Adding 21 Pin Sound

[Will Hay]

I have a diesel I'd like to add sound to.

It currently has a 21 pin decoder in but the 21 pin sound decoders are over £100 and I just can't bring myself to spend that, regardless of how good [loksound, for example] they might sound.

Can I put a hornby 8pin sound decoder in without loss of function, with an adapter?

Thanks.

[ColinB]

Yes, you can. I have done it with many of my Bachmann diesels. The only issue I have had is the 21 pin to 8 pin adaptor is too high in some locos, so you can't get the body on properly, which is a particular issue with class 37s where there are light connectors at the bottom of the body that don't make contact. You are better off getting a 21 pin "break out" board LaisDCC sell them so does another firm. You then rewire the TTS decoder to the breakout board. You can also wire the speaker wires which allows you to wire the speaker to the main PCB of the diesel. If I remember rightly in Class 66s you can use the adaptor there is enough height.

The only thing you have to be aware of is some locos use all 6 functions for lights, so if if you use an 8 pin TTS decoder you may lose some functionality eg. Hattons class 66 and some Dapol diesels.

[Chrissaf]

Can I put a Hornby 8pin sound decoder in without loss of function, with an adapter?

 

Without loss of function cannot be guaranteed. It really does depend upon how many of the 21 pins of the DCC socket are being used within your loco.

 

At the end of the day a Hornby TTS 8 pin sound decoder only uses 8 pins (the two wires for the speaker being separate]. Thus only 8 of the 21 pins of the loco connector can be connected to. The ones that are not connected to may have critical use in your particular loco for which the manufacturer chose to use a 21 pin decoder.

 

For example, your loco may be sound ready and have a speaker [or wiring for a speaker] all ready integrated into the loco. The speaker connection would typically appear terminated on Pins 9 and 10 of the loco 21 pin male connector.

 

The drawing below [created for a previous similar question] shows one way to use a TTS decoder in a 21 Pin loco, but with the caveat that some features that require certain pins of a 21 pin decoder may not function.

 

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Note that these particular adapter board products will require a wire strap placed across one or other of the solder pad pairs on the adaptor board. These wire strap positions define which function of the 21 pin adaptor are enabled with the 8 pin decoder. Thus some knowledge of the pin function layout on a 21 pin interface is required and, of course, which ones are needed in your particular loco model.

 

EDIT: Colin posted whilst I was writing mine.

 

[Will Hay]

Thank you.

 

The beautiful behemoth in question is the Bachmann Class 70.

 

https://www.dropbox.com/s/5v6wuybfn0xwxvx/20201106_233001.jpg?dl=0

[Howbi]

A very good 21 pin breakout board is available here ...... it has speaker connections if required......HB

[ColinB]

The Strathpeffer Junction one is easier to wire up than the LaisDCC one, although the LaisDCC circuit board is better made, although the LaisDCC one means you need to know which pin on the 21 pin socket does what. With the Bachmann class 70, look in the data that came with the loco and look for the light functions. Usually Bachmann only use 3 functions front lights, rear lights and cab lights., on the ones I have converted (class 37, class 47 and class 66). Dapol tend to use all 6, as do Hattons on their class 66. I always use the breakout board, the converters to me once fitted are too high and unless you are lucky, make it difficult to put the body back on. I did actually damage one TTS decoder using a converter, but as I said before that was on a class 37, where there is not much space between the location and the roof.

[Chrissaf]

The negative con in my opinion of using the Strathpeffer is that you have to cut off the 8 pin plug on the TTS decoder as well as having to know all the pin functions and get them connected correctly [even with the colour code labelling on the board].

 

With the LaisDCC and Bachmann adaptors in my image there is no wiring up as such [apart from choosing which solder bridges to implement] as they just plug together the decoder and loco.

[Howbi]

@Chris.......the point of using the Strath adaptor is where there is insufficient height above the pcb to plug in the other convertor with the 8 pin plug on top as is the case with many diesels......HB

[ColinB]

@Chrissaf the LaisDCC board I am talking about is the 21 pin breakout board. I normally use the LaisDCC breakout board, but I have just finished doing one with the Strath adapter. I prefer the LaisDCC, although it is harder to wire as you have to know the corresponding 21 pin equivalent. It has plated through holes on the PCB and is easier to solder to. In both cases, yes you have to cut off the 8 pin connector, but in my case I test it on the tester before I cut the 8 pin header off. If by chance it fails, then I have to resolder the 8 pin header back on, but they is just a price you have to pay. I must admit it is a much neater arrangement and tons easier to insulate.