Hello!
I got an assignment in class to design a pre-amplifier, based on op-amps, for a mic->speaker circuit but the simulation doesn't confirm my calculations and I can't figure out what is causing my problem.
The amplifier should have a voltage gain of 26dB (20x times), lower cut off frequency of 100Hz and a upper cut off frequency of 10kHz. I blocked the lower frequencies with a high pass filter on the signal which works perfectly. The higher frequencies are blocked by a capacitor parallell with a resistor in the feedback loop
I calculated the cut off frequency to be about 10kHz (should not be less) by choosing R and C to both match 10kHz = 1/(2*pi*R*C)
I chose R=180k Ohm and C=82pF
These are then connected to ground through a 10k resistor giving the circuit 20 times amplification.
Everything but the higher cut off frequency is looking well, it's 1.4kHz off. Why? I think it might be because of the capacitor in the loop being to small.
Any ideas?
Screens of the simulation
// Linuxxon
I got an assignment in class to design a pre-amplifier, based on op-amps, for a mic->speaker circuit but the simulation doesn't confirm my calculations and I can't figure out what is causing my problem.
The amplifier should have a voltage gain of 26dB (20x times), lower cut off frequency of 100Hz and a upper cut off frequency of 10kHz. I blocked the lower frequencies with a high pass filter on the signal which works perfectly. The higher frequencies are blocked by a capacitor parallell with a resistor in the feedback loop
I calculated the cut off frequency to be about 10kHz (should not be less) by choosing R and C to both match 10kHz = 1/(2*pi*R*C)
I chose R=180k Ohm and C=82pF
These are then connected to ground through a 10k resistor giving the circuit 20 times amplification.
Everything but the higher cut off frequency is looking well, it's 1.4kHz off. Why? I think it might be because of the capacitor in the loop being to small.
Any ideas?
Screens of the simulation
// Linuxxon