% Author: Dr. Matthias Jung, DL9MJ
% Year: 2020
\begin{circuitikz}
    \draw(0,0) coordinate(u0)
        to [mic] ++(0,3) 
        to [amp, box, -*, l={\qty{0,3}-\qty{3,4}{\kilo\hertz}}] ++(2,0) coordinate(o1)
        to [short, -*] ++(1,0) coordinate(o2)
        to [short] ++(1,0) coordinate(o3)
        to [vR, invert, mirror, name={knecht}] ++(0,-3) coordinate(u3)
        to [short, -o] ++(3,0) coordinate(u4);

    \draw(u3)
        to [short, *-*] ++(-1,0) coordinate(u2)
        to [short, *-*] ++(-1,0) coordinate(u1)
        to [short, *- ] (u0);

    \draw(o1)
        to [stroke diode] (u1);

    \draw(o2)
        to [stroke diode, invert] (u2);

    \draw(o3)
        to [open] ++(1,0) coordinate(o4)
        to [lowpass, l={\qty{3}{\kilo\hertz}}, -o] (o4-|u4) coordinate(o5);

    \draw(o4)
        |- (knecht.wiper);

    \draw(o5)
        to [open, name={h1}] (u4);

    \draw(h1.center)
        node[rotate=+90](kerl){Oszillator};
    \draw(kerl.north)
        node[anchor=south, rotate=90]{zum};
\end{circuitikz}