MRC + Aztec = DCC sound for N scale

By David Popp, senior editor

Published: Thursday, November 30, 2006

(Photos by Bill Zuback)

The wait is over for N scale modelers who've been dreaming of miniature sound decoders for Digital Command Control (DCC) operation. Model Rectifier Corp. (MRC) has teamed up with Aztec Manufacturing to offer a one-two punch for easy installation of a DCC sound decoder in most Atlas N scale road diesels.

Model Rectifier's new plug-and-play decoder is designed to replace the printed-circuit board (PC) in many Atlas diesel models, including the GP38 we used for our test. In conjunction, Aztec provides milling services to prepare Atlas locomotive frames to accommodate the MRC decoder and its 13mm x 18mm speaker. Though you must purchase the decoder and the milled frame separately, the installation can be completed in less than an hour.

The new N scale sound decoder from MRC is similar to its HO scale cousins, offering a variety of features, including advanced consisting, operation-mode programming, and 19 functions. The decoder also offers an assortment of sounds and 15 different horn and eight bell selections to choose from. You can even adjust the bell's ring rate. All sounds, including the incidental noises, have individual volume controls, accessible by programming the decoder's configuration variables (CVs).

Aztec mills space in fuel tank for the speaker, as well as a channel in the frame for the speaker's wires.

You begin the decoder installation by disassembling your locomotive and sending the frame to Aztec (www.aztectrains.com). The firm mills the frame so there's space for the speaker, wires, and decoder. Because Aztec machines the manufacturer's original frame, you can rest assured that all of the locomotive's drive components will fit properly in the finished model.

Once you have the decoder and milled frame, installation is basic-ally a matter of reassembling the locomotive. Though this is called a plug-and-play decoder, installing one is a bit more complex than that, so it's important to pay close attention to the instructions and double check your work during reassembly. On our sample, I assembled the pieces on top of the engineer's side of the frame. This seemed to be the best approach.

To begin, I laid the frame half flat on the workbench and added the motor and worm gear pieces. The decoder replaces the locomotive's PC board, slipping into four tabs (two on each half) in the frame. With the motor in place, I carefully slipped the decoder into the tabs on the frame half. You'll need to apply a little pressure to get the board to fully seat.

Perhaps the trickiest part of the installation was to get the motor contacts to line up with the contact pads on the bottom of the decoder. It took a bit of fiddling, but I finally managed to get what I thought was a good fit. I then added the second half of the frame and the trucks, and installed the chassis screws.

I tested the engine and found that the motor worked sporadically, but its sounds and lights were functioning normally. This meant I was having motor-to-decoder contact trouble. After taking the frame apart again, I cleaned the contacts with a little 70-percent isopropyl alcohol, repositioned them, and then reassembled the engine and tested it. This time it operated very well - cleaning the contacts did the trick.

When installing the decoder, make sure the motor's contact strips make good connections with the decoder's contact pads.

Performance. I put the locomotive through its paces on the MR test track, trying all the various sound files for horns and bells before making my selections. As delivered, MRC's sounds are all set to maximum volume, which was much too loud for the little engine or its speaker. Within 10 minutes, however, I had adjusted all the individual volume CV values to either 1 or 2 (out of 0 to 4) and achieved more-realistic results. The programming-on-the-main feature made these CV adjustments easy, and once the volumes are set, you should never need to change them again.

I must admit that I was skeptical about seeing an easy-to-install sound decoder for N scale locomotives anytime soon, but MRC and Aztec have done it. This project required little more effort than most drop-in decoder projects I've done, and it was much easier than any installation requiring soldering. Model Rectifier Corp.'s sound decoder and Aztec's milled frames provide a nice option for N scale modelers who want to add sound to their diesels.

Diesel sound decoder
Price: $84.98 (decoder only)

Manufacturer
Model Rectifier Corp.
80 Newfield Ave.
Edison, NJ 08837

Features
Advanced consisting
Diesel engine sounds: 15 air horn selections, 8 bell choices, 19 accessory functions
Drop-in installation in most Atlas road diesel locomotives
13mm x 18mm speaker

Frame milling service
Price: custom milling of Atlas N scale diesel locomotive frames, $20 each; (modeler must supply original Atlas frame to Aztec)

Manufacturer
Aztec Manufacturing
2701 Conestoga Dr., no. 113
Carson City, NV 07205
www.aztectrains.com

Frame styles available
TM3100S for Atlas GP38, GP40, and GP40-2; TM3101S for Atlas SD35; TM3102S for Atlas SD7, SD9, SD24, and SD26; TM3103S for Atlas B23-7, B30-7, and B36-7; and TM3104S for Atlas Dash 8-32BW, Dash 8-32BWH, Dash 8-40B, and Dash 8-40BW locomotives.
Milling is also available for Kato SD40 and SD45 models, but decoder installation requires some soldering