The control tower project 1

The control tower project

Organizing digital components — Part 1

By Ernest H. Robl

A recent discussion in the Reynauld’s Forum led me to take another look at using Roco digital amplifiers as boosters – something I knew I was going to need for my layout. Ultimately, this led me to the construction of the component rack pictured below.


This component rack is not a masterpiece of carpentry by any means, but it looks like it will do its intended job. More detailed descriptions of the parts are provided with illustrations in the second part of this article.

Due to the length of this article, I divided it into two postings. The first describes why I came to the conclusion that I needed this component rack; the second part describes how it was built and how the components in are organized.


While this is probably not the place for a detailed discussion of how digital command control (DCC) for model railroad works, a little background may still be useful for those who are just starting to look at digital operation.

In digital operation, the tracks supply two things to your digital (decoder-equipped) locomotives:

  • Electric current
  • A digital signal that the decoder uses to obtain instructions and then uses to determine how much of the track current is supplied to the motor, lights, etc.

Unlike with analog 2-rail DC operation, where the amount and polarity of the track voltage determines how fast the motor(s) in your locomotive(s) run, and in which direction, with digital DC operation, the track voltage and polarity are constant.

You have a digital control station, which sends both the current and the digital signals to the tracks. However, for reasons too complex to get into here, there are limits as to how much current the main control station can supply to the tracks. So, if you have a large layout and operate many trains (which in digital operation still consume some current event when standing still), you will reach the limits of how much power your control station can supply to the tracks.

The need for boosters

This is where boosters come in.

It’s important to note here that I am using the Roco Multimaus-based control system – though all other digital control systems, including those using three-rail AC power, operate in a similar manner.

In the illustrations with this article, you will notice that I am using both Roco and Fleischmann digital components. The digital components of the current systems of these two brands are functionally identical, and fully compatible. Only the external labels or the colors of the items are different.

With boosters, you divide your layout into booster districts, which are electrically insulated from each other – with insulated rail joiners in both rails at the border points.

Boosters supply their own current – fed by their own transformer or other power supply – to their districts, while relaying the digital signals from the main command station. Trains can travel seamlessly from one booster district into another, continuing to receive the digital commands from the main control station.

The boosters are connected to the main control station with a network cable called a booster bus, the exact configuration of which will vary by manufacturer and control system.

The Roco system

For its Multimaus based system, Roco offers two distinct components:

  • A digital amplifier, which, together with one or more Multimaus and other controllers constitutes the main control station (In the Z21 system, the main Z21 unit is the control station.)
  • Digital boosters

Nominally, you can only use one digital amplifier; and digital amplifiers cannot be used as boosters – because they do not have the correct network connections.

However, the current versions of both the Roco digital amplifiers and boosters actually use the same circuit board, just with different connectors. (This is not true of some earlier versions of these components!)

Discovery of this quickly led to the creation of so-called “Umbau” (conversion) boosters, made from digital amplifiers. Why? Because these amplifiers come with most digital starter sets. As digital start sets provided a very cost-effective means of acquiring both rolling stock and track components, many people ended up purchasing more than one digital start set – and ended up with multiple digital amplifiers.

(For a discussion of digital start sets, see my earlier Blog posting entitled “Christmas in July.”)

I was aware that Roco amplifiers could be transformed into a conversion booster by opening them up and soldering in an additional booster bus connector. This, of course, also involved cutting a new hole into the case of the amplifier for that connector.

But, some research on the Internet showed that you really did not have to do any soldering or cutting to create a conversion booster.

In normal operation, as intended by Roco, boosters are daisy-chained from the main command station, which can be a digital amplifier for Multimaus controllers or a Z21 station. For daisy-chaining, your boosters (including conversion boosters) would need two booster bus ports: One for booster in (from the main control station or previous booster) and another for booster out, to the next booster in the chain.

