I've been trying to build a two stage amplifier with transistors.
I've made a one-stage amplifier and it works as expected (I'm using GNUCAP and gEDA), when I then try to stick an additional stage onto the output of the first stage, I get distortion.
My idea was to have a resistor on the emitter with a capacitor in parallel, so the AC would be amplified, but the DC would have a gain of only 1. This worked fine with the first stage.
The second stage, with the transistor base connected to the output of the first stage, has an identical setup.
However, the second I plug the second stage in, when I look at the base voltage, instead of getting a nice sine wave (thats what i've been testing it with), I get a weird stepped graph. I'll try and get a picture.
Here is my circuit:
Note, there is normally a capacitor of 9 nF on the second stage with a 4.5k resistor in parallel (instead of the 1k) , just my last test was to see what happened if I removed it.
The base output looks like this:
My thoughts is that it good be input and output resistance, but I'm not sure.
I've also tried putting in a resistor in between the base of Q2 and the collector of Q1, with no beneficial effect. I only did it because I've seen it in other two stage amplifiers, but I have no idea why they did it!
Any help would be much appreciated, I've been pulling my hair out for over a day now!
NOTE: R3 is meant to be 4.5k... whoops! I'll fix that up soon.
I've made a one-stage amplifier and it works as expected (I'm using GNUCAP and gEDA), when I then try to stick an additional stage onto the output of the first stage, I get distortion.
My idea was to have a resistor on the emitter with a capacitor in parallel, so the AC would be amplified, but the DC would have a gain of only 1. This worked fine with the first stage.
The second stage, with the transistor base connected to the output of the first stage, has an identical setup.
However, the second I plug the second stage in, when I look at the base voltage, instead of getting a nice sine wave (thats what i've been testing it with), I get a weird stepped graph. I'll try and get a picture.
Here is my circuit:
Note, there is normally a capacitor of 9 nF on the second stage with a 4.5k resistor in parallel (instead of the 1k) , just my last test was to see what happened if I removed it.
The base output looks like this:
My thoughts is that it good be input and output resistance, but I'm not sure.
I've also tried putting in a resistor in between the base of Q2 and the collector of Q1, with no beneficial effect. I only did it because I've seen it in other two stage amplifiers, but I have no idea why they did it!
Any help would be much appreciated, I've been pulling my hair out for over a day now!
NOTE: R3 is meant to be 4.5k... whoops! I'll fix that up soon.
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