I’ve noticed there doesn’t seem to be a lot of decoder installation threads particularly when sound is involved, so I decided to document my latest sound decoder installation. Hopefully this will encourage others to take the plunge into sound. The locomotive I’m using is an N-scale Kato “mid-production” SD40-2 number 176-8203. This is one of the units with the new style screw-less frame. The SD40-2 is shorter then the SD70/80/90 units so installing this decoder in those units should also be possible. The decoder I’ll be installing is an ESU LokSound micro. I ordered the decoder with sound file number 72841, which is an EMD 645 16 cylinder turbo with dynamic brakes. I also ordered the ESU 397-50339 speakers which are a pair of 13mm 50 ohm speakers. The ESU decoders use 100 ohm speakers. Unfortunately the smallest speakers they sell are actually 50 ohms so you have to install two in series. I don’t think the smallest 100 ohm speaker they have will fit. I decided on the ESU decoder for a couple of reasons. First I’ve used these decoders in the past and like the sound and motor control. Secondly I think it will fit, the decoder is only .4” wide. A Tsunami is .5” wide which I don’t think will fit in the narrow shell of this style engine. Additional supplies I ordered were a couple of 1000 ohm surface mount resistors for the front and rear LEDS. The ESU decoder lamp circuits need the resistors when powering LEDS. This installation will require some milling of the frame halves, however I intend to do the milling with tools that most modelers should have available. Basically I’ll be using a Dremel tool. The only “special” tool I’ll be using is a ½” Forstner bit, I’ll use this to drill the speaker holes through the fuel tank because I think this style bit is less likely to split the plastic. Disassemble the locomotive following the instructions on Kato’s website. http://www.katousa.com/N/SD40-2/maint/disassembly.html
Once the locomotive is disassembled it’s time to begin making room for the speakers. The first thing I did was to mark the center of the fuel tank on one half of the frame. I then marked the center of each speaker .26” from the center line. This should allow about .2” between the speakers. Then I put the frame half back inside the fuel tank and transferred the scribe marks to the tank. On the inside of the fuel tank are two small tabs. These create a gap between the frame halves at the bottom of the frame. The gap needs to be there but the tabs are in the way of the speakers so I moved the tabs. Using a chisel I sliced the tabs off. I then attached the tabs to one of the frame halves using some CA glue. At this point I temporarily put the motor back in the frame and put the fuel tank back on just to make sure everything still fit together. Everything was okay so I took the motor out and put it in a safe spot where metal filings from the frame won’t get on it. It’s time to start drilling holes. Place the fuel tank on a piece of scrap wood with the inside up. I started with a small pilot hole from the inside of the fuel tank at the locations I marked for the center of the speakers. Now using the ½” Forstner bit drill the holes for the speakers. Put the center point of the Forstner bit in the previously drilled pilot holes and use a low speed without a lot of pressure. Next I put the frame halves back in the fuel tank. With the frame halves back in the fuel tank I marked the locations of the two speakers on the frames with a scribe through the holes just drilled in the fuel tank. This way everything should line up later. Using a dremel tool I ground clearance holes for the speakers. Take your time and grind a little metal away at a time. I temporarily placed the speakers in the holes in the fuel tank and periodically test fit the frame halves. By sticking one of the frame halves into the fuel tank at a time you can check your progress and see where you need to remove more of the frame. Just make sure you clean all the metal filings off the frame before test fitting so no metal filings end up stuck to the speaker magnets.
Once I had sufficient clearance I put the motor back in the frame and tried fitting the fuel tank and speakers. With the motor in place the speakers don’t recess into the fuel tank far enough. The speakers hit the bottom crossbar on the motor bracket. When I first started planning this installation I thought there wasn’t going to be enough depth between the bottom of the motor bracket and the bottom of the fuel tank.. The only solution that I can see is to remove the bottom of the motor bracket. I removed the motor from the bracket then sliced the bottom crossbar off. After putting the motor back in the bracket and re-assembling the frames and fuel tank the speakers now recess far enough into the tank that they aren’t sticking out the bottom. Now that I had enough room to get the speakers installed it was time to make room for the decoder. The decoder has surface mount capacitors on one side. I intend to mount the decoder so these are facing down on the right side of the locomotive. In the photographs I marked the areas where I removed material in red. Again I would remove a little metal and then test the fit. Once I thought I had the frame milled enough I test fit the shell over the decoder by assembling the frame halves with the motor and fuel tank. I temporarily laid the wires out the bottom of the frame through the truck mounting hole and then installed the shell. Once I was sure the shell fit on properly with the decoder in place it was time to move on to modifying the light board.
