Now, I’ll state right off, that this was not my invention. But some folks might find this little circuit a useful and easy way to implement the idea.
Check out Lance Mindheim’s April 20, 2012 blog entry on under-layout sound (you’ll have to scroll down quite a ways). The basic idea is to take a sound decoder such as a Soundtraxx Tsunami, hard-wire it directly to the DCC track bus, and replace the speaker with a circuit that allows you to plug in a set of headphones, or an amplifier and room-size speakers.
Once the sound decoder is wired up, it can be “consisted” with a non-sound DCC locomotive, and provide big-speaker sound for a tiny little locomotive. By using headphones, the problem of stationary sound coming from a moving loco is eliminated, and the rest of the folks in the house will appreciate it as well.
Lance hand-wired his decoder using spade lugs and a terminal strip. It’s a nice setup.
I thought that a small circuit board or two might make things a little easier for folks who want to do this. Enter the UTS-1 and UTS2 under table sound boards.
The UTS1 board basically consolidates the wiring for the decoder-to-headphone interface and makes it easy to install. There are convenient screw terminals for the track bus, decoder leads, and transformer leads, and a 1/4″ headphone jack for your audio output. The board requires an external transformer, the Radio Shack 273-1380 audio isolation transformer (or equivalent). There is no amplificaton, but the sound decoder has enough power to drive a basic set of headphones by itself. Volume control is managed via the sound decoder’s gain setting CVs.
The UTS-2 board expands on the UTS-1 board by moving the transformer onboard, simplifying the installation.
The UTS-3 board goes to a 1/8″ stereo headphone jack, but integrates the keep-alive cap for the decoder onto the board for a neater install.
And of course, all 3 boards feature a handy M3 sized screw hole for mounting to your layout.
The output jack is stereo, but because the source audio is mono, the mono output is wired to both left and right outputs.
Now, this is just a “coming soon” announcement. You can see the boards at OSH Park by following the links above, and you can order your own if you like (at your own risk) but I haven’t tested them yet for any problems such as component clearances, wrong-sized pin holes, and the like.
Once I get a set built up and tested, I’ll take some photos and make them available as complete boards.