Saturday, June 9, 2018

multi stage amp part 3

If you downloaded the program you should be able to plug in the numbers I used and solve the circuit to receive this screen. I used simplest circuit and E12 resistor, 100 Hz cut off, 9V, 2N2222.

The only change I made was the frequency. At 100 Mhz the program give the same resistor values. C1 and C2 changed to match the frequency requirement.
Here we see the frequency set to 1 GHz. Again the only change is the capacitors. So as I said get the DC bias right and then look at he the AC requirements and be aware the programs will not error check your parameters.

 The 2N2222 datasheet says the high frequency is 250 MHz so our 1 GHz amp will not work! If you run the numbers and change the transistors you will find a lot of transistors will work in our circuit. Changing the E12 resistor selection will give different resistor values from one transistor to another. The E12 pack has the fewest values and the E96 has the most. For general hobby work we should not need 1% resistors.
The other thing to look at here is the input and output Z. It seems overlooking the Z factors is a common error. If I build this circuit and it works well and add a second stage exactly like it the amp will fail to function. Why? I used a 1K input and 50K output. The second stage will overload the first and 'kill' the signal.
So in order to add a stage we must set the input on the second stage to the output of the first (even more). Maybe this is why we see so many one active device circuits?
Next time.

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