Installing an MRC Brilliance
sound decoder in the Atlas GP40.

August 2006

Over the last couple of years I've received many requests to install sound decoders in N scale diesel engines.
I had been reluctant to take on what I thought would be a difficult job. Then I received in the mail from
Aztec Manufacturing a frame for an Atlas GP40 that had been milled to allow installation of the speaker and wiring
that come with MRC's new Brilliance N scale decoder. As luck would have it, someone who I was already installing
decoders in several engines for asked me if I would install a sound decoder in his Atlas GP40. Fellow N scaler Jim
Reising had already done one of these for Aztec and had posted his notes and photos on the Atlas forum. This
was a great help in getting me started. So I decided to take on this project. This is the story of how it went.


Refer to the photo above:

After disassembling the engine, I test fit the decoder board on each half of the Aztec milled frame. One needs to be careful
handling the decoder board with it's attached speaker and wires. Notice on the left side of the photo one of the speaker wires
is already broken off. I was later able to re-attach it. I found that the fit lengthwise was tight and was concerned about
what appeared to be some of the electronic components on the decoder board touching the frame. I filed about .020 inches
from each end as shown in blue in the photo.

Refer to the photo at left:

As it turns out, I probably didn't need to file anything off the frame. I found that the component that was seen touching the frame was slightly out of position. I was able to heat up the solder joints and move it. The decoder board then fit fine with room to spare. If you get one like I would suggest you take it back to your dealer unless you are comfortable soldering surface mount components.

Refer to the photo at left:

With the board type decoder installations on Atlas engines, I have always hard wired the decoder motor outputs to the motor brush caps. Before removing the motor brush caps from the motor, I scratch a mark on the top of the motor housing to indicate TOP. Using orange and gray wires saved from installations of wired decoders, I cut about 1 inch of orange and 1-1/2 inch of gray wire and attach one end of each to the motor brush caps as shown in the photo. Then I connected the orange wire to the motor output pad toward the front of the decoder board and the gray wire to the pad that is toward the rear.

Refer to the photo at left:

Using a needle file, I file a slot across the upper and lower parts of the plastic motor housing and when re-assembling the frame route the gray wire through these as shown. I also used a small amount of ACC adhesive to secure the gray wire into the slots.

Refer to the photo above:

After some experimentation I decided that I got the best sound from the speaker with it pointed down, and with the tank on.
For this reason I did not drill any holes in the bottom of the tank. To keep the speaker magnet from shorting the frame
sides together, I insulated the back of the speaker with kapton tape.

Refer to the photo at left:

On the first test run the rear truck of the engine
derailed while going through a turnout. I found that
this was being caused by the speaker wires
interfering with the movement of the rear truck. To
prevent this from occurring I placed a small amount of
ACC adhesive on the frame and when it was tacky set
the speaker wires on it side by side so that they
were flat.

Notice in the photo that the speaker wires are very
close to the rear flywheel when routed between the
frame sides to get to the speaker. Care needs to be
taken here not to let the wires interfere with the
flywheel and also not to get any ACC adhesive on it.

Refer to the photo above:

This is what the assembled frame should look like. Notice the the speaker wire gets routed through the groove milled
on the right side of the Aztec frame. I secured this with a piece of kapton tape. I was wondering what the difference in
weight of the engine might be with the large area of the fuel tank milled out for the speaker. Turns out that the
complete engine with the sound decoder weighs 74 grams compared to the stock engine weighing 84 grams.

In conclusion I found this installation to be quite worthwhile. The sound quality was amazing for such a small speaker.
As soon as the engine was placed on the track with the DCC system activated, engine idling was heard with
occasional air release sounds also heard. With my Digitrax Chief system and DT100 throttle I was able turn the bell
on and off with F1, sound the horn with F2, manually activate an air release with F3, and make a coupling and
uncoupling sounds with F4. It is my understanding that with the MRC DCC system several other sounds can be heard
and controlled. With this new decoder and an Aztec frame, sound will be much easier to have in N scale.