Example 1: CT SL51-4 with 23mm round speaker

The Bachmann OO Class 24/25 diesel... installation guide for DCC sound. Note that these examples are for the 21pin version which has only 3 lighting functions (directional head/tail lights and joined cab lights). For the 2021 version, there is a different guide, which needs a 5-function MX644C decoder instead.

First example... Not much to this installation... just remove the body shell, plug in the 21-pin MTC decoder (may need to trim the pins a little to allow the decoder to sit a bit lower (the SL51-MTC does not have 'through' holes!), connect a 23mm round 8ohm speaker (no space for any enclosure on this one), and you're done. The speaker is not fantastic, but it is certainly a simple job!

Example 2: Zimo MX644D with Zimo SugarLump speaker

Next example is a Class 24, which comes with a half-hearted enclosure for a speaker already, but this didn't fit any of the better speakers, so decided to remove this provided baffle, thin the roof plastic just a little, and install a Zimo SugarLump instead - plenty of noise and still pretty easy to do. We've also added drivers both end, and independently controlled cab lights. The decoder used here is a Zimo MX644 21pin...

Example 3: Zimo MX644D with Zimo LS26X20X08-1W Dumbo speaker

After popping off the body, we grind off the small lip in the speaker area - this will allow the Dumbo speaker to fit properly flat in the bay. Just good enough to go in underneath the roof fan.

Add cab lights and crew both ends. The cab lights will be independently controlled.

Using FA2/AUX3 and FA3/AUX4, we solder the cab lights directly to the feet of the 21pin plug on the board. Some care required to do this, but better than soldering direct to the decoder. Add a resistor on the +VE side for each cab light, and solder these to the +VE pin. We've used yellow SMD LEDs in this case.

Connect up the speaker - there are pads provided on the model's circuit board for this. Tidy the wires up.

We've added a YouChoos SuperCap6800uF to the mix too - this is connected direct to pads on the deocder.

Reassemble and test!

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.