# Common Emitter Audio Amplifier Question

Discussion in 'Audio' started by kzriwoga, May 28, 2012.

1. ### kzriwoga

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May 28, 2012
I'm tring to build an audio amplifier. I decided to use a basic common emitter amplifier circuit as a starting point and added a speaker to it.

I have some questions about the circuit.

1-) Is 2n2222 ok for this circuit?

Results of DC analysis: Vce = 10.06V and Ic = 1.26mA (I guess, these values will be used for choosing the transistor.)

2-) What's the output voltage of a standart mp3 player? Can it be 300mVp as I read somewhere?

3-) When I assume ß = 150 and input = 300mVp , the output is -2,13Vp . I guess it gives 1w power to speaker. Is there something wrong?

4-) Is connecting speaker parellel to output R ok?

Thank you..

Last edited: May 28, 2012
2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
1) a) probably, b) no

2) a) not sure b) could be (seems reasonable)

3) without a load I guess your voltage swing could be several volts, but with that load, no. You will get nowhere near 1W, more like microwatts.

4) no, not really. It reduces your output impedance from around 12k to around 4 ohms. The voltage swing will be (at most) 9 mV (and your power around 20uW)

3. ### kzriwoga

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May 28, 2012

Last edited: May 28, 2012
4. ### BobK

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Jan 5, 2010
You cannot build a practical power amplifier the way you are trying to do it. You would need something like a 4 Ohm collector resistor and the current flowing when properly biased would be over 1 Amp and be dissapating over 4 Watts in the transistor and over 4 Watts in the resistor even when producing no sound!

You need a push-pull output stage, which has 2 transistors, one to source current and one to sink it.

Is there a reason you do not want to use an IC 1W ampliier, which will be way better than building one out of transistors?

Bob

5. ### CDRIVEHauling 10' pipe on a Trek Shift3

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May 8, 2012
It will probably produce smoke.

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May 8, 2012