A Sound Investment

In December I was tempted by a couple of pre-owned locomotives I saw for sale online. One was a Proto 2000 GP20 painted for the Santa Fe that I thought about modifying to represent one of the 1990s-era TP&W GP20s that I grew up watching. The other locomotive was an undecorated Athearn SW1500 that I would have painted as TP&W #306. While the prices for each locomotive were reasonable, I opted against buying either of them because (1) I didn't want to add more locomotive projects to my queue and (2) neither of these locomotives was likely to get much run time on my layout, so my time and money could be better spent on something else. So, rather than add more locomotives to my fleet I decided to enhance one of my existing locomotives by adding sound. Quality over quantity.

On-board sound is a possibility for me now that I have converted my layout to DCC, but I've been a bit hesitant to take the plunge due to both the expense and the effort required to retrofit sound into older locomotives. At $100+ apiece, sound decoders are not only pricey but also cost more than I've paid for any of my locomotives. Most older HO locomotives weren't designed with sound in mind and the example installations I've seen tend to require milling of weights to make room for the speaker and/or have wires running everywhere under the shell. After my experience adding a non-sound decoder to my Proto 2000 GP30 I wasn't interested in an even more difficult sound decoder installation, but then I discovered the WOWDiesel kits from TCS. There are many versions of these kits that have been engineered to fit in specific locomotives.

The obvious candidate for my first sound locomotive was my favorite, C424 #801. WOWDiesel kit ATL-1 is designed for this Atlas locomotive and others that have similar mechanisms. No milling is required; you simply remove the rear weight and replace it with the speaker mount that's included in the kit. The kit includes a motherboard that's a drop-in replacement for the stock Atlas light board, so the wiring is limited to connecting the existing truck, motor, and headlight wires to the new motherboard along with the 2 speaker wires. The decoder plugs into the motherboard to complete the installation. The installation looked to be about as simple as a sound retrofit could be, so I decided to go for it. 

The starting point for this project. I'll reuse the DP2X non-sound decoder in a different locomotive.

The rear headlight is mounted on the rear weight, so removing this weight as part of the sound installation means I have to make a new rear headlight mount. Prior to disassembly, I took some measurements of the headlight's position. The top of the weight is 1" above the top of the main (black) frame and the tip of the LED is 1 15/32" away from the forward end of the weight.

I disconnected all of the wires from the original circuit board, removed the board, and removed the rear weight. 

Here are the contents of the WOWDiesel kit. From left to right, the decoder, the motherboard, and the speaker and its mounting hardware.

There are no printed installation instructions included with the kit. The TCS website has a comprehensive library of example step-by-step decoder installations with photos, and these are the de facto instructions for the kit. 

I snapped the motherboard over the tabs on the motor mounts, and then installed the 3D-printed speaker mount with the two screws provided. The two wires from the rear truck get routed up through the slots on the sides of the speaker mount and then under the leading edge of the speaker mount towards the motor.

Next I soldered the two purple wires to the tabs on the speaker. On my first attempt I soldered the wires going the other direction because I thought the tabs should go closer to the motor, but in this orientation the tabs interfere with the wires from the rear truck. I then reversed the purple wires so I could mount the speaker with the tabs to the rear of the locomotive. 

I installed the speaker in its mount (but didn't glue it in place yet) and then connected all of the wires to the solder pads on the motherboard. I approached the solder connections like lighting the candles on a birthday cake; start with the innermost locations and then work toward the outside (and try not to burn yourself). The wires to the rear LED seemed a bit short but the front LED wires were longer, so I swapped the two LEDs from their original placement. The red wires on the LEDs are the positive leads. Once I was done with the soldering, I installed the decoder onto the 21-pin plug on the motherboard.

The online instructions suggest using hot glue to attach the speaker to its mount but also caution not to get any glue on the speaker. I had zero confidence in my ability to neatly use hot glue for this task, so I opted to use a silicone adhesive instead.

Bruce Petrarca's article "How Do I Get the Sound Out?" in the August 2012 issue of Model Railroad Hobbyist does a great job of explaining how speakers should be mounted to optimize the sound quality. Basically, both sides of the speaker need to be isolated from each other so that the sound waves from the front of the speaker don't cross paths with the sound waves from the back of the speaker. The TCS speaker mount kind of does this by routing the sound from the back (magnet) side of the speaker down and out of the model around the rear truck, but there is nothing to stop the sound from the top of the speaker from going around the rear of the speaker mount and taking the same path out of the model. I decided to add styrene baffles to the front and rear of the speaker mount to force the sound from the top of the speaker to go straight up and keep it away from the bottom of the speaker. 

