Master Fader im Stereo Summing Box ToolMix32
Analog Summing Gear ToolMix
The picture shows two of the 16 stereo inputs of a stereo summing box ToolMix32 and the master section with master fader, fader on switch that inserts the master fader, and the PFL to Output switch that routs the PFL master to the main output when a PFL switch is pressed.
Stereo Summing Box ToolMix32

ToolMix32 detailed View Master Section