In a circuit schematic of a stereo audio amplifier, I found the following component:
It is the potentiometer used for the balance. Upper line is one of the channels, lower line is the other one. Central, bold line is ground. The variable resistor seems to be "bridged" between the two lines.
1) Conventional potentiometers have a simple, unique output which is a fraction of the input voltage; but this one needs to have two complementary outputs. Does such a potentiometer have a specific name?
2) Removing this potentiometer (which is very similar to this image), the amplifier still works, with just one channel. How is it possible? Looking this part of the schematic, after removing the variable resistor, both the channels should be isolated with respect to ground: so, they should exhibit the same behaviour.