However, you can connect your boosters a different way: You can purchase a relatively inexpensive booster bus network hub (available on eBay – search under “Roco Fleischmann booster”). With that, your control station is connected to the hub and all boosters are also connected to ports on that hub.

As all digital amplifiers (being used as boosters) already have one booster port, that’s all you need to connect that unit to the network hub.

Important: When a digital amplifier is used as a booster, you cannot connect any control units (Multimaus, Route Control, etc.) directly to that unit. To prevent anything from accidentally being connected to those ports, you may want to put a piece of tape over them.

My project

I had already determined that my future layout would probably need four or five electrical districts (one supplied by the main control station and three or four supplied by boosters). Four boosters is officially the limit set by Roco, though there are work-arounds for using more boosters on extremely large layouts.

I already had two “extra” digital amplifiers, as well as one purpose-built Roco 10765 booster.

So, then the question became whether to distribute the boosters around the layout or to locate them at one central spot. Several factors weighted in favor of a central location:

  • At a central location, it would be easier to power all the components on and off.
  • At a central location, it would be easier to have an overview of the indicator LED lights on all the components to see possible problems.
  • Because of the shape of my planned layout, the wire connections between the boosters and the actual feeder connections to the tracks would not be that long, even if the digital components were centrally located.

There appeared to be only one major drawback for having all the boosters at one central location:

  • There would be a lot of cables – power, component (booster bus), and track connection – to work with at one location.

But that single point appeared manageable and was outweighed by the other reasons for keeping all the boosters at one location.

So, once the decision was made to centrally locate all the boosters, I also concluded that I needed some type of rack for these and their related components.

Recent developments

Roco and Fleischmann are phasing out the current Roco 10764 digital amplifier and Roco 10765 booster units (and their Fleischmann equivalents). The two brands will continue to offer Multimaus controllers, both as an individual item and as a component with some digital starter sets.

However, it appears that for future starter sets with a Multimaus controller, a new amplifier, designated as a “z21 Start” unit will be supplied.

There are still starter sets in the supply pipeline with the 10764 (and the Fleischmann equivalent) amplifier. And, of course these units are also widely available on the used item market.

Please note: Any use of digital components other than as intended and described by the manufacturer, particularly opening them up and soldering in new connections, will void their warranty. Carefully research whether or not you want to do this after considering the risks.

In the second part

In the second part of this article, I’ll tell you about how I built the component rack and about the components in it.


5 Responses to The control tower project 1

  1. Rey P. says:

    Good article Ernest, I learned a few things that I did not know!!

    • Tom Weaver says:


      I appreciated your article because I am new to digital operations and just learning about central control stations (Märklin), boosters, and other components. Your article answered questions in my mind. For example, do I need to segregate track segments serviced by different boosters? Since my digital project is in the concept phase, your article was very helpful.

      Thank you.

  2. Pierre says:

    Hi ! Wow what a big project you got here!

    I have 2 680801 Fleischmann boxes.

    I’d like to connect them to use one of them as a booster. I understood that i only have to link the 2 “booster out” pins together …

    Could you tell me what type of cable should i use ?
    Thank you very much for your answer !

  3. Ernest Robl says:

    Glad you found the post of interest.

    The Fleischmann 680801 is the same as the Roco 10764.

    The cable used to connect amplifiers to boosters is Roco 10757. (You can find shorter third-party versions of this cable on the Internet.)

    Please note all of the following:

    If you use an amplifier as a booster, make sure that the only connections are to the booster port and the track out port — and, of course, the power in port. All other connectors should be covered up.

    I am not sure whether you can (or should) directly connect the two units together without going through a booster hub, as described in my post.

    By using an amplifier as a booster, you are going against Roco/Fleischmann instructions — though plenty of people have apparently done so successfully. You are doing this at your own risk.

    – Ernest

    • Pierre says:

      Many thanks for your answer
      I know that it isnt presented by the manual … well if it works for you it should work for me !
      Thanks you again !

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