Voltage reduction of the digital command control’s supply voltage:

The reduction of voltage can be done by reducing the voltage supply of the digital command control. The maximum track voltage of a digital command control depends on it’s voltage supply.
Unfortunately, some of the digital command controls don’t work at low supply voltage. So it is the best way to ask the manufacturer of the digital command control before purchasing it.

Digital command controls supplied by an AC voltage:

Using the light output of the Märklin Mini Club* transformer instead of the provided transformer of the digital command control reduces the track voltage to the right level.
To supply more than just a few digital locos, it makes sense to use the more powerful transformer from Märklin* (e.g. 6711). This will work pretty good for first tests, but when running many locomotives at the same time the transformer should have enough power (according to the power of the provided transformer of the digital command control) to ensure the supply of the digital command control and the locos.
Similarly it is possible to reduce the transformer’s voltage, placing a series of diodes between the transformer and the digital command control to reduce the track voltage.

This works with the digital command controls of Rautenhaus**, the ROCO Multimouse***, and the ROCO Lokmouse-2*** .

Digital command controls supplied by a DC voltage:

Similarly to the reduction of the AC supply, the voltage reduction of an DC supplied digital command control works, too. Replace the original digital command control power supply by a supply with a 12V DC regulated output voltage. The power supply needs to have at least the same ampacity like the original power supply. Of course, it should have the same connector and it needs to have the same polarity at the connector.

This works with the most digital command controls like the Märklin* Mobile Station 2*, the Trix Mobile Station 1 and 2*, the FCC of D&H**** and MTTM***** and many more.

Voltage Reduction of the Track Voltage:

An easy solution to reduce the track voltage offers the DSR (digital voltage reducer). This device limits the track voltage to protect electronic components as well as motors and bulbs.
The board is inserted between the digital command control output and the track. No modification in the digital command control or other type of transformer is required. The output voltage is free adjustable to 12V.
If the DSR is installed as a part of your layout, any digital command control can be used without minding about the voltage reduction any more.

For more information about the DSR, please refer to AMW:
amw.huebsch.at/produkte/dsr.htm
As well the DSR is available at the 1zu220-shop under the heading AMW:
http://www.1zu220-shop.de

The reduction of voltage can also be done by a series of diodes which have to be installed between the output of the digital command control and the feeder tracks, but it has the disadvantage that the short circuit detection of the digital command control doesn’t work any more. Therefore, the diodes should be the last possibility to reduce the digital track voltage. 

Finally, a very important tip for the startup:

Please remove all capacitors of all feeding tracks of your layout. Please look for feeding tracks, that might be anywhere in your layout, but are not used for feeding.
Of course, this has to be done at your programming track, too. These capacitors disturb the digital signal in such a way, that nothing works correctly!

Any further questions?

Feel free to write me an email and ask your questions.

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*) Märklin, Märklin Mini Club, Trix Mobile station and SelecTRIX are registered trademarks of
   Gebr. Märklin & Cie. GmbH, D-73033 Göppingen (Germany).

**) Rautenhaus is a registered trademark of
   Rautenhaus Modellbahntechnik; Bürgermeister-Mävers-Str. 2a; 28857 Syke (Germany).

***) ROCO Multimouse and ROCO Lokmouse are registered trademarks of
   Modelleisenbahn GmbH, Plainbachstraße 4, A-5101 Bergheim (Austria).

****) Doehler und Haass  is a registered trademark of
   Doehler & Haass GmbH & Co. KG, Eichelhäherstraße 54, D-81249 München (Germany).

*****) MTTM Modellbahn Technik Team München, Wasserturmstraße 30, 85551 Kirchheim