Here's the speaker mount with my baffles installed. The rear baffle doubles as the rear headlight mount, and I sized it based on the measurements I took before removing the rear weight. The bottom of the front baffle is slotted to clear the rear driveshaft and allow the rear headlight wires to pass through. I trimmed the tops of the baffles to match contours of the inside top of the shell at each location. I glued the rear LED to my new mount with Microscale Krystal Klear.

At this point, I tested the mechanism on the layout without the shell installed. Everything worked! The engine sounds seemed a bit quiet, but I figured they would be louder with the shell installed.

The baffles route the sound waves from the speaker straight up, but there were no openings on the top of the stock shell to let them out. To remedy this, I opened up 8 slots in the radiator grille. I drilled 8 #72 holes in each slot as shown, and then trimmed out the remaining plastic with my knife. 

 

Here's the bottom view of the completed slots. The clear plastic insert for the rear headlight and number boards prevented me from opening up any of the slots in the fifth row of the radiator grille.

I touched up the orange paint on the modified grille with a mix of 3 parts Vallejo Model Air 71.083 Orange and 1 part 71.130 Orange Rust. This mix was a bit lighter than the factory paint, but close enough for this application, especially after the next step.

To make the opened slots less obvious, I applied about 3 coats of Vallejo 76.518 Black Model Wash to give the radiator grille some depth. This product was easy to use and produced the desired effect, but I found that it took several hours to completely dry between coats.

Once the black wash was dry, I reinstalled the shell on the mechanism to test the complete installation. As expected, the engine sounds were much louder with the shell in place; however, I quickly identified three issues that I easily could have prevented before reassembling the locomotive: (1) the white styrene of the rear baffle was visible through the open slots; (2) when running in reverse, the light from the rear headlight was also visible through the open slots; and (3) when running with the sound muted, a soft thumping sound indicated that a wire was making contact with the drive train. None of these issues was critical, but they bothered me enough to take the shell back off and fix them now rather than later. The rear headlight issue was embarrassing. How did I not think of that?

I painted the rear baffle black and put a strip of black electrical tape over the exposed top of the rear LED. One of the black wires from the rear truck was touching the drive shaft, so I pulled the rear truck wires tighter and taped them to the front baffle. If I do another one of these installations in an Atlas locomotive, I might drill holes in the front edge of the speaker mount for the truck wires rather than routing them through the same space as the drive shaft.

With the installation complete, the next step was to program the appropriate engine and horn sounds. The Alco C424 was equipped with a 16-cylinder Alco 251B diesel engine. I haven't heard one of these running in real life, so I didn't know what it was supposed to sound like. The WOWDiesel decoder has two distinct options for the Alco 251. The one identified as "251 Turbo (Locomotive 1)" has loud, snorting exhaust, especially during the startup routine, while "251 Turbo (Locomotive 2)" is noticeably quieter. The names aren't very descriptive and I didn't know which option was best for the C424. I emailed TCS tech support and they told me that Locomotive 1 is a recording of an RS-23 (inline 6-cylinder 251C) and Locomotive 2 is a recording of an RSD-12 (V-12 251B). Neither is a C424, but I'm not bothered by that because I don't know enough about real locomotives to appreciate the nuances of various engines. I ended up selecting the Locomotive 2 option. 

I didn't know much about locomotive horns before this project. I knew that Leslie and Nathan were the two major horn manufacturers, but that was about it. The Five Chime Consultants Railroad Airhorn Guide (http://atsf.railfan.net/airhorns/index.html) was an excellent reference. After reading the airhorn guide and closely examining many prototype photos of TP&W 801, I concluded that the 801 was equipped with a Nathan P3 horn in the 1970s. The horn casting on the model is not a Nathan P3 and is not mounted in the correct location, but I decided to leave it as-is for now.  

The verdict? I'm very happy with how this project turned out. I think it sounds great, and the installation went pretty smoothly. I won't be equipping every locomotive I have with sound, but I probably will do so eventually for a few favorites.