8 - fach:

is an 8 channel audio generator with knobs for frequency selection, on the side is a filter knob and a switch for high / low.

7 - buttons:

is a 7-step, non-chromatic tuned tone generator controlled by a circuit board of a heater controller,
it comes with pitch and tune controls and a switch for frequency selection.

super - simple - thing:

the easiest way to generate electric sounds is this. 

audio oscillation with the simplest components.