< I just remembered that my Ce (which I am using to split my resistors to give me my midband gain) will have a low frequency cut off as well of 40hz.
And that Ce = 1/2 pi*f*re (re being what I just calculated)
Ce = 1/pi*40*25 = 318uF.
Strangely that had no effect on the lower cut off frequency of my graph (which stays at about 8hz!) and no matter what size capacitor I put there my lower freq cut off isnt effected when it has to be I would have thought, am I wrong? In fact i found that putting any value for CL is having no effect on my cut off frequency either, only C1 does!
audioguru said:
For the input filter calculation, you forgot to include the input impedance of the transistor.
Ok so data sheet says
hfe (beta) // IC = 10 mA; VCE = 10 V // hfe = 75
So
75*25 =1875 ohms for my input impedance of my transistor, which is quite big. As it is in series with my emiiter resistance I just add that to my value of TOTAL R
SO
C1 = 1/2pi*40*TOTAL R
Where Total R = Rs + R1//R2 + Input Impedance of transistor.
And my cut off has shot up to 20hz which is much closer
Sorry for all the detail, i just want to run my calcs here as i have no confidence in getting them right by myself.
The fact that it only goes up to 20hz is probably down to my CL and Ce not having any effect at all. In fact i even deleted my CL and my frequency plot from my bode plotter was unchanged, i dont know why, could that be to how the bode plotter is connected up?