In your Source 2, set it to a 'single-channel' instead of 'multi-channel', set the channel to transparency, then set that channel to 'Value' and set the value to 100%. Currently you don't have a value set for your blender to blend. :> You could also just use your current shader with the transparency set to value-100%, but then the renderer would have to access each channel, blend the settings (0) and then display the result. Instead, with a single-channel, it only has to blend the transparency channel. I hope this helps! :>