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 Bachman Doodlebug -adding sound
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Engine Wiper

Posted - 04/22/2011 :  1:22:35 PM  Show Profile  Reply with Quote
Be warned: I am a novice at installing decoders!
Not a stranger to DCC, just installing decoders...

OK, I've been looking around the web for a few weeks, seen advice here and there, but nothing deffinitive that answers my questions.

Last week I received a new Spectrum Doodlebug, DCC-equipped for lights and locomotion.
I want to add sound. Who doesn't?

PLEASE point me in the right direction- do I need to out-and-out replace the existing decoder? Can I add a sound-only decoder?
Should I be looking at N-scale decoders/speakers due to the space limitation?

Country: USA | Posts: 123


Posted - 04/23/2011 :  09:44:43 AM  Show Profile  Reply with Quote
Hi Steve, welcome to the crew.
Soundtraxx has the TSU 750 (Although there are others to choose from) which is a gas driven engine and sounds, in my opinion, more like a Doodlebug motor/generator set. It is also very small in size, and the forward baggage compartment has enough room to mount a speaker. I would baffle the speaker and drill a number of small holes in the floor to help direct the sound out of the shell. The hardest part is getting the shell off the frame. Use a thin screwdriver and then place toothpicks between the shell and frame in about four places on the ends and the shell will lift off easily.
Also, for more reading info, Model Railroader on August 1, 2004 in the DCC section has an article that tackles this project and they explain how to install a decoder in a Bachmann gas-electric. The gas-electric (doodlebug) is a great model. Unfortunately, despite being DCC-ready, converting the Bachmann unit to Sound DCC can be a bit tricky. Though the model has plenty of room for an N scale decoder, the wiring used on a standard medium (HO) sound decoder plug stands too tall when plugged into the gas-electric's DCC socket, keeping the roof from fitting back on properly.
I found CVP Products (www.cvpusa.com) makes a special plug that you use in small spaces. It plugs into the DCC ready spot, and then you wire in your decoder of choice into it.
Unlike a standard plug, CVP’s is wired from underneath, leaving no wires above to interfere with the doodlebugs roof. To add the CVP plug, only some basic soldering is required. See picture below. The pins and wires are now on the same side of the board. I hope this makes sense to you.

Edited by - desertdrover on 04/23/2011 10:34:05 AM

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Posted - 04/23/2011 :  10:42:55 AM  Show Profile  Reply with Quote
You might consider an Exciter instead of a speaker, like Bachmann is using in the new Porter engines.

There's been some discussion elsewhere on this but I can't find it right now.
Certainly would take less room and be easier to install.

Dave Mason
D&G RR (Dunstead & Granford) in On30
“Those who would give up essential liberty to purchase a little temporary safety, deserve neither liberty nor safety.”~Benjamin Franklin
The 2nd Amendment, America’s 1st Homeland Security

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Engine Wiper

Posted - 04/23/2011 :  12:21:19 PM  Show Profile  Reply with Quote
There is info for this on the 'Net, I have found it the past with Google searches. Just never kept the links.
Tsunami and LokSound will work.
Also do a You Tube search.

Soundtraxx also has the TSU 750 which is a gas driven engine and sounds, in my opinion, more like a Doodlebug motor/generator set. It is also very small and I believe that the baggage compartment has enough room to mount the speaker. I would baffle the speaker and drill a number of small holes in the floor to help direct the sound out of the shell. The hardest part may be getting the shell off the frame. I used a thin screwdriver and then placed toothpicks between the shell and frame in about four places on the ends and the shell lifted off quite easily.

Just in case, you might be interested in the below links.

I do not know if Bachmann has solved the issue in the first link.


Usually the below link is needed.


The stall current is, 0.6 amps. Max run amps is 0.2 amps. Many use the 1000 Tsunami. A Tsunami Micro,750, should work fine. Less cost than the LokSOund.
The Galloping Goose is what many are using.


