# Common emitter amplifier design

#### Exjay

Joined Nov 19, 2015
99
I was trying to design an audio amplifier using the common emitter configuration. So I surfed the web for circuit. My calculations gave me an R1, R2,Rc and Re are respectively 4.7kohms, 1kohms, 56kohms and 12kohms. I don't know how to calculate the values of the coupling and bypass capacitor for the range of audio frequency. Please easy on me as am a beginner in electronics

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#### BobTPH

Joined Jun 5, 2013
5,762
You calculate the capacitors based on the the load (for the output capacitor) and the input impedance for the input capacitor. You want an RC filter with a corner lower than the lowest frequency you want to amplify. If you did the calculations, there should be a formula for the input impedance, which will depend on the biasing resistors, the emitter resistor and the beta of the transistor.

I cannot read your posted photo, when I click it, I get a very unreadable gran on gray enlargement.

Bob

#### Exjay

Joined Nov 19, 2015
99
You calculate the capacitors based on the the load (for the output capacitor) and the input impedance for the input capacitor. You want an RC filter with a corner lower than the lowest frequency you want to amplify. If you did the calculations, there should be a formula for the input impedance, which will depend on the biasing resistors, the emitter resistor and the beta of the transistor.

I cannot read your posted photo, when I click it, I get a very unreadable gran on gray enlargement.

Bob
audio frequency are between 20Hz-20kHz, is 20Hz my lower frequency? Again how will I calculate the output capacitor

#### dl324

Joined Mar 30, 2015
15,113
You want the capacitor impedance at 20Hz to be significantly smaller than the load impedance.

#### Exjay

Joined Nov 19, 2015
99
This is my new modification

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