#### Acestuff

##### Newbie level 3

The problem is that these filters have 2 resistors in them; all the information on the internet refers to 1 resistor in the filter! I am using this equation:

Code:

`f_c = 1/(2πRC)`

With the low pass filter:

Intuitively I know that (excuse the poor terminology!) if I used the equation with just the 10k resistor, the cut-off frequency should be lower than calculated with the equation I stated because there is voltage "leaking" through the 100k resistor.

The use of Thevenin's theorem to solve this problem comes to mind. I'd then get a 9.09...kohm resistor in series with the output which would fit into the equation.

However, this means the denominator of the f_c equation is lower thus a higher frequency will be calculated. This goes against my intuition that the frequency should be lower!

I don't know where I'm going wrong so any help you can give would be amazing! The amount of time I've wasted thinking about these problems...

Low Pass:

High Pass:

(Input from top, output to right)