An Atlas S2 and S4 get sound!

I know it has been a long time since my last post.  I have been busy getting my business going.  The good news is that my business plan is complete and it’s full speed ahead trying to make some cash.

p11203521I did take a break from work this weekend.  I had ordered two MRC 1663 decoders made for Atlas S2’s and S4’s and picked them up yesterday.  I installed one last night and the other one this afternoon.  I took a little more time this afternoon and took a bunch of pictures to show the install.

p11203551The loco I chose for this decoder is the first Atlas S2 (I think) that I bought.  I can’t remember what it was painted for originally but I stripped it and started a paint job on it years ago and never did finish it.  This was one of the first locos I installed a decoder into – long before NCE started producing their replacement decoder made for these locos.  I put a Digitrax somethingorother decoder in it and squeezed it into the cab.  It was a tight fit.  I used the NCE decoders in two other S4’s and it was a much simpler install.

Anyway, back to the MRC decoder…


After I stripped out the old decoder I was left with this.  I test fit the new decoder and, as they say in the instructions, I would have to grind a little off the rear end of the weight to fit the speaker.  Some folks say to just remove the top weight and install the decoder, but I decided to leave it.

p11203591The loco I did last night was a used one I had picked up at a show a couple years ago.  It had an old Lenz decoder in it and the previous owner decided it didn’t need the top weight.  When I put the MRC decoder in it there was nothing to grind so the install went very quickly.  There isn’t a whole lot of extra weight to the top section anyway, so you could just leave it off.

p11203611This photo shows where the clearance problem is.  In order to insert the screw to hold the decoder in place the speaker needs to move about 1/16th inch toward the front of the loco.  I took out my trusty Dremel and a suitable grinding wheel and went to work.  I did this well away from the loco so that there was no way any of the fine material would get into the motor.p11203621

I worked slowly so I wouldn’t take off too much.  I didn’t want it to be a hack job.  It didn’t take long to trim off just enough so that the screw hole lined up perfectly.


This photo show just how much I had to take off.  You can barely notice the indent in the weight, but it was enough.  I was about 10 minutes into the job at this point.

p11203651The next step was to put the weight back into place and add some electric tape on top to insulate it from the bottom of the decoder.  I’m not sure this step is necessary since the bottom of the decoder looks like it is already coated with insulating material, but it says to do this in the instructions and it is better to be safer than sorry later.

p11203671There is a tab on the bottom of the decoder that makes contact with the top of the motor.  This tab is one of the contacts to supply power to the motor and must be bent at an angle to assure good contact.  The other power contact for the motor is made through the screw that attaches the decoder to the locomotive.

p11203691After I put the decoder in place on top of the weight, tightened up the screw, and soldered the pickup wires the installation is complete – Only about 20 – 25 minutes after starting the job.  The only soldering that was required was to attach the 4 pickup wires that bring power from the rails to the decoder.  The solder pads for these wires are a little small but clearly marked and easy to solder to.  The decoder sat up a little on the speaker end, but flexed back down when the shell was installed.  I think the tab to contact the motor on the bottom of the decoder might have been the cause. I then put the locomotive on the programming track to make sure all was well and then put the shell back on.

I use DecoderPro to program all but the address of my locos.  The software makes it very easy to program decoders, especially sound units.  So I fired up my 12 year old laptop that I use for this purpose and explored the decoder to see what it could do.

p11203761As I expected from previous experience with MRC decoders, there are very few speed options.  They are fine if you run the loco by itself, but it is very difficult to speed match locos for consisting.

p11203741I also found that in order to get the loco to just barely start to move at speed step one I had to adjust the start voltage quite high.  Then when I tried to set the top speed I had to bring the max. voltage wayyyy down, but if I brought it too far down the start voltage would mess up.  So, in the end I decided that good slow speed adjustment was more important than a lower top end and set values of 11 for start voltage and 20 for max.

p11203751Another thing I didn’t like about these decoders is the coarse volume adjustment.  Other sound decoders I use have very fine adjustment of volume, but these decoders have only 4 settings – from 0 – 3.  Setting 2 and 3 are way too loud for my liking.  Setting 1 is a little too loud, but livable.

One other thing I didn’t particularly like was that I couldn’t get the decoders to program on the main.  It very tedious trying out various CV settings to see how they affected the decoder – moving the loco from the programming track to the main track several times while making adjustments.

Other than those things it seems like a pretty good decoder, especially if you don’t plan on consisting the loco.  If you do be prepared for a lot of give and very little take.  I’ll likely not put either of these two into a consist, but I might give it a try.

In the end I think the MRC 1663 is worth the money.  It would be difficult to add sound to an Atlas S2 or S4 using most other sound decoders without a lot of work and modifications.




