Hello,

Just working my way through the course, onto lesson 9 using LTSpice. When trying to simulate the 3rd order Butterworth filter with Fc = 25kHz I got the following:

If I then switch to using an ideal op-amp I get the following, which agrees with the filter calculation tools:

This was done based on the suggestion from here: https://electronics.stackexchange.co...len-key-filter

Is this a quirk of LTSpice, or is the first simulation showing us something more "real-life" than the ideal calculations? In which case we may need to alter component values or op-amps for a better result. I'm new to LTSpice simulations, maybe it is the case we need to use ideal op-amps to gain sensible results. Can anyone comment on this?

Thanks, also great course!

Anthony

Just working my way through the course, onto lesson 9 using LTSpice. When trying to simulate the 3rd order Butterworth filter with Fc = 25kHz I got the following:

If I then switch to using an ideal op-amp I get the following, which agrees with the filter calculation tools:

This was done based on the suggestion from here: https://electronics.stackexchange.co...len-key-filter

Is this a quirk of LTSpice, or is the first simulation showing us something more "real-life" than the ideal calculations? In which case we may need to alter component values or op-amps for a better result. I'm new to LTSpice simulations, maybe it is the case we need to use ideal op-amps to gain sensible results. Can anyone comment on this?

Thanks, also great course!

Anthony

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