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How to disable or filter out the constant 3 VAC ...

How to disable or filter out the constant 3 VAC lighting supply on track output terminals of MRC sound / power / lighting 9000 power supply for model train operation?

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A 60Hz filter of some type (presuming you're in the US). How much do you need to reduce the AC component? Is it actually causing you some kind of problem?


I take it that you wish to apply 0-12 VDC to your tracks as with most model train layouts.

Here is the circuot that should smooth out your DC.  It is called a Pi-filter because of its resemblance to the Greek letter, Pi.

Stack five or six of these circuits in series and your current will be virtually flat DC.

Capacitor input filter.svg

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Actually, you could also use a "voltage clamper" that shunts voltages above or below any preset limit to ground or neutral.  These circuits are available at any HAM fair, Rado Shack, or CED outlet.  They use a high-low bipass Selenium gate to set whatever voltage and current you wish to deliver.

You will find three rheostats on the older models: high bias, low bias, and neutral bus voltage.  Newer models from Fluke have a digital readout and are utterly reliable.

Since you are dealing with 12 VDC and miliamperes, opt for the lowest power system to get the greatest sensitivity at the most reasonable cost.

Good luck!

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