Decoders and Sound

Updated: 7 November 2008

I originally purchased 3 Soundtraxx GWR decoders from ZTC Controls but now I favour the more recent ESU LokSound decoders from South West Digital. I have fitted the ESU decoders to my Finney 61XX and to my David Andrews SR/BR U class 2-6-0. I also have ZTC216B, ZTC225, TCS and ESU LokPilot decoders.

I built an enclosure in plastic card around the motor and gearbox in my 61XX. This includes a "tray" on which the ZTC470 and suppressors sit. The pickups are mounted on the side of the enclosure. The speaker is enclosed under the tray and points down to the track between the frames. I have used a ZTC196 oval speaker.

The first picture shows the sound decoder on top of the plastic card enclosure. The circuits to the left include the ZTC filter kit and resistors for the 1.5V bulbs in the decoder function circuits. The pickups can be seen on the PCB mounted on the side of the enclosure.

In the second picture the enclosure has been tipped back to show the speaker pointing down between the frames. The enclosure rests between the frames. I intended to add a bracket to the chassis spacer so that it can be screwed down firmly but this installation has now been replaced by the ESU LokSound decoder.

I still have a Soundtraxx decoder and cam fitted to my Finney 47XX. The cam is shown below.

It consists of a brass collar fitted with a grub screw. A plastic sleeve, from plastic tube, is glued on to the collar and 4 self adhesive copper strips fixed to the sleeve. A piece of double sided PCB is soldered to the adjacent chassis stretcher. The PCB is gapped with a phosphor bronze wiper soldered each side of the gap. The PCB is wired to the Soundtraxx decoder. Three washers made from the next size of plastic tube are fixed to the sleeve using plastic solvent. These keep the wipers away from each other.

The principle seems to be working and this method of construction is much cheaper than using etched PCB discs. I am having a bit of trouble with one of the strips which seems to give me a double chuff when running slowly. That might just be a bit of solvent on the copper strip. I had intended to make another cam for my 61xx with slightly wider strips to give longer chuffs at slow speed but that has been superceded by the ESU decoders which have better electronic control of the synchronisation of chuffs to wheel revolutions.

The next sequence of pictures shows the installation of the ESU decoder and speaker in my David Andrews SR/BR U class 2-6-0.

Plastikard strips were glued to the sides and front of the ESU 40x20 speaker enclosure. This slides between the frames and rests on 2 nickel silver strips soldered on the inside of the frames behind the cylinders. The frame spacer needs to be cut back to be level with the horizontal plate and some relieving of the back of the cylinder frame is need so that the cylinders nicely lock the speaker in place.

The speaker blocks access to the body fixing screw so I soldered a brass bar to the footplate behind the buffer beam. This was drilled and tapped 6BA to match a plate soldered between the main frames as shown below. The 2 6BA screws which now hold chassis to body are visible in the view above. As I found to my cost the screws should be cut so that they don't meet the footplate causing any weak solder joints to separate!

I used the new plate as part of a solution to the pony truck jumping off the track. I turned and drilled a brass weight which is screwed to the top of the frame of the pony truck as shown below.

This adds welcome weight to the pony truck. The new plate rests on the top of the weight when the chassis is sitting level. The sprung hornblocks are arranged so that the driving wheels only move down below centre. This means that the pony truck is only free to move upwards when the driving wheels hit a bump lifting the loco. I have not had any problems with derailments using this method. The diameter of the weight is set so that it acts as a stop against the frames preventing the wheels touching the front steps. A further refinement will be to reduce the diameter of the bottom end of the brass weight, which is visible below the buffer beam, to that of the prototype spring arrangement.

The view above also shows the speaker and its enclosure and the cradle which surrounds the ABC gearbox. The view from the back of the cradle is shown below. The cradle is made up from Evergreen strip and plastic sheet and screwed to 2 brass L sections which are soldered to the inside of the frames between the gearbox and the rear pickups.

The decoder can be seen on top of the cradle. The piece of veroboard ahead of the decoder includes 2 2-pin plugs for attaching the speaker and eventually a smoke unit. Another piece of veroboard is screwed to the brass L sections between the frames as shown below. This holds a 4-pin plug and socket so that a dummy plug can be fitted for running on DC layouts.

The cradle fits within the firebox. I plan to hide the gubbins below the frames with an ashpan. I also have to refit the driving wheel springs.

As delivered my ESU LokSound GWR 2 cylinder decoders from South West Digital have 12 function assignments. However the ZTC511 only supports 8 functions so some compromise was necessary.

First I needed to find out which SWD sound is in each sound slot.

For example, as delivered F3 is allocated to the Medium Whistle. This is set by CV161 and CV164 which both contained 3 so sound slot 3 contains that sound.

This was repeated for all the function assignments before overwriting any of them.

To reallocate the Medium Whistle (sound slot 3) to F2 change CV155 and CV158 to 3.

Here are all the changes I made. I arrived at them by considering the use of the ZTC 622 handheld with its need to shift for F4-F7 and double key for F8. As far as possible I have reassigned the functions on my other decoders to match these. I may need to make further changes when I introduce lights, smoke and possibly uncoupling but that will wait for another day.

F0 Acceleration/deceleration on/off

CV142 = 1

CV143 = 0 no sound slot

CV145 = 1

CV146 = 0 no sound slot

F1 Short whistle

CV149 = 2

CV152 = 2

F2 Medium whistle

CV155 = 3

CV158 = 3

F3 Long whistle

CV161 = 4

CV164 = 4

F4 Shovelling coal

CV167 = 5

CV170 = 5

F5 safety valve

CV173 = 6

CV176 = 6

F6 Cylinder drain

CV179 = 8

CV182 = 8

F7 Boiler drain

CV185 = 7

CV188 = 7

F8 Sound on/off

CV190 = 4

CV191 = 0

CV193 = 4

CV194 = 0