A while ago I needed a very simple pasive miker to join one stereo and two mono signals together before amplifying them...
There is some mixed information on how to properly connect a mono signal to a stereo input, but most of it uses active mixing.
I looked at a few schematics, like Tomi Engdahl's simple line mixer, and combiner, and the All Electric Kitchen simple mixer.
For my needs I finally made this simple ciruit that mixes the signals and allows to ajust the levels of each channel independently, before the amplification stage.
|mono/stereo passive mixer board|
600dpi (aprox. 51x48.5mm)
|mono/stereo passive mixer component layout|
|Picture of the actual board|