\documentclass[
  crop,tikz,convert={
    outext=.svg,
    command=\unexpanded{
      pdf2svg \infile\space\outfile
    }
  },
  multi=false]
{standalone}[2012/04/13]

%\usetikzlibrary{...}% tikz package already loaded by 'tikz' option
\usetikzlibrary{positioning}

\makeatletter

\begin{document}

  % \begin{tikzpicture}
  \begin{tikzpicture}[
      rounded corners=2pt,
      inner sep=5pt,
      line width=.6pt,
      node distance=.8cm]

    % background grid & fill
    \fill[black!40!white] (0,0) rectangle (14,8);
    \draw[step=1cm,gray,very thin] (0,0) grid (14,8);

    % sources y=7
    \node (jack) at (2,7) [draw] {male mini-jack};
    \node (soundcard) at (8,7) [draw] {DJ Soundcard};
    \node (microphone) at (5,7) [draw] {microphone};

    % mixer y=5
    \node (mixer) at (3.5,5) [draw] {mixer};
    \node (headphones) at (6,5) [draw] {headphones};

    % amps y=3
    \node (subamp) at (2,3) [draw] {sub amp};
    \node (topamp) at (5,3) [draw] {top amp};

    % speakers y=1
    \node [draw] (topl) at (1,1) {top\\left};
    \node [draw] (sub) at (3,1) {sub};
    \node [draw] (topr) at (5,1) {top\\right};

    % wiring (sources - mixer)
    \draw (microphone.south) -- (mixer.north);
    \draw (soundcard.south) -- (headphones.north);
    \draw (soundcard.south) -- (mixer.north) node[midway,above] {$C_1$};
    \draw (jack.south) -- (mixer.north) node[midway,above] {$C_2$};

    % wiring (amps - speakers)
    \draw (mixer.south) -- (topamp.north) node[midway,above] {$C_3$};
    \draw (mixer.south) -- (subamp.north) node[midway,above] {$C_4$};

    % wiring (amps - speakers)
    \draw (subamp.south) -- (sub.north) node[midway,above] {$C_5$};
    \draw (topamp.south) -- (topl.north) node[midway,above] {$C_6$};
    \draw (topamp.south) -- (topr.north) node[midway,above] {$C_7$};

    % cable legend
    \node (legend) at (11,4) [draw, text width=5cm] {
      \textbf{Cables}\\
      $C_1$ - mini-jack (F) - 2xRCA (F)\\
      $C_2$ - 2xRCA - 2xRCA\\
      $C_3$ - jack - jack\\
      $C_4$ - jack - jack\\
      $C_5$ - Unknown\\
      $C_6$ - Unknown\\
      $C_7$ - Unknown\\
    };

  \end{tikzpicture}
\end{document}