Sound Decoder Installation Tips
From My Experience

A sound decoder installation introduces a whole new set of challenges. I'm slowly adding sound decoders and speakers to some of my HO locomotives. Here are some sound decoder installation tips from my experience.

One of the most challenging aspects to a sound decoder installation is where to put the speaker. I have an older Bachmann Spectrum 2-8-0 in which I had installed a silent decoder. I decided this would be a good test for me. 

Bachmann Spectrum 2-8-0 Soundtraxx Tsunami
Decoder Installation

Spectrum 2-8-0 at Underhill North with a
Soundtraxx Tsunami light steam sound decoder installation
Tsunami sound decoder installation


The first thing I did was an Internet search about this locomotive because I had been told that there were wiring issues. The locomotive has two plugs connecting the engine to the tender, a two-prong plug and a four-prong plug. However, the wiring is all red with a couple of black wires and I had no idea which wires connected to the motor and which went to the right and left rails. I knew the motor was isolated because I had already installed a silent decoder using an 8-pin NMRA plug to the existing board.

I was loathe to take the engine apart to follow the wires and tried using a pin in an alligator clip attached to my meter to get a reading through the plugs. This was not very successful.

The next step I took was to check Tony's Train Exchange website for information. I found an old reference in the Decoders and Installations section about installing a DSD150 in a Bachmann Spectrum 2-8-0 or 4-8-2. (I think this was Tony's specific decoder for the original run of Bachmann 2-8-0 locomotives before Bachmann made some changes. This decoder has been discontinued.)

The page I found had a color-coded diagram of the plugs. The small plug has a red and a black wire attached one above the other. The black goes to the left rail pickup and the red wire goes to the right rail pickup. The 4-pin plug has (from right to left) the orange and gray motor wires and the blue common for the lights and the white for the headlight.

Using this as a guide I unsoldered all the wires from the back side of the plugs. Then I confirmed which front and rear wheels on the tender trucks went to the right and left rails. 

Using the diagram as a guide I hard-wired a Soundtraxx Tsunami Light Steam decoder (TSU-1000) to the plugs following the NMRA color-code convention.  The engine does not have a backup light on the tender (yet). 

At this stage I did not connect the speaker wires.  I took the engine to my Lenz programming track to put in the address and to confirm that I didn't have a short. 

I had also bought a PowerPax programming-booster from Tony's Train Xchange. They recommend this because the Tsunami decoders have an inrush current that some systems can't handle. I haven't installed the PowerPax yet. 

My Lenz system accepted the address without trouble. I didn't use my Decoder Pro software to change any other CVs.

i installed the PowerPax before fiddling with the sounds. After confirming that the locomotive would run I went to work on the decoder sound installation. Tony's Train Xchange recommended an 8 ohm mini-oval speaker mounted in a snap fit mini-oval speaker enclosure.

These are made by QSI Solutions. The enclosure is 14 x 25 mm and will fit under the coal load. I had used some two-sided sticky tape to lay the decoder on the central weights on the tender floor after cutting off the prongs that had held the original boards. 

It's necessary to leave room at the end of the decoder for the screw that holds the shell in place. After snapping out the coal load I turned it over and drilled a bunch of tiny holes in the load using my Dremel. I used a #64 drill bit because that was the smallest I had on hand.

 The holes are not noticeable after the coal load is reinstalled. It was also necessary to drill two small holes in the base of the speaker enclosure in order to route the wires from the decoder to the speaker. There wasn't enough clearance for the enclosure at first. I used my X-Acto knife to hack out enough space beneath the coal load to fit the speaker. There's a platform beneath the coal load that also has a weight glued to it.

 I had to remove the weight to make room for the speaker enclosure and then reglued the weight next to the enclosure. The speaker faces up beneath the coal load.

 It would be possible to affix a speaker without an enclosure to the bottom of the coal load and use the hollow shell of the tender for air movement. 

 I didn't try this although I found a photo of this sound decoder installation method in Tony's Picture Gallery under Locos.  The caption is Bachman Spectrum 2-8-0 with Soundtraxx steam. (Note: spelled with one "n").

Speaker Wiring Tips

Several years ago I had installed a Soundtraxx sound decoder in an Athearn A-B combo. I had put an Edgeport Speaker (810086) in the B-unit. I think these speakers were made by Pacific Fast Mail in the early days of sound, long before DCC. The engine kept stopping and the sound would cut out. I don't remember how many times I had the A unit apart trying to locate the problem. I polished all the mating surfaces (this was an old Athearn engine) and rechecked the wiring over and over again. 

Lo and behold, when I was looking for information about the Bachmann sound decoder installation I stumbled on a page by Don Fishman from April, 2006 in the DCC Sound section of Tony's Tips about speakers. In the article was a section on Dual Speaker Wiring and some background on speakers and ohms. While many speakers for our purposes are 8 ohms, some aren't. Newer Digitrax speakers use 32 ohms and many LokSound has 100 ohm speakers.

What I didn't understand was that higher ohm speakers use less current. I began to wonder if the edgeport speakers were rated at lower ohms and were overloading the decoder. After some more digging I found information that Edgeport speakers could be 4 to 6 ohms. I replaced the Edgeport speaker with a 1-inch 8 ohm speaker in a Soundtraxx 1-inch speaker baffle kit using the full chamber, single speaker configuration. Everything now works fine and the 1-inch speaker sounds terrific.

The article also explains that it is possible to wire two speakers in series. Connecting two 8-ohm speakers in series doubles the impedance to 16 ohms. 

The higher impedance won't overload the Tsunami circuit. If you're experiencing problems or are trying to get better sound from your speaker installations, check out Don's article for an explanation of power, watts, impedance and other factors.

There's lots of excellent information on Tony's Train Exchange website. If in doubt, send them an email or give them a call. I did.

Some Extra Tricks

After running the engine for awhile it began to act up by stalling for no good reason. Bill Payne and I took the engine apart to try to find the problem. (Iit eventually turned out to be loose screws on the tender trucks that weren't making good contact.) In the process we damaged the metal fingers on the engine that rub against the back of the drivers to make electrical contact. I managed to source a new underframe from Bachmann. Installing it beneath the cover plate was tricky because of the brake hangers that must be positioned just right. It is easy to squash the tiny pickup fingers. This turned out to be a two-person job with one person holding the two pieces in the aligned position as the other person slowly positioned the metal fingers. We tried both plastic glue and ACC glue to hold the two pieces together while they were reattached to the locomotive but neither glues would work with the slippery plastic. The two pieces kept falling apart. Bill Payne came up with a solution I would never have thought of: a length of thread.

We tied thread around the pieces in three places to hold them together, reinstalled the assembled underframe and cover plate with the two small screws, and then cut the thread and pulled the threads out. This is all easier to do with two people in order to make a tight knot in the threads while the two halves are held together. It is an ingenious solution when glue won't do it.

While I'm at it here's another trick. I don't have a decoder tester. In order to test decoders to see if they still work, I attached the orange and grey leads to an old motor and clipped the red and black leads to my programming track. I didn't bother checking the lights. I used the setup to see if the decoder would play back its address or accept a new address. If I didn't get an error message it meant the decoder was probably OK. I installed an 8-pin harness to make it sort of "plug 'n play". This is a bit of a "rube goldberg" method, especially if you have to remove a hard-wired decoder from a locomotive but it may solve a problem for you if you run into the same issue. I haven't tried this with a sound decoder but it should work if you have a booster for the programming track such as a PowerPax from Tony's Train Xchange.

Tony's Train Xchange is at:  https://tonystrains.com/



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