I removed the existing surface mount resistor from the Kato light board then removed parts of the etching in the locations shown in the attached pictures. The easiest way to remove the etching without damaging the fiberglass circuit board is to use a fine abrasive bit in the Dremel tool and lightly touch the bit to the portion of the etching to be removed. The bit I used was a small ball with a diamond abrasive surface. Practice on the middle section of the board if you feel you need to. I removed the etching in three spots: the etching attached to the left side of the front LED was cut to create a spot to attach the resistor for the front LED. The etching attached to the right side of the rear LED was cut to provide a spot for the resistor for the rear LED. The hardest cut to make was the one to disconnect the right side of the front LED from the part of the etching that contacts the frame. After I made this cut I temporarily installed the board and checked the resistance between the frame and the front LED connection. Make sure you get the LED completely isolated from the frame. This isn’t really that terribly difficult it just takes a little patience. After the etching cuts are made cut the board at the spots shown in the picture. The two ends will be mounted without the center portion of the board.
Now for the assembly. I mounted the speakers in the fuel tank as shown in the attached picture. I test fit the fuel tank onto the frame halves with the motor installed to make sure the speakers weren’t pushed in to far. Then I took the fuel tank back off the frame and glued the speakers in place with CA.I then soldered two pieces of six inch long 30awg wire to the speakers and a short piece between the speakers as shown in the picture. Note how the wire between the speakers routes close to the speaker. I actually glued the wire to the speakers so it stays in place during the rest of the assembly process. To insulate the bottom of the motor place a piece of Kapton tape on the part of the motor exposed by removing the bottom of the motor bracket. This should prevent it from coming in contact with the speakers. Put the bronze contact strips back in the frame halves and assemble the frame, motor and fuel tank. I passed the two long wires between the motor and the left frame and put the frame/motor into the fuel tank. Pull any excess wire towards the top of the frame. I cut the brown (speaker) wires from the decoder leaving about an inch of wire. I also removed the six pin connector from the rest of the wires. I then routed the wires from the speakers through the slot in-between the frame halves towards the front of the locomotive and temporarily set the decoder in place. Now I was able to cut the wires from the speakers to length and splice them to the speaker wires from the decoder. I used liquid electrical tape to insolate the splices but you can use heat shrink if you have thin enough pieces. Now I mounted the two light boards. The front one is easy it just slides back into place. I mounted the rear board by gluing it to a piece of 1/8” x 1/8” styrene I glued to the frame. I only applied glue to one side of the frame so I would be able to take everything apart if I had to. Once the light boards are in place run a wire from the front board etching mark for the blue wire to the rear light etching for the blue wire. Use the picture showing the modifications to the light board for the locations. I routed the wire in between the frame halves. Next I ran the yellow wire from the decoder under the decoder and back to the rear light board I cut the wire to length and attached it to board.
With the wires run to the rear light board and speaker in the slot between the frame halves, I placed a piece of kapton tape over them to hold them in place. Then I put the decoder in place and taped it down. Now it’s simply a matter of cutting the remaining wires to length and soldering them in place. The white wire goes to the front light board. The grey wire goes to the left motor terminal and the orange goes to the right motor terminal. I soldered the wires to the terminals and then covered them with kapton tape to keep them from snagging on the shell when it’s installed. The black wire goes to the left etching on the front light board and the red goes to the right etching on the front light board. The green and violet wires aren’t used and were cut short to get them out of the way. Re-attach the trucks. At this point the locomotive should be ready to run. Take a few minutes to review your work. Make sure none of the wires will interfere with the moving parts. Set the locomotive on a piece of track and test it. I like to make sure everything is working before replacing the shell. Once your satisfied everything is working install the shell and re-test.
