Kit: Zimo MX644D with Zimo Dumbo LS18X13X13-1W and 3x 330uF Tantalums for stay-alive
Another great new model from Dapol, the GWR Diesel Railcar runs smooth, has plenty of built-in lighting and is easy to fit DCC
sound into! Here is our donor model, number W10...
The body simply clips out and up easily - no screws to undo. The interior lighting bar and cab lights are revealed and the
whole wiring (at least the visible part) is very neatly done indeed. Some tiny switches on top allow you to control whether the
interior lights, cab lights and rear lighting is active, but it comes factory set so that everything is available under DCC, so
nothing to change there. You can see the 21pin DCC socket through a little slot in the side.
A screw either end holds the interior moulding in place, so remove these and gently free the moulding - a little sticky is
present to keep it neat. Be careful as you ease the moulding up, as there are wires in the centre that attach to the model's
PCB, and they are relatively short.
Bit of a bird's nest underneath, but at least it is all in one place and the wires are flexible ones.
Use a flat-head screwdriver to ease the 21pin blanking plate up from the outside at the same time as encourging it up with
finger nails from the inside. It is quite tight, but will come off with a little patience. Our kit then, is the Zimo MX644D
21pin sound decoder with YouChoos GWR Railcar sounds (recently updated), and Zimo small Dumbo LS18X13X13-1W speaker. It is the
only Dumbo that will fit in the space available, but does so quite neatly.
Protect the decoder will a little Kapton tape, after adding blue and grey wires for stay-alive (more on that in a moment).
The speaker is tight on height, so just secure down with some thin double-sided tape, ensuring that some of the drilled holes
in the bottom are still open - add more to the sides with a hand-drill if you feel the need.
There is no space for a standard electrolytic capacitor, so we've opted for 3x 330uF Tantalum 16V capacitors, joined in
parallel to give 990uF total, which is plenty, especially considering the model picks-up pretty well anyway. These capacitors
have the positive edge marked 'KO' with a bar on the top side, so this joins to the blue +VE wire that we added to the decoder
earlier. Cover the Tantalums in Kapton tape and slot neatly down the side of the speaker - perfect fit.
Tidy the wires in and pop everything back together - should go easily, and we're all done!
Photo shoot time on our diorama of Mini Box...
Kit: MX644D; Zimo SugarLump
Photos and words for this example kindly provided by Roger at Keen Systems.
This alternative installation has the advantage of intensifying the sound from the railcar. I realised that the installation of
the speaker is not the problem. The poor sound is as a result of the design of the railcar itself. The sound was being sent
into the body of the railcar through holes in the floor above the speaker position and then being muted by the body, along with
the holes in the chassis being blocked by the speaker itself.
Here I chose a Zimo SugarLump 8ohm 1w 12mm speaker. These are very powerful for their size with very strong magnets. Then
create a resonant cavity.
First two strips of 0.75mm plasticard strips are set onto the floor of the chassis between the holes to lift the speaker away
from the holes. The speaker has been laid on its side.
A length of 0.75 mm plasticard is set in the grove between the decoder and the speaker position to form a wall. A sheet of 20th
plasticard is glued over the holes in the floor to cover the seat recesses. When the interior is replaced a resonant cavity is
formed which magnifies the sound by as much as three time. WOW!