I neglected to mention that on a new install there is a metal screw through the bottom of the frame into the motor.  The NCE ATLS2/S4 decoder includes a nylon screw to replace the metal one to isolate the motor from the frame.  It also includes Kapton tape to be put under the motor to further isolate it from the frame.  The MRC decoder includes neither, but I have read that you can buy nylon screws and that some people have used a small amount of rubber adhesive to secure the bottom of the motor.  In either case, the bottom side of the motor must be isolated from the frame.


12 Responses to “An Atlas S2 and S4 get sound!”

  1. Will says:

    I didn’t realize that ‘they’ now made decoders with integral speakers! I take it though, that these decoders are particular to the S2/S4 and aren’t cross-compatible. Have you installed a regular sound decoder yourself, before?

    They are made to fit an HO Atlas S2/S4, but they might also work in a Proto S2/S4. The sounds are Alco sounds so it might even work, with some modification in other Alco engines. I’m not familiar enough with the particular engine sounds to know if they would be appropriate for other Alco models. But there are a bunch of different horn and bell sounds that you can customize those for particular models. MRC included dynamic brake sounds even though the S series did not have dynamic brakes.

    I have installed two other sound decoder. The first was an old SoundTraxx sound only decoder that I put in a dummy SW1200. It was a messy install. The second was a Loksound Steam decoder that I put in my Proto 0-8-0. I should have got the oval speaker – it would have fit much better than the round one.

    Sound decoders are getting much smaller now. There are several offerings that can even fit into N scale locos, with some modifications. I know Loksound makes some very small ones. It is amazing the sound that can come from those tiny speakers of 1/2″ or less.


  2. Doug says:


    Thanks for the report and pictures.

    Have you tested the decoders on short recovery? Which has been an issue with MRC decoders factory installed in Athearn locos.


    They seem to have a delay built into them so that they do not start up until 15 seconds or so after power is applied. I think this would allow the system to start up and not immediately detect the high in-rush of current to sound equipped locos as a short.


  3. Ed C says:

    Thanks for the quick tutorial. Looks like I will be taking the DCC plunge shortly, ordering my Lenz system next week so I may pick your brain when it comes time to convert the fleet.



    Lenz? Great choice! Anytime you need help just ask. Although I’m sure you won’t need much help. It is Lenz after all.


  4. Dan Watkins says:

    Thanks for the info regarding the installation of the MRC1663. I have an older (20 years or more) Atlas S2 that I want to equip with a decoder/sound combination. From my postings on DCC4EVERYONE, it appears the MRC 1663 will be adequate for me. Your pictures and description will make the installation go much more smoothly for me.

    I’m a little concerned about the volume issue but it sounds like you ended up getting adequate results in the end. This will be my first foray into sound so I won’t be able to judge it by anything else – I’m just looking forward to finally having sound in a unit.


    Dan, thanks for your comment. Sound truly adds a new dimension to model railroading. This is one of the easiest sound decoders I’ve installed, but I haven’t installed many. Just be sure you isolate the bottom of the motor from the frame and you’ll be all right.

    I am a little disappointed that the volume cannot be adjusted lower. I don’t like to be able to hear my locos across the room. It is more realistic to have the volume level low so you can hear a train coming in the distance, it gets louder as it gets closer to you, and then fades off into the distance as it gets farther away. But I think I can live with the lowest volume level.

    Good luck!


  5. Bernie Halloran says:

    I found your S2/S4 MRC install article just what I needed. About two weeks ago, I got three of these 1663s and found the instructions wanting, especially about nylon screws and grinding. These will be my very first sound installs, but it will be a good long time before they run. My old road (MR Oct 06) was sold along with the old house, five years later, I’m ready to start building benchwork again. You noted using Lenz and a Decoder Pro. Lenz got me back into model railroading back in the late 80s, early 90s? I was faced with having to block wire and just didn’t want to do it. Anyhow, thanks a bunch for the tips and I’ll peek into the Bayside and Tidewater more frequently.

    Wow! Thanks for the wonderful comments Bernie! I’m glad I could help.

    The NCE decoders for these locos included everything you need to install then, including Kapton tape and the nylon screw. It’s too bad MRC didn’t think of including those items and I didn’t notice in their instructions anything about isolating the motor. Sorry I didn’t take any pictures of that part of the install but it was already done since both locos had decoders.

    I dug out my Oct. ’06 MR and sure enough, there you are! It was a very nice looking layout! I’ll bet it was hard to see it go. We got started in DCC back in the late ’90’s with the Atlas Commander (made by Lenz). When it was time to upgrade it made sense to go with Lenz since the systems were compatible and we already had a few XPA’s. The addition of a computer interface and DecoderPro have really simplified programming. Do you use DecoderPro?


