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I would think that the impedance of the capacitors in both cases would be negligible in the range of audio (500 ohms at 300 Hz). So I cannot see how the circuits would perform any differently, but something keeps nagging me that there's something about it that I'm not seeing. That's why I'm asking for opinions.
Here is a schematic with the difference shown.
Are you implying that resistance is irrelevant to AC?What's the relevence of that?, it's an AC mixer, no DC involved.
The impedance at the inverting input is so low that you can assume it is zero. This is true because of feedback. It has nothing to do with the input impedance of the op amp.I see the difference. My question was:
If the Z on the output side of the capacitor is the same for both circuits (op-amp input) will the freq. response be the same?
You imply no but I have trouble seeing that. If the Z is very high at the op-amp what difference does the time constant really make except for some phase difference?
I see the difference. My question was:
If the Z on the output side of the capacitor is the same for both circuits (op-amp input) will the freq. response be the same?
You imply no but I have trouble seeing that. If the Z is very high at the op-amp what difference does the time constant really make except for some phase difference?
I'm guessing you still don't understand why the impedance at the summing node (inverting input) is zero. When I first was learning op amps almost 50 years ago, there was not a lot of literature available on the subject. For me, understanding the concept of virtual ground (earth) was the key to the whole puzzle. After that, everything fell into place.I always read and think about your posts, when I see them.
I understand that if the cap is small there is a difference in how the circuits will perform.
Not to confuse the issue and, perhaps this is obvious, but there is actually a very small signal at the inverting virtual ground input which equals the output voltage swing divided by the open loop gain of the op amp. Since the typical open loop gain is over a 100k for most op amps, this voltage is a fraction of a mV, thus, for most practical purposes, the virtual ground has a negligible or "no" signal and its apparent impedance is a fraction of an ohm.I've mentioned a couple of times 'virtual earth mixer', which is what it is (or should be), the feedback round the opamp makes the inverting input have no signal on it at all (virtually at earth potential)