Modeltronics Steam Micro Sound Steam Modeltronics Compound Air pump Modeltronics

Railcommand Make Some Noise. Really!

Sound for my model railroad has always been an interest of mine. When I first was looking into command control, it was between Onboard, CTC-80 and CTC-16e. I selected CTC-16e and as soon as Railcommand came out, selected it.

In adding sound to Railcommand, there is really only one rule. The sound must be self-contained. In other words, you cannot transmit the sound “through the rails”. The rails are already being used for the command signal.

Sound modules used to be prototype-sized electronics crammed in a scale-sized dummy locomotive or permanently attached car. Nowadays with surface mount technology and IC’s, sound units can be added to powered units quite easily. Modeltronics are small sound units that can be made compatible with Railcommand. I recently added a Modeltronics steam sound module to a Life-Like Proto 2000 2-8-8-2. The Railcommand MINI receiver, sound unit, air pump unit, power unit and speaker all fit in the tender! However, there is virtually no room to spare.

The Modeltronics instructions state that it is “incompatible” with all command/carrier control systems. This is only partly true. I’ll explain later. The Modeltronics Steam Sound Unit is designed to be powered from an on-board 15-volt battery with the chuff circuit powered from the variable track voltage. Since Railcommand places 18-volt on the rails that we can use, we can omit the battery and add a small power circuit for sound. We’ll wait on the chuff circuit for now. To prevent adding noise to the receiver, I chose to use 9 volts.

I will not attempt to cover specific unit installations but rather how to convert the Modeltronics module for use with Railcommand. Follow the Modeltronics installation manual for specifics for your needs. There are only two modifications to the steam sound unit for use with Railcommand.

I created a small ‘power circuit” that replaces the battery and on/off switch. The power circuit will correct polarity and lower the track voltage to a usable level. In fact, it can be also used to power lighted cars or FREDs, but that is another topic for another day. The power circuit rectifies track power from the rail and regulates it via a small 9v regulator. There are three parts to the power circuit; a small bridge rectifier, a voltage regulator and a filter capacitor.

Why 9v and not the 15v as supplied from the battery? Because 15v introduces noise that affects locomotive and receiver performance. The track voltage is not high enough for a 15v regulator to regulate. I have not had any problems using 9v to power the sound system. I tried both a 12v and a 15v regulator which introduced some noise and gave me undesirable locomotive performance.

I chose to wire the AC input pins of the bridge to pins 4 and 8 of the DCC plug, which is track pickup. This eliminates any excess power through the receiver and it does not interfere with its operation. NOTE: You do not want to place a capacitor on the regulator inputs as you could actually place noise into the command signal giving erratic operation from the receiver to the motor.

NOTE: Be very careful that when you solder leads to pin 4 and pin 8 that they do not short to adjacent pins. Damage will resort.

Below is a schematic of the power circuit. This is the circuit that replaces the Modeltronics battery and on/off switch. All other parts remain the same. The circuit will supply 100mA of power to the sound circuits. It will be ample to power the sound unit which is rated at about 35mA.

The 9v out and GND leads are just like the battery terminals. Using the Modeltronics wiring diagram as supplied in their instruction manual, I wired the module substituting my power circuit for the battery and on/off switch. After hooking it all up and reassembling the tender, I put it on the track and had a nice hiss sound from the blowers and my compound air pumps cycling every four seconds. This was the easy part.

Now for the chuff circuit. Mount the driver switch as instructed in the Modeltronics manual. The changes to the circuit are a little more complicated in wiring but it can be done in an evening. It does not use battery power and seems to be a different circuit all together. The chuff circuit works from track power.

First, I’ll give a little background. As designed, the Modeltronics steam circuit is geared towards working with standard DC systems with variable voltage on the track. The variable voltage controls the chuff volume. On a DC-based system, the voltage on the track would determine a loud chuff or a soft chuff. Since it is too risky to wire the chuff circuit using the motor outputs, I chose a simpler way! (NOTE: Big problems can exist with potential noise generation in the receiver and potential to have the motor connections come in contact with the track power thereby destroying the receiver. The chuff circuit works just fine at a steady volume using Railcommand.)

I settled on regulating the track power again through another small circuit. The diagram shown below contains the original chuff circuit and the modified chuff circuit. The original circuit corrects the track polarity through a bridge and sends the voltage on to the sound circuit and makes the chuff sound. The driver switch on the engine makes and breaks contact as the driver rotates. The back of the driver has insulators to turn the chuff off. That is how the chuff works and makes sound.

What I had to do was drop the voltage down to 9v so the volume matched the hiss and pumps and to clean the potential for noise. Since this is separate from the receiver, I cleaned the voltage a little more by adding a resistor and an input capacitor without any adverse reaction.

Now, one good side-effect. With track power coming in to power the sound circuit via the first circuit, there is a “sneak” circuit in the sound unit. With the tender and the locomotive on the track, the blower and the pumps working, I temporarily clipped the wire from the locomotive switch to either side of the chuff circuit bridge rectifier until I got the chuff sound, thereby completing the circuit. If you’ve already mounted your driver switch, you can swap the pin 4/pin 8 to reverse the track pickups to complete the circuit. I then wired everything up, joined them together and now I have a nice looking (and nice sounding) steam locomotive. One other side-effect is that I tend to run it slower so that I can hear the chuff as it is working. To fast and it sounds like one long chuff that never stops.

The process took a little work but now I have a beautiful articulated steam locomotive that hisses and pumps up air and chuffs when it moves. The working elements are wonderful! Even when I work on my layout, I tend to power up the track and work with the hiss of steam and air pumps working in the background. It’s relaxing and better than music! Now where is that diesel sound module and my SD40T-2?