
Fitting DCC Sound Decoder & Speaker Into A Bachmann Class 66

FITTING A DCC SOUND DECODER
In this article we’ll take a look at fitting a DCC Sound Decoder & speaker into a Bachmann Class 66 model. The model i’ve chosen for this article is the Bachmann 32-979 Class 66 – 66412 in Malcolm Rail / DRS livery. This model comes as 21 pin DCC ready model.
Model as supplied from the factory runs on tradition analogue control. It has a 21 pin DCC decoder socket with a blanking plug in the decoder socket, which allows the model to run on non DCC layouts. To convert to DCC remove the blanking plug & plug a DCC decoder into the decoder socket. It’ll then run on DCC controlled layouts.
Sound decoders range in various prices from Hornby’s Budget TTS sound decoders up to the likes of those by Legoman Biffo, Digitrains, Howes, Southwest Digital, YouChoos & many more. The sound decoders usually come supplied with a speaker these are either already soldered on to the DCC Sound Decoder or separate speaker for soldering on to the decoder or the loco model PCB board.
The sound decoders have sound files installed on them, & usually have an instruction sheet giving info about what all the sound functions do, C.V. settings, sound volume settings etc. A lot of sound decoders have around 29 functions an example list of functions is shown here for a diesel model:
Typical Function list for a diesel model
F0 Headlight/rearlight (if fitted to locomotive)
F1 Engine start/stop
F2 Horn high-low
F3 Horn low-high
F4 Brake squeal
F5 NOTCH up
F6 NOTCH down
F7 Return to IDLE
F8 Thrash
F9 Cold start override
F10 Compressor
F11 Door slam
F12 Fan
F13 Horn high
F14 Horn low
F15 Primer
F16 Slow flange squeal
F17 Spirax valve
F18 Horn short low
F19 Horn short high
F20 Wagons buffering
F21 Wagons clanging
F22 Coupling
F23 Dispatch whistle
F24 Buffering
F25 Aux (if used in locomotive)
Depending on what speaker you use effects the quality of sound so it’s worth upgrading the speaker from the standard one that comes supplied with the sound decoder. The likes of Bass Reflex speakers are recommended as these get the best out of the sounds. Other speakers worth looking at are the ‘Earth Mover’ by Leggoman Biffo, & Zimo 3D range of single / twin speakers. A number of modellers are also fitting the likes of i-Phone speakers into their models too! If your model is tight on space for a speaker it’s worth looking at one of the sugar cube type speakers.
Before buying an upgrade speaker make sure you check that your chosen speaker is suitably rated for the sound decoder. The DCC sound decoder retailer will be able to advise you this. Below can be seen a few examples of the different type of speakers mentioned above.
Fitting the decoder & Speaker
Tools You’ll need are…
- Posi-drive Screwdriver
- Four pieces of card or Plasticard
- Wire Cutter / Wire Stripper Tool
- Soldering Iron
- Optional: Peco Loco Servicing Cradle
First test run the loco & run in for an hour on traditional DC control. Place the loco upside down in the Peco Servicing Cradle (or just use a soft cloth instead). Unscrew the four screws that hold the body on. These are located either side of the fuel tanks below the inner ends of the bogies. I’ve circled the screw locating holes as seen on the right.
With this speaker i found it was a tiny bit too long & was pushing the back of the cab interior forward. This interfered with the refitting of the loco body. So a smaller twin bass speaker by Zimo as seen in the second photo on the right has been used instead.
(Note: The Bass reflex speaker can be positioned in the loco fuel tank area but this does mean some cutting of the full tanks is needed.)
- The red wire goes to SP+
- The black wire goes to SP-
Solder the two wires to the tabs as shown in the photo. However if you don’t do soldering you can push the wires through the holes on the tabs & hold in place with a black sleeve instead. You’ll see a black tab sleeve to the left in the photo, contact Bachmann service / spares department via this link http://service.bachmann.co.uk/ to purchase spare PCB board black tab sleeves.
Sound Volume
If the volume of the sound is too high or too low you can turn the sound up or down. To do this place the loco on to the programming track.
- Select CV Read & call up CV63
- Read what CV63 reads back as & make a note of that number
- Select CV write & call up CV63
- To turn sound down
- Select CV write & call up CV63
- Pick a number lower than what CV63 read back at & type that in & hit confirm
- Test run with sound on. Repeat reprogramming CV63 until happy with volume of sound
- To turn sound up
- Select CV write & call up CV63
- Pick a number higher than what CV63 read back at & type that in & hit confirm
- Test run with sound on. Repeat reprogramming CV63 until happy with volume of sound
If you mess it up you can do a decoder reset which puts the decoder back to as you first bought it. To reset call up CV8 & select 8 & hit confirm. This will set the decoder & as well as resetting the loco address back to number 3.
In this video will give you some idea of the different sounds & functions (Skip to around 1:59 into the video) https://www.youtube.com/watch?v=unMXd7eBx0Y
Happy modelling

Great instructions – very useful. How about using a few strips of thin but relatively strong plastic from a yoghurt pot.
Your welcome 🙂 That’s a great idea using the yoghurt pot plastic for helping to remove the body.