Wall Adapter Power Line Hum Filter


IMG_20151129_153126I have been struggling with the horrible hum that gets injected into my projects. So I decided to do something about it. Demonstrated here is a simple piece of shop gear that filters and regulates a 12 VDC to 9 VDC  power for my Audio projects. This would be very good for SDR radios that work off Wall Adapters.


IMG_20151201_141552_editThe schematic is simple enough and is the typical LM317 adjustable regulator. Preceding this regulator is a Filter capacitor and a resistor series white LED.

Diode upper prevents 470uF from discharging thru the IC during an input short circuit. Diode right, protects against  discharge through the IC during an output short circuit. Filtering post regulation is done with the 470uF capacitor and final smoothing with the 0.1uF Mica capacitor. Power comes from the wall adapter and when you plug it in it’s on and doing it’s job. Plug this into a patch power cable and into your guitar pedal or even your stereo headphones amp, or perhaps any device that needs a clean source of DC from a wall adapter.

IMG_20151201_140855_editAfter sketching the chassis to scale I arranged the components in the diagram but failed to take into account the pin arrangements for the LM317 and I had a bit of trouble later when the legs of the regulator were out of order. This should be corrected on your circuit if you build one.

IMG_20151129_150144I used pre-drilled circuit board that had copper on one side. After placing and testing locations for components, I etched the board normally and then added components in the proper locations. Also in the chassis, installed are input and output jacks and the LED hood.




IMG_20151129_150205Component side of the board, with a makeshift heatsink on the regulator needed a bit of size adjustment to get to fit in the case






IMG_20151129_150259Board placed in the chassis for trial fit.







IMG_20151129_153013Completed wiring and black tape insulators to the bottom of the board and inside of the chassis.

Inside of the lid was also taped to keep the heatsink from grounding.




Hum Be Gone… it worked right off the bat. I had a bit of adjustment to the variable resistor, but that was minor. Plug in your wall adapter and then plug into the amplifier after the hum filter and it’s dead quiet. So this is a really good tool as I can use it with my headphone amp and my guitar pedal projects.






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