Bachmann's EZ DCC is very limited in what you can do with it. For example, I have read that is supports decoder (locomotive) addresses only up to 9. Control of sounds is probably similarly limited.
Whether you can fit sound into a DDT and the GP40 depends on whether there's any place to put a speaker. For the DDT, I think that's a definite no.
Another factor to consider is whether a locomotive runs well enough to justify conversion to DCC. In many cases it's not worth the cost of a decoder. New locomotives would probably be more advisable.
Your post has probably sparked another food fight, but here goes:
Bachmann EZCommand is a very limited system. It can control engines with addresses between 1 and 9 and can control 1 DC engine on address 10, which is actually 0. It can access functions 1 through 9. It's expandability is VERY limited.
There are a few people in here who like it, but the vast majority do not. There are several competing products that are only a little more expensive, but which can grow with you as you expand your knowledge.
My personal preference is Digitrax. Others in here prefer MRC, Lenz, ESU, NCE, Etc.
Dave
Lackawanna Route of the Phoebe Snow
Let me say first off that I have nothing against the EZ Command system. It's a good system for what it does. It allows you to easily run DCC equipped locos with a minimum of trouble. It controls motor and light functions and can access sound functions 1 through 9 on many sound decoders. The only thing that can be programmed is the locos address. Adresses 1-9 are supported, address 10 can be added if a Bachmann DC controller is connected. While I used an EZ Command for 2 years I would suggest that you save your money and get a good entry level system that can be programmed, such as the Digitrax Zephyr. Others have had good luck with systems from NCE and other makers but I no knowledge about those systems. A word on Bachmann decoders. They are simple 2 function decoders that don't have many of the functions of a simple 2 function Digitrax decoder such as the DZ125 which is what I use in many of my locos including a very heavy pair of SDP40F's.
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