#7 Adapting an 8-Pin Hornby TTS Sound decoder for use with a 21-Pin Chassis

A short tutorial on converting an 8-pin Hornby TTS Sound decoder for use with a Bachmann 21-pin locomotive, such as their Class 37 or Class 47.
While the majority of Heljan locomotives also come with a 21-pin DCC socket, it is recommended that you do not use a TTS decoder with their products given their higher current draw.
In the video, the 8-pin adaptors shown are made by LaisDCC and DCC Concepts. It is understood that Bachmann also make an adaptor. There may be others too.
Manufacturers have also produced different versions of the adaptor over the years, some of which come with AUX solder pads while others do not, so the manufacturer is not necessarily a guarantee of a particular design.
You can find the schematic in image form here: StrathpefferJunction/photos/a.2156466537917020.1073741829.2149839818579692/2162071747356499/
UPDATE: It is now possible to buy 21-Pin break out boards which, if used in place of the 8pin to 12pin adaptor, would negate the plug removal step, however they are currently more expensive per unit and often only come in packs of 5, so the method shown in the video is still the cheapest option.
Items required for this project are:
- Hornby TTS Sound decoder
- 8-pin to 21-pin adaptor
- Expo modelling saw
- Soldering iron, solder & liquid flux (optional)
- Various tools, including: jeweller's screwdrivers, small side cutters and an exacto knife and needle files.
You can buy a 5-pack of the 8-pin/21-pin adaptors here: amzn.to/2HzZ6Ik ...or buy a single 8-pin/21-pin adaptor here: amzn.to/2HF7Htc
Thank you very much for watching.
Please comment, like, share and subscribe!
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[@1BCamden]

Excellent level of detail, much appreciated

[@thetrainspotter7]

Thankyou so much for this helpful tutorial. I was wondering for the last year why my Bachmann 66 cab lights weren’t working with TTS but now it’s fixed so I’m a happy bunny.

[@StrathpefferJunction]

I'm glad to hear that it came good for you! Tts decoders are a decent option for many situations. 🙂

[@tonyslight826]

great how to ,thank you.

[@StrathpefferJunction]

My pleasure!

[@brooklynroad8581]

Ive fitted the 8 pin to 21 pin adapter into my Bachmann 21 pin class 37 and the sound is ok, and the body whent back on OK. excellant video.

[@StrathpefferJunction]

Many thanks for the kind words. It's touch and go with these models. I've found with some, the body just about goes on ok, but it applies pressure to the decoder adapter and pcb, which I'm not entirely keen on in terms of longevity of solder joints etc. I've also had one where the body went back on ok and bother where no matter how much shoogling I did, I just couldn't get it back together and closer inspection showed the pcb to be slightly high off the chassis and on the other. So, these days I just fit a hardwired adaptor as I rarely change the decoders out once they're in there. All adds to the fun of it! 😋

[@brooklynroad8581]

Lets hope mine last. Now trying class 20, 8 pin and 21 pin version. will let you now how I get on. It would be nice if Hornby brought out a 21 pin version in its TTS sound where applicable

[@StrathpefferJunction]

Yes, it would be, but I doubt they will unfortunately. The tts chip is based on their basic decider, which I think is 8 pin only. They'd probably have to either tack it onto their more expensive sapphire one or develop a new 21 pin variety of basic decoder. Best of luck with the c20. They can be quite a tight fit!

[@pierre-de-standing]

Nice instructional vid, helped a lot. Fitting the chip and speaker in a Bachmann 37 is really tight, but I managed it. What hasn't gone well is that the locos performance is very poor. Did you find the same and if so, was it just some changes to the CVs and if so, what ones did you change - sorry about all of the needy questions. Cheers - Pete

[@StrathpefferJunction]

Sometimes changing CV 150 on a TTS chip can help. I've found that the second motor profile is often better for non-Hornby members. The TTS chips normally come with CV 150 set to 0, sometimes changing this to 1 will help immediately. There's also further tweaking you can do to these CVs. The Hornby TTS manual should explain in more detail.

[@SimonLivertonCentral]

Very nice tip David, I can see me doing that, I have used the ESU 51967 21MTC adapter in the past...Simon

[@StrathpefferJunction]

+Simon -Liverton Central Thanks, Simon. There are other methods, and I have seen a 21-Pin break out board used, but I think these 8-pin to 21-pin adaptors are currently the cheapest way to do it. They work our at about £3 each (or thereby) each, whereas the cheapest breakout boards I could find came out at about £5.20 each, plus you had to buy five at a time.

