DCC decoders are hard to choose, lately I have been using the Doehler & Haass SD18A quite a lot.

SD18A Overview

The Doehler & Haass SD18A decoder boasts a Next18 Digital interface. Next18 is a modern digital interface more and more common in European N scale models. I have already praised Next18 here, and discussed other interfaces in a quite popular article here.

Some brands like Arnold are now selling locomotives with Next18 instead of the aging NEM651. Also, I have showed many times you can fit Next18 in old trains with a bit of DIY (e.g. here, here or here).

The SD18A is an all-in-one DCC, Motorola an Selectrix sound decoder. If you’re not sure what this means, head to my introduction to train sounds here.
Its direct competitors on the European market are for example the ESU Loksound Micro v4.0 Next 18 (part no 54898), or the Zimo MX658.

One of the main advantages of the SD18A is clearly its price. At around €60 including VAT, it is up to 30% cheaper than the competition.
But it’s also flatter than the Zimo or ESU with a footprint of only 25.0 * 9.5 * 2.8 mm. Now all Next18 sound decoders will fit into commercially available locomotives with a proper Next18S interface. But if you’re outfitting an old train, with little vertical space, the reduced height may come very handy.

Doehler & Haass SD18A in review: bottom view

Bottom view

Doehler & Haass SD18A in review: top view

Top view

Doehler & Haass SD18A in review: side view

Side view

Installation, as with any Next18 decoder, takes only a second if the locomotive is already equipped with a Next18 interface. Be careful! Some locomotive only accept non-sound Next18 decoder that have a smaller form-factor (closed to the old NEM651 decoders).


The decoder has everything you’d expect from a Next18 decoder, including 2 extra function outputs that can be used for interior lighting or other functions.
With the latest 2015 firmware, D&H even added 2 other (non amplified) function outputs that can be accessed by soldering on the decoder (unfortunately, the Next18 interface doesn’t provide for enough connections).

As for sounds, it’s got a 32Mb memory to store up to 190s of audio, which should be enough for most sound projects (although quite limiting if you like to store very long sound sequences).

Head on to the Doehler & Haass SD18A page for a precise description and tech specs.


CV programming is no problem with any DCC or SX2 command station. Of course, you could also use the Doehler & Haass programmer if you prefer.

As with all D&H decoders, some might found the advanced settings limited in comparison with ESU or Zimo. There are, for example, no blinking options for light outputs. This won’t be a problem for most EU customers, but comes handy for North American model railroaders.
I personally find the D&H options completely sufficient for my needs. More importantly, I find D&H decoders behave very well with motors with default settings; more so than some competing decoders.
The good side of this is also that Doehler & Haass decoders are much easier to program. I for example don’t like the Zimo options, with hundreds of CVs, since I just need a few of them.

Sound choice

Doehler & Haass has been developing more and more sound projects in the last 2 years. You can have a look at the available sound projects here.
This sound library is quickly growing, however, it is still much smaller than those from ESU or Zimo. If you really want the right exact sound for your train, you may not found what you want at D&H. For me, it’s often close enough. Here is an example on a small diesel railcar (full details here):

As usual you can ask most stores to upload those existing projects when buying the decoders. You can also use the Doehler & Haass programmer reviewed here to upload or customize any project. For now, as opposed to Zimo, all D&H sound projects are free of charge.

Sound upload

If you’ve got the brand’s programmer, then you can upload or change the sounds yourself. Zimo and ESU allow you to do this via the track, meaning even without opening the locomotive.

Unfortunately, the Doehler & Hass SD18A does not allow you to do that. To upload new sounds, you need to connect the SUSI interface of the decoder to the SUSI plug of the D&H programmer.
This means you will not only need to remove the decoder from the locomotive to change sounds, you will also need some adapter to connect the SUSI pins of the decoder to the Programmer.

For now, I don’t think the brand offers any specific adapter. The large Doehler & Haass Next18 adapter does have SUSI pins ready though. So I have built a little board to help me upload sounds easily:

Doehler & Haass SD18A in review: custom SUSI programming board

Custom SUSI programming board

Doehler & Haass SD18A in review: with D&H programmer

With D&H programmer

If you’re interested in customizing sounds, also have a look at my post about the D&H Programmer.


At around €60, the SD18A is really a bargain for a modern Next18 sound decoder. It comes with the usual set of Doehler & Haass CVs and good behavior with locomotive motors.
In all my tests, sound was good. Nevertheless, as with most N scale sound locomotives, the speaker choice/position is more important for sound quality.

Compared with the competition, the SD18A has 2 main disadvantages:

  • Access to a still limited sound project database, but growing every month
  • For DIYers, the need to connect the SUSI interface to upload sounds (no programming track uploads)

For those who are ready to live with those 2 caveats, the SD18A is an excellent sound decoder, especially for N scale. I have installed Next18 decoders in several locomotives and haven’t had any problems.