Problem with State Variable 12dB VCF

[le_barde]

Hi,

I've built this state variable 12db filter and got something I would like to know if it's normal. If not, any help would be appreciated.
To be brief, the highest cutoff frequency I can get is around 800Hz, what seems very low to me. If Res is at the minimum and Cutoff at the maximum, LP will still cut the highs a lot, HP also won't let me cut the low frequencies so much.

Here is a little measurement I did.

A square signal around 1kHz applied to the first input.


Here is what I measure after the first capacitor and the 2 input resistors. (U4-A TL082 pin 2).
When I saw this, i thought the resistor values or the cap could be wrong, because the signal is already really altered. But I've tried to bridge the signal from the input to the amp-op input. The level was obviously a lot louder, but still no high frequencies coming out at the LP output.


Now here is what I get at the LP output. (what is pretty much the same like above, but amplified).


Here is what my RME measures. (normally a 1k square signal has lots of higher harmonies like shown on the last picture):


Last one, the RME measuring the dry signal (bypassing the LP filter, what I should normally get with the cutoff knob being turned at its maximum, right ?).



So, wondering if that's the normal 12db MFOS VCF behavior... But that would astonish me..

Thanks for your help!

[le_barde]

all right, I've found my mistake.
C2 and C3 were 2200pF in my building instead of 220pF capacitors.
Now it works all fine