Saturday, June 9, 2018

bypassing the emitter resistor

The amp with a gain of 30.  As I said before get the DC set and then look at the AC. The amp was designed for a DC gain of 30. The emitter resister is producing degenerative feed back. It sets the DC bias between the emitter and base and reduces the AC gain. Let's look at the effect of bypassing the resistor.
I bypassed the resistor with the same value we used on the output coupling. The gain went from under 30 to  a little over. Let's try a larger cap.
Now the gain went from 30 to 50. What should the bypass be? Remember the rule of thumb is to set the values with a 10 to 1 ratio. The value will depend on the frequency. Xc should be 1/10 of the emitter resistor at the lowest frequency we want to amplify.
So load an amp and try some different values to see the effect.

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