both the guitar and the aux input. Any idea why that would be? Since it's a mono-amp - seems like everything is working fine. Is there something that needs to be shorted to get both sides to work?

Guitar amplifiers are generally mono amplifiers (an electric guitar creates a mono signal). 1Wamp generates an stereo signal for headphones though but you would need to use an stereo to mono jack adapter like the one on the picture below:

They go pretty cheap on eBay...