People want sound for their locos. Throttle Up! (SoundTraxx) makes a whole array of sound units specifically for DCC. However, there are two problems that can arise. The first one is lack of room for the sound decoder and speaker in some powered locos. The second is lack of enough power for some larger scale locos.

Throttle Up! was going to produce sound decoders with more current for O and G scale locos. But since they had to deal with the first problem, they developed the DSX line to solve both problems.

The DSX sound decoder is like any other sound decoder, except that it doesn't have motor or light drivers. It receives its commands via DCC packets like any other decoder, but can't drive the loco's motor or control the lights. But that's OK for what it was designed for.

For situations where there's not enough room in a powered loco for the sound decoder and speaker, the DSX can be mounted in a dummy loco or freight car. Personally, I use a freight car. It's easier to match a freight car to a variety of locos than it is to match a dummy to a variety of other locos. And the freight car sound unit allows you to have a short, single-loco train. In any case, simply put power pickup on the freight car or dummy loco, install the DSX decoder as normal, connect the speaker to it, and voila! - sound.

Use the sound car/loco as the lead address to MU one or more powered locos to. This will provide you with direct control of the bell, horn, and other background sounds. When you give the MU consist throttle, the loco(s) will go and the sound will ramp up with it as normal - a perfect setup without problems. Note that you will not have direct control of the functions on MUed locos. To control the lights of an MUed loco, you'll have to select it's base address and control it's functions from there.

For G scale, the DSX can be used in conjunction with a larger motor-driving decoder in the same loco. Since it's usually O and G scale where this is the case, there's usually more than enough room for everything. Further, there's ample room to rig a disconnect system for each decoder.

When you have two decoders in the same loco, you can't put just one decoder on the programming track to program, then the other. Since both decoders are wired to the same power pickup of the loco, both decoders are on the programming track together. Problem is; the two decoders need different programming. With them both on the programming track at the same time, the sound decoder would also get the motor driver's programming, and the motor driving decoder would also get the sound decoder's programming. Needless to say, this is a good way to confuse a couple of decoders.

The solution is to provide a single pin plug/socket connector for each decoder. The black and red wires are used for power pickup. All you have to do is disconnect either one (or both) of these wires to make the decoder go dead. As such, you can disconnect one decoder while programming the other and vice versa.

There is another solution for this problem. This solution requires a system that is capable of OPS-Mode Programming. It also requires the two decoders to have their base addresses programmed differently from each other, before installation. Once installed, all programming is done via OPS-Mode. To make them run together, you would program the motor driver decoder's address into CV19 of the DSX sound decoder. CV19 is the Decoder-Assisted Consisting CV. In addition to CV19, you need to program CVs 21 and 22 to have direct control of the sound functions via that CV19 address.

You may also need to remap some function outputs. If you plan to use more than front and rear lighting, some of the sound functions may conflict with the light functions on the motor driver decoder. If that decoder has function remapping, remapping those functions to ones not used by the DSX is generally the best way. However, most regular decoders don't have that option (Train Control Systems decoders do have limited remapping, Digitrax decoders have none). So, you may have to remap some of the sound functions to avoid the conflict. This could result in your sounds being activated with non-standard buttons - such as turning the bell on and off with Function 3 instead of Function 1.

When a decoder has an address in CV19, it responds to that address for control. But when programming via OPS-Mode, it responds to the base address. So, even though you're controlling it via the CV19 address, you'll have to select its base address before entering OPS-Mode Programming.

CV19 can only hold a two-digit address, limiting you to using a two-digit address for the loco. If you want to use four-digit addresses, this method can't be used - go back to the decoder disconnection method for programming.

Even though space is tight, some people want to use the DSX with a lower-cost motor-driving decoder just to save a few dollars. Trust me, you'll earn every dollar you save. When it's a necessity to use two decoders to have sound, go ahead and use the above means to have it. You'll be way ahead to get the DSD sound decoder for situations where the decoder and speaker can both fit in the powered loco.

One of the problems you run into when using two decoders is synchronization of the motor sound to the speed of the loco. If it's a steam loco, you can install a cam on your loco drivers to make the chuff happen exactly right. With auto-chuff, or with a diesel, you're left with the adjustment in the DSX itself to try to match the sound to the speed. Most of the time that is adequate. Sometimes it just won't match close enough. In this case you have to program the motor-driving decoder to match the speed to the way the sound sounds. Sometimes this can be done with V-Start, V-Mid, and V-Max (if the motor-driving decoder has those features). In some cases, the user-loadable table may be required to get it to match close enough.

Overall, the DSX is a wonderful product when used for what it was designed for - in a dummy loco or freight car, or installed with another decoder in a G scale loco where you have room to include disconnects for programming. It's only when trying to install it with other decoders in smaller locos that the programming hassle can become more than the savings are worth.