Car Stereo AUX In – Low Pass Filter

Low pass filter from WikipediaThe AUX in Jack I added to my car stereo works great with one exception, when the CD player isn’t playing you can hear static, or whatever the radio is tuned to.

I’m not the only one with this problem, but I’m having trouble finding the other sites…
What I want is to allow the voltage from the RF module to the AMP, without the Audio signal making it to the AMP. I want a low pass filter.

I started with an article on Low-pass filters on Wikipedia. The human hearing range is about 20Hz to about 20,000Hz. I want signals lower than 20Hz to pass and higher frequencies blocked. The Wikipedia article gives a formula, but not the units for the calculation.

I found this website, which I used to calculate values of 150 Ohms and 47,000 nano Farads.

I grew up working with micro Farads, not nano Farads, so I did a little bit of searching and turned up this webpage, which indicates that a nano Farad is 1/1000th of a micro Farad. So 47,000 nano Farads (nF) is 47 micro Farads (uF).

150 Ohms and 47 uF are pretty standard values and should be easy to find. I should only need one resistor and one capacitor, per channel, making this an extremely easy project. Once the filter is made, I’ll post the results

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