I'm working on the circuits in this article: http://grad.uprm.edu/tesis/naranjobueno.pdf
The filter circuit is on pg. 80 of 156

I used 1/(2pi*RC) to figure out the component values for the filter circuit. I ran a simulation on LTSpice with the components and the LF356 sub and the results were good. Then I built the circuit using the values and its not giving the same results.

some information on the wanted functions:

Low Pass Cutoff = 200KHz
High Pass Cutoff = 4kHz

Here is what I'm actually getting:

1st stage
High Pass cutoff= 30kHz R=6.8k C= 5.6n

2nd stage
High Pass cutoff= 30kHz R=18k C=2.2n

3rd stage
95% of voltage is lost across input resistor
R=8.2k C=100n

I'm using ceramic capacitors and carbon film resistors. The capacitors I've had for a long time and could be bad or something but the resistors are fairly new.
Please can anybody tell me what I did wrong? Any suggestions or comments would be very helpful.

Thanks.

 

I'm working on the circuits in this article: http://grad.uprm.edu/tesis/naranjobueno.pdf
The filter circuit is on pg. 80 of 156

I used 1/(2pi*RC) to figure out the component values for the filter circuit. I ran a simulation on LTSpice with the components and the LF356 sub and the results were good. Then I built the circuit using the values and its not giving the same results.

some information on the wanted functions:

Low Pass Cutoff = 200KHz
High Pass Cutoff = 4kHz

Here is what I'm actually getting:

1st stage
High Pass cutoff= 30kHz R=6.8k C= 5.6n

2nd stage
High Pass cutoff= 30kHz R=18k C=2.2n

3rd stage
95% of voltage is lost across input resistor
R=8.2k C=100n

I'm using ceramic capacitors and carbon film resistors. The capacitors I've had for a long time and could be bad or something but the resistors are fairly new.
Please can anybody tell me what I did wrong? Any suggestions or comments would be very helpful.

Thanks.

Nothing makes sense here:
1. Sallen and Key Butterworth filters don't have equal-valued resistors AND capacitors. Here are low pass and high pass calculators.
2. For your low pass values, R=8.2k, C=100n has a 200Hz cutoff, not 200kHz. As I said, though, use the calculator.