Taking Things up a Notch with Digitrax Sound Decoders

Since expanding the layout, I have found the need to build more trains and also find more motive power to pull them.  I am finally pulling old power (and rolling stock) out of boxes as well as purchasing others to balance out closer to SP's '78 roster, and putting decoders in them...  so why not try some sound decoders?  MRC was out from what feedback I got from others, so I started looking at the Digitrax drop-in decoders.  On a recent visit to Ron Sipkovich's Cajon Pass layout, I had the opportunity to hear Digitrax's 645 prime mover and other sounds used in the SD40-2 first hand.  With its small speaker, this decoder did not match up to the Tsunami or Loksound decoders that I have heard in N scale cowl units (bigger spkr), but if I could stuff a 10 X 18mm speaker into an N scale hood unit, I was pretty much sold, especially considering there was no major milling and I got the same performance and reliability as their non-sound counterparts.  Latest acquisition to the fleet here that needed sound, were a set of Intermountain Tunnel Motors.  Since receiving some help from fellow Forumites on the Atlas forum (thanks Tivo), I found that the Digitrax SDN144A0 (used in Atlas GP38), was a possible candidate for the Tunnel Motors.  So I bought a few to verify as a worthy prospect.  It is pretty close to a straight drop-in install, with only a few minor issues to resolve.  I had to modify the frame halves by carefully prying the ears to get the .024" needed for the thicker decoder board.  Don't get too crazy or one can easily crack the frame ears.  I have encountered this before, and in some cases I will take a Dremel cut-off wheel to open the gap a bit more.  After taking the calipers to the shell and speaker widths, I noted that it was a tighter fit than I was comfortable with, but pretty close.  I wanted to be able to disassemble the unit for maintenance without the 10 X 18mm speaker getting stuck inside the shell, so some filing of the speaker and the body shell were in order.  Removal of about .010" overall, and I was able to slide the shell on and off smoothly.  So far I am happy with the user friendliness of the decoder settings and feel like I have adequate control of all the sound levels.  With the speaker sitting in the back and partially under the decoder, the sound still resonates pretty well.  I got the volume on max for some of the sound schemes, but toned down for others resulting in an acceptable balance for the layout's ambient room noise.  Still have to load the 645 sound scheme files in this version, but once I get the PR3 programer here, that should be easy enough.  The headlight has to peer over the capacitor that sits in the front, so it is a bit dim and needs further work, but I have to revisit sometime soon to add more full SP light packages on my lead units anyhow...
...and a pic showing how the components fit:

After tackling a Tunnel Motor, I decided to try an install with the same SDN144A0 decoder in an Atlas SD9, but more filing (speaker and inside of  shell), and headlights still to reckon with.  On this unit the decoder was too thin and ended up being too loose between the frame tabs.  Instead of trying to shim with styrene, I ended up adding a small amount of solder to each decoder pad for more reliability.  Another fairly straight forward install with no major modifications.  I took the previous decoder out of the SD9 and swapped it into a GP40-2 that has now been added to the fleet.  As time permits, I will push forward with lighting effects to include more SP light packages, and also put some premium sound / speakers in my early Kato power (Loksound and larger spkrs in U33Cs and other SD's), but short term these drop-ins are a quick and easy way to get sound started on the layout.  For now, just my lead units will have sound, but hearing a full consist roll by on Tim Dickinson's BN layout (each with its own distinct characteristics), has pretty well hooked me at this point... so there's no stopping me now!