Digitrax Sound Decoder Preview

by Don Fiehmann

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SoundFX Decoders
The long awaited Digitrax SoundFX Decoders are finally available. Digitrax now joins the growing list of aftermarket sound decoder manufacturers, which include Soundtraxx, LoKsound, MRC and soon QSI.

The new SoundFX decoder on the left is shown with matching 1.1 inch (28mm) speaker
enclosure. Speaker enclosure sold separately, 8 ohm speakers may also be used.

The new Digitrax sound decoders follows the recent trend of having downloadable sound abilities. The SoundFX decoders have all of the normally expected features of Digitrax decoders plus many new features. Some of the new sound features are: Customizable 8 Bit Sound, 3 simultaneous voices, downloadable Sound (with Digitrax PR2 and SoundLoader software), 4 Megabit Sound Memory, and the new Playable F2/Whistle. There is also a cam input synchronizer for steam engine chuffs.

All you have to do to convert the SoundFX to another locomotive is to load a new sound scheme. (Digitrax name for sound files) The SoundFX decoders are now used in Tower55 and Kato locomotives.

The sound decoder comes as two parts. One is the sound decoder (SDH104k1) and the other is a small function board (FN04K1). These two are soldered together in the combo package. The instructions show connections to function board for adding additional lights. The additional light functions could be programmed as ditch lights. A 1.1 inch 32 ohm speaker and a 330 µf capacitor are connected on the end of a few inches of wire. There are two LEDs mounted on the ends of the printed circuit board for forward and reverse lights. The decoder comes with a 12 page instruction manual. There are three version now available for aftermarket installation in Kato locomotives:

Locomotive Part Number
AC4400 SDH104K1(A) & FN04K1 Sound & Functions Combo
SD38-2 SDH104K1(B) & FN04K1 Sound & Functions Combo
F40PH SDH104K1(C) & FN04K1 Sound & Functions Combo

The only difference in part number is the letter after the part number. The decoders are the same, the difference is the sound scheme that is loaded into the decoder to match the locomotive. I’m sure there are more to come.

The SoundFX decoders use a 32 ohm speaker. The speaker that comes with the decoder is 1.1 inches and does not have an baffle or enclosure. The speaker mounts in the KATO diesel fuel tank and uses the tank as a baffle. If you are not installing this decoder in the designated locomotives, you may need a speaker enclosure. The decoder may fit other Kato locomotives, but the speaker may need to be installed somewhere other than the fuel tank. If you need a baffle I found that Tony’s SpeakEZ 1.1 inch (28mm) enclosure is a perfect fit. There are three parts to the enclosure, the end cap, the housing and extension.

Bench Test
I find that it is a good idea to bench test a decoder before it is installed. The manual does a good job of telling how to install the decoder in a Kato locomotive. The problem is there is no information on how to connect the decoder for use in other locomotives. Wires are connected to the decoder, but no information in the manual as to their function.

There are two connections on the side of the decoder for track power, that was easy to find. In order for the read-back on the programming track to work correctly a motor or load resistor needs to be connected to the motor output for the decoder. I finally determined that the two screw mounting holes were also the connections for the motor. Instead of soldering to these connections I put in a couple of 2/56 screws with plastic washer on one side to avoid shorting on component. First was to check for shorts. That was OK. I also installed the enclosure on the speaker.

When I started there was no sound. I turned the throttle up and that started the sound. When I stopped, the engine sounds would stop. I was using an NCE system, when using the Digitrax Zephyr the sound would continue. After some reading the manual states that this can happen with some systems. Setting CV11 to 00 corrects this problem.

One of the decoder's features is Smart Power Management. This allows reading back CVs on the programming track and preventing booster overload. I tested the read back with both a Digitrax Zephyr and an NCE system. Both systems were able to read decoder CVs with no problems.

The volume was too loud. I set the master volume level to 4 and the sound improved. The bell volume was too low even before I cut back the master volume. I raised level and got a better balance between the horn, bell and engine sounds. The bell sounds electronic and it may be on the prototype AC4400. I found that increasing the bell rate (CV146 = 3) sounded better. There was no reverb with either the horn or bell, they just ended.

There are start up and shut down sounds along with transition sounds when going from idle to run.

There is an alternate and playable horn available. I changed to the alternate horn. The horn is changed with CV150. The sound changed and had a higher pitch. Function F7 plays the standard road crossing horn sequence or two longs a short and ending is a long blast. After changing the horn type, the new sound worked for the normal function, but it reverted to the old horn when F7 was used.

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