State-variable filter problem.........

[Learner]

Hi guys,
I am trying to build a state-variable audio filter and it simply just doesnt work as it should, by changing R3 and R4 it suppose to change the cut off frequency but I've simulated and built it on the breadboard they both seems to get the same result.

Bandpass don't appears to work as bandpass and highpass don't work as highpass, well lowpass actually have the same response as bandpass

Something is just not right and I do not know what it is, can somebody help me!!!

Thanks in advance!


**broken link removed**

**broken link removed**

 

[Humungus]

It seems the choise of components is quite capricious. Wy don't you calculate the transfer function and see the dependence of each output on components values?

Then you could see what components to change.

 

[Learner]

Hi Humungus,
The problem is that the HP, LP and BP don't seem to appear displaying the right shape of response, the value I have in the circuit should cut off at 15hz . I just don't understand what I have done wrong in the simulation, is it possible that the simulator simply don't work correctly? :roll:

I am using Orcad Pspice student version by the way......