So, you're a 12:00 flasher, eh Jan?
Isolation transformers are built typically with a 1 to 1 ratio. Five volts in is five volts out. The protection comes from the fact that the second coil is not connected to the first, which is connected to mains. As a result, touching a part of the circuit connected to the second coil will not result in a deadly shock. The design of the transformer depends upon the usage that the circuit will draw, typically resulting in larger and heavier transformers needed for higher current applications.
Isolation transformers are not just for isolating electronics from mains voltages. it is also useful for separating parts of a circuit so that power is transmitted while protecting sensitive electronics. Chips and sensitive electronics require a small voltage; anymore can destroy the chip. In contrast, motors, solenoids, relays and many other components require larger voltages. These circuits may need to interact, and the device that protects the more sensitive components is the isolation transformer.
In short, having an isolation circuit in the audio adapter keeps you from being shocked by the power from the iPod (or other devide) through your BP100.
Something like that anyhow.. (*in a hushed voice* Is she gone yet?
)
Regards,
Brian