They usually used a Winton Distillate Engine until the 1940's and switched to a diesel. I think some use the Emd 567 sound for that era.



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Engine Wiper

Posted - 04/24/2011 :  06:14:13 AM  Show Profile  Reply with Quote
Thanks everyone, I believe you've all answered my questions. Replacing the existing decoder then is the way to go, and I have no problem with that. I have taken the shell off to re-paint/decal it, and looked at the connection because I had seen that webpage about Bachmann's schematic, only thing is I can't remember if it was fixed or not! Too impatient to get it looking pretty, the shell is now back on. Taking it off wasn't all that hard, in fact I took the time to lube and grease it up some, to maybe ease the noise it's known for. When I put the shell back on, one of the sides doesn't perfectly snap into place (which bugs me but you can't tell visually unless you turn it upsidedown to look) but alot of the noise is now gone! I've seen mentioned that the sides did have something to do with the noise and it's true.
The exciter sounds like a good option being 1-1/4" diameter. Have to look into that some more, thanks for the tip!

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Engine Wiper

Posted - 12/27/2011 :  7:51:34 PM  Show Profile  Reply with Quote
Reviving an old thread for an update or two.
I've quieted the bug about as much as I can. Anyone stumbling onto this looking for the same noise issues problem can maybe benefit. The link above from girr.org was extremely helpful, especially in noise-reduction, and I'm kinda basing my sound install on his, with a speaker over the driver's compartment pointing downwards out the drive truck open area. (I'm very very tempted to place a second speaker under the body, hidden in a fabricated tool-box shape, but we'll see how this goes first.) My tabs from the pcb board are real tight, the motor is seated properly, everything has been greased nicely (but I added some after taking the cover off the drive truck). All the gears are O.K. I glued all the window glazing down as best I could using canopy glue squirted around the edges after gently prying them up a bit from the inside, using the testors stuff that won't fog clear plastic. It isn't a perfect job as the next couple of times I pried that tricky shell off some came loose again, but the areas near the motor are in fact nice and snug. I've lived with that for several months, but today got a wild hair and decided to really do things up. I have some Ace hardware foam double-sided tape, the kind you use around windows. I experimented with it under my track/cork for sound deadening (and really not all that impressed with it in that usage), but I cut some in about a 1/2 inch strip and placed it onto the shell right under the baggage windows. The tape is maybe 3 inches wide, so I trimmed it to make it fit corresponding to the notched area on the body frame (right where the motor is if you look downwards at it with the roof off- that's how I lined it up before re-installing the shell). It's like they notched it that for this purpose. This tape is too thick, maybe 1/4 inch, but by sticking it onto the shell, leaving the backing on (so it won't stick to the motor itself and to act as 'lubrication' for the following-) then pinching it to make it thinner and quickly putting the shell on, it is VERY nice and snug. I've noticed a deffinate reduction it any vibration. This tape, when pinched in towards the shell like this, gives you maybe 10 seconds of time before it re-expands to its original thickness, but maybe it would just slide on with that tape-backing anyways. I'd considered putting some over the motor to prevent any direct vibration onto the pcb board (a VERY tight fit!) but without it I think its good 'nuff. Now with the shell FIRMLY on and the roof on also, I can stand back and from about 5 feet can't hear it unless it's in a tunnel-type area. I'd said before that my shell sides bowed outwards just a hair, noticeable only to me when holding the loco upsidedown, but now I've realized it wasn't pushed all the way 'down' and it's snug as a bug is ever gonna be in a rug. Turns out part of the cow-catcher was interfering with a proper seating, so consider taking that off till done with shell-work.
The reason I revive this thread is my new decoder is on the way. Prep-work and measurements were being done over the Xmas holiday for a speaker and 'homework'. I was all set to go with a Soundtraxx TSU-750, but at the last minute decided on the TSU-1000. Bigger, a bit cheaper, but the real reason was to add a reverse light and probably marker lights. Can't do that with the -750, at least using FX1 and FX2. I thought "you'll regret it later if you don't...", and that voice in my head is usually correct :)

