You still have a big problem, the total base resistance, that is the value of the 2 resistors R1 and R2 in parallel with each other, should be around 10 times your emitter resistance.
You need to either increase your emitter resistor (recommended) or decrease the base resistors to fit this criteria.
Remember where I said the transistor Base loading is negligable (β X Re)? With the emitter resistor so low it isn't negligable, it is equivalent to a 500Ω in parallel with R2, 1.2KΩ, assuming the transistors β is 50. See what I mean?
What are you trying to accomplish with your design? This sets the design criteria. You keep jumping all over the place with your values, instead of tweaking it. This creates a moving target, it is hard to state anything with certainty, conditions that were negligable with one layout become major on the next.
So lets go through the DC analysis on your latest design.
R1 = 12KΩ, R2 = 1.2KΩ, R3 = 3.9KΩ, R4 = 10Ω, Vcc = 12V, β = 50
Base to Ground Resistance = 353Ω
Base Voltage = 0.34V
At this point I'm stopping because you don't have enough voltage on the base to reliably turn the transistor on, for it to conduct. It isn't in a predictable state anymore. You've gone from saturated to barely turned on.
Gain = 390, Given the transistor has a max gain of 50 this doesn't work either.
The design formula for a basic transistor amp with no R2 and R4 are different. There the transistor Beta (β) rules.
You need to either increase your emitter resistor (recommended) or decrease the base resistors to fit this criteria.
Remember where I said the transistor Base loading is negligable (β X Re)? With the emitter resistor so low it isn't negligable, it is equivalent to a 500Ω in parallel with R2, 1.2KΩ, assuming the transistors β is 50. See what I mean?
What are you trying to accomplish with your design? This sets the design criteria. You keep jumping all over the place with your values, instead of tweaking it. This creates a moving target, it is hard to state anything with certainty, conditions that were negligable with one layout become major on the next.
So lets go through the DC analysis on your latest design.
R1 = 12KΩ, R2 = 1.2KΩ, R3 = 3.9KΩ, R4 = 10Ω, Vcc = 12V, β = 50
Base to Ground Resistance = 353Ω
Base Voltage = 0.34V
At this point I'm stopping because you don't have enough voltage on the base to reliably turn the transistor on, for it to conduct. It isn't in a predictable state anymore. You've gone from saturated to barely turned on.
Gain = 390, Given the transistor has a max gain of 50 this doesn't work either.
The design formula for a basic transistor amp with no R2 and R4 are different. There the transistor Beta (β) rules.
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