KB871: Keller SU1990 Sound Unit with Digitrax Decoders

This article was last updated on Oct. 30, 2010, 11:34 a.m. | Print Article | Leave Feedback

You can easily control sound units like the Keller SU1990 by using the function leads on Digitrax Decoders and DCC command station that can control decoder functions. These instructions for connecting a Keller Engineering Diesel Sound unit to Digitrax DH83FX & DH140 series decoders was writtne many years ago.  Any modern Digitrax decoder with 4 function leads can be used.

Equipment Needed:

1) A Digitrax Throttle, Booster/Command Station or other DCC command station capable of controlling decoder function outputs.

2) Any Digitrax decoder with at least 4 function leads will work here.

3) The locomotive you wish to convert, be sure to check the stall current & choose an appropriate decoder.

4) Soldering iron, solder, heat shrink tubing and tools.

5) 1 (one) 47 kilohm 1/4 watt 5% resistor.

6) 2 (two) 1N4148 diodes

7) 1 (one) 33 uF/ 25V Bipolar Electrolytic, part number P1127 from DigiKey Electronics. (800) 344-4539.

8) Keller Engineering SU1990 Diesel Sound Unit, with documentation to verify correct wire colors and usage.

9) See Diagram A-1 to determine if you need an LM78L05 +5V regulator. DigiKey Part number LM340LAZ-5.0.

How to make it work:

1) Test the Locomotive and Decoder, and install the decoder as detailed in its instructions. Connect the RED, BLACK, ORANGE, GRAY, YELLOW and WHITE wires to the locations indicated in the instructions. Verify that the locomotive works properly and the lights can be controlled before continuing. Connect the BLUE, GREEN, VIOLET and BROWN wires according to the following instructions. See Diagram A for DH83FX and other decoders with 5 function leads & Diagram B for DH140 & other decoders with 4 function leads.

2) To ensure the sound unit does not draw excessive idle current we STRONGLY recommend inserting a BIPOLAR electrolytic capacitor in one of the YELLOW speaker leads on the Keller Sound Unit. This capacitor is not direction sensitive and may be hooked up in either YELLOW lead. An example of this part is the 33 uF/ 25V Bipolar Electrolytic described above.

3) Sound Unit Power hookup. Allows sound unit to be turned off if desired. If you wish to use the F3 function for some other purpose e.g. strobe light control, or if you are using a DH140 decoder with no F3 function, go to step 3B. 3A) To use the F3 Function to allow switching on/off of the sound unit. Connect one of the BLUE track power feed wires of the Diesel Sound unit to the DH83FX BLUE wire (may be shared with Light Commons). Connect the other BLUE track power feed of the Sound unit to the BROWN (F3) lead of the DH83FX and heat shrink the joint. See Diagram 1. With this connection the Sound Unit will only generate sound when the F3 function is ON. 3B) Sound unit always on when loco is on live track: Connect the BLUE track power feeds of the sound unit to the Left and Right hand track power pickups also used by the Decoder.

4) Bell hookup: Connect the DH83FX GREEN function lead (F1) to the Bell connection of the sound unit via a 47Kilohm 1/4 watt 5% resistor. Heat shrink the resistor and connection. Check the sound unit documentation to verify the correct wire or point to connect to.

5) Whistle hookup: Connect the DH83FX VIOLET function lead (F2) directly to the Whistle connection of the Sound unit.

6) Exhaust hookup: Connect the BROWN Sound unit Exhaust Mute control wire to the cathodes of the two small diodes connected to the motor power feed from the decoder (ORANGE/GRAY wires). Be sure to follow the diode polarity shown in the diagram.

Check the installation to ensure all wiring is correct and properly protected from shorting out. Place the loco on the track and ensure it still moves properly. Use the DCC command station to turn on the F3 function and the speaker connected to the sound unit should give the "idling" buzz. If you turn on the Command station's F1 (Bell) function, the Bell should sound. Using the DT200 when you press down the F2 (Whistle) button, the Whistle will sound as long as you hold the button down. If you start the loco moving the Exhaust sound should increase. Now you have "all the bells & whistles!" This completes the installation.


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