Heljan O Gauge Prairie with 21pin Sound Decoder and ADAMTC Booster Board approach

Kit: Zimo MX644D in ADAMTC board with LS40X22X09-2W Dual Dumbo and 17000uF SuperCap

Well done Heljan for taking the plunge with this steamer - solid feel, lots of weight and good detailing. Initial look reveals a chamber underneath designed for a 23mm round speaker, and in the boiler, a socket board intended for an ESU LokSound V4 'L' sound decoder. That would make it fairly easy to do a DCC Sound installation, but we want Zimo, and we can MUCH better with the speaker too!

Unfortunately, the ESU socket board is non-standard - in fact, there is no industry standard for large scale decoder sockets as such, and Zimo's similar offering (the MX696S) is not compatible. Therefore we need another option.

The boiler is totally empty otherwise, so if we remove the socket from the model, we have enough room for a mid-range combination using a 21pin MX644D sound decoder (normally for OO scale), but with an adapter board (the ADAMTC) which boosts the motor output to a decent 1.8A continuous, and 2.5A peak for a short period. This is enough for the Prairie.

We remove the factory socket from the model, and carefully transfer the wires across to the ADAMTC board one-by-one. A slip of Kapton tape wraps the MX644D decoder, plugged into the board, and above (secured with Black Tack), we stick the excellent Zimo dual Dumbo speaker, the LS40X22X09-2W. In addition, there is just enough room to add a 17000uF SuperCap, which is compatible with the ADAMTC board (apart from the boost of motor output, the ADAMTC board also allows connection of 16V capacitors, whereas the MX644D normally only accepts 25V+ capacitors). The model comes with a firebox glow light, which can be connected to the ADAMTC via the Common Positive (plus resistor) and the FA1 output. All neatly squared into the boiler, the body slots back on (quite tight!) and all is done!

NB Alternative speakers would be IceCube40X18X09-2W or IceCube28X18X09-2W. Use one not so tall for a slightly easier installation.

All back together, and a stunning result - loud, and a number of seconds backup power from the SuperCap! Like this model... a lot!

Here is the wiring required on the ADAMTC:

Initial photos courtesy of John Philips

Please note that these guides are provided as useful resources for you, as-is. YouChoos cannot be held responsible for errors in the information, or for any damage caused to your models or equipment if you choose to follow any of the steps detailed here.