audio - DIY mixer - use diodes to prevent input potentiometers influencing each other - Electrical Engineering Stack Exchange
Eddy Bergman.com: Synthesizer Build part-17: MIXER and PASSIVE ATTENUATOR in one.
Professional Sound Mixer Circuit - Homemade - YouTube
DIY Passive Audio Mixer – SB_
Audio Mixer, 4 in 1 Out Volume Adjustment Mini Stereo Mixer DC 5V-12V 3.5mm Sound Selector Amplifier DIY Headphones Amplifier for PC Laptop Headphone : Amazon.co.uk: Musical Instruments & DJ