I posted a link to my AZL CN SD-75i video (https://vimeo.com/48699100) yesterday and now I'm getting requests on how to do it. ESU makes the Loksound Select micro (73800 series) and you pick which specific engine sounds you want. I got the SD-70s sound installed and sent to me. http://www.trainboard.com/railimages/uploads/11098/IMAG0422.jpg Everything in the picture was included. I only had to solder on the speaker wires. The ID number on the chip is NOT for a SD-70 but a F-7 - another work in progress... The decoder comes with an eight wire plug which has been cut off (after testing on my DCC test rig which has the matching plug). I cut the enclosure into pieces to seal the speaker. In the next picture you see the speaker glued into the shell tilted as much as possible. The scrap pieces of styrene (enclosure pieces) were glued in to seal the back. If you want to get all the sound you can out of the speaker, you need the back sealed like the enclosure box does. http://www.trainboard.com/railimages/uploads/11098/IMAG0418.jpg Sides of the bottom frame removed right up to the car weight. This lets the sound out. http://www.trainboard.com/railimages/uploads/11098/IMAG0419.jpg The usual six wires (green and blue not used) are soldered onto the six contacts on the engine circuit board. Just like the TCS Z-2 is done. http://www.trainboard.com/railimages/uploads/11098/IMAG0416.jpg A notch is cut into the clip which holds the engine together. This is so the wires can angle down. Another notch is cut into the shell of the boxcar for the wires. http://www.trainboard.com/railimages/uploads/11098/IMAG04241.jpg Another notch is cut into the bottom of the engine shell to let the wires through. All the notches on the engine do not show and the engine could be put back to "stock". http://www.trainboard.com/railimages/uploads/11098/IMAG0420.jpg The wires fed into the top slot (well some). http://www.trainboard.com/railimages/uploads/11098/IMAG0421.jpg All the parts together. http://www.trainboard.com/railimages/uploads/11098/IMAG0415.jpg I did replace the yellow LED with a white one on the front. When I first assembled the engine, I glued the wires to the frame. Then I had to fix the engine and had to pull the wires loose. Found out I broke the white wire inside (front headlight did not work afterward) and I am replacing the whole white wire. I used a black felt pen to "paint" the "hoses" so it looks better. So you see how easy it can be to install sound next to any engine you want. THE AZL GP-7, GP-30 and GP-38-2 could all be done exactly the same way. There are other speakers available that are smaller and you could put it into a smaller boxcar.