[@BarnabasJunction]

Excellent tutorial 👍 I had been wondering this recently and up pops your vid. Thanks for sharing.

[@StrathpefferJunction]

+Barnabas Junction No problem. Glad you enjoyed it!

[@jerryallen34]

Hi Dave, hGreat channel, thanks for pointing me in the right direction, Lol. Have subbed to. Agree, Heljan and TTS don't mix! Cheers Jerry

[@StrathpefferJunction]

+Jerry Allen Many thank indeed, Jerry. Glad you found it helpful.

[@H105]

Ive wired up one of these adapters, but I'm having a few issues. When power is applied the loco plays a AWS cab warning alarm without any input from me .. also the front lights come on untill I apply some speed and the lights turn red on their own. Have I done something wrong or is the Hornby TTS chip faulty?

[@TheWGLOVER]

A very timely video. I made the mistake of buying the Class 47 decoder for my Heljan Class 47, but after surfing the web, decided best not to fit it. I have just purchased a Bachmann Class 47 to use it on, and a LaisDcc 8 / 21 Pin Adaptor NEM652 Chip to 21MTC Loco Part No.860004 DCC. Looks like I am going to have fun here. I wonder if it would be possible to solder a 4 pin socket to the adaptor, and leave the Decoder intact. Again, a great video.

[@StrathpefferJunction]

+William Glover Wise choice, I suspect! I think the class 47 tts sound is actually pretty decent (especially with a better speaker), and I run it in a couple of my bachmann 47s now. You probably could solder a socket arrangement in place, but I have found that I so rarely remove decoders once fitted, if I ever did want to swap one out, having kept the 8 pin plugs in my spares box, it's probably less faff just to solder it back on again.

[@TheWGLOVER]

Strathpeffer Junction I like the Sugarcube Flame speakers. Much fuller than those supplied.

[@paulharrington1140]

Hi you can desolder and take the 8 pin socket off the board and solder the hornby 8 pin plug into the socket and cut off the pins, saves wiring each wire

[@StrathpefferJunction]

Hi Paul. Many thanks for the comment and suggestion. Yes, I saw Barnabas Junction doing this more recently in a video. I'm happy doing it this way as I don't mind soldering and I prefer having less solder joints and a less bulky end result, but if the plug comes away easily for you with a soldering iron (I've heard one person say it doesn't always work, although I've not tried it myself), it may be slightly quicker going down that route. What I tend to do now is buy the 21-Pin adaptors without the 8 pin socket and just solder the wires to the break out tabs on it. It's pretty quick. I did a more recent video on that method. Certainly a few different approaches out there 🙂

[@darrelldeltic807]

Lovely tutorial, was wandering if you knew of an adaptor that converts a v3.5 loksound class

[@StrathpefferJunction]

Hi Darrell. Sorry, only just noticed this comment. Do you mean a 21-pin V3.5 to be used in an 8-pin chassis? Or vice versa?

[@darrelldeltic807]

Strathpeffer Junction ha ha yes sorry for dropping that one in ! Yes it was a 21 pin v3.5 and I hadn’t thought how I was going to fit it into an 8 pin 🤔 you both gave some good advice and I’ve opted for a 21 pin pcb , I’ll let you know how I get on fitting it 👍

[@StrathpefferJunction]

+Darrell Deltic Excellent! Let us know how you get on 😀

[@roydom5]

As always great video - thanks! I'm trying to add a stay alive to a 21pin ESU decoder although I've read that you shouldn't solder onto the chip directly. So I thought perhaps the only solution is to replace it with a Zen 8 pin nano and use an 8 pin to 21 pin to conversion board from DCC and keep the original decoder for another project?

[@StrathpefferJunction]

You could certainly go down that second route if you like, but I'm not sure there's necessarily anything wrong with hooking up a stay alive to the ESU one. Which model of esu decoder is it?

[@roydom5]

@@StrathpefferJunction It's a LokPilot v2.0

[@StrathpefferJunction]

Ah. That's an older one and I'm not sure if they're so easy to work with re stay alives. I don't have any of them unfortunately (I think the oldest I have now is a LokPilot 3.5).

[@roydom5]

Strathpeffer Junction thanks , I see that now. Replaced it with a zen black and will keep the esu for a future conversion!

[@cainesanders5845]

Hello amazing video I have just bought a sound decoder and am wondering how do I turn the volume up the model is a TTS decoder

[@StrathpefferJunction]

Hi Caine. The easiest way to quickly set the volume of a TTS decoder is via CV178. It has a range of 0 to 8. You can't read that CV, but just write a number from 0 to 8 to it and the overall volume will change. Do be careful not to overdrive the speaker, however, as it won't sound great. You can get much better results by switching out the sotkc speaker for something better (so long as it's 8 ohms).

