Modification to change Pitch on 
The Electric RR Sound Commander Boards.
Click on images for larger view

As good as The Electric Railroad's Sound Commander boards are, at this point they only have a limited assortment of sounds available.

By changing R-31 to a variable resistor you can tweak the pitch of the sounds to simulate larger or smaller sounding locos.

This modification WILL VOID the WARRANTY 

Be sure to verify the boards functionality before you make this modification
Carefully remove R-31. I take a micro diagonal cutter and carefully chip it off and then clean up the remaining pads with a solder iron. 
 


Be careful not to damage the traces. 
R-31's original value is 100k ohms and we are replacing it with a variable value of 47 to 147k ohms.

This is the trimmer circuit board made of a piece of vector board and a 47k ohm resistor and a 100k ohm trim pot with pigtail leads to connect to the bottom of the sound board.
        Schematic of trimmer board
The Radio Shack part numbers are:

100k variable resistor: 271-284

47k resistor: 271-1342

 

The leads form the trimmer board are connected to the bottom of the sound board on the IC-3 connections pins 5 and 9.
The trimmer board is secured to the top to the sound board with a piece of double sided foam tape.  

Set the variable resistor to it's middle setting to start. Test the board for proper functions and then adjust the variable resistor to the sound that matches the pitch of the loco you need. You will find that you can get a big throaty whistle of a Challenger from the Pennsy sound chip for example. 

All of the boards sounds will be lowered in pitch  by this adjustment.

This will work for steam as well diesels.

Experiment and you will be intrigued with the results.

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