Second stage output
Drawing
I built the above bandpass filter using lag lead combination for filtering +/-2.5 Vp-p square wave @ 125 kHz, but the extracted sine wave have zero crossing distortion,tested at another frequency @ 64 kHz using suitable capacitor value, zero crossing distortion exist...
@periblepsis actually I tried bypassing with a capacitor at the first stage.I think 100 pF.Didn't noticed any change,so didn't took it further.I ll do for both stages and update
Just by curiosity, what does the output look like on the first amplifier and right after the second amplifier? (I'm asking because it can help us find the root cause)
If you're not able to go back in the lab until tomorrow, perhaps in the meantime you can simulate this 🙂
@Colin I will update scope picture tomorrow..i saw the waveform at first stage,it looked kind of triangular with peaking(overshoot like)at top.Simulation [ would love to but my software expertise is not even average,slowly learning:)]
@bobflux yes absolutely. Solderless and without decoupling on individual IC...only a big storage capacitor on Linear regulator output(was prototyping and frequency was also not very high so didn't go for perf board).
OK, I'll vote for the power supply being the problem. Simulation is unlikely to reproduce it unless you get a good opamp model that includes the output stage and interacts properly with the power supply... most opamp models are too simplified for that, including the one I got for your opamp. I guess tomorrow you should probe the supplies with the oscilloscope and post a screenshot!
It seems to me that you have a fake op-amp chip. You probably have LM358 instead of TL074. Try to add a 1k resistor between the opamp output pin and Vee.
Discussion on question by dhuwarkesh:…
Discussion on question by dhuwarkesh:…