# Cut-off or Corner Frequency

#### kaname08

Joined Sep 22, 2010
37
HI everyone, i really really need your help guys, we are about to do a small signal amplifier, but i need to know what coupling and bypass capacitor to use,so in order for me to solve it i need to know the corner or cut-off frequency to be used base on this formula :

Ce2 = 1/(2*pi * FL * Xce2)

pls help me guys,how will i get the frequency??,,,,

#### Audioguru

Joined Dec 20, 2007
11,248
One capacitor in the signal circuit reduces the output -3dB (x 0.707) which is called the cutoff frequency. Two capacitors (an input capacitor and an output capacitor) cause a reduction of -6dB so their values must be doubled for the entire amplifier to have the required low cutoff frequency.
The formula for frequency is 1/2 x pi x RC.

#### crutschow

Joined Mar 14, 2008
34,032
...............
The formula for frequency is 1/2 x pi x RC.
To clarify, that should be 1/(2 x pi x RC).

#### kaname08

Joined Sep 22, 2010
37
but i still dont have a Capacitance and where will i get this resistor??

#### Audioguru

Joined Dec 20, 2007
11,248
You use simple arithmatic to calculate the resistor and capacitor values. Then you buy them.