Mark, absolutely great job. Couple of questions. I had about given up on Loksound decoders in N Scale because the horn sound never seemed adequate to me. Back in the day when you could extract the .wav files from a project and modify them, you could amplify the horn sounds but you can't do that anymore. Did your installation result in adequate horn volume? Also, along the same line, you are using the fuel tank as an enclosure if I understand your instructions correctly. Did that turn out to be enough of an enclosure to produce good volume sound? Again, great job. I hope that more folks find ways to hard wire sound decoders in N scale diesel locomotives. Thanks for sharing this. ....Tom
Tom, thanks for the kind words. When I installed the speakers I applied glue all the way around the speaker to seal it to the fuel tank. The fuel tank and motor cavity form the enclosure. With the shell installed it sounds to me like the enclosure is tight enough to provide good volume. Having the speakers exposed also helps make the sound louder and clearer, I just have to be careful not to handle the locomotive in that area. Of course the speakers are only 13mm in diameter and are never going to provide the base sound a 12" sub-woofer would. Overall, I think the volume is quite good, I actually may end up turning it down a little. I can easily hear the horn from ten feet away and this may be to loud. As far as modifying the sound files, I'm not sure if you can extract the sounds with the programming software, but I know you can modify and reload the files if you have the original wave files. I don't have the programmer hardware so I haven't played with the software other then to preview the sound files prior to ordering the decoder.
Mark, Very nice. Looks like you did some research to get this done. You also did some R&D. Cut and fit and then re cut to make fit. All in the R&D field. One thing to keep an eye on. With the speakers being so close to the track, watch out for metal filings or foreign material being picked up by the speaker magnets. NICE JOB!
After reading Tom's question concerning horn volume I got to thinking; "it sounds loud enough to me" isn't really a good way to describe the volume. I looked around and found an old sound level meter and checked the volume produced by several different sound equipped locomotives. I'm not claiming this is an accurate scientific study but at least it provides a less subjective comparison. I placed each locomotive on my layout and then sounded the horn with the engine stationary. I held the sound meter 18" from the locomotive and recorded the readings. Kato F7A with ESU Loksound and 16 x 25mm speaker - 76dB Kato SD40-2 with Digitrax SDN144K1E and 1/2" speaker - 66dB Kato SD40-2 with ESU Loksound and dual 13mm speakers - 70dB Athearn FP45 with factory Tsunami speaker size unknown - 64dB The F7A has the largest speaker and also the most volume. Maybe that's a coincidence maybe not. This engine has the speaker located above the frame over the rear truck. The dual 13mm speakers in the ESU equipped SD40-2 were louder then the single 1/2" speaker in the other SD40-2. The 1/2" speaker is almost exactly the same size as one of the 13mm speakers. Both these engines have the speakers in the fuel tanks. I'm not sure where the speaker is located in the FP45 or what size it is.
Speaker size will be a big factor in the volume. Sound is air waves- the larger the speaker the more air it will move. Therefore more volume. Like drag racers say- there is no substitute for cubic inches.
Any alternatives to hacking up the light board to power the decoder? I was thinking about doing a toner transfer process and printing up my own PCB, but seems like a lot of work. Anyone have suggestions?
You don't really need a circuit board for the light assemblies. You could use LEDs glued to a support to hold them in place. Then solder a resistor to one leg of each LED and connect these to the decoder. I used the original light board because I figured I wasn't going to ever do anything else with it.
Yes I agree with you about the lights, I'm just looking for a clean alternative to hacking up the factory light board.
I installed an ESU LokSound DCC Sound decoder in my ATSF SD40-2 diesel engine, along with a Sugar Cube speaker, and it sounds awesome! Next up, the Atlas SD26!
Any chance of posting a video of your loco? I've got a couple of ESU Micro Select decoders with Sugar Cube speakers and am trying to find the time to get them put in a couple of Atlas diesels.
Very nice.... And I love all the front lights on that model. I have several of those and need to see if I can add ditch lights. This looks great
Very nice job! I've had a busy summer work wise and still haven't got my installs done. I hope to get a chance before the end of January but I've got a total living room redo scheduled between now and then. So much to do and not enough time to do it in!
