It's often recommended to improve the AC gain of a common emitter amplifier by putting a bypass capacitor paralell to Re, thus effectively decreasing the Ze for the signal and increasing the gain.

My question is: Won't this also lower the Z input (AC) for the amplifier? If Ze(AC) is only 100Ω or so, won't that lower Zin(AC) to around 10k (assuming a β of 100)?

 

Hello,

Lowering Ze will lower Zin, that's life.

 

Adding a capacitor across the emitter resistor increases the voltage gain by removing the negative feedback provided by the emitter resistor. Then the distortion becomes extremely high at fairly high levels.

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Uncle $crooge

 

well audioguru sums it up the bypass capacitor is chosen to reduce the i/p impedance at signal levels hence giving more gain but its value should be carefully chosen.its not preffered where you need very good signal.not a popular technique.if you want a large voltage gain use a follower instead else use class b amp.

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I just cant come up with a good one!

 

My calculation of the input impedance of the 2N3904 was double the amount shown on its datasheet. I was wrong and used the much higher DC current gain, hFE instead of the lower AC current gain, hfe.

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Uncle $crooge

 

hI!!!!!!!

do u hav a schematic diagram of Low-Cost Digital Echo/Reverb Microphone Preamplifier?

plssss... give meh a rply about this!!!!!!1

thanks!!!!!!

 

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Torben

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