  6. […] MRC 1663 Decoder For Atlas S2/4’s Ok, so we’ve had some problems with our sound decoders since we installed them a few weeks ago.  If you missed that post – here it is. […]

  7. Chris Ruhl says:

    Hello, Scott

    Thanks for your posts on this topic. I did want to chime in on the issue of isolating the motor from the frame.

    I’m new to DCC, having been a DC operator for 41 years. Honestly, it’s a blessing. I did my research and yes, I read the emphasis on isolating the motor from the frame.

    There is NO mention of this in the MRC instructions. I suspected that this is left out because isolating the motor from the frame isn’t necessary with this decoder. I decided to follow MRC’s instructions exactly as written. I removed the weight but did NOT disturb the motor in any way. I used Kapton tape to cover the weight as mentioned in MRC’s instructions.

    I even installed the 20-ohm resistor that MRC asks to be done in the wiring to my programming track. I wanted to be absolutely sure that I followed all to the letter in case the decoder did blow and I could honestly say to MRC that I carefully and completely followed their directions.

    Conclusion: There is NO need for a plastic screw and tape for motor isolation with this decoder.

    Logically speaking, MRC would not leave out such a critical step. They would be receiving tons of blown decoders from irate modelers.

  8. Chris Ruhl says:

    An additional thought on DCC and motors: My local DCC dealer made it a point to stress that the motor brushes, not necessarily the motor itself, were to be isolated.

    A case in point: After I did the S2, I decided to install a NCE D31SR decoder in a brass United Crown UP 4-8-4. This decoder has enough current and stall current ratings for the old, open frame, five pole motor in this 40-some-year old lokie.

    Brass locomotives often strike fear in the DCC modeler because they are all metal. I didn’t remove the old, five pole motor and didn’t isolate it from the frame — I simply made sure that both open-frame motor brushes were isolated from the locomotive frame. This involved disconnecting the tender wire from one brush and a short jumper from the other brush to the motor frame. Orange went to one brush, gray to the other brush, black and red to the usual places. I was running in a matter of minutes.

    I’d say that locomotive already had the motor isolated from the frame. But that I mean that some locomotives provide power to one or both poles of the motor through connections with the frame. With those locos you must isolate the motor (by that I include the brushes) from its connection to the frame before installing a decoder. This usually requires installing tape over part of the motor so it does not contact the frame.

    Some locos, like the one you are referring to do not use the frame to get power to the motor (brushes). So all you have to do is disconnect the wires from the motor, and install the decoder. Dead simple.

    Thanks for the comment!


  9. Paul Stumbo says:

    Hello Scott – I have the Atlas made in Austria version of this S2. How do I get the shell off so that I can install a decoder?
    I do not have any instructions. If yours is also made in Autria, please help.

    Thanks – Paul

    If it is the same as mine you just pop off the cab (the cab and the rest of the shell are separate pieces). The cab is held on by small tabs on each bottom side. Once it’s off the nose comes off quite easily. Don’t forget to remove the railings first. You might have to gently pry the bottom of the cab on each side with a small jeweler’s screwdriver.

    Good Luck!


  10. Bob says:

    I’ve installed a number of MRC sound decoders. I’ve found that a resistor of about 50 ohms in series with either one of the speaker leads will reduce the sound volume to a reasonable level.

    Perhaps I’ll give that a try! Thanks Bob!


  11. Scott, loved the article. Full of great advise and answers to readers questions. I really like my Atlas S2 and want to go DCC to get sound and found your article by chance. Did you ever get the sound set to your liking? That does concern me as I have a small room for my layout do not want the sound blasting. The only other sound decoder I know of is by QSI but the .75 amp fuse makes it not possible to run on my 20 year old S2.

    I’ve got the sound set to where I can live with it (just slightly on the loud side) but there is still the issue of speed matching for consisting. Since there are no real speed adjustments in the decoder it would have to be consisted with a loco using a different decoder so that one can be adjusted to match the MRC decoder.

    If you do get one and lose sound but not control (the loco will still move) then you have discovered the undocumented, or hard to find if it is there, mute feature. If you turn the lights off and on too fast it will mute the decoder. If it happens just turn the lights off and on quickly and the sound should come back.

    If you have no sound and no loco control (the loco will not move) then the decoder is likely “shut down”. This happens with 3 or 4 presses of function 8. To start it up you must activate any other function – I use F6.

    Good luck in your hunt for sound for your S2. The MRC will work as long as you are aware of its limitations.

    Thanks for visiting!


  12. I did take the plunge and got the decoder.
    Yes it is loud.
    I do not have the software you use and have to use the CV on my NCE system.
    What is the CV number for the master volume?

Leave a Reply