Manufacturer Description:

Modules A-138p/o are used to built a simple performance mixer (instead of an external stand-alone mixer). Module A-138p is the 4-fold input module.

A-138p features:
4 channels

controls and inputs for each channel
input (3.5 mm mono socket)
signal LED (as a coarse monitor of the incoming level, the level is measured after the gain control)
mute switch
gain (control to adapt different audio levels)
Level (the main volume control)
Aux
Pan
internal jumper for each channel to choose between Aux pre/post main Level control

internal connection to the output module and to other A-138p modules
A-138p requires A-138o (no stand-alone use)

Width: 16TE / 16HP / 80.9 mm
Depth: 40 mm (measured from the rear side of the front panel)
Current: 0 mA