[@cainesanders5845]

@@StrathpefferJunction how do I find the cV 178 I have my my locomotive set to Channel 4 but everytime I try to input tn8 to turn the volume all the way up it just changes to Channel 8 if I hold the function button it will just play the other sound if that makes sense any ideas of what I'm doing wrong

[@StrathpefferJunction]

How you programme decoders varies between dcc controllers. Not all are able to programme decoders either. What do you use?

[@cainesanders5845]

@@StrathpefferJunction hello sorry for the late reply I have a select controller

[@TheWGLOVER]

I now have my Bachmann Class 47 (nicely run in on dcc), a LaisDcc adaptor, a DCC MTC 21-pin to NEM 652 8-pin decoder socket adaptor. and a brand new Class 47 TTS decoder. Can you just clarify the following? The DCC adaptor is the better one to use. f0 will operate the directional lights. Will f25 aux. operate the Bachmann cab lights, if not, can it be made to? Is it feasible to remove the 4 pin plug by sucking off the solder, or is it soldered both sides?

[@StrathpefferJunction]

+William Glover Yes, on the TTS 47 chip: 1. F0 will operate the directional lights. 2. F1 will start the sound. 3. The aux channel is on Function 25. So, F25 will operate, say, the cab lights if fitted (depending on the 21-8pin adaptor, as I mention in the video, you may need to do nothing to make this work or you may need to solder across the solder tabs). I've done this conversion three times now. Once, I was able to suck the solder off from the back enough that I could then prise off the socket. One the two most recent, I couldn't get enough solder off it, so I had to saw it. These ones appeared to have little metal inserts in the holes that the socket pins fitted into and they made it hard to clear the solder. Once I'd sawn off the 8 pin socket, I flowed solder over these to fill them in and formed solder tabs. On the other two conversions, there were not such metal inserts and I just flowed solder into the holes left by the pins, again to create solder tabs for the decoder wires.

[@StrathpefferJunction]

William Glover Sorry, I forgot to answer your question about with adaptor is better to use. They all go by some many names, often with one manufacturer using one name for something different to another, it's hard to say without seeing a photo of the two you have. If you want to drop me an email at [e-mail], I can let you know which, in my experience, is the better option or if it's much of a muchness. The hardest part of this project is removing the socket. That's probably the bit that takes the longest and needs the most care. I sawed it off very slowly!

[@darrelldeltic807]

Sorry pressed wrong button 😱 start again! Do you know of an adaptor to convert a 21 pin sound decoders to 8 pin? And I’m not sure which terminals are for the speaker, sorry 2 questions 😊 cheers Dazza

[@StrathpefferJunction]

+Darrell Deltic I have looked high and low for one, but I've not come across a company that does them. I had a LokSound 21-Pin that I wanted to use on an 8-Pin Class 24, but in the end I just had to get a spare 8-Pin loksound reblown. I would have thought there'd be a bit of a market for them, but perhaps not enough to make it cost effective. If you could easily buy the 21 pin sockets, it may be easier enough to knock one up as the 8-Pin plugs are pretty standard across other areas of electronics, but as I said in the video, I've not yet found a supplier for stand alone 21-Pin sockets...surely they must exist?!

[@DungeWoodRailway]

Darrell Deltic I think the Hornby Sapphire decoder comes with a harness that allows you to use it in an 8 pin loco, not sure if you can acquire the harness by itself though? Cheers Paul

[@StrathpefferJunction]

+Dunge Wood Model Railway I'm not sure that the harness is actually 8-Pin to 21-Pin socket though? I'll need to check. I though it perhaps introduced another type of socket/plug into the mix? I'll see what Google throws up!

[@StrathpefferJunction]

Dunge Wood Model Railway Just checked. You're absolutely right, Paul. I had been thinking about the Gaugemaster ones. The Hornby harness does have a 21 pin plug, but I can't find them listed as a standalone item. I'm sure there must be folk out there with spare harnesses...perhaps, Darrell, you could ask on a Facebook group?

[@StrathpefferJunction]

There's a good thread on options here: www.rmweb.co.uk/community/index.php?/topic/22206-21-pin-sound-into-8-pin-loco I think the 21-Pin break out board is fairly expensive for what it is, and doesn't look to be all that common in UK shop stock.

[@davidcurrie8564]

02:43 i bought one from hampshire models (ebay)

[@StrathpefferJunction]

I now sell a range of dcc adapters that I designed and make myself here in the UK. Lots of options and more variations for different situations on their way in the new year. All available here: www.strathpefferjunction.com Happy Christmas 🙂🎅🎄

[@davidcurrie8564]

@@StrathpefferJunction i wished i'd known that mate, i'll keep that for next time i need one Merry Christmas Mate🎅

[@StrathpefferJunction]

No worries. Just drop me a line. Always happy to help!

[@davidcurrie8564]

@@StrathpefferJunction Cheers Mate!

[@leecharlton3010]

hi dont suppose you have any cv adjustments for a bachmann class 40 with a tts decorder in it as cant get mine to run smooth with the sound

[@StrathpefferJunction]

Hi Lee. Have you tried changing the motor algorithm? It ships with cv150 set to motor algorithm 1, but sometimes algorithm 2 better suits the motor. To change algorithms, just alter cv150. For algorithm 1 write 0 to cv150, and for algorithm 2 write 1 to cv150. That might be all that's needed - it's sometimes worked wonders with the odd loco of mine. You can also tweak the algorithm parameters if need be via cv151 to cv154.

[@StrathpefferJunction]

The Hornby manual for the TTS decoder explains a wee bit more about it: www.humbrol.com/media/wysiwyg/4-1495_Class_40_TTS_WEB.pdf

[@TheWGLOVER]

Hello, me again. After much trepidation I managed to get the top off. That was not for the faint hearted. Bachmann should employ some user friendly Designers. I fitted the TTS decoder using the fitted plug to make sure everything worked. I confirmed all but the f25 cab light. This requires putting the body back on, and I am in no hurry to go through all that again. Can you explain the pin 3 green aux./21 socket interface? Do you need to solder across the pads, and which ones? The sugarcube Flame speaker I intended to fit has no chance. Can you recommend something? I should have stuck with steam.

[@StrathpefferJunction]

Hi William. Yes, if you want the cab light to work on F25 once you've soldered on the modified adaptor, you need to link the two solder pads next to "J4". I have used just a blob of solder on one conversion and it worked fine, or you can solder a tiny piece of wire, but that is very fiddly. Once you've added this link and have everything installed in the loco, the Aux channel controlled by F25 will work the cab lights.

[@StrathpefferJunction]

Regarding the speaker, There are few options, depending whther your loco is a new style Bachmann 47 or an old one. If it's a new one with a depression for the speaker, you could go with a fairly standard 20x40 8 ohm speaker. Depending on how new your Bachmann Class 47 is, it may have come with a speaker housing that would fit one of these speakers, otherwise you would need to fabricate a housing out of plasticard. Either way, seal all the air gaps with blue or black tack. Similarly, you could use something like this, which is the same dimensions but a smaller speak with its own enclosure. The sound is reasonable in my experience, and perhaps marginally better than the stock 20x40 speaker: www.ebay.co.uk/itm/4x-20x40-MM-8-Ohm-Bass-Speaker-DCC-Sound-Hornby-Bachmann-Loksound-Zimo-TTS/263434862081?hash=item3d55f0fe01:g:b5cAAOSwoRBaWkOX

[@StrathpefferJunction]

And if you have one of the old chassis with no depression for the speaker, you may find that putting two very small speakers in parallel or series would work. YouChoos have a good selection. I think the TTS chip has to has 8 ohm, however, so you'd need to be careful about combined impedance. You could put two 4 ohm speakers in series to get 8 ohms, which should work fine with a TTS chip.

[@StrathpefferJunction]

+William Glover Hi William. How did you get on with the installation?

[@TheWGLOVER]

Strathpeffer Junction I had everything ready, speaker recommended by youchoos, plug etc ready for soldering , and I fractured my ankle. I can't get upstairs at the moment and am feeling so frustrated. I have removed the 4 pin socket entirely from the adaptor, and reckon I can solder the decoder plug directly in the board.

[@TheWGLOVER]

Youchoos use this one SPK-LS26X20X08-1W - Zimo 3D Dumbo (single) speaker (26x20x6mm 1W/8ohm in 3D-printed enclosure) youchoos.co.uk/Index-Resource.php?L1=Guides&Item=OOCL47

[@kevallsebrook3232]

could you not use a Gaugemaster adapter 21 to 8

[@StrathpefferJunction]

Assuming we're talking about the same thing, that is basically what I used in the video. In some locos - and this was one - the is very little clearance between the 8 pin socket and the roof of the body. When you add an adaptor into the mix, either the body doesn't fit or it compresses the pcb and connectors, which isn't going to be good for them longer term. This approach circumnavigates those potential issues. It's just one solution though, and there are others. 🙂