Page 13 - January February 2012

Left: Recently released Athearn “Ready-to-Roll” HO scale GE U50 “double diesel” after installation of a Soundtraxx dual FDL-16 Tsunami decoder. Note front equipment blower is visible through mesh
Right: completed sound installation in Athearn U50 model, with hood removed. Points to note:
(1) Cab interior with crew members added;
(2) Front equipment blower (yellow) above 1-inch speaker and with capacitor located inside;
(3) Soundtraxx Tsunami TSU-1000 decoder (purple) with 9-pin connection, displacing front PCB “B”(part S59);
(4) Rear main PCB “A” (part S51) showing connections for front headlight (disconnected to allow removal of hood);
(5) Rear 1-inch speaker with rear blower housing and backup lamp above
over the top of the decoder and printed circuit boards, and not down the narrow sides where the shell is already a tight fit. Once the speakers have been secured in place and wired up, it is time to replace the cab interior and the blowers, and recon- nect the rear light. But what about that capacitor we left float- ing about?
Well, I noticed that the blower assemblies were only pinned together, not glued, and could easily be separated. Closer exam- ination suggested that the capacitor would fit snugly inside the front fan housing, and by clipping off the simulated “flexible connection” and drilling holes through the back of the housing and into the blower fan housing, and then running the capaci- tor wires through these, the problem was solved. When the body shell was replaced (remembering to reconnect the head- light) it was hard to tell that any changes had been made. What of the sound quality now that the speakers are installed and essentially open on both sides? Well, the volume could be louder and the bass response is not wonderful. But most sound-
Above: This view shows how the front PCB has been moved and attached (upside-down) to the underside of the rear PCB with double-sided sticky tape, thus making room for the Tsunami decoder. It also shows how little room there is over the rear 1-inch speaker for a baffle
This view shows how there is no room over the front speaker for a proper sound baffle. Note that the hood walkways rest on the flat part of the chassis allowing no room above the flat speaker, even if the “blower” was discarded. Note also how the decoder capacitor has been placed inside the blower housing. The decoder is held upside-down on the motor mount by double-sided tape plus black insulation tape
equipped models sound better with the volume turned down below maximum, and whilst it is subjective, I find the sound acceptable. Both the horn and bell sound fine. There are a couple of ways that the sound might be improved: one could close the fan and radiator openings with sheets of styrene, thus making the shell into a sound box. But this would be imperfect because of the openings for the running gear, and besides, it would ruin the best feature of the model!
Perhaps a more practical alternative would be to glue thin sheets of plastic over the pre-drilled speaker holes on the underside of the chassis, making the holes and depth of the chassis itself a baffle; the sound mostly then coming up from the rear of the speakers. I have not tried this yet, but I may get around to experimenting with the idea at a future date. In the meantime, although this was a unique sound installation, I hope that my experience proves useful to those who wish to add DCC sound to their own Athearn U50, and that it gives encouragement and confidence to others who may be consider- ing adding decoders to any model.
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