DCC Sound question

Model Railroader General Discussion (Model Railroader)
1

I’ve been using DCC since 1996, and Dynatrol since 1987. My layout runs exceptionally well, with only a could stalls through switches during a recent operating session (almost the whole shebang, used car cards, had a train diagram, but still working on the timetable, and writing train orders).

My motive power all has NCE decoders installed, all of them either DA102 or D102s. I don’t yet have any of the silent running decoders.

I oil my track, and I’ve had phenominal results. Prior to my last operating session, the layout didn’t see a train around the complete main for over seven months (I’ve been working on modules for a O scale hi-rail group I also belong to). Ran a train around with absolutely no stalls, and let it spread around a little oil. Had to clean the wheels on my P2K 0-8-0, but other than that, all the motive power ran great.

I haven’t made my switches “DCC friendly”, and I don’t power the frogs through any means. The only place I am having some “temporary” problems are on recently ballasted sections, which I have success working out over time.

If you do a white glove test on my track, it is filthy. But with DCC, it doesn’t seem to mind.

So, now after this background info, here is the DCC sound question.

A friend of mine has left a couple of sound equipped brass locomotives at my house, as he doesn’t have a home HO layout (he is building an appx. 20x30 O scale hi-rail layout in his house). The locomotives are Digitrax DCC decoder equipped, and have Soundtrax sound decoders.

The sound constantly cuts off when it goes through my switches, which I assume is due to intermittent voltage drops. The locomotives do not stall out.

I’d like to start adding sound to my locomotives, especially with all the DCC sound offerings starting to show up, and the price coming down. But, if this is what I have to look forward to, I’ll have to pass. I’m not about to rewire the RR to get these decoders

2

Or you could make certain the sound equipted locomotives are more sure footed. I have an FT ABBA set that has all 32 wheels picking up power. All the units are MUed together. It has never lost electrical contact even on the worst connected track.

Depends on the exact unit, but usually yes. A capacitor has to be soldered into the middle of the sound circuit, which of course voids the manufacturer’s warrantee. This will also have the side effect of increasing the start up current drawn as the capacitor charges. Note this capacitor is NOT simply across the DCC signal portion of the decoder, that could ruin the DCC signal across the entire layour. It is much more complicated than that, and to be absolutely certain of the location one would need a schematic diagram of the decoder.

3

Jerry,
For starters, that Soundtraxx decoder is several years old…positively ancient in technology terms. Other companies have come out with more advanced sound decoders since, but so far these are all in pre-installed locos as in BLI and Atlas’ QSI sound boards.

IIRC, a capacitor could be added to Soundtraxx decoders to help them over bad or dirty track, but I’d have to look at the manual to see what kind and where to wire it.

Modern sound boards from QSI have capacitors in them, which does lead to a large “in rush” current load if you have a lot of them (even when muted, these capacitors all must charge). However, this can be overcome via electronics at the booster by slowing down the power up of the layout.

Coming this fall, Digitrax (www.digitrax.com) is releasing their own brand of sound decoders with uploadable sound. Looking at the advertisements, it looks like there is a capacitor on a plug to the board.

Paul A. Cutler III

Weather Or No Go New Haven

4

I just put a Soundtrax DSX in my 2-8-2 Mike. I installed the capactior as the tech sheet stated. It seems to help but it still misses a beat on ocassion. You really have to go up to about a 2200 uf cap to really get smooth operation. Of course the cap is so large it has trouble fitting in most locos. I think the one Soundtrax rec is about a 47 uf. Very small. I choose a DSX(sound only decoder) rather than a DSD for that very reason. I stuck with a Digitrax decoder for the engine and the DSX for sound. So when the sound skips a beat the engine decoder keeps on going. I also recently put a DSD (sound and engine decoder)in a GP-9 and it stops and starts so much that I quit using it. hopefully the new Digitrax sound decoders will address this problem and I can upgrade my GP-9.
Terry

5

I have an old DSD Sountraxx decoder to which I added the capacitor as the technician recommended. I soldered wires to the PC board and added the capacitor at the end of the wires, where I had room in the engine. You don’t have to solder the capacitor directly to the board to make it work.

As mentioned above, I also have one sound decoder in an MUed diesel set with all wheels picking up power to an internal bus in the engines. Never misses a beat.

Mark C.

6

Thanks for the feedback guys. I’ll have to get the decoder manuals from the owner, and with his permission, perform the mod. Doesn’t sound difficult.

Armed with this new knowledge, I think I’m going to try equipping one of my steam locos.

regards,
Jerry

7

Jerry:

Sound decoders are very sensitive to dead frog turnouts, which it sounds like you have. If the locomotives (brass steamers are the worst offenders) don’t have all wheel pickup, the sound decoder will cut out as the loco passes over a dead frog, even though it doesn’t appear to affect the loco much (flywheels tend to keep the motor turning for a fraction of a second, so the loco will actually coast over the dead frog) but the loss of power to the sound decoder is immediately apparent.

You either need to:

  1. Improve the power pickup on the loco so it’s all wheels on both sides of the loco;
  2. Go to live (powered) frog turnouts;
  3. Install something in the sound decoder to make it less suseptible to intermittent interruptions in current (capacitor or battery).

I’m currently looking into HO scale battery powered wireless DCC adapted from the Airwire900 system put out by CVP. CVP tells me they have modelers who have adapted their system for HO and it works pretty well. For more on Airwire900, see: http://www.cvpusa.com/doc_center/flyer2_june_2005.pdf

8

Let me add that each of these options has their advantages and disadvantages.

Improving loco power pickup.
Depending on how the loco is designed, this could be as simple as soldering a couple extra wires somewhere to completely reworking the frame and wheelsets.

Going to live frog turnouts.
If you have turnouts with isolated metal frogs that are simply unpowered, this would involve soldering a feeder to the metal frog, then adding contacts to the turnout activation with a micro switch to route the frog power based on the direction the turnout is thrown.

If your turnouts have a frog with plastic components, then you’ll have to replace the turnout to get a powered frog.

Live powered frog turnouts will cause more shorts to occur at turnouts, which can be a bad thing if you don’t have robust short management on your DCC layout.

Make sound decoder less suseptible to brief interruptions in track power.
Adding capacitors to your sound decoder will ease this problem but creates problems of its own, such as increasing the inrush current when you power up the layout. If you have enough high-inrush current sound locos on your DCC layout and you get a short, it can cause your booster to refuse to reset after a short because the high inrush power up current fools the booster into thinking the short is still present.

This problem seem most often to occur with QSI locos and Digitrax boosters. Other sound decoders (like Soundtraxx) and non-Digitrax boosters seem more forgiving, allowing more sound-equipped locos on the layout before this threshold is reached.

And of course battery powered wireless DCC in HO is bleading edge stuff, and is barely reaching the practical stage just now. It has it’s own quirks and issues that need to be resolved to make it main-stream practical and affordible.

9

JerryZeman:

YOU HAVE TWO PROLEMS of which you are apparently unaware.

]
IT IS. Stalls occur where there is poor electrical pickup - ATLAS switches, with dead frogs for example.

WRONG! OIL attract’s dirt. Oil my loosen it - move it around, but it will also coat wheet’s with ‘gunk’…

YES.

  1. Non-conducting frog’s;
  2. Oily track