This simple module is used to provide the gain switch settings. A 12-position single pole rotary switch is used to select resistor values. A 2-pole connector connects the module to the MPM-3 preamp module. This allows different gain switch modules and configurations to be used should it be required.

This module comes in two flavours, the only difference being the rotation of the switch on the PCB. The one used in the images of the AX1250 used a knob with the grub screw not directly behind the pointer. A second one can be used with knobs with the fixing screw directly behind the pointer.

The rotary switch used is a sealed C&K type.

MPM-3B Circuit (pdf) MPM-3B BOM (pdf)
MPM-3B PCB (pdf)  

 

Back of gain switch module

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Assembly showing resistors and switch mounting on reverse side

Front view of gain switch module

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

This version of the gain switch module is suited for knobs with a particular grub screw offset.