Older photos from the 30's-40's show lantern-style marker lights but some pics from the 50's on up to recent times show none. Prototyping the 50's I removed them (they looked a bit goofy with a big white paint blob on them anyways) but may add Tomar working ones or make my own flush-mounted ones with LEDs in a ring. I've got the Tomar adlake lights on my parlor car and they look awesome, but toned-down a bit with a bit of grimy black over the jewels. Looking at those pictures again, I kept noticing a sun sheild on the driver's front and side- windows, so added some with small styrene, carefully beveled on 3 sides to make it look the correct thickness to scale. Glued on with CA glue, carefull to not get too close to the clear window.

I know, "it didn't happen unless their are pictures".
Those will be forthcoming, before and after pics too.

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Engine Wiper

Posted - 01/23/2012 :  7:07:14 PM  Show Profile  Reply with Quote
Okay, solder day is here. Remember, what I am escentially doing ia a decoder swap from the 'bug's stock decoder to a Tsunami TSU-1000 and adding speakers and a reverse light. Today doing some last minute refresher reading and looking things over, I notice the stock decoder goes to a pcb board/plug that has two resistors(?) going from pin 2 to pin 3 as a trace on the reverse side. Pin 2 on this is a yellow wire of couse, and pin 3 isn't used, but I can't understand why there would be resistors there, since the 'bug doesn't have a reverse light. Can anyone shed some light on that? I wouldn't think I'd have to connect my Tsunami to that little pcb board, but I better ask.
Also, and this is perplexing me a bit and cannot find anything on the web about it- the blue and yellow wires! All diagrams show running them to the lights (LEDs) when converting a non-DCC ready loco, but mine IS DCC already, so I run the wires out to the LED (blue to anode, yellow to cathode w/ resistor of course) then return them back to the plug (pins 2 and 7), correct?
FYI, the headlight (white wire) is attached to the main pcb board and is all done by trace connections, so I couldn't use that as a reference.
Thanks in advance!

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Posted - 01/23/2012 :  9:09:32 PM  Show Profile  Reply with Quote
There is a little more than just adding DCC to a Bachmann Doodlebug as Rich (richg1998) pointed out above. This issue has to be corrected first. http://home.roadrunner.com/~mrwithdcc/doodleb.html Also, if you have Model Railroader magazines look in the DCC Corner section of the August 2004 page #98 and it will show you how to install a decoder into a Bachmann Doodlebug. And those resistors you talked about are two diodes, and they will have to be removed.

Edited by - desertdrover on 01/24/2012 09:13:07 AM

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Posted - 01/24/2012 :  01:10:50 AM  Show Profile  Visit nhguy's Homepage  Send nhguy a Yahoo! Message  Reply with Quote
I've done several Bachmann engines. To tell you the truth it is easier to just dispose of the Bachmann board and hard wire in the Soundtraxx decoder. Those resistors and caps do have a bearing on how the locomotive operates, especially at slow speed. I have done a few engines and I always end up yanking out the Bachmann electronics board.

Just mark or map your wiring and your should be fine. There are pads where you can solder wires for the function controls.


Bill Shanaman
New Haven RR
Hartford Division
in Colorado.

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Posted - 01/24/2012 :  09:43:06 AM  Show Profile  Reply with Quote
For the circuit board modifications, although you can simply pull the dummy plug from the DCC socket and add the decoder after the problem fix first, you may want to make a few modifications to the lighting circuit board. I reworked the wiring so I could control the passenger compartment lights (using function Fl on the decoder) separately from the headlight, as shown in photo I posted in last post. (The extended white and black wires for interior lighting). Shown in that picture.
I hooked up my doodlebugs to run together. The headlight is on in whatever direction it is going at the time. When I did mine, I installed two Digitrax DZ143 decoders for power in each unit, and a Soundtraxx DSX ( sound only) decoder into one of the units passenger section between the seats and blacked out from view with black plastic walls in the center aisle. I followed the article from the Model Railroader as far as hooking up the decoder to the Bachmann circuit boards.

