I had this idea today, and I don’t know how it would work, but I discovered that if I connect speaker wires to my track, and then play train sounds from my stereo, that the motors will play the sounds like a speaker. so then I hooked up a speaker to the locomotive pickups and that worked even better. Well, then I tried to run power on the rails at the same time, but it didn’t really work that well and my stereo shut off, probably to save itself. It turned back on when I pressed the power and it still works, but now I’m wondering if there is a way to make it work somehow. If it was possible it might be a neat way to go for people who don’t want to run DCC.
Be careful son, your main amplifier in your stereo wants to see typically 8 ohms for a load. If you short that out or overload the output transistors, “pop goes the weasel”
I would agree on being careful, but still a very interesting experiment. Hmm…
This was done commercially starting in the 1960’s with the PFM sound system 1 followed by the sound system 2. The sounds were generated in a console and sent along the rails to the locomotive. The consoles also contained a throttle. On the sound system 2, you could buy endless cassettes to provide more sounds than the console could generate itself. One definite advantage to todays pushbutton whistles was the whistle on these systems was a lever and you could actually “play” the whistle just like the prototype. There was another system available at the time called McGuffin??? not as sophisticated. Modeltronics also offered a self contained module that provided generic chuffs and airpumps for steamers and a “general” diesel sound for diesels, both of which ran off of a 9v battery.
Sweet, maybe I’ll look into those old things. Obviously I need to be careful of my stereo as well. It seems like all you need to do is have it so the sound waves always operate so that the current driving the train is the dead point, and the waves go slightly above or below that in order to create the sound. I imagine it wouldn’t be hard to solder something up that would allow you to plug in any DC controller and an amplifier. Then I could run my laptop through the amp and play all the sounds from it. I could even play music on it from iTunes, haha.
Check the auction sites. These things are seen there every now and then. Going cheap as well.
Sure, this CAN be done, and was done quite successfully “back in the day”.
The sound signal is a complex form of AC and could be shorted out through the throttle. A choke must be used to pass the DC from the throttle while blocking the sound currentAt the other end, capacitors must be used to keep the DC from burning out the speaker.
Since high power can burn out the voice coil of a small speaker, limit the power output of the amplifier to 2 watts (RMS rating) or 6 watts (EIA peak-to-peak rating).
A bi-polar capacitor 250 mfd. @ 25V needs to be installed in one line input from the amplifier and another of the same in one line of the onboard speaker.
The choke is placed in line of the throttle output and must be a low resistance type, no more than 2 ohms to avoid voltage drop at full throttle.
You also need to protect the amplifier itself. Pulse throttles can send part of their output to the output circuit of the amplifier even through the capacitors that block DC. Protection diodes must be added to the circuitry of the amplifier to prevent damage to the output transistors.
Throttle noise can be another problem. It is difficult to filter out the rectangular wave pulses generated by full performance throttles. At low speeds, the pulses create an annoying rattle in the speaker. More conventional throttles produce a hum, which is a little more tolerable because the frequency isn’t in a range where the speaker is efficient. The rattle is the more persistent of the two problems because the rectangular wave forms contain many high frequency components. You can reduce the rattle and hum by reducing the value of the capacitor in series with the speaker. The limit is about 25 mfd. each. There will be a reduction in low-frequency sound, since the capacitors can’t distinguish between good and bad sound.
Motor noise can also be a problem. A .047 mfd. ceramic disc capacitor across the motor leads will usually cure this.
Using these basic protections, it is possible to
This is conceptually how all the older on-board sound systems work. PFM, PBL, etc. Well not really that simple, because they put a constant 300KHz signal to the rails that carries the sound. They isolate the DC power from the sound by the use of filters and capacitors. The sound is prevented from getting to the motor with a choke. Likewise the DC is filtered from the sound unit and speakers via a capacitor.
So if you really want to pursue this, if you add a capacitor in series between the track and your amplifier, it will keep the DC out of the amplifier. Likewise put the same size capacitor in series with the speaker. The size of the capacitor will determine which frequencies get through. It will also block some of the lower frequencies. A speaker without the capacitor would fry with the DC power applied.
If you really want to pursue this you might consider picking up a cheap stereo from the local 2nd hand store to experiment with. Try two 100uf electrolytic capacitors wired + to + in series to block the DC. OR try to find a Pacific Fast Mail (PFM) locomotive tender module (LTM) on ebay or somewhere. It has directions.
Better yet, just watch for a PFM or PBL sound system to show up on ebay. The PFMs have come down in price greatly. The DCC systems are just now starting to get some of the features that these systems have.
Texas and Mark, thanks a ton. This info really helps. I know enough about electronics to know what you’re talking about, but not enough to have figured that out myself without a couple weeks of research. Now if I can run my dash 9’s around while having them play the Black Eyed Peas hit, My Humps.
Why not do some homework and see if there are any locomotives available you like that have DCC and sound that will run on DC current? A lot of them will.
Well, hmm, it is possible to go do it the other way and run DC power but digital sound?
I had a similar idea a couple months back. What I suggested is using the rails to send a signal from the sound decoder to a sub-woofer under the layout. That would solve the complaint that the decoder small speakers don’t do low frequencies well. At the ime most people agreeed the idea showed promise.
I just found out that the PBL sound system is still available. PBL’s website doesn’t reflect this, but there is a notice mentioning their current availability at www.mikesnarrowgauge.com
If you want to experiment, there were complete circuit diagrams published in Model Railroader and other magazines in the past. Both steam and diesel sound systems were published which use the PFM / PBL principle of operation. By the way, this approach was first developed by Herb Chaudiere, and other fellows in creating a display layout called the Puget Sound. These days, an On30 modeler by the name of Gordon North is the undisputed expert in designing and modifying such systems.
-Ed