My Loco "soundscape" audio project finally works!

Thanks to all those of you in the trains.com forums who know about electronics and helped me with suggestions here on everything from how transformers work to calculating resistor values.  Electronics are still a mystery to me.

My goal in this was to have fun with some leftover sound decoders and combine my interest in audio and computers with HO train modelling.  I also wanted to switch from installing sound decoders in my locos ( I have converted quite a few) and create a tunable soundscape of loco audio that could be MU'd to any regular DCC loco.  I was encouraged when I read a post from someone (forgot who, I'm afraid) who said he'd hooked up a decoder in a stationary setup that gave quite a realistic "in the cab" experience.  Although I think what I have got is more like trackside sound. 

The project took 6 months from my early musings to the finished product (with a month off for a holiday overseas).  Half the time was spent learning what I needed, and the other half driving back and forth to the city to get the components.  It didn't help that two parts I used had failed unbeknownst, and delayed me no end trying to puzzle out why I was getting nowhere fast.

In the end this is what works for anybody that cares to know:

I used the suggested Soundtraxx DSX stationary decoder circuit with small audio amps, but no potentiometer.

However, I reversed the transformers because the level was too intense, and the pot had a very small range of effectiveness..either full on or a small partial turn shut off the signal.  No good.

A great benefit of this is that the decodes run very, very coolly.  In fact they don't even warm up.  When connected via the Soundtraxx circuit they ran hot.

As is, the signal leaves the transformers at line level and is then jacked in to the AUX IN of the stereo receiver.

I found that each decoder needs its own transformer.  Combining decoder output in any fashion, either through terminal strips or switches with a common transformer, would result in the signal being dissipated or something.  I am an amateur, so I am not sure.

Also, the six transformers had to be switched through a double pole rotary switch.  When I had them in parallel through a terminal strip the signal was also dissipated.

I had to add another complete audio circuit for each decoder because my Digitrax Zephyr would not recognize the presence of a decoder with the transformer in the way.  I would not be able to alter CVs to MU these decoders with the moving locos....which was the object.  Therefore I inserted 6 DPDT switches.  These shift the signal from the transformers and output, to an internal 8 ohm speaker.  When I need to program the decoder, I must have this switch in the correct position.  This is not a bad thing as it provides another security level against inadvertently powering up two decoders at once and feeding the signal from one back onto another.  To to that I would have to ignore the power LED and throw 4 switches incorrectly.

The small internal speaker also makes a good test circuit when making connections.

I was able to find all the major components amps, speakers etc. in storage around the house, except for the equalizer.  After initial tests I found the audio quality was quite good just through the bookshelf speakers.  But I thought I could make it better with the equalizer by splitting off the low frequencies to some old 12 inch woofers and fine tuning the horns and bells.  The decoder frequencies are not subwoofer level but they certainly can rumble  But the horns and bell become muddied if this is done with just one set of speakers.

The Behringer equalizer was a very good idea (for $75 brand new).  It gives wonderful fine tuning, bringing up the bell and whistle and tuning out a couple of small buzzes and whines that seem to develop from the DCC (although I have not gotten to grounding everything properly).  It also allows me to optimize the setting of each decoder.  The LCs have different properties than the DSXs, for example.

So far I have installed two DSXs, one Soundtraxx DSD LC EMD 1st Generation and one 2nd Generation [the Soundtraxx DSD LCs need resistors to simulate a load on the motor leads or the controller won't recognize them.  I used 100 ohm 1/4 W resistors].  I can't cover all bases, but I have chosen decoders to give a range of size and era of loco, whether it is a switcher or a 6 axle loco moving about.  The LCs actually have a better sound than the DSXs this way, but do not have as many sound features.

I want to experiment with a Digitrax Soundbug and have yet to install a steam decoder.  I haven't decided if I should use a spare Tsunami, or get another DSX.  I had a Soundbug working for all of 2 minutes, then I literally smoked it because I didn't cover the circuit board with tape and had an alligator clip fall across it.

Now the two sets of speakers go up on their brackets in the layout room and the amps and equalizer go on to some shelving beside the control area of the layout. 

Why am I doing all this?  Messing around with the AV equipment was my job before I retired early from teaching.  I enjoy being able to combine this with model railroading.  I guess that's what intrigued me a while back when I discovered model HO trains now made sounds. And with Decoder Pro I can also mess around on the computer with my trains.  And my wife thinks I am just "playing with trains" down in my basement cave.  Hah!  this is serious.  It looks more and more like the interior Cheyenne Mountain down here in my cave.

In the end, I'll just say that those little HO decoders can sure shake the walls when desired.

Next experiment, maybe a wireless camera on the loco and flat screen monitor opposite the command area.....maybe.