An NCE decoder N12SR in the article installation was used. You can still make it a sound decoder by following their instructions for hookup.

Edited by - desertdrover on 01/24/2012 10:06:41 AM

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Engine Wiper

Posted - 01/24/2012 :  3:15:43 PM  Show Profile  Reply with Quote
Thanks for the quick repiles, but what you've told me is kinda the same as what I keep running into in my own searches. I have no dummy plug, and I have no issue with the 'cut the green wire/trace' because it already has a stock decoder. My board has an LED for the headlight, and the underside has 2 tiny rectangular LEDS soldered-in on traces for the passenger compartment lighting (In other words, I'm not too keen on removing the board and hardwiring it, although it would give my passengers more head-room, so it is an option).
My board looks nothing like all the other images I usually see. Here it is, and notes about what I am referring to:

As you see, the mini-board is actually the plug that I was going to replace with a proper NMRA 8-pin plug for the Tsunami, but notisced those resistors/capacitors.
Does this help??

Edited by - Ironhand_13 on 01/24/2012 3:16:57 PM

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Posted - 01/24/2012 :  3:35:50 PM  Show Profile  Visit simon1966's Homepage  Reply with Quote
So what you have there is a stock 8 pin socket. The "mini board" gives pause for thought. Hard to tell from the photo, but it looks to me as if they may be resistors on the miniboard. If so they could be the in-line resistors needed for the LED's. This would be quite an unusual situation. A better close up of the top and bottom of the mini board would help.

There seem to be many iterations of this beast. Mine has no 8 pin plug so was a hard wire job.

Edited by - simon1966 on 01/24/2012 3:42:01 PM

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Posted - 01/24/2012 :  5:51:58 PM  Show Profile  Reply with Quote
I am at a loss here. Assuming you did buy this as a factory installed decoder Doodlebug, it would be the first I have heard of it. As far as I knew, Bachmann Spectrum never had a decoder in them. Maybe change their circut boards, yes, but decoder installed is a new one for me. So, I can't offer any help or advice now.
I know Simon is good at getting to the bottom of these type things though.

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Posted - 01/24/2012 :  6:03:37 PM  Show Profile  Visit simon1966's Homepage  Reply with Quote
Louis, it would appear that it is factory installed, the latest ones are being offered with DCC, so this is certainly a new light board that does not seem to be showing up on any web searches.

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Engine Wiper

Posted - 01/24/2012 :  6:35:29 PM  Show Profile  Reply with Quote
The decoder is marked Bachmann item no. 44915, and as I stated earlier, this unit is less than a year old. All functions are stock, no remapping or anything. The bug has internal lghting and a headlight, both can be turned off with function 0, and both are dimmable with function 1. Only the headlight turns off in reverse direction, while the passenger compartment remains on. I will add that when the headlight is turned off, the passenger compartment gets a bit brighter.
If you look at these pics, you'll see what I said earlier about the trace from these resistors(?) goes from the yellow wire (pin 2) to the un-wired pin 3.

So how's that grab ya? You think I should just ignore this mini-board and wire up my Tsunami to a regular pin, or splice my wires to this?

Also still wondering about wiring up blue and yellow wires- tap into them for my new reverse light, and return them to their respective pins?

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Posted - 01/24/2012 :  6:50:23 PM  Show Profile  Visit simon1966's Homepage  Reply with Quote
Hmm, well here is my guess. The resistors on the miniboard are for the internal lights in the passenger compartment and that this is being fed off the yellow lead (rear light)

I would not be surprised that if you plug the Tsunami via an 8 pin plug that the internal lights may stop working. IN which case you would have to figure out a way of tapping into the tracks for them. I have to say that if this was my install I would hard wire and get rid of the spurious electronics on the stock light board.

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