Horn for Cheap

There has long been a need in this hobby for a good horn somewhere between an expensive Phoenix Sound system and the stand-in auto or scooter horn.  This has been the subject of many internet discussions with no resolution – until now.  This simple and effective horn system can be built for less than $20 and can replicate any horn you like, from a Nathan K3 to a Southern 5-chime steam whistle, so long as you can produce a recording or have access to the real thing.  It’s built with two components: powered computer speakers and the guts of a recordable greeting card.  Just about any powered speakers should work, but the ones I use work nicely with common 12vdc and most should work fine with some basic electrical knowledge.  I purchased the OG-691A speakers at a local computer store but they are available online through several sources.  Just don't buy the OG-691, they are mono speakers that don't put out nearly as much volume.  These are barely adequete as they are.

The other item is the greeting card sound module, available from Electronics123.com at this writing the item was directly on the front page or click this link.

The first thing to do is record your favorite horn sound to the sound module.  I recommend this web site for some good samples.  Some experimentation will be needed to get a good recording that can be ‘played’ by using the power tab to get short or long bursts.

Before disassembling the speakers, for your safety I recommend cutting off and disposing of the 120v plug.  Then take apart the one with the controls by removing the four screws in the back.

Note the voltages marked on this transformer.  If you are using different speakers this is the best way to find your input voltage.  The 10v is voltage at full load, under normal conditions this transformer will provide up to 14v, so our input voltage of 12v from the battery is perfect.  I used the same connection points before the bridge rectifier so battery polarity is not an issue.  If this is Swahili to you, don’t worry, just follow the instructions and it will work fine.

The bottom of the circuit board.  The thicker blue wires are where you will connect the power from the battery and the red, white, and blue wires are where you will connect the output from the sound module, ie the wires that you will unsolder from the speaker on the sound module.  Begin by unsoldering the blue wires and removing the transformer and power cord.  Solder on two wires that will connect to the battery, I used the power cord with the plug cut off.  Then unsolder the three wires from the sound plug and unsolder the white wires to the speaker on the sound board.  I didn’t have any extra small wire and the white wires to the sound module speaker were a little short, so I borrowed some wire from the connection to the other speaker.  I wasn’t planning on putting it very far away inside my loco anyway.  The finished connections are shown in this photo.

Shown is the completed connections to the speaker board.  Note the small white jumper between where the red and white wires connected.  This allows the use of both speakers thereby doubling the volume.  I now use a section of the existing wire and just solder the red and white wires to the same place on the sound module.

Shown here I have bent the power tab up to expose two pads on which to solder the wires to an activation button, it must be a normally open momentary pushbutton.  I found that solder doesn't stick well to the stainless steel clip without special flux, it failed at Train Mountain and is now soldered to the circuit board underneath this clip.  I’ve put the button in a hole drilled in the top of the speaker for demonstration purposes, but longer wires to your normal horn button on the control pendant or panel would be much more useful.  Also note that I’ve used a small screw to secure the sound module to the post vacated by the transformer.  The red wires appear to go to the activation button, but they are still attached to the record switch which is out of sight.  Recently I've taken to removing the power cable and re-routing it through the other hole, then hot-gluing the microphone into that hole, with the record switch glued externally next to it so I can change the recorded sound without disassembling the speaker.  The hot glue is also convenient to prevent the power switch and the volume control from changing in the middle of a run.

Connect the new power wires to a 12vdc source and enjoy the sounds of real railroading.

Of course if this all seems too complicated, completed systems are available in the price list.

Copyright Roy Stevens