The Digitrax SDN136PS is small and easy to incorporate in small engines. I have used it in HOn3 and now in scale. On the very small engines I have installed it in a box car or combine linked to he tender. Great sound and function.
The decoder is fine but the supplied speaker is really lame, I replaced the speaker with a 18mm baffeled one (MRC) and the sounds and volume was great.
The 136 is small in size and I have been able to install them in N scale steam locos. Most go into the tender, and others I install in a box car or passenger car attached to the tender. Sound is not as good as units with larger speakers, but that is the speaker and not the decoder. I have used these units in ON30 with larger speakers with great results..
Digitrax SDN136PS is an excellent product. I installed it into my locomotive and it functions well. Which makes my locomotive a good addition to my layout. I recommend this product to anyone who wants to purchase it.
I'm actually rather impressed with the quality of sound from something so small, and inexpensive! I put it into a Norris Engine I was working on, and it fit perfectly in the tender.