Amazon.com: Audio Mixer, DIY Headphone Amplifier, Mini Stereo Mixer 4 in 1 Out with Volume Adjustment, 3.5mm Sound Selector Amplifier for PC Laptop Headphone, : Home & Kitchen
Making an Audio Mixer : 20 Steps (with Pictures) - Instructables
MakeProAudio Propels Makers Forward With DIY Pro Audio Kit for Raspberry Pi | audioXpress