I created this https://www.circuitlab.com/circuit/r2kea4/verstarker/=20
circuit. You can open it and simulate it in your browser, no additional=20
software needed btw.

But simulating creates a weird pattern. Is this really the output or=20
just some flaw in the simulator?

What you see is an amplifier on the left side and a signal mixer on the=20
right side. So the result of the first amplifier acts as second source.=20
Measurement is taken at R15.
--=20
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