Skip to main content

Gang, I have found these decoders in a trade in box. What are they? One is marked as SP 4365 on one side, SD9E on the other. has Red, Black, 2 Purple, Brown leads with the Purple attached to a 8 ohm speaker. The speaker fits perfect in the MTH fuel tank shown. The other is marked GP60 with Red, Black, 2 Purple leads.  Are these sound only?  Thus for piggy back to a motor control only decoder?  Thanks, Bruce in Mount Airy, MD  


Images (1)
  • IMG_7658: Sound decoders ?
Original Post

Yes, with only those wires, they are sound only.   In my opinions, nice ones if they work.    Yes you install them in addtion to a motor/light etc control decoder.     When a decoder has only red and black wires and 2 purples, for the speaker, it is sound only.     Full blown would also have orange and grey for motor and white, yelloe and blue for lights.    

The red and black wires on yours connect to the track pickups the same as the control decoder.

if you use them you need to be able to disconnect both decoders easily as you cannot program them both at the same time. used to put a slide switch in for this. I have two EMD one Alco and a steam one . one still in the package with instructions. they were nice when there were no high currant sound decoders as they were separate from the motor controller. if someone wants them make me an offer for all 4 , they are just collecting dust here.  Rick

Or you can program them both to the same long address but different short addresses. Then set CV29 to long address in both to run them together.

To program either one, set CV29 in the long address to short address, and they will separate out to their different short addresses to be programmed individually.

Then when you're done, set CV29 in both to long address again and they're ready to run with the long address.




This sounds like the way to go. I was just about to find a switch to wire in when I saw your suggestion. I am not sure how to go about programming them both to different short addresses as I do not know what the decoder type (other then digitraxx) I have for the sound. ( does that matter? ) When I wired it to the NCE decoder and used find decoder type in decoder pro, I reset the address as long / 4351, didn't that reprogram both to 4351?  If so, how do I change one but not the other?   Thanks, Bruce in Mount Airy, MD 

Bruce, the white decoder is 99% likely a Soundtraxx DSX as others have said. Soundtraxx has user manuals for their older DSD decoders upon which the DSX was based, and a DSX addendum on their site under "old models" or such like.

Fortunately CV29 is one of the NMRA DCC standards that most decoder manufacturers follow well. So you can use CV29 to switch between long and short addresses the exact same way in pretty much all DCC decoders.  

There are several CV29 calculators online.  Below an example from the Digitrax site. In my example, I first set the short address in the NCE to be 34. And I set the short address in the DSX to be 12. I set the long address to be 1234 in both decoders. 

Now if I set CV29 in both decoders to a value of 34 they both now respond to the long address 1234:

If I then set CV29 in decoder(s) 1234 to 2, both decoders will now respond to their short addresses, so the NCE becomes 34, and the DSX becomes 12. 


Now I can program other CVs in NCE 34 and DSX 12 separately as needed. And when I'm done, I set CV29 in both 34 and 12 back to a value of 34 so they both now respond to address 1234.

Note that CV29 being 34 vs any other value has some other effects that you can see in the calculator. The important bit for this exercise is that you choose between short and long addresses!   

BTW, if you can get JMRI DecoderPro, this can be a lot easier than using a throttle for programming.



Images (3)
  • mceclip0
  • mceclip1
  • mceclip2

Thanks Pete, I have been looking at the info supplied. I'm not so prideful to admit I am lost!  And l don't want to be. I think the thing I am failing to understand is how do I program one of 2 decoders when they are hard wired together?  With decoder pro, I am reading CV1 = 45 CV17 = 208  CV18 = 255 ( which also are the same values from the calculator ) CV29 = 45   Basic tab shows long address is 4351 and primary is 45 / extended = 4351    If I go to my NCE procab, the only response comes from loc:4351 with control of lights, speed, direction and sound functions on the main.  I have learned ( with much help from the JMRI group ) to program lights/direction/ on the NCE decoder part of this with decoder pro. . I do not have any control of sound items like master volume or able to change horn, etc.  The sound tabs are blank. I sense I am close to a light bulb moment.  Please bear with me.   Many thanks, Bruce in Mount Airy, MD



Well Bruce, as it happens, the confusion is all my fault (not for the first time). 

It's been many years since I did this last, and I left out the vital first step, sorry. To start with you do need to separate the decoders' rail pickup wiring so you can set their separate short addresses and identical long addresses individually on the Programming Track.

Once you have done that, they can be wired together and installed.  Then you can do all your subsequent programming on the Main with your throttle or ideally JMRI DecoderPro, by changing CV29 back and forth as I outlined above.

I hope I didn't ruin your day.      


 Actually Pete you’ve just made my day!  I just could not figure out what I was missing with both the decoders being wired together. I may have found a workaround! As I have studied your replies a lightbulb may have gone off. I have added a new loco with decoder Pro and used a short address of 12  for one decoder and a long address of 1234 following your example. used a short address of 34 with a long address of 1234 for the other decoder.  Selecting address 1234 on the  NCE Pro cab  gives me full control of sound, lights and motion. In decoder pro I seem to be able to  program the sound decoder or the NCE decoder. My issue now seems to be not knowing the exact CV to be able to change things like the horn. I’m assuming this is just because I have a very old sound decoder that is not supported. I cannot find a manual on anyone’s site for a DSX or a DSD decoder,  or a CV list, but I’m still searching.  Thanks,  Bruce in Mount airy Maryland 

Add Reply

OGR Publishing, Inc., 1310 Eastside Centre Ct, Suite 6, Mountain Home, AR 72653
Link copied to your clipboard.