It seems that N gauge steam locomotive model design has come almost full cycle. More than a decade ago, Graham Farish would routinely cram all the electrics and motor in a locomotive and leave the tender largely empty. In recent years, Dapol and Graham Farish reversed that trend by moving everything to the tender (although the latter has now gone back to locomotive drive), adding better pick-ups and providing maximum weight in the locomotive for traction.
The current range of Dapol tender models take a hybrid approach, placing an ultra-smooth motor in the tender and mechanics in the locomotive with a drive shaft through the cab, meaning that half the tender is now empty in many cases. This gives DCC sound enthusiasts a chance to accomplish something we have been longing for since our OO friends first started showing off their wonderful sound-fitted locomotives - DCC sound in our beloved N gauge equivalents.
❚ YouChoos GWR Hall Class sounds on Zimo MX648
❚ YouChoos SugarCube7 speaker
❚ Crushed Lump Coal
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❚ Quality soldering iron with fine tip
❚ Hand files
❚ Small Philips screwdriver
❚ Fine cutters
❚ Wire cutters/strippers
❚ Thick super-glue
❚ Electrical tape
Pop off the tender body, being careful not to break the plastic retaining clips as it lifts off, pressing in from the sides to release the body clips. This reveals the six-pin DCC socket mounted at an angle in the rear of the tender space.
De-solder the socket circuit board and remove the capacitor and resistors so that you are left only with the bare pick-up tabs and motor terminals. These components are only required for DC running and can cause issues with DCC, giving confusing 'Back EMF' results to the decoder. They need to be removed. Be careful when unsoldering from the motor brush pins as these have a habit of moving around when they're hot.
File down the circuit board mounts flat as this is where to mount the YouChoos SugarCube7 speaker. The speaker’s 15mm x 11mm footprint fits perfectly between the pick-up tabs, and the total height of 7mm is a comfortable fit too - no modification required to the enclosure. You might find it useful to file an angle off the rear of the motor housing plastic to give the decoder wires space, but it's possible to get everything in without doing this if you're neat.
The Zimo MX648 decoder is prepared here, shortening the six wires as required (red + black for pick-ups, orange + grey for motor, 2 x purple for speaker).
All other wires are de-soldered from the decoder so you have as few wires to fit in as possible (ask YouChoos to do this for you if you are not confident with your soldering). Solder the six wires - black to left pick-up, red to right pick-up, grey to left side of motor, orange to right side of motor and the two purple speaker
The speaker is mounted on a double-sided sticky pad.
Cut and file the whole coal load area of the tender body, as the decoder will sit on top of the motor and eventually be covered in a new custom coal load. The whole of the coal moulding will need to be filed, as the MX648 is exactly the same size! Start with a mini-drill if you like, then move to hand files as you near the edges.
This is a great moment to test everything - first check that all electrical connections are clear of each other and test the direction of travel (if it is opposite to what you expect, swap the orange and grey wires around).
With the decoder covered in electrical tape (overlapping a little to cover the entire hole), press it right through so it sits flush on the motor top and click the tender body back into place. If you’ve filed the hole enough, it should go perfectly flush. You may need to adjust, or even flip the decoder over to get good motion out of the motor. Once you're happy with the fit, and the motion, reconnect locomotive and tender and test thoroughly before proceeding.
If there is any gap between the decoder and the sides, fill it with Blu-tack. Then, using glue (a thick one that doesn’t run too much, such as Loctite Ultra Gel), drop and smear across the tape and Blu-tack to cover the whole coal load area and generously sprinkle crushed coal ballast (we used crushed Woodland Scenics ‘Lump Coal’) and press into the glue gently, tipping off the excess and leaving to dry.
Can I do this to other Dapol steam locomotives?
The great thing about this technique for installing DCC sound into the ‘Hall’ is that the same process can be applied to many of Dapol’s other tender locomotives. The Gresley A3, A4, BR ‘Britannia’ and 9F 2-10-0, for example, can all be given a similar treatment. As long as the tender is long enough to get the speaker behind the motor, and the coal load above the motor is long and wide enough for the MX648, it’s no problem.
For even more DCC articles, click here.