Graham Farish N gauge Class 66 diesel with MX660 sound, lights and stay-alive

Kit: MX660 (drop-in PCB sound decoder); Minnow4; Independent cab lights; Drivers; SACC16 with 2x 330uF Flat Tantalums for stay-alive

It is often the case with Farish diesels that the MX660 will go in without needing to modify the chassis at all. Well, this is almost true for the 66 - at least the MX660 will go in without any problems, but the problem is the speaker...

Without compromising the chassis or the speaker, the only option we have is the Minnow4. This can be fitted with minimal milling off one end of the chassis, but not much. The trick is to mill just enough that the cross-hair top of the bogie is still able to stay in position. The metal shelf for the speaker to sit on will be thin, but not wafer-thin. In fact, we've done another CL66 without needing to mill at all, so it is more for comfort of space if you feel up to it!

The Minnow4 will sit on that shelf, plastic down, secured by either some thin double-sided tape, or a tiny dab of glue. The MX660 sits on the centre of the chassis, mounted on electrical tape, which is then given a layer of double-sided tape to hold it in place.

With pickups, motor, and speaker connected, we can test the model's motion and sound. The Minnow4 is fairly quiet sitting on top of the chassis like this, but don't worry - the sound increases considerably once the body goes back on later.

The gap to get your soldering iron tip into for the motor terminals is very narrow - more so than some of the other Farish diesels, so you may find it easier to dismantle the chassis and solder the orange/grey wires on with the motor out. Red and black wires go from the MX660 to the pickups - we have small copper strips with a hole punched, and re-use the original PCB's screws.

For the factory lighting, this has 5 connections, which is a bit unncessary - 3 are for positive, 1 for negative of the red light, and 1 for negative of the white lights. We simplify this by adding a bridge wire to go across from E-to-D-to-B, which are the positive ones. Then connect fresh wires from the back through to the pads - blue for positive, white for the white lights and yellow for the red light, which is closer to DCC standard.

We drill small holes in the cab backs for our cab lights, add drivers and connect those up to the MX660. No resistors required as the decoder's outputs are all low-level already. There are 6 aux output on the MX660, so we make the reds independent from the whites, and the cabs on the 5th and 6th outputs.

We also decide to add a small stay-alive to aid with running - a SACC16 with 2x 330uF Flat Tantalums are wired up. In retro-spect we probably should have put these at the other end, to avoid the roof-box that protrudes down into the body at this end, but with some careful filing of the box, it all fits nicely.

All finished and running reliably.

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