R3, C4 positive feedback or negative feedback?

 

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Two inversions make it clear that this is a positive feedback, but due to shifts in the internal capacitances of the transistors, it can already be negative?

 

Two inversions make it clear that this is a positive feedback, but due to shifts in the internal capacitances of the transistors, it can already be negative?

Note that the feedback is connected via R3 to the emitter, not the base of VT1. What difference, if any, will it make to the feedback?

 

But after all, the voltage only drops on R3 and not the inversion of the signal!?

 

Try looking at it a different way:
What happens if the signal on the input goes more positive? The collector of VT1 will go more negative because more collector current will flow through R1. That same current will flow through R2, so what happens to the emitter? What happens to the base to emitter potential when the AC feedback through C3/R4 to the emitter goes more positive, and how does that effect the collector current?
There is also a DC feedback path through R4. Did you take that into account? Is it positive or negative feedback?

 

If the input signal becomes more positive, the collector current will increase, and the voltage drop on R2 will increase, this will close the base-emitter junction and the collector current will decrease. With alternating current, the same thing will happen when it passes through R2, will it close the base-emitter junction?

 

If the input signal becomes more positive, the collector current will increase, and the voltage drop on R2 will increase, this will close the base-emitter junction and the collector current will decrease. With alternating current, the same thing will happen when it passes through R2, will it close the base-emitter junction?

Yes, the same thing will happen. It will reduce the base/emitter voltage, so will that change the gain of the amplifier? Is that negative feedback?
You have looked at the feedback path through C3/R4 but is that the only thing that will change the gain of the amplifier?
What is C3 doing?

 

Once the base/emitter voltage decreases, the collector current will also decrease and the gain will decrease. C3 is this negative feedback?

 

Yes, it is negative feedback. I hope you understand the circuit better now and can follow all of the feedback paths correctly.

 

Yes, thanks.