# Thevenin Resistance in a op amp circuit

I created this circuit and I am struggling on trying to figure out the Thevenin resistance for this circuit. • You’ll figure it out with smaller pieces – Tony Stewart Sunnyskyguy EE75 Sep 29 at 0:35
• You mean the output impedance at node $V_{out}$? In dc, the output impedance is your resistor $R_6$. In ac, if you consider a zero output resistance from the op-amp, then it becomes $C_4$ impedance in parallel with $R_6$. – Verbal Kint Sep 29 at 7:06
• Are you sure about the values of R4 and R5? At DC C3 makes the feedback unity, but even at higher frequencies you get almost unity gain because the gain becomes 1+R5/R4=1.01. – Lorenzo Donati supports Monica Sep 29 at 11:19
• Look at all the different Req an TC=T different time constants and resistor ratio for NFB gain – Tony Stewart Sunnyskyguy EE75 Sep 29 at 15:49
• If you're super lazy to analyze it you can always put it into SPICE and put a current source on the output and measure the voltage output while doing an AC analysis. – hatsunearu Sep 29 at 20:01