Hi All!
I finally discovered the problem: !PHASE¡
Yesterday I went to visit some friends , they had good scopes and signal generators. We discovered that each stage in my circuit is slightly out of phase in some degrees: 5-10º, and this adds up in each stage.
This is why I have this frequency response, as if the low end made the high frequencies disappear a bit..
I changed some feedback capacitor values for smaller ones, and that improved the phase response of the circuit.
The circuit i posted is not the full circuit, because I wrongly thought my problem was in the final stages... but no.. :
Lessons learned.: :
1. Get a proper scope.... :
Pc soundcard scopes...not so useful...
2. To have a large but not too large input bandwidth.
3. Mantaining in each circuit the same Resistor/capacitor Ratios.
4. It is also about experimenting with resistor/caps values...
I expect to fix all of this in the next week or so, i will post a new frequency response graph ASAP.
Thank you very